Report from the NA61/SHINE Experiment at the CERN SPS,” Tech

CERN-SPSC-2020-023 / SPSC-SR-278 02/10/2020 erdcino hsatceo at fi salwda pcfidi h CB-. license. CC-BY-4.0 the in specified as allowed is it of parts or article this of Reproduction c UOENOGNSTO O ULA EERH(CERN) RESEARCH NUCLEAR FOR ORGANISATION EUROPEAN 00CR o h eeto h A1SIECollaboration. NA61/SHINE the of benefit the for CERN 2020 eotfo h A1SIEexperiment NA61/SHINE the from Report h ENSSa fOtbr22.Tedcmn eest h rpslSPSC-P-330. proposal the to at refers experiment document The NA61/SHINE 2020. the October of of plans as and SPS status CERN the the on reports document This h A1SIECollaboration NA61/SHINE The tteCR SPS CERN the at coe ,2020 2, October Contents

1 Introduction6

2 New results 6 2.1 New results for strong interactions physics...... 6 2.2 New results for neutrino and cosmic ray physics...... 21

3 Software and calibration upgrades 26 3.1 Native SHINE software...... 26 3.2 Calibration...... 30

4 Hardware upgrade 31

5 Beam request for 2021 and plans for data taking in 2022-2024 33 5.1 Beam request for 2021...... 33 5.2 Request for measurements in 2022-2024...... 36

6 Very Low Energy Beams 37 6.1 Physics with Very Low Energy Beams...... 37 6.2 Working Schedule...... 38

7 Ideas for additional measurements after LS3 38 7.1 Measurements with ion beams for physics of strong interactions...... 38 7.2 New measurements with anti-proton beams for physics of strong interactions 42 7.3 Measurements for physics of neutrinos and cosmic-rays...... 44

8 Summary 46

2 The NA61/SHINE Collaboration

A. Acharya 9, H. Adhikary 9, A. Aduszkiewicz 15, K.K. Allison 25, E.V. Andronov 21, T. Antićić 3, V. Babkin 19, M. Baszczyk 13, S. Bhosale 10, A. Blondel 4, M. Bogomilov 2, A. Brandin 20, A. Bravar 23, W. Bryliński 17, J. Brzychczyk 12, M. Buryakov 19, O. Busygina 18, A. Bzdak 13, H. Cherif 6, M. Cirković´ 22, M. Csanad 7, J. Cybowska 17, T. Czopowicz 9,17, A. Damyanova 23, N. Davis 10, M. Deliyergiyev 9, M. Deveaux 6, A. Dmitriev 19, W. Dominik 15, P. Dorosz 13, M. Droba 6, J. Dumarchez 4, R. Engel 5, G.A. Feofilov 21, L. Fields 24, Z. Fodor 7,16, A. Garibov 1, M. Ga´zdzicki 6,9, O. Golosov 20, V. Golo- vatyuk 19, M. Golubeva 18, K. Grebieszkow 17, F. Guber 18, A. Haesler 23, S.N. Igolkin 21, S. Ilieva 2, A. Ivashkin 18, S.R. Johnson 25, K. Kadija 3, N. Kargin 20, E. Kashirin 20, M. Kiełbowicz 10, V.A. Kireyeu 19, V. Klochkov 6, V.I. Kolesnikov 19, D. Kolev 2, A. Korzenev 23, V.N. Kovalenko 21, S. Kowalski 14, M. Koziel 6, A. Krasnoperov 19, W. Kucewicz 13, M. Kuich 15, A. Kurepin 18, D. Larsen 12, A. László 7, T.V. Lazareva 21, M. Lewicki 16, K. Łojek 12, V.V. Lyubushkin 19, M. Maćkowiak-Pawłowska 17, Z. Majka 12, B. Maksiak 11, A.I. Malakhov 19, A. Marcinek 10, A.D. Marino 25, K. Marton 7, H.-J. Mathes 5, T. Matulewicz 15, V. Matveev 19, G.L. Melkumov 19, A.O. Merzlaya 12, B. Messerly 26, O. Meusel 6, Ł. Mik 13, S. Morozov 18,20, Y. Nagai 25, M. Naskr ˛et 16, V. Ozvenchuk 10, V. Paolone 26, O. Petukhov 18, R. Płaneta 12, P. Podlaski 15, B.A. Popov 19,4, B. Porfy 7, M. Posiadała-Zezula 15, D.S. Prokhorova 21, D. Pszczel 11, S. Puławski 14, J. Puzović 22, M. Ravonel 23, R. Renfordt 6, D. Röhrich 8, E. Rondio 11, M. Roth 5, B.T. Rumberger 25, M. Rumyantsev 19, A. Rustamov 1,6, M. Rybczynski 9, A. Rybicki 10, S. Sadhu 9, A. Sadovsky 18, K. Schmidt 14, I. Selyuzhenkov 20, A.Yu. Seryakov 21, P. Seyboth 9, M. Słodkowski 17, P. Staszel 12, G. Stefanek 9, J. Stepaniak 11, M. Strikhanov 20, H. Ströbele 6, T. Šuša 3, A. Taranenko 20, A. Tefelska 17, D. Tefelski 17, V. Tereshchenko 19, K. Thoma 6 A. Toia 6, R. Tsenov 2, L. Turko 16, R. Ulrich 5, M. Unger 5, D. Uzhva 21, F.F. Valiev 21, D. Veberiˇc 5, V.V. Vechernin 21, A. Wickremasinghe 26,24, K. Wojcik 14, O. Wyszyński 9, A. Zaitsev 19, E.D. Zimmerman 25, and R. Zwaska 24

1 National Nuclear Research Center, Baku, Azer- 13 AGH - University of Science and Technology, baijan Cracow, Poland 2 Faculty of Physics, University of Sofia, Sofia, 14 University of Silesia, Katowice, Poland Bulgaria 15 University of Warsaw, Warsaw, Poland 3 Ruder¯ BoškovićInstitute, Zagreb, Croatia 16 University of Wrocław, Wrocław, Poland 4 LPNHE, University of Paris VI and VII, Paris, 17 Warsaw University of Technology, Warsaw, France Poland 5 Karlsruhe Institute of Technology, Karlsruhe, 18 Institute for Nuclear Research, Moscow, Rus- Germany sia 6 University of Frankfurt, Frankfurt, Germany 19 Joint Institute for Nuclear Research, Dubna, 7 Wigner Research Centre for Physics of the Hun- Russia garian Academy of Sciences, Budapest, Hungary 20 National Research Nuclear University 8 University of Bergen, Bergen, Norway (Moscow Engineering Physics Institute), 9 Jan Kochanowski University in Kielce, Poland Moscow, Russia 10 Institute of Nuclear Physics, Polish Academy 21 St. Petersburg State University, St. Petersburg, of Sciences, Cracow, Poland Russia 11 National Centre for Nuclear Research, Warsaw, 22 University of Belgrade, Belgrade, Serbia Poland 23 University of Geneva, Geneva, Switzerland 12 Jagiellonian University, Cracow, Poland 24 Fermilab, Batavia, USA

3 25 University of Colorado, Boulder, USA 26 University of Pittsburgh, Pittsburgh, USA

4 The NA61/SHINE Limited Members

N. Antoniou 1, P. Banasiak 8, S. Bordoni 9, N. Charitonidis 9, P. Christakoglou 1, G. Christodoulou 9, A. Datta 4, A. De Roeck 9, F. Diakonos 1, P. von Doetinchem 4, S.J. Dolan 9, D. Gawli´nski 8, M. Grzelak 8, T. Hasegawa 2, S. J ˛edrzejewski 8, A. Kapoyannis 1, J. Kempa 8, T. Kobayashi 2, U. Kose 9, J. Koshio 3, D.R. Kowcun 8, M.O. Kuttan 6, O. Linnyk 6, W.C. Louis 5, B. Meller 8, C. Mussolini 9, T. Nakadaira 2, K. Nishikawa 2, A.D. Panagiotou 1, T. Pawlak 8, J. Pawlowski 6, D. Piotrowski 8, W. Rauch 7, K. Sakashita 2, S. Schramm 6, T. Sekiguchi 2, M. Shibata 2, A. Shukla 4, J. Steinheimer-Froschauer 6, H. Stoecker 6, M. Tada 2, M. Vassiliou 1, C.F. Vilela 9, J. Wiktorowicz 8, and K. Zhou 6

1 University of Athens, Athens, Greece Frankfurt, Germany 2 Institute for Particle and Nuclear Studies, 7 Fachhochschule Frankfurt, Frankfurt, Germany Tsukuba, Japan 8 Warsaw University of Technology Plock Cam- 3 Okayama University, Japan pus, Poland 4 University of Hawaii at Manoa, USA 9 CERN, Geneva, Switzerland 5 Los Alamos National Laboratory, USA 6 Frankfurt Institute for Advanced Studies,

5 1 Introduction

This annual report presents the status and plans of the NA61/SHINE experiment [1] at the CERN SPS. The report refers to the period October 2019 - October 2020. The document is organized as follows. New results are presented in Section2. Status of the software and calibration upgrades is summarized in Section3. An overview of the hardware upgrade is given in Section4. The beam request for 2021 and plans for data taking in 2022- 2024 are presented in Section5. Finally, ideas for measurements after LS3 are summarized in Section7. The summary in Section8 closes the paper.

2 New results

2.1 New results for strong interactions physics

The NA61/SHINE strong interactions program is based on beam momentum scans (13A – 150A/158A GeV/c) with light and intermediate mass nuclei (from p+p to Xe+La). The main physics goals include: search for the second-order critical end-point in the temperature versus baryo-chemical potential phase diagram (looking for non-monotonic behavior of critical point signatures, such as transverse momentum and multiplicity fluctuations, intermittency signal, etc., when system freezes out close to the critical point), study the properties of the onset of deconfinement (search for the onset of the horn, kink, step, and dale 1 structures [2,3] in collisions of light nuclei). In recent years, the program has been extended by Pb+Pb collisions where the open charm production, as well as collective effects are studied. Based on the obtained results, few years ago NA61/SHINE introduced a concept of two onsets in nucleus-nucleus collisions at the CERN SPS energies (described in 2017 Status Re- port [4]): onset of deconfinement (beginning of QGP formation – collision energy threshold for deconfinement) and onset of fireball (beginning of formation of a large cluster which decays statistically – system-size threshold for creation of statistical system). This section summarizes new preliminary and recently published physics results from the program on physics of strong interactions. The results on spectra and yields as well as on fluctuations and correlations are presented. They are ordered and labelled according to the NA61/SHINE physics goals, i.e. the study of the onsets of deconfinement (OD) and fireball (OF), the search for the critical point (CP) and others (O).

2.1.1 (OD, OF) Final results concerning p+p interactions and onset of deconﬁnement

NA61/SHINE results on the collision energy dependence of the K+/π+ ratio and the in- verse slope parameter of kaon mT spectra in inelastic p+p interactions were published in Phys. Rev. C [5]. The NA61/SHINE p+p results were compared with the corresponding world data on p+p interactions as well as central Pb+Pb and Au+Au collisions. The comparison uncovered a similarity between the collision energy dependence in p+p interactions

1 2 Dale is a minimum in the energy dependence of squared sound velocity cs , see Ref. [2] and Fig.1( right)

6 and central heavy ion collisions – a rapid change of collision energy dependence of basic hadron production properties in the same energy range. At the same time results confirm, with higher significance, previously reported striking differences between results for p+p interactions and heavy ion collisions. Possible interpretations were briefly discussed. Understanding of the origin for the similarity between results on heavy ion collisions and p+p interactions is one of the key objectives of heavy ion physics today. Emerging results from the NA61/SHINE, (nuclear mass number) – (collision energy) scan, as well as the results from LHC and RHIC on collisions of small and medium size systems qualitatively change the experimental landscape. In parallel, significant progress is needed in modelling of collision energy and system size dependencies which would extend the validity of models to the full range covered by the data.

2.1.2 (OD, OF) Final results on π− production in Be+Be

NA61/SHINE measurements of π− production in 7Be+9Be collisions at beam momenta from 19A to 150A GeV/c were recently accepted for publication in Eur. Phys. J. C [2]. The Landau hydrodynamical model of high energy collisions [6,7] predicts rapidity distributions of Gaussian shapes. In fact, this prediction is approximately conﬁrmed by the experimental data, see Ref. [8] and references therein. Moreover, the collision energy dependence of the width was derived by Shuryak [9] from the same model under simplifying assumptions, and reads: √ 8 c2 s 2( −) = s NN σy π 4 ln , (1) 3 1 − cs 2mp 2 where cs denotes the speed of sound, and cs = 1/3 is a value for an ideal gas of massless particles.

The above prediction is compared with the experimental data on the width (σy) of the rapidity distributions of π− mesons produced in central nucleus-nucleus collisions and inelastic nucleon-nucleon interactions in Fig.1( left)2. The model calculations are close to the measured dependence on the beam rapidity ybeam. However, a linear increase with ybeam provides a better fit to the measurements as shown by the straight line fit. The deviations were attributed to the changes in the equation of state [11, 12], which are effectively parametrised by allowing the speed of sound to be dependent on collision energy. The measured values of σy differ very little between the studied reactions in the SPS energy range. 2 By inverting Eq.1 one can express cs in the medium as a function of the measured width of the rapidity distribution. The energy dependence of the sound velocities extracted from the data are presented in Fig.1( right). The energy range for results from Be+Be collisions and inelastic p+p reactions is too limited and the fluctuations in the data are too large to allow a significant conclusion about a possible minimum. Data on central Pb+Pb and Au+Au collisions cover a much wider energy range.√ Here the sound velocity exhibits a clear minimum (usually called the softest point) at sNN ≈ 10 GeV, consistent with the reported onset of deconfinement [13, 14].

2 For p+p interactions the ﬁgure shows isospin symmetrized values denoted as N+N [10]

7 y 3 2 s 0.6 c σ NA61/SHINE WORLD NA61/SHINE WORLD N+N Pb+Pb 0.55 N+N Pb+Pb 2.5 Be+Be Au+Au Be+Be Au+Au 0.5 linear fit 2 2 0.45 Landau, cs=1/3 1.5 0.4

0.35 1 0.3 0.5 0.25 AGS SPS RHIC AGS SPS RHIC 0 0.2 0 2 4 6 10 102 y beam sNN (GeV)

Figure 1: Comparison of the Landau hydrodynamical model with rapidity distributions of charged pions produced in central nucleus-nucleus collisions and inelastic nucleon-nucleon interactions. Left: The width σy of the rapidity distributions of negatively charged pions in central Be+Be, Pb+Pb [13,14] (Au+Au [15,16]) reactions and the width σy of the average of rapidity distributions of positively and negatively charged pions in p+p [10, 17] (denoted as N+N) as a function 2 of the beam rapidity ybeam. The dotted line indicates the Landau model prediction with cs = 1/3, while the solid line shows a linear ﬁt through the data points. Right: The speed of sound as a function of beam energy as extracted from the data using Eq.1.

Pions are the most copiously produced hadrons (≈ 90%) in collisions of nucleons and nuclei at SPS energies. Their multiplicity is closely related to the entropy produced in such interactions [18]. Within the Fermi and Landau models the entropy S is expected to increase as

S ∼ F , (2) where the Fermi collision energy measure F is deﬁned as

√ 3 √ 1/4 F = ( sNN − 2mN) / sNN , (3)

where F denotes the volume of the system. Since the number of degrees of freedom g is higher for the quark-gluon plasma than for confined matter, it is also expected that the entropy density of the produced final state at given energy density should also be higher in the first case. The following simple relation describes the expected dependence [19]:

S/V ∼ g1/4 F . (4)

Therefore, the entropy and information regarding the state of matter formed in the early stage of a collision should be reflected in the number of produced pions normalized to the volume of the system. This intuitive argument was quantified in the Statistical Model of the Early Stage (SMES) [20]. The increase with collision energy of the mean number of produced pions hπi, normalized to the mean number of wounded nucleons hWi [21] is expected to be linear when plotted against F. The rate of increase is related to the number of degrees of freedom as given by Eq.4. This simple prediction is modified at low collision energies,

8 where absorption of pions in the hadronic matter is expected to signiﬁcantly decrease the ﬁnal pion yield [20]. Figure2 displays the ratio of mean pion multiplicities 3 to mean number of wounded nucleons as a function of F. The new measurements of the hπi/hWi ratio in central Be+Be collisions are compared to a compilation of results from central Pb+Pb (Au+Au) collisions and inelastic nucleon-nucleon interactions. Above F ≈ 2 GeV 1/2, the slope of the Pb+Pb dependence is about a factor 1.3 higher than for nucleon-nucleon interactions. The ratio in central Be+Be collisions follows the ratio for central Pb+Pb collisions up to F ≈ 3 GeV 1/2, whereas at the top collision energy the Be+Be ratio is close to the ratio for N+N interactions. Note, that W was derived using the EPOS model and therefore depends on the details of the model. Using other models may lead to 5 – 10% differences. 〉 W 〈

/ 5 〉

π NA61/SHINE 〈

4 g Be+Be

a N+N [17] 3 WORLD

2 d N+N [13]

g Pb+Pb [13, 14] 1 g Au+Au [22, 23] 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 ≈ 1/4 1/2 F sNN (GeV )

Figure 2: The "kink" plot showing the ratio of mean pion multiplicity hπi to mean number of 1/4 wounded nucleons hWi versus the Fermi energy variable F ≈ sNN . Results from central Be+Be collisions are compared to measurements for inelastic nucleon-nucleon reactions and central collisions of heavier nuclei. Results of Be+Be collisions are shown with statistical (vertical lines) and systematic (shaded band) uncertainties. All other results are presented with total uncertainty.

2.1.3 (CP) Final results on ﬂuctuations of identiﬁed particles in p+p

Measurements of multiplicity fluctuations of identified hadrons in inelastic proton-proton interactions at the CERN Super Proton Synchrotron were recently submitted to arXiv [24] and Eur. Phys. J. C. The paper contains the results on fluctuation analysis based on second

3 The mean number of produced pions hπi is calculated as hπi = 3 · hπ−i for nucleus-nucleus collisions and hπi = 1.5 · (hπ+i + hπ−i) for N+N interactions

9 and first order moments of multiplicity distributions of identified hadrons in p+p interactions at 31, 40, 80, and 158 GeV/c taken in 2009. Four different measures of multiplicity fluctuations are used: the scaled variance ω and the strongly intensive measures Φ, ∆, and Σ [25, 26]. Data analysis was performed using the Identity method which corrects for incom- plete particle identification [27, 28]. Moreover, the results were also corrected for: (i) losses of inelastic events due to on-line and off-line event selection, (ii) losses of particles due to detector inefficiency and track selection, (iii) contribution of particles from weak decays and secondary interactions (feed-down). Strongly intensive quantities are calculated in order to allow for a direct comparison with corresponding results on nucleus-nucleus collisions.

)] 1.2 )]

p EPOS1.99 p VENUS4.12 0.1 1.1 SMASH1.5 (p+ 0.05 π [ 1 [K (p+ Σ

Φ 0 0.9 −0.05 0.8 −0.1 0.7 6 8 10 12 14 16 18 20 6 8 10 12 14 16 18 20 sNN [GeV] sNN [GeV]

Figure 3: The collision energy dependence of Σ[π(p + p¯)] and Φ[K(p + p¯)] in inelastic p+p interactions. The solid, dashed and dotted lines show predictions of Epos1.99, Smash1.5 and Venus4.12 models, respectively. Statistical uncertainty is denoted with bar (smaller than the marker size) and systematic uncertainty is indicated with red band.

Examples of results for fluctuations of different hadron types are shown as a function of collision energy in Fig.3. In general, one finds that all quantities for negatively charged hadrons are close to expectations for independent particle production (for the Φ quantity it is 0; for other quantities there are two reference values, 1 for independent particle production and 0 for no fluctuations). For all and positively charged particles there is no obvious common trend. The deviations from the values (0 or 1, depending on a measure) predicted for independent particle emission are probably the result of various known processes, e.g. conservation laws of electric, baryonic and strangeness charges, or resonance decays as well as KNO scaling of the multiplicity distributions [29–31]. The measurements of NA61/ SHINE were compared with string-resonance models SMASH [32], EPOS1.99 [33, 34] and Venus4.12 [35,36]. None of the models agree with all presented results. In a number of cases qualitative disagreement is observed.

10 2.1.4 (CP) Preliminary results on higher order moments of multiplicity and net-charge in Be+Be at 150A GeV/c

Results from the higher order moments of multiplicity and net-charge in central Be+Be collisions at 150A GeV/c were released as preliminary and presented during Quark Matter 2019 conference [37]. These results were compared to the ones obtained in p+p interactions. The expected signal of a critical point is a non-monotonic dependence of various fluctuation/correlation measures in a system size and energy scan. A specific property of the CP – the increase in the correlation length – makes fluctuations its basic signal. Special interest is devoted to fluctuations of conserved charges (electric, strangeness or baryon number) [38, 39]. In order to compare fluctuations in systems of different sizes one should use intensive quantities, i.e. quantities insensitive to system volume. Such quantities are constructed by divi- sion of cumulants κi of the measured distribution (up to fourth order), where i is the order of the cumulant. For second, third and fourth order cumulants intensive quantities are defined as: κ2/κ1 , κ3/κ2 and κ4/κ2. The obtained system size dependence of net-electric charge at 150/158A GeV/c is in agreement with the EPOS model predictions. More detailed examination of system size dependence of the same quantities for negatively and positively charged hadrons (Fig.4) shows very different system size dependence. Moreover, none of the measured quantities of h+ − and h are reproduced by the EPOS model. This disagreement indicates that we do not fully understand the underlying physics of how fluctuations are induced. Thus, more detailed studies are needed. 1 2 2 κ κ κ /

central A+A at 150/158A GeV/c / central A+A at 150/158A GeV/c / central A+A at 150/158A GeV/c

2 1.5 3 4 - 2 - -

κ h κ

h κ h h+ h+ h+ - h EPOS 1.99 h- EPOS 1.99 5 h- EPOS 1.99 + h EPOS 1.99 h+ EPOS 1.99 h+ EPOS 1.99 Poisson Poisson Poisson 1 1

0 0 NA61/SHINE preliminary NA61/SHINE preliminary NA61/SHINE preliminary p+p Be+Be Ar+Sc p+p Be+Be p+p Be+Be 0.5 1 10 102 1 10 1 10 〈W〉 〈W〉 〈W〉

Figure 4: Preliminary NA61/SHINE results on the system size dependence of multiplicity ﬂuc- tuations of h+ and h− at 150/158A GeV/c as a function of the mean number of wounded nucleons, hWi. Statistical uncertainty was obtained with the bootstrap method and it is indicated as a dashed black bar. Systematic uncertainty/bias: p+p and Ar+Sc – corrected data with estimate of − − + systematic uncertainty (except published κ2/κ1[h ] = ω[h ] and ω[h ] [40]); Be+Be – uncorrected data with estimate of systematic bias. Systematic uncertainty/bias is indicated with a blue/red bar.

11 2.1.5 (CP) Higher-statistics preliminary results on intermittency analysis in Ar+Sc at 150A GeV/c

New results from a proton intermittency analysis of inelastic 40Ar+45Sc collisions at 150A GeV/c have been released as preliminary. These include higher event statistics and improved event selection quality compared to the analysis presented in the 2019 Status Report, and were reported for the first time in the Proceedings of the 45th Congress of Polish Physicists [41]. A scan was performed in centrality, as determined by the energy deposited in the PSD calorimeter; as in the previous analysis, 5% centrality intervals were examined; these were broadened to 10% intervals, as well as the full 0-20% range available, in order to mitigate the effects of relatively low event statistics. Candidate protons were identified by fitting a sum of asymmetric gaussians to dE /dx distributions for selected pT and ptot bins. Selected proton purity was 90% or higher. The Second Scaled Factorial Moments (SSFMs) for selected protons (original and mixed events) were calculated. Results for the correlator ∆F2(M) for the 10% and 20% centrality intervals are shown in Fig.5. Original sample data values and their bootstrap standard errors are plotted against confidence intervals (68–95–99.7%) of the ∆F2(M) distributions obtained from 1000 bootstrap resamplings of the analyzed events. Fig.5( bottom right) com- pares the experimental ∆F2(M) values against ∆F2(M) obtained from uncorrelated proton background with the same inclusive characteristics as the original 40Ar+45Sc events.

Based on the observed ∆F2(M) conﬁdence intervals for the 10–20% most central set, one can conclude that SSFMs differ from zero by about ∼ 1 − 2σ, indicating a borderline statistically signiﬁcant separation of real data from mixed events (background). The same conclusion is drawn by comparison to random background, Fig.5( bottom right).

Unfortunately, reliable confidence intervals for the intermittency index φ2 could not be obtained through simple power-law fits due to values for different bin sizes M being correlated. Therefore, intermittency status is currently inconclusive for 40Ar+45Sc collisions at 150A GeV/c. The quality and uncertainties of ∆F2(M) power-law scaling remain still to be established, and a proper method for estimating φ2 confidence intervals is being sought. The analysis is ongoing.

2.1.6 (CP) Preliminary results on intermittency analysis using cumulative variables in Ar+Sc at 150A GeV/c

Results from the intermittency analysis in transverse momentum space in cumulative variables of mid-rapidity protons produced in inelastic 40Ar+45Sc collisions at 150A GeV/c for several centrality selections have been released as preliminary. Initially the analysis was carried out to verify results presented in Section 2.1.5. Therefore, event and track selection cuts (except proton identiﬁcation) are the same.

12 NA61/SHINE Ar+Sc 150, cent.0 - 10%, pur > 90% NA61/SHINE Ar+Sc 150, cent.10 - 20%, pur > 90% 1 1 median median 68% C.I. 68% C.I. 95% C.I. 95% C.I. 99.7% C.I. 99.7% C.I. data data

0.5 0.5 ) ) ( (

0 0

-0.5 -0.5 0 5000 10000 15000 20000 0 5000 10000 15000 20000

NA61/SHINE Ar+Sc 150, cent.0 - 20%, pur > 90% bkg vs SHINE Ar+Sc 150, cent.10 - 20%, pur > 90%

1 1 median median 68% C.I. 68% C.I. 95% C.I. 95% C.I. 99.7% C.I. 99.7% C.I. data data

0.5 0.5 ) ) ( (

0 0

-0.5 -0.5 0 5000 10000 15000 20000 0 5000 10000 15000 20000

40 45 Figure 5: The correlator ∆F2(M) for Ar+ Sc 0–10% (top left), 10–20% (top right), and 0–20% (bottom left) most central collisions at 150A GeV/c (black points); error bars correspond to bootstrap standard error; colored bands indicate bootstrap conﬁdence intervals; solid blue line gives the median value of bootstrap samples. Bottom right: 10–20% most central ∆F2(M) (black points) compared to ∆F2(M) of simulated random background protons, for the same event statistics.

Protons were selected using a graphical dE / dx cut based on the theoretical Bethe-Bloch curves. A complementary analysis of energy loss in TPCs revealed, that the method ac- cepts approximately 60% of all protons and introduces contamination of kaons at the level of 10%. The analysis introduced two signiﬁcant variations – use of cumulative variables and uncorrelated points. Using the px and py components of transverse momentum introduces dependence on the single-particle pT distribution. Therefore, the components were ﬁrst trans- formed into their cumulative equivalents [42]. This transformation was proven to preserve the critical power-law dependence on M.

Moreover, the F2(M) values for different M are independent, as each data point was calculated using a separate sub-sample of available events. This removes possible undesirable correlation but at a cost of limited statistics.

Figure6 shows results for F2(M) for experimental data and mixed events. No critical signal is observed. This analysis is ongoing.

13 NA61/SHNIE Preliminary 2.0 /V GeAc/V 0-20% Ar+Sc at 150 (M) 2

F data 1.5 mixed

1.0

0.5

0.0 0 10000 20000 M2

Figure 6: The Second Scaled Factorial Moments (F2(M)) of proton candidates as a function of number of bins M in cumulative transverse-momentum variables for 0–20% most central inelastic 40Ar+45Sc collisions at 150A GeV/c and mixed events. The points are uncorrelated.

+ 2.1.7 (OF) Final results on Ξ− and Ξ production in p+p at 158 GeV/c

The production of Ξ(1321)− and Ξ(1321)+ hyperons in inelastic p+p interactions at beam momentum of 158 GeV/c were recently published in Eur. Phys. J. C [43]. Double-differential distributions in rapidity y and transverse momentum pT were obtained from a sample of 33M inelastic events. They allow the determination of rapidity distributions dn/dy and extrapolation of the spectra to full phase space to determine the mean multiplicity of both Ξ− + and Ξ . The Ξ mean multiplicities measured by NA61/SHINE in inelastic p+p interactions are used to calculate the enhancement factors of Ξs observed in centrality selected Pb+Pb, in semi- central C+C, and in Si+Si collisions as measured by NA49 [44] at the CERN SPS. The results for mid-rapidity densities are shown in Fig.7( left) as a function of hNW i. The enhancement factor increases approximately linearly from 3.5 in C+C to 9 in central Pb+Pb collisions. This result is compared to data from the NA57 experiment at the SPS [45], the STAR experiment at RHIC [46] and the ALICE experiment at LHC [47]. The published enhancement factor reported by NA57 at the CERN SPS was originally computed using p+Be instead of inelastic p+p interactions. Since strangeness production is already slightly enhanced in p+A collisions [48], this is not a proper reference. With the advent of the NA61/SHINE results on Ξ production in p+p interactions a new baseline reference becomes available and it is used here for the recalculation of the enhancement observed in the NA57 p+Be and A+A data. The agreement between the enhancement factors calculated using the NA49 and the NA57 A+A (p+Be) data is satisfactory. The STAR data show a slightly lower enhancement, but the enhancement observed by ALICE is signiﬁcantly lower. Figure7( right) shows the rapidity + densities dn/dy of Ξ at mid-rapidity per mean number of wounded nucleons divided by the corresponding values for inelastic p+p collisions as a function of hNW i. Apart from a

14 slightly ﬂatter rise the overall picture remains unchanged. ] ] - NA49 (NA61/SHINE p+p) + NA57 (NA61/SHINE p+p) Ξ sNN (GeV) Ξ sNN (GeV) [ NA57 (NA61/SHINE p+p) [ STAR

y=0 17.3 y=0

E STAR ALICE 10 17.3 E 10 17.3 ALICE 200 200

2760 2760

1 1

1 10 102 103 1 10 102 103 〈N 〉 〈N 〉 W W Figure 7: The strangeness enhancement E at mid-rapidity as a function of average number of − + wounded nucleons hNW i calculated as the rapidity density for Ξ production (left) and Ξ production (right) in nucleus-nucleus interactions per hNW i divided by the corresponding value for p+p interactions. Red circles represent the NA49 Pb+Pb at√ 158A GeV [44], blue squares NA57 p+Be, p+Pb and Pb+Pb at√ the same center-of-mass energy sNN = 17.3 GeV [45], magenta√ tri- angles STAR Au+Au at sNN = 200 GeV [46], and gray diamonds ALICE Pb+Pb at sNN = 2.76 TeV [47]. The systematic errors are represented by shaded boxes.

The NA61/SHINE data on charged Ξ production in inelastic p+p interactions are important for the understanding of multi-strange particle production in elementary hadron interactions. In particular, the new NA61/SHINE results constitute essential input for theoretical concepts needed for the modelling of elementary hadron interactions and of more complex reactions involving p+A and A+A collisions. In Fig.8 an example of the experimental results of NA61/SHINE are compared with predictions of the following microscopic models: EPOS 1.99 [33], UrQMD 3.4 [49, 50], AMPT 1.26 [51–53], SMASH 1.6 [32, 54, 55] and PHSD [56, 57]. + In our recently published paper [43] measurements of Ξ− and Ξ spectra in inelastic p+p interactions at 158 GeV/c were performed by the NA61/SHINE experiment at the CERN SPS. These measurements were compared with the results obtained at higher energies, and it was + − √ shown that the mid-rapidity Ξ /Ξ ratio in p+p at sNN = 17.3 GeV is around 0.4, while at higher energies it becomes unity. The NA61/SHINE results were also compared with the measurements in A+A collisions at the same energy. The ratio of rapidity densities dn/dy of Ξ− measured in nucleus-nucleus collisions and inelastic p+p collisions at 158A GeV, when normalised to the same averaged number of wounded nucleons hNW i, rises rapidly from p+p towards peripheral Pb+Pb collisions. This strangeness enhancement was found to decrease with increasing centre-of-mass energy. Furthermore, the NA61/SHINE results were compared with UrQMD,EPOS,AMPT,SMASH and PHSD model predictions. It was concluded that the EPOS model provides the best description of the NA61/SHINE measurements. Fi- + nally, the mean multiplicities of Ξ− and Ξ hyperons were compared [43] with predictions

15 − − ×10 3 ×10 3 )

1.5 - NA61/SHINE NA61/SHINE NA61/SHINE - Ξ Ξ (a) + (b) (c) EPOS 1.99 Ξ EPOS 1.99 EPOS 1.99

dn / dy 1.5 UrQMD 3.4 dn / dy UrQMD 3.4 UrQMD 3.4 AMPT 1.26 AMPT 1.26 1 AMPT 1.26 ) / dndy (

SMASH 1.6 1 SMASH 1.6 + SMASH 1.6 Ξ 1 PHSD PHSD PHSD dn/dy ( 0.5 0.5 0.5

0 0 0 −2 0 2 −2 0 2 −2 0 2 y y y

+ + Figure 8: Rapidity spectra of Ξ− (left), Ξ (middle) and Ξ /Ξ− ratio (right) measured in inelastic p+p interactions at 158 GeV/c. Shaded bands show systematic uncertainties. UrQMD 3.4 [49, 50], EPOS 1.99 [33], AMPT 1.26 [51–53], SMASH 1.6 [32, 54, 55] and PHSD [56, 57] predictions are shown as magenta, blue, black, gray and green lines, respectively.

of the Hadron Gas Model (HGM). It turned out that the HGM predictions are very close to the experimental results when the φ meson is excluded from the HGM ﬁt.

2.1.8 (O) Final results on search for pentaquarks in p+p at 158 GeV/c

Pentaquark states have been extensively investigated theoretically in the context of the con- stituent quark model. In recent NA61/SHINE paper published in Phys. Rev. C [58] results of − − − + + − + + an experimental search for pentaquarks in the√Ξ π , Ξ π , Ξ π and Ξ π invariant mass spectra in proton-proton interactions at s=17.3 GeV are presented. + + Figure9 shows the background-subtracted sum of Ξ− π−, Ξ− π+, Ξ π− and Ξ π+ invariant mass distributions. Superimposed is a similar (Fig. 3b in Ref. [59]) distribution observed by NA49 renormalized to the same number of selected p+p interactions.

400 NA61/SHINE 200 NA49 scaled

0 Entries / 7.5 MeV

−200 1.8 2 2.2 2.4 M(Ξπ) (GeV) + + Figure 9: The background-subtracted sum of the Ξ− π−, Ξ− π+, Ξ π−, and Ξ π+ invariant mass spectra after selection cuts following exactly the procedure of the NA49 experiment. The red squares are the NA61/SHINE data, the blue points correspond to the renormalized NA49 distribution (Fig. 3b in Ref. [59]) in which a narrow peak with signiﬁcance of 5.6 standard deviations is visible.

16 √ In conclusion, the NA61/SHINE analysis of p+p interactions at s=17.3 GeV with 10 times larger statistics compared to the NA49 analysis [59] does not show any indication of narrow −− 0 ++ 0 − Ξ3/2, Ξ3/2, Ξ3/2, Ξ3/2 states. No signal is observed in invariant mass distributions of Ξ + + π−, Ξ− π+, Ξ π−, and Ξ π+. This is particularly true for the mass window (1848 – 1870 MeV) in which the NA49 collaboration had seen an enhancement with signiﬁcance up to 5.6 standard deviations.

2.1.9 (O) Final results on φ meson production in p+p at 40–158 GeV/c

Final results on φ meson production in p+p collisions at 40, 80 and 158 GeV/c beam momenta, discussed in the previous report, have been published in Eur. Phys. J. C [60]. They include the ﬁrst ever measured double-differential spectra of φ mesons as a function of rapidity y and transverse momentum pT at 80 and 158 GeV/c proton beam momenta, and single-differential spectra of y or pT for beam momentum of 40 GeV/c. Compared to existing data on φ meson production in p+p collisions, they show consistency but superior accuracy of the NA61/ SHINE measurements. Compared to UrQMD3.4, EPOS1.99, PYTHIA6.4.28 and a statistical model HRG, it appears that none of these models can properly describe all the experimental observations.

2.1.10 (O) Final results on K∗(892)0 production in p+p at 158 GeV/c

∗( )0 + − Final results on K 892 production,√ via its K π decay mode, in inelastic p+p collisions at beam momentum 158 GeV/c ( sNN = 17.3 GeV) were published in Eur. Phys. J. C [61]. Measurements of the production of short-lived resonances are a unique tool to understand the less known aspects of high energy collisions, especially their time evolution. In heavy ion collisions the yields of resonances may help to distinguish between two possible freeze-out scenarios: the sudden and the gradual one [62]. Namely, the ratio of K∗(892)0 to charged kaon production may allow to estimate the time interval between chemical and kinetic freeze-out. The lifetime of the K∗(892)0 resonance (≈ 4 fm/c) is comparable to the expected duration of the re-scattering hadronic gas phase between the two freeze-out stages. Conse- quently, a certain fraction of K∗(892)0 resonances will decay inside the fireball. The momenta of their decay products are expected to be significantly modified by elastic scatterings, pre- venting the experimental reconstruction of the resonance via an invariant mass analysis. In such a case a suppression of the observed K∗(892)0 yield is expected. Such an effect was indeed observed in nucleus-nucleus collisions at SPS, RHIC and LHC energies (see Ref. [61] for a list of references). The ratio of K∗/K production (K∗ stands for K∗(892)0, K∗(892)0 or K∗±, and K denotes K+ or K−) showed a decrease with increasing system size as expected due to the increasing re-scattering time between chemical and kinetic freeze-out. In the analysis of the NA61/SHINE data the template method was used to extract raw K∗(892)0 signals. In this method the background is described as a sum of two contributions: background due to uncorrelated pairs modeled by event mixing and background of correlated ∗ pairs modeled by EPOS1.99. For K (892)0 production the template method was found to

17 provide a better background description than the standard one which relies on mixed events only. With the large statistics of NA61/SHINE data (52.53M events selected by the interaction trigger) it was possible to obtain double-differential transverse momentum and rapidity spectra of K∗(892)0 mesons. The full phase-space mean multiplicity of K∗(892)0 mesons, obtained from the pT-integrated and extrapolated rapidity distribution, was found to be (78.44 ± 0.38 ± 6.0) · 10−3, where the ﬁrst uncertainty is statistical and the second one is systematic. It is in agreement with the NA49 result [63], equal (74.1 ± 1.5 ± 6.7) · 10−3, obtained for the same collision system and beam momentum. However, instead of analysing in separate pT bins, as in NA61/SHINE, the NA49 experiment used one wide pT bin (0 < pT < 1.5 GeV/c). The NA61/SHINE K∗(892)0 yield, divided by charged kaon multiplicity, was compared to corresponding NA49 Pb+Pb data [63] (Fig. 10; see Ref. [61] for the origin of hK+i and hK−i yields). These ratios allow estimation of the time interval between freeze-outs in Pb+Pb collisions. Surprisingly, this time appeared to be longer than in Au+Au/Pb+Pb collisions at RHIC and LHC energies (see Ref. [61] for the numerical values). It suggests that either the system life-time between freeze-outs is indeed higher at SPS or the K∗(892)0 regeneration effects start to play a signiﬁcant role at higher collision energies. The large uncertainties of K∗/K ratios in C+C and Si+Si collisions in NA49 (Fig. 10) pre- vented us from an attempt to estimate time between freeze-outs for smaller collision systems at 158A GeV/c beam momentum. The large statistics of Be+Be, Ar+Sc and Xe+La data recorded by NA61/SHINE may, in future, allow to perform such analyses not only for 150A GeV/c but also for the lower SPS beam momenta, where the K∗(892)0 productions have never been measured before.

18 〉

+/- NA61/SHINE: 〈K*(892)0〉/〈K+〉

K 1 〈 〈 0〉 〈 -〉 / NA61/SHINE: K*(892) / K 〉 0 〈K*(892)0〉 / 〈K+〉 NA49 NA49 (p+p: NA61) - 〈K*(892)0〉 / 〈K 〉 0.8 NA49 NA49 (p+p: NA61) K*(892) 〈 0.6

0.4

0.2

0 1 10 102 103 〈N 〉 W

Figure 10: The system size dependencies of hK∗(892)0i/hK+i and hK∗(892)0i/hK−i yield ratios in p+p, C+C, Si+Si, and Pb+Pb collisions at 158A GeV/c. NW denotes the number of wounded nucleons taken from Ref. [63]. For better visibility the NA61/SHINE points are shifted on the horizontal axis. Figure taken from Ref. [61].

2.1.11 (O) Preliminary results on EM effects in Ar+Sc collisions at 40A GeV/c

The existence of the positively charged spectator system influences the trajectories of charged particles produced in the nucleus-nucleus collision: the repulsion of positive pions and at- traction of negative pions results in the modification of the π+/π− ratio in the final state [64]. This phenomenon has been observed for Pb+Pb collisions at 158A GeV/c by the NA49 collaboration [65] and for Ar+Sc collisions at 150A GeV/c by NA61/SHINE [66]. It has been found to bring new information on the space-time evolution of the system [64, 67, 68]. Presently, new results have been obtained on this electromagnetic (EM) distortion of charged pion spectra for Ar+Sc collisions at beam momentum of 40A GeV/c. The experimental data has been obtained with a minimum bias trigger. Charged pions were identified via measurement of their specific energy loss within the active volume of NA61/SHINE Time Projection Chambers. Centrality selection was ensured on the basis of the forward energy deposited in the Projectile Spectator Detector. The presented analysis is the first study of minimum bias Ar+Sc reaction data in the NA61/SHINE experiment.

+ − pL(pion) Fig. 11 shows the π /π ratio plotted as a function of xF = for six different pL(beam nucleon) values of pion transverse momentum pT. Both variables are given in the collision center-of- mass reference system. A clear depletion of this ratio is visible at low pT of the pion. This

19 Figure 11: The π+/π− ratio in (a) intermediate centrality and (b) peripheral Ar+Sc collisions at 40A GeV/c. The forward energy (centrality) selection is indicated in the top left corner of each panel.

effect slowly increases from intermediate centrality to peripheral collisions as a consequence of the corresponding increase of spectator charge. The largest effect is observed at xF = 0.15 = mπ/mp, which corresponds to pions moving at same velocity as the spectator system (y ≈ ybeam). The presented result is the ﬁrst observation of the spectator-induced EM effect in Ar+Sc reactions at 40A GeV/c, and the ﬁrst observation of this effect in peripheral small systems at the SPS.

2.1.12 (O) Final results on two-particle correlations in azimuthal angle and pseudorapidity in Be+Be

Final results on ∆η∆φ correlations in central Be+Be collisions were submitted to arXiv [69] and to Eur. Phys. J. C. Apart from looking for critical point and quark-gluon plasma signatures, it is of interest to study speciﬁc physical phenomena that happen during and after the collision. The two- particle correlation analysis in pseudorapidity (η) and azimuthal angle (φ) disentangles different correlation sources which can be directly connected with phenomena like jets, collective ﬂow, resonance decays, quantum statistics effects, conservation laws, etc. Two-particle correlations in ∆η and ∆φ were studied extensively at RHIC and LHC and different mechanisms were proposed as their explanation. The NA61/SHINE collaboration already performed an analysis of two-particle correlations as a function of azimuthal angle and pseudo-rapidity differences of hadron pairs in p+p collisions [70] and, recently, in the most central Be+Be interactions [69], at different beam momenta from 19A to 158/150A GeV/c. The

20 Figure 12: Comparison of two-particle correlation function C − 1 (see Ref. [69] for details) for the range ∆η ∈ (0, 0.5) in collisions of p+p (blue) and Be+Be (red). Columns from left to right show results for: all charge pairs, unlike-sign pairs, positive pairs, and negative pairs. NA61/ SHINE data results are shown by markers (circles for p+p and squares for Be+Be), model results by lines (solid lines show EPOS while dotted lines – resonance-string model UrQMD). The results for p+p interactions were additionally scaled down by a factor of 5. Only statistical uncertainties are shown. structures observed in p+p correlation function were interpreted as a result of resonance decays, momentum conservation and Bose-Einstein correlations. In Be+Be collisions, one can see patterns that are qualitatively similar, but strongly suppressed by combinatorial background. The most noticeable difference as compared to p+p is a signiﬁcant enhancement in near-side (∆η, ∆φ) = (0, 0) region (see Fig. 12). This enhancement grows along with incident momenta and it is not predicted by theoretical models used for comparison to data (UrQMD and EPOS). We plan to extend the analysis to heavier systems (such as Ar+Sc) to improve our understanding of this observation and its origin.

2.2 New results for neutrino and cosmic ray physics

The NA61/SHINE collaboration has a program of hadron production measurements for long-baseline neutrino oscillation experiments at FNAL and J-PARC. These measurements improve knowledge of the neutrino ﬂux produced in accelerator based neutrino beams. NA61/SHINE measures total cross sections and differential spectra of hadron yields from thin and replica neutrino beam targets. Furthermore, the collaboration performs hadro- production measurements relevant for the interpretation of air-shower data at ultrahigh energies and measures fragmentation cross sections for the understanding of Galactic cosmic- ray data.

2.2.1 Production cross section of p+C interactions at 31 GeV/c for T2K (J-PARC)

The production cross section of 30.92 GeV/c protons on carbon is measured by the NA61/ SHINE spectrometer by means of beam attenuation in an identical copy (replica) of the 90-

21 cm-long target of the T2K neutrino oscillation experiment. This method of direct production cross section estimation minimizes model corrections for elastic and quasi-elastic interactions.

Analysis of the recorded 1.2 M events gives the probability, Psurvival, that a beam particle avoids production interactions inside the 90-cm-long target. Then the production cross section σprod is calculated using the relation:

−L·n·σprod Psurvival = e , (5) where L is the target length and n is the number density of carbon nuclei. Note that a production interaction is deﬁned as any interaction in which new hadrons are born. The preliminary production cross section is

+1.9 σprod = 227.6 ± 0.8(stat) −3.2(sys) −0.8(mod) mb. (6) This direct measurement is aimed at reducing the uncertainty on the T2K neutrino ﬂux prediction associated with the re-weighting of the interaction rate of neutrino-yielding hadrons. This analysis has been ﬁnalized recently and it is now being prepared for publication.

2.2.2 Hadron spectra in π++Be and π++C interactions at 60 GeV/c (FNAL)

In the momentum range that is relevant for the current and future long-baseline neutrino program at Fermilab, there is very little existing data on the spectra of hadrons that are produced by pions that re-interact in the neutrino target. An analysis of the interactions of 60 GeV/c π+ with thin, ﬁxed carbon and beryllium targets was completed and published in 2019 [71] using data collected in NA61/SHINE in 2016. Integrated production and inelastic cross sections were measured for both of these reactions. In an analysis of strange, neutral 0 hadron production, differential production multiplicities of Ks , Λ and Λ were measured. Lastly, in an analysis of charged hadron production, differential production multiplicities of π+, π−, K+, K− and protons were measured. These measurements will enable long-baseline neutrino experiments to better constrain predictions of their neutrino ﬂux in order to achieve better precision on their neutrino cross section and oscillation measurements. The results for π+ resulting from the interactions of 60 GeV/c π+ with a thin carbon targets are shown in Fig. 13.

2.2.3 Hadron spectra in p interactions at 60 GeV/c (FNAL)

NA61/SHINE has analyzed proton data sets collected in 2016 and has already published inelastic and production cross sections, as discussed in the 2019 status report. Using the same data sets of 60 GeV/c protons on thin carbon and aluminum targets, measurements of differential hadron production yields are now being performed. Similarly to the π+ analysis 0 0 ¯ ± described in Sec. 2.2.2, spectra of neutral V particles (KS, Λ, Λ) and charged hadrons (π , K±, proton) are measured. Some preliminary results, including only statistical uncertainties, are shown as a function of momentum in Figures 14 and 15 for a chosen interval in production angle θ. Estimations of systematic uncertainty are ongoing and expected to be ﬁnalized shortly.

22 Figure 13: Measurements of momentum spectra of π+ resulting from π+ + C at 60 GeV/c interactions are shown (from [71]). The NA61/SHINE results are compared to the predictions of several different Monte Carlo simulations.

23 NA61/SHINE Preliminary NA61/SHINE Preliminary NA61/SHINE Preliminary

•1 + •1 + •1 π : [60, 100] mrad NA61 p+C@60 GeV/c (stat. only) 0.14 K : [60, 100] mrad NA61 p+C@60 GeV/c (stat. only) p: [60, 100] mrad NA61 p+C@60 GeV/c (stat. only) 2.2 NA61 p+C@31 GeV/c (stat.+syst.) NA61 p+C@31 GeV/c (stat.+syst.) 0.45 NA61 p+C@31 GeV/c (stat.+syst.) FTFP_BERT FTFP_BERT FTFP_BERT

) [GeV/c] 2 ) [GeV/c] ) [GeV/c] θ QGSP_BERT θ 0.12 QGSP_BERT θ 0.4 QGSP_BERT 1.8 FTF_BIC FTF_BIC FTF_BIC 0.35 n/(dpd n/(dpd n/(dpd 2 2 2 d 1.6 d 0.1 d 0.3 1.4 0.08 1.2 0.25

1 0.06 0.2 0.8 0.15 0.04 0.6 0.1 0.4 0.02 0.05 0.2

0 0 0 2 4 6 8 10 12 14 16 2 4 6 8 10 12 14 16 2 4 6 8 10 12 14 16 18 20 p [GeV/c] p [GeV/c] p [GeV/c]

Figure 14: An example of momentum spectra of charged hadrons resulting from p + C at 60 GeV/c. From left to right, ﬁgures correspond to π+, K+, and proton. The NA61/SHINE results are compared to the predictions of several different Monte Carlo simulations, as well as former NA61/ SHINE p + C at 31 GeV/c measurements.

NA61/SHINE Preliminary NA61/SHINE Preliminary NA61/SHINE Preliminary •1 0 •1 Λ •1 Λ KS: [60, 100] mrad NA61 p+C@60 GeV/c (stat. only) : [60, 100] mrad NA61 p+C@60 GeV/c (stat. only) : [80, 160] mrad NA61 p+C@60 GeV/c (stat. only) 0.12 NA61 p+C@31 GeV/c (stat.+syst.) 0.18 NA61 p+C@31 GeV/c (stat.+syst.) FTFP_BERT 0.035 FTFP_BERT FTFP_BERT QGSP_BERT ) [GeV/c] ) [GeV/c] ) [GeV/c]

θ QGSP_BERT θ QGSP_BERT θ 0.16 FTF_BIC 0.1 FTF_BIC FTF_BIC 0.03 n/(dpd n/(dpd 0.14 n/(dpd 2 2 2 d d d 0.025 0.08 0.12

0.1 0.02 0.06 0.08 0.015 0.04 0.06 0.01 0.04 0.02 0.005 0.02

0 0 0 2 4 6 8 10 12 14 2 4 6 8 10 12 14 16 18 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 p [GeV/c] p [GeV/c] p [GeV/c]

Figure 15: An example of momentum spectra of V0 hadrons resulting from p + C at 60 GeV/c 0 ¯ is shown. From left to right, ﬁgures correspond to KS, Λ, and Λ. The NA61/SHINE results are compared to the predictions of several different Monte Carlo simulations, as well as former NA61/SHINE p + C at 31 GeV/c measurement (except for Λ¯ , for which no 31 GeV/c measurement was available).

24 2.2.4 Hadron spectra in p interactions at 120 GeV/c (FNAL)

Proton-Carbon interactions collected at 120 GeV/c are currently being analyzed. This data set was taken after the addition of the Forward Time Projection Chambers (FTPCs), which signiﬁcantly improved acceptance in the forward region of phase space. Progress is being made toward a production cross-section measurement, which will be used for normalization of the differential spectra. The new SHINE-native dE / dx calibration includes support for the FTPCs, enabling particle identiﬁcation at and near the beam momentum.

2.2.5 New results for cosmic-ray physics

Air Shower Physics In the reporting period, the collaboration worked on finalizing the publication of reactions measured to improve the understanding of cosmic-ray induced air showers. This publication will provide the final release of data with pion beams at 158 and 350 GeV/c on a thin carbon target and will in particular feature the production spectra of ± ± ¯ 0 ∗0 0 charged hadrons and identified particles (π ,K , p(p),¯ Λ(Λ),KS,K , ω and ρ ) as reported previously in [72–77].

Cosmic-Ray Anti-Nuclei Our studies of the formation of light anti-nuclei (in particular, anti-deuteron) in nuclear collisions aim to understand the background to searches for Dark Matter in the Galaxy. The production of anti-nuclei in hadronic interactions is not well understood. The predicted anti-nuclei ﬂuxes from cosmic-ray propagation models are highly correlated with antiproton production in proton-proton interactions. Hence, high-precision antiproton production cross sections at different collision energies near the production threshold of different light anti-nuclei are especially important. Large p+p data sets with about 55 million events recorded at 158 GeV/c from 2010 and 2011, and about 9 million events at 400 GeV/c from 2016, are in the process of being analyzed. The main goal of the dE/dx-based analysis is to produce high-precision (anti)proton spectra, along with kaon and pion spectra as well. The particle spectra and their correlations will be used to test and tune hadronic generators like EPOS-LHC. The time-of-ﬂight analysis of these data sets to investigate deuteron production is also underway.

Fragmentation of Cosmic-Ray Nuclei A pilot run [78] on the feasibility of nuclear fragmentation measurements relevant for Galactic cosmic rays took place in December 2018. 3 days of test data for the measurement of Boron production in C+p interactions were recorded and a preliminary measurement of the fragmentation cross section of C on p to B was presented in [79] and established the possibility of this type of measurement with NA61/ SHINE. Currently the cosmic-ray group focuses on the extension of this analysis to individual isotopes and lower-mass nuclei like Be and Li. Although the test data from 2018 provides only limited statistics, a full analysis of all produced particles provides important lessons for the physics data taking foreseen in 2021 and 2022 (see Sec. 5.1 and Sec. 5.2).

25 3 Software and calibration upgrades

As was reported in past status reports, NA61/SHINE has been migrating its software from the “Legacy” framework to a new software framework, called SHINE. This migration was necessary for various reasons, such as lack of the Legacy software’s extendability to new detectors, out-of-dated physics models for the particle interaction simulations, and require- ment for 32-bit builds. Since we have stopped using most of the Legacy software and some core components have been implemented into the SHINE framework via wrappers, this section will focus on the status of the native SHINE framework.

3.1 Native SHINE software

3.1.1 SHINE framework

Since the previous status report 3 software releases were made. Most of the changes were associated with further development of the native Monte Carlo simulation and event reconstruction, described in dedicated sections below. Further work was conducted to integrate better with centrally provided software facilities. Layered LCG software stacks were adapted in our lcgcmake toolchains. Jenkins build slaves were rebuilt using a new Puppet conﬁguration based on the CERN’s bagplus Puppet module providing a lxplus-like setup of virtual machines. This assures that the software environment for building and testing of the SHINE software is the same as that of the primary production environment — lxplus and lxbatch clusters. It also facilitates future transitions to newer operating systems. Thanks to overcoming some technical problems with the help of the EP-SFT group, the same compiler version, gcc 8, is now used for both 32 and 64 bit builds. Previously older gcc version was required for 32 bit builds. Also automatic, periodic Coverity checks of the SHINE software were re-enabled, although the use of the tool still requires better integration in the NA61/SHINE workﬂow.

3.1.2 Monte Carlo simulation

AGEANT4-based Monte Carlo simulation chain has been implemented and tested since the last report. It will be used for all gathered reactions. In most cases GEANT4 simulation of the PSD detector will be used. In addition, a fast PSD simulator has been developed in order to avoid the time and resource consuming GEANT4 simulation. It can be also used for already simulated data. Mass production of MC data has been started. Progress on the event reconstruction is discussed in the next section.

26 3.1.3 Event reconstruction

The native SHINE reconstruction has undergone signiﬁcant development since the previous report. The underlying Kalman Filter infrastructure has been improved upon. A campaign is underway to compare the results of the Legacy reconstruction to the native SHINE reconstruction. Individual updates are detailed below.

(i) Kalman Filter Tracking Updates. The Kalman Filter algorithm was previously implemented using a single-pass, back- to-front ﬁltering algorithm. This method returns track parameter estimations at the most upstream point on a track. The new implementation uses the Rauch-Tung-Striebel (RTS) smoothing algorithm, which provides an improved estimation of track parame- ters at any point along the track. This algorithm performs the Kalman Filtering procedure in one direction, storing the current result and covariance matrix at each point. The ﬁt is then performed in the opposite direction, again storing the results and covariance matrices. At each point, the estimates are combined in a weighted manner, using the covariance matrices associated with each estimate. (ii) Time-of-Flight (ToF) Updates. Since the last report, ToF modules for the ToF simulation and reconstruction have been developed; the ToF-F simulation module has been completed and is performing as expected. For data taken in 2017 and 2018, ToF-F was employed with DRS4 readout electronics. For this data sets digitization, simulation and reconstruction algorithms are under development.

3.1.4 TPC Krypton Calibration

TPC front-end electronics channels typically exhibit large gain fluctuations of up to 50%. These fluctuations impact TPC cluster positions, which are calculated using the weighted mean of pad positions and recorded charges. The fluctuations also significantly impact dE/dx resolution and particle identification capability. In order to calculate and correct for these large inherent fluctuations, we introduce a radioactive 83Kr isotope with a well-known decay spectrum into the TPCs. The prominent 83Kr decay peak at 41.6 KeV is used to calibrate the electronics channels. A new edge-detection technique was introduced to identify the upper edge of the decay peak, which enables calibration of noisier electronics channels or channels with fewer decays. The channel gain is then obtained by calculating the average decay peak position for each sector and normalizing the individual channel peak positions. These gains are then applied during reconstruction. An example of the uncorrected and corrected collected charges and decay spectra can be seen in Fig. 16.

3.1.5 dE/dx calibration

A comprehensive TPC dE / dx calibration software package has been developed for the SHINE-native software framework. This calibration process is critical for identifying pro-

27 Figure 16: Effects of the 83Kr calibration procedure on electronics channel response in FTPC1. Large variations in channel gains can be seen before calibration (upper left plot), and a much more uniform response is achieved with calibration (upper right plot). The 83Kr spectrum is poorly-resolved before calibration (lower left plot), whereas the individual decay peaks are well- separated after calibration (lower right plot).

duced particle types. The calibration process consists of four steps: (i) Time-dependent gain correction (ii) Drift loss correction (iii) TPC sector normalization (iv) Front-end electronics chip gain correction Each of these calibration steps is performed with a centralized philosophy: a calibration module processes a set of data and extracts the relevant TPC point charge information and stores it in a light ROOT TTree. A specialized calculation application then processes the resulting ROOT ﬁles and creates ﬁles containing the computed corrections, as well as QA plots displaying the corrections.

(i) Time-dependent gain correction The time-dependent gain correction accounts for variations in the TPC amplification voltages as a function of time, typically on the order of 5 - 10%. Each distinct TPC amplification region, or TPC sector, is connected to a distinct high-voltage distribution channel, and thus requires its own correction. The calculation application accumulates cluster charges and calculates a statistic reflecting the magnitude of the charges. The

28 magnitudes are then smoothed and normalized to the average charge for the sector. This results in a time-dependent gain correction factor. The factors are recorded in ten-minute intervals and stored in a ﬁle, available for use as a correction during reconstruction. Charge variations after correction are typically less than 1%. (ii) Drift Loss Correction The drift loss correction restores charge lost during electron drift from the ionization point to the ampliﬁcation plane. This correction depends on the assumption that particle production is approximately symmetric in azimuthal angle φ. Using this princi- ple, the cluster charge magnitude is computed as a function of y, the drift coordinate, around the beam position (y = 0). Cluster charges with larger drift distances are observed to have smaller magnitudes when compared to clusters with smaller drift distances. An asymmetry factor a(y) is computed using the cluster charge q(y):

q(y) − q(−y) a(y) = (7) q(y) + q(−y)

The factor a(y) is a constant as a function of y to first-order. These constants are calculated for each TPC sector and stored in a file for application during reconstruction, where a cluster’s charge is corrected based on its y-position. Charge asymmetry after correction are typically on the order of 1%. (iii) TPC Sector Normalization Each individual TPC amplification region will possess a unique gain factor. In order to achieve percent-level dE /dx calibration, the amplification regions must be accurately normalized. To calculate the normalization factor for each TPC sector, we must choose a physical reference. Due to the large availability of pions in most TPC sectors, we choose the expected pion mean dE/dx value as a reference and normalization. To perform the normalization a module separates TPC clusters on well-fit tracks by TPC sector and calculates a truncated mean dE / dx value for the segment of track. These dE/dx values are stored for each TPC sector. The calculation application contains a likelihood fitter that performs a five-particle fit to the selected tracks, returning yields for electrons, pions, kaons, protons, and deuterons. The input tracks are binned into fine momentum slices, and the fit is performed in momentum bins containing a sufficient amount of tracks. An example fit can be seen in Fig. 17. The offset from the nominal Bethe-Bloch expectation for the pion distribution is recorded for each of the momentum slices, and a weighted combination of these off- sets is taken as the normalization factor for the TPC sector. This normalization factor is applied to each cluster contained in the corresponding TPC sector during reconstruction. (iv) Front-End Electronics Chip Gain Correction The chip gain correction accounts for variations in the TPC front-end electronics chips and other spatially-dependent gain effects, such as amplification wire sag or fringe field effects. To calculate the correction, each cluster charge is normalized to its track mean dE/dx and associated with a front-end amplification chip. The normalized charge and chip number are stored. The chip gain calculator reads the gains for each chip and

29 Figure 17: (Color online) An example ﬁt for one TPC sector. The deviation of the pion distribution location (red) from the nominal Bethe-Bloch pion expectation is used to calculate the sector normalization constant.

calculates a correction factor, if enough entries for the chip are found. The calculator application then creates a calibration ﬁle and stores the computed gains for each chip. These gains are applied according to the cluster’s chip number during reconstruction.

3.2 Calibration

Calibration activities and upgrades during last year are: (i) TPC dE/dx calibration software package was developed for the SHINE-native software framework (see previous subsection) and tested. (ii) The TPC drift velocity (vdrift) and T0 calibration algorithm was significantly modified and optimized. The new stage (pre-Stage2) of the procedure is responsible for time dependent corrections of vdrift in TPCs. The stage2 is now used only for scaling of Vdrift. The technique of matching between MTPCs tracks and TOF hits was significantly improved. (iii) The new manager for residual corrections of cluster positions was supplemented by the distributions of absolute values of residuals in addition to distributions of mean values. The graphical presentation of distributions was significantly improved in the QA software for residuals of cluster positions. (iv) The tracking in the magnetic field was extended to the region of new target position in the data collected with Vertex Detector. It improved the precision of the calculation of cluster position residual corrections.

30 (v) The new SHINE module for TOF calibration was prepared and tested. Additional selection of TOF signals based on TDC values was implemented. (vi) The PSD calibration software was supplemented by the procedure of longitudinal shower proﬁle correction especially important for Pb+Pb data samples (vii) The data samples of Xe+La collisions at 40A and 150A GeV/c beam momentum were fully calibrated. The data sample of Xe+La interactions at 75A GeV/c was preliminary calibrated. Energy loss (dE / dx) calibration was prepared for p+Be, p+C, p+Al collisions at 60 GeV/c beam momentum as well as p+Be, p+C at 120 GeV/c.

4 Hardware upgrade

During the Long Shutdown 2 at CERN (2019-2021), a significant modification of the NA61/ SHINE spectrometer is ongoing. The upgrade is motivated by the charm and neutrino pro- grams, both of which require a tenfold increase of the data-taking rate to about 1 kHz. The charm program also requires doubling of the phase-space coverage of the Vertex Detector. This, in particular, requires the following: (i) construction of a new Vertex Detector, (ii) replacement of the TPC readout electronics, (iii) implementation of new trigger and data acquisition systems, (iv) upgrade of the Projectile Spectator Detector, (v) construction of new ToF detectors for particle identification at mid-rapidity.

Figure 18: Upgrades of NA61/SHINE planned to be completed during the LS2 period.

31 Figure 19: Schedule of the NA61/SHINE upgrade, status for end of September 2020

The detector upgrades are graphically summarized in Fig. 18 and discussed in detail in Refs. [80–82]. Note, that planning described in some of the Technical Design Reports from Ref. [82] is not up to date, as most of the documents were prepared in 2019 and were not updated since then.

Current detailed schedule of the upgrade for all subsystems is presented in Fig. 19. Work on the upgrade follows the schedule and no obstacles are seen to complete the upgrade by summer 2021 and have full readiness of the NA61/SHINE detector for the first beam delivered to North Area in July 2021. Updated version of the planned spending profile is shown in Table1. Additionally the table presents the planned source of funding. The spending profile takes into account the recent approval of the Polish-German Beethoven, Polish-Norwegian Grieg and US DOE grants.

Table 1: Spending proﬁle of the NA61/SHINE upgrade. All funds are granted assuming 210k CHF yearly contribution to the NA61/SHINE common fund. year 2018 2019 2020 2021 2022 sum source of funding US DOE (USA) grant (32%) TPC upgrade - 50k 450k - - 500k Greig (Poland/Norway) grant (48%) CF (20%) VD - - 130k - - 130k CF (100%) PSD - 55k - - - 55k INR (Russia) NA61/SHINE contribution MRPC ToF 50k 90k 376k 10 - 526k JINR grant (100%) BPD - - 30k - - 30k Beethoven (Poland/Germany) grant (100%) Maestro (Poland) grant (52%), TDAQ - 130k 120k - - 250k Beethoven (Poland/Germany) grant (48%) JINR grant (30%), DRS4 - 40k 90k - - 130k US DOE (USA) grant (70%)

32 Recently ﬁnancial resources required for the TPC, PSD, MRPC ToF, BPD and TDAQ upgrades are covered by already approved grants. In 2019 about 160k CHF has been saved to cover the hardware expenses in 2020. This saving and the granted contributions to the 2020 common fund (200k CHF) allow to cover the cost of the upgrade of the Vertex Detector (130k CHF) and the 2020 installation of the ALICE electronics (50k CHF).

5 Beam request for 2021 and plans for data taking in 2022-2024

5.1 Beam request for 2021

The first NA61/SHINE beam request for 2021 was submitted to the SPSC in the 2018 [81]. It was subsequently recommended by the Committee [83] and approved by the Research Board [84]. The request assumed that the SPS beams for physics will be available from April to December 2021. Due to the COVID-19 pandemic the beam schedule had to be modified and its most recent version [85] assumes the SPS beams for experiments from July 12 (Mon- day) to December 10 (Wednesday), 2020. In order to comply with the new beam schedule NA61/SHINE changed the beam request for 2021 and the new request reads: Commissioning and calibration period: (i) July 2021: two weeks of a hadron beam for the detector commissioning, (ii) August 2021: one week of access for fixing uncovered issues, (iii) September 2021: three weeks of a hadron beam for the detector commissioning and calibration runs. Time between the three periods as well as the last period and the first physics run is needed to prepare and implement solutions of potential problems. The original schedule assumed a three-month long gap between the last detector commissioning run and the first physics run. In the new schedule this gap is reduced to several weeks and thus in this short period only minor issues can be fixed. In case of major problems the proton period in October/Novem- ber 2021 will be used for final commissioning and tests. Physics with secondary hadron beams: (i) October/November 2021: 5 weeks of proton beam at 31 GeV/c for data taking for neutrino physics. The requested 5 weeks of data taking for neutrino physics are needed to improve measurements of hadron flux from the T2K replica target as discussed in 2018 Addendum in Sec. 8.1 [80]. That Addendum originally requested four weeks of replica target data followed by one week of super Sylon thin target data. The T2K collaboration has since requested a full five weeks of replica target data, as this is most critical to their current physics program. Super Sylon is being considered as a material for future T2K targets, and thin target data on Super Sylon at NA61/SHINE may be requested in the future.

33 9 RESULTS 100

SK: Neutrino Mode, ν µ SK: Antineutrino Mode, νµ

Horn & Target Alignment Horn & Target Alignment Hadron Interactions Hadron Interactions 0.3 Material Modeling 0.3 Material Modeling Proton Beam Profile & Off-axis Angle Number of Protons Proton Beam Profile & Off-axis Angle Number of Protons Replica 2010 Error Replica 2010 Error Horn Current & Field Replica 2009 Error Horn Current & Field Replica 2009 Error Thin Error Thin Error Fractional Error Φ×E , Arb. Norm. Fractional Error Φ×E , Arb. Norm. 0.2 ν 0.2 ν T2K Work in Progress

0.1 0.1

0 0 10−1 1 10 10−1 1 10 Eν (GeV) Eν (GeV) SK: Antineutrino Mode, ν SK: Neutrino Mode, νµ µ Figure 20: T2K ﬂux uncertainty as a function of the neutrino energy. Black and red line show the Horn & Target Alignment Horn & Target Alignment total error and the error from hadronHadron Interactions production,respectively. Hadron Interactions 0.3 Material Modeling 0.3 Material Modeling Proton Beam Profile & Off-axis Angle Number of Protons Proton Beam Profile & Off-axis Angle Number of Protons Replica 2010 Error Replica 2010 Error Horn Current & Field Replica 2009 Error Horn Current & Field Replica 2009 Error Thin Error Thin Error Fractional Error Φ×E , Arb. Norm. Fractional Error Φ×E , Arb. Norm. 0.2 ν 0.2 ν

0.1 0.1

0 0 10−1 1 10 10−1 1 10 Figure 21: The momentum and angle distribution of the charged kaons exitingEν (GeV) from the T2K tar- Eν (GeV) get, which contribute to neutrino at the far detector. Black lines outside the red box indicate the SK: Neutrino Mode, νe coverage of the NA61/SHINE replica 2010 data. We plan to expand the coverage in the highSK: Antineutrino Mode, νe momentum region (red box) by accumulating higher statistics data. Horn & Target Alignment Horn & Target Alignment Hadron Interactions Hadron Interactions 0.3 Material Modeling 0.3 Material Modeling The planned measurements ofProton the Beam hadron Profile production& Off-axis Angle on T2KNumber replica of Protons targets are crucial to Proton Beam Profile & Off-axis Angle Number of Protons Replica 2010 Error Replica 2010 Error predict the T2K/Hyper-K neutrinoHorn Current ﬂux & Field and its uncertainty.Replica The 2009 current Error uncertainty is cal- Horn Current & Field Replica 2009 Error culated based on the published results of the 2010 replica targetThin Error measurements at NA61/ Thin Error Fractional Error Φ×Eν, Arb. Norm. Fractional Error Φ×Eν, Arb. Norm. SHINE [86], as0.2 shown in Fig. 20. The uncertainty on the absolute ﬂux is around 5 % at the0.2 neutrino energy peak at 0.6 GeV while it is above 5 % at the high energy region. The largest source of the uncertainty is still the hadron production. The remaining uncertainty can be

0.1 0.1

34 0 0 10−1 1 10 10−1 1 10 Eν (GeV) Eν (GeV) SK: Antineutrino Mode, SK: Neutrino Mode, νe νe

0.1 0.1

0 0 10−1 1 10 10−1 1 10 Eν (GeV) Eν (GeV)

Figure 74: Total ﬂux uncertainty at SuperK with replica 2010 tuning. νµ Ratio of FHC 250kA

1.1

1.05

0.95 Ratio 0.9

0.85 NA61 2010 binning 0.8 NA61 expanded binning 10−1 1 10 Neutrino Energy [GeV]

Figure 22: The expected improvement of the T2K flux prediction with new replica target data. This plot shows a ratio of nominal neutrino flux to the one calculated with hadrons covered by the NA61/SHINE data. The red dots represent the ratio in case the 2010 replica target coverage. If the production of the high momentum charged kaon is measured, it is expected that the ratio will become to the blue dots and an improvement of the T2K/Hyper-K flux prediction at the neutrino energy more than 4 GeV is expected. improved by further understanding of hadron production from the replica target. Based on the previous measurements [86], we will try to improve the systematic uncertainty of the hadron production measurement by placing the replica target closer to the spectrometer, which will reduce the significant uncertainty associated with backward extrapolation . Moreover, the high neutrino flux uncertainty at the high energy region is due to a lack of knowledge of high momentum charged kaon production from the replica target. Figure 21 shows the coverage of the existing replica target data at NA61/SHINE. If the production of the high momentum charged kaons is measured, an improvement of the T2K/Hyper-K flux prediction at the neutrino energy more than 4 GeV is expected as shown in Fig. 22. The reason why the high momentum charged kaon was not measured in the 2010 replica target run is the limited statistics. Therefore, a further data taking of the replica target is necessary. Among the requested 5 weeks of data taking, 30 days will be utilized for the replica target data taking to accumulate the high momentum charged kaons. The remaining 5 days will be utilized for commissioning and calibration data taking. Physics with lead beams: (i) November/December 2021: three weeks of Pb beam at 150A GeV/c for charm hadron measurements in Pb+Pb collisions, (ii) December 2021: one week of a secondary (fragmented) light-ion beam at 13A GeV/c for nuclear fragmentation cross-section measurements.

35 The requested three weeks of data taking for heavy ion physics are needed for measurements of charm production in Pb+Pb collisions at 150A GeV/c as discussed in Sec. 4 of 2018 Addendum [80]. The run will provide about 20% (about 100M events) of the total statistics of events for this reaction (Pb+Pb at 150A GeV/c) requested in the Addendum. This would allow for first systematic results on charm hadron production in central and mid-central collisions, see Table 3 in 2018 Addendum [80]. In particular, it will enable important results for peripheral Pb+Pb collisions, see Table 3 in 2018 Addendum [80]. The collection of the remaining event statistics is planned to be performed in 2022 and 2023 (see Sec. 5.2). One week of a secondary light-ion beam for the measurement of fragmentation of intermediate-mass nuclei relevant for the propagation cosmic rays in the Galaxy. This will allow us to record 30% of the data needed to match the precision of nuclear cross sections to the precision of flux measurements of modern space-based cosmic-ray experiments [87]. The full beam request and reactions to be studied was detailed in Secs. 7.1, 9.2 and 10 of [80]. Based on the experience of the successful pilot run [78, 79], one week of data taking will allow for a first high-statistics physics result on the Boron production in C+p interactions. Moreover, this first week of fragmentation data with the new detector setup will allow vali- dation of new procedures of data taking based on the experience of the pilot run and make it possible to adapt them to the upgraded detector. In particular, we will investigate how the increased dynamical range of the new TPC electronics together with alternating sector-wise high-voltage settings in the TPCs can improve the measurement of the charge of the frag- ments. The collection of the remaining event statistics with final settings is planned to be performed in 2022 (see Sec. 5.2).

5.2 Request for measurements in 2022-2024

The request for measurements in 2022-2024 was presented in detail in 2018 Addendum [80]. The SPSC recognised the broad interest of the NA61/SHINE physics programme after LS2 [83, 84], as outlined in the 2018 Addendum. The measurements requested for 2022-2024 are a continuation of measurements approved for 2021 and they are listed below. Physics with lead beams: (i) 2022: four weeks of Pb beam at 150A GeV/c for charm hadron measurements in Pb+Pb collisions, 2022: two weeks of a secondary light-ion beam at 13A GeV/c for nuclear fragmentation cross-section measurements for cosmic-ray physics, (ii) 2023: six weeks of Pb beam at 150A GeV/c for charm hadron measurements in Pb+Pb collisions, (iii) 2024: six weeks of Pb beam at 40A GeV/c for charm hadron measurements in Pb+Pb collisions. For detail on the open charm related beam request see Sec. 4.4 and, in particular Table 2, of 2018 Addendum [80]. For details on the secondary light-ion beam request for cosmic-ray physics see Sec. 7.3 of 2018 Addendum [80].

36 Physics with secondary hadron beams: A series of measurements are planned to further refine estimates of the LBNF neutrino flux at the DUNE detectors. These measurements will require the following beams configurations: (i) 2022: four weeks of K+ beam at 60 GeV/c for thin-target graphite cross-section measurements, 2022: four weeks of 120 GeV/c proton beam at 120 GeV/c for thin-target titanium cross- section measurements, (ii) 2023: four weeks of 120 GeV/c proton beam for measurements on a LBNF/DUNE prototype target. For details on the secondary kaon beam request for neutrino physics see Sec. 8.4 of 2018 Addendum [80]. These data are critical for reducing flux uncertainties in the high-energy tail of the neutrino flux at DUNE, which is dominated by neutrinos from kaon parents. No data on kaon interactions at the relevant energies is currently available. The titanium data will additionally constrain interactions in the LBNF target containment vessel, which will be made of titanium. The long target data will provide a level of precision in DUNE flux estimation that is not possible with thin-target data alone, similar to what NA61/SHINE data has been able to accomplish for T2K. Although NA61/SHINE is making no formal request for secondary hadron beam in 2024 in this document, commissioning runs for the Very Low Energy Beam (see Section6) are likely to be requested in the future. NA61/SHINE requests the SPSC recommendation of the measurements planned for 2022- 2024 as given above.

6 Very Low Energy Beams

6.1 Physics with Very Low Energy Beams

NA61/SHINE, in collaboration with EN-EA experts, is developing a design of a very low energy (VLE) 1-20 GeV beamline. This possibility has been studied by a dedicated working group that has held regular meetings. Preliminary simulations of this new beamline branch have demonstrated that this beamline will open a new spectrum of physics opportunities. One such opportunity is measurements of low energy hadron (π±, K±, p) secondary interactions for the T2K and future Hyper-K experiments. These measurements would also be important for understanding the LBNF flux near DUNE second oscillation maximum, which is approximately 800 MeV. This beamline will be also useful to measure low energy proton interactions on a mercury target to understand neutrinos from spallation neutron sources, such as MLF at J-PARC (Japan) and SNS at ORNL (US), since no hadron production data exist in the low- GeV region. VLE proton beams can also be used to improve predictions of atmospheric neutrino flux. In particular, sub-GeV atmospheric neutrino fluxes are poorly understood, primarily due to the limited availability of hadron production data on proton- atmosphere interactions below 20 GeV. Finally, data from this beamline will also inform flux predictions for the Fermilab SBN program, which uses an 8 GeV proton beam.

37 6.2 Working Schedule

All of the interested physics communities (accelerator-based neutrino, atmospheric neutrino, and spallation source experiments) have strongly requested studying and building a Very Low Energy (VLE) beamline before CERN’s Long-Shutdown3 (LS3). In particular, a VLE beamline after LS3 would be too late to beneﬁt the JSNS2/J-PARC E56 sterile neutrino experiment at MLF. Taking into account the community’s request for earlier realization, NA61/ SHINE, with the strong support of EN-EA experts, will therefore aim to construct the VLE beamline before LS3, given the endorsement of the SPSC. A preliminary schedule for design and installation of this new beamline is available below. (i) September 2020 - May 2021 : Studies of layout and performance of a new low energy beam-line (ii) December 2020 - May 2021: Partial integration studies and analysis of feasibility and cost. Dedicated instrumentation studies R&D (iii) January 2021 - May 2021: Feasibility study (in terms of installation possibilities). In- strumentation R&D (iv) May 2021 - September 2021: Iteration with various groups (EN-EL, TE-MSC, EN-EA, BE-BI) for manpower & resources The situation will be revisited next year where the exact outlook on performance, possibilities and cost of installation for this beam-line can be assessed in more detail. To optimally meet the needs of the groups requesting this beamline, installation and commissioning should happen within the following 2-3 Year End Technical Stops (YETS), so that data taking can occur in 2023-2024. The NA61/SHINE collaboration is writing an addendum that details the physics case for this beamline and includes a beam request.

7 Ideas for additional measurements after LS3

Results obtained by NA61/SHINE and overall progress in physics on strong interactions, neutrinos and cosmic-rays indicate a need to extend NA61/SHINE measurements beyond the ones planned for the period 2021-2024. New measurements should be conducted after the Long Shutdown 3. Physics arguments and required beams are brieﬂy summarized below.

7.1 Measurements with ion beams for physics of strong interactions

Measurements of the system size dependence of hadron production properties at different collision energies were carried out by NA61/SHINE to search for the deconﬁnement critical point and to establish system size dependence of effects related to the onset of deconﬁne- ment. As a result an unexpected phenomenon has been discovered. Its presentation requires a brief introduction.

38 There are two models often used to obtain reference predictions concerning the system-size dependence of hadron production properties [88] - the Wounded Nucleon Model (WNM) [21] and the Statistical Model (SM) [89]. For the K+/π+ ratio at the CERN SPS energies they are: (i) The WNM prediction: the K+/π+ ratio is independent of the system size (number of wounded nucleons). (ii) The SM prediction: in the canonical formulation incorporating global quantum number conservation the K+/π+ ratio increases monotonically with the system size and approaches the limit given by the grand canonical approximation of the model. The rate of this increase is the fastest for small systems.

Figure 23: Measurements of the K+/π+ ratio in p+p, Be+Be, Ar+Sc and Pb+Pb collisions: system size dependence at 150A GeV/c [90](left) and collision energy dependence [5](right). Predictions of the Wounded Nucleon Model [21] and Hadron-Resonance Gas Model [91] are shown for comparison (left).

Figure 24: Measurements of the scaled variance ω of the multiplicity distribution of negatively charged hadrons in inelastic p+p interactions and central Be+Be and Ar+Sc collisions [92]: system size dependence at 150A GeV/c (left) and collision energy dependence (right).

Figures 23 and 24 show the unexpected result [90, 92]. The K+/π+ ratio in Fig. 23 and the scaled variance of the multiplicity distribution at 150A GeV/c in Fig. 24 are similar in inelastic p+p interactions and in central Be+Be collisions, whereas they are different in central Ar+Sc

39 collisions which are close to central Pb+Pb collisions. Both reference models, WNM and SM (represented here by the Hadron-Resonance Model [91]), qualitatively disagree with the data. The WNM seems to work in the collisions of light nuclei (up to Be+Be) and becomes qualitatively wrong for heavy nuclei (like Pb+Pb). On the contrary, the SM is approximately valid for collisions of heavy nuclei. However, its predictions disagree with the data on p+p to Be+Be collisions. The rapid change of hadron production properties when moving from Be+Be to Ar+Sc collisions is referred to as the onset of ﬁreball. From Fig. 23( right) follows that the increase of the K+/π+ ratio depends on the collision energy. On the other hand, the scaled variance ω of the multiplicity distribution shows only weak collision energy dependence (see Fig. 24( right)). The physics behind the onset of ﬁreball is under discussion [91].

Figure 25: A ﬁrst idea on a possible NA61/SHINE beam request for the data taking period after the CERN Long Shutdown 3.

NA61/SHINE has started a discussion with representatives of the CERN BE and EN departments on possibilities to perform systematic measurements of the effect by conducting a detailed two dimensional scan with low and intermediate mass nuclei at the CERN SPS. Figure 25 presents a draft of the beam request for the data taking period after the CERN Long Shutdown 3. The measurements will require a signiﬁcant improvement of the quality of the ion beams at low momenta (below 40A GeV/c). Two options are under consideration: (i) A strong improvement of the ion emittance from the machine would be necessary but this seems to require studies from the machine side in order to understand the possibilities that can be made available for that. EN-EA and BE-OP experts will follow up proposals for trying to mitigate these issues. (ii) One option to improve the beam quality could be the implementation of Gabor-lenses (GL) into the existing beam line. Therefore, experiments are planned to test to what extent the luminosity can be improved by using this type of lens. Gabor-lenses use a

40 static confined electron column for the focusing and manipulation of positively charged particle beams. The focusing force is a result of the self-field of the confined electrons and therefore it is radially symmetric. The focal length is given by the confined electron density, which was measured in previous experiments to be around 1015 m−3. Based on this result, table2 gives the focal lengths of an eight-meter long chain of Gabor-lenses, two meter each. Momentum / GeV/c Energy / GeV γ Focal length / m 5 4.149 5.421 68 10 9.106 10.70 138 20 19.08 21.34 276 80 79.07 85.27 1105 140 139.1 149.2 1934

Table 2: Focal lengths of an eight meter chain of Gabor-lenses for different proton beam energies.

The focal strength is anti-proportional to the length of the lens. Therefore, it is possible to reduce the focal length by additional Gabor-lenses in a possible final focus chain. Be- sides focusing, other effects of beam-electron cloud interaction are possible, which may cause a manipulation of radial particle beam density. Depending on electron density distribution inside the GL, the beam profile can be shaped to match the requirements on luminosity. The NNP-group of Goethe University Frankfurt therefore suggests the implementation of Gabor-lenses in the existing beam line. If the lenses are turned off, they will act like a drift-section and the beam dynamics are given by existing quadrupoles. In the case of operation, the implemented lenses could be used without or in addition to the existing beam optics and will provide a smooth focusing along the final focus chain. For the evaluation of the performance of Gabor-lenses different numerical models are used. In a first step, the genetic algorithm code AcceleratorConstructionSet2 is used to find the best position of a number of Gabor-lenses in the existing beam line and the best settings of focal strength for them and the existing quadrupoles (see Fig. 26). In a next step a detailed beam dynamics study is performed using TraceWin to investigate possibilities to improve the beam quality. The information about the interaction of a relativistic charged particle beam with a static confined electron column will be studied with GabLensM3. A first prototype of a two meter long Gabor-lens (GL2000) was designed and constructed at Goethe-University Frankfurt in 2019 (see Fig. 27). The behavior of an electron column as a function of the confinement will be investigated by the use of several diagnostic tools in the following months. The design of Gabor- lenses for low energy hadron beams will be started in 2021 and based on experimental data measured on GL2000. Depending on possible project founding (BMBF), the first devices can be put out to tender at the end of 2021. Technical prototyping and negoti- ations with commercial suppliers already started. Figure 28 shows a Gabor-lens with reduced length of 0.4 m to study technical issues of construction and production. In a first step, it is foreseen to install an 11 m meter test setup at H4-beamline, which consists of four Gabor-lenses of two-meter length each with diagnostic and pumping stages in between. First experiments using relativistic hadron beams might be possible from 2023. In case of a successful proven enhancement of the beam quality an implementation of the Gabor-lenses in H2-beamline should be possible during LS3. Further,

41 Figure 26: Example for an implementation of at least 41 m Gabor-lenses within the H2-beamline.

Figure 27: Gabor-lens prototype GL2000 on its test bench at Goethe-University Frankfurt. It is equipped with several diagnostic tools to characterize the properties of the conﬁned electron column.

increasing the number of lenses is considered to prepare high quality, low energy ion and hadron beams for NA61/SHINE experiments.

7.2 New measurements with anti-proton beams for physics of strong interactions

A new idea of measurements of collisions of anti-protons with elementary and nuclear targets has been proposed in Ref. [93]. The authors argue that the relatively slow progress in the understanding of baryon stopping processes over the last three-four decades was due to the limitations inherent to the older experimental data sets [94]. These limitations, which were the necessity of very doubtful basing of the phenomenological analysis on protons as a proxy for the total baryon number, and the lack of full, hermetic coverage in terms of baryon rapidity and transverse momentum, still remain a serious obstacle for baryon stopping stud-

42 Figure 28: First Gabor-lens constructed by a commercial supplier (left) and its operational test (right). ies e.g. in the LHC sector. On the other hand, they are largely lifted for experimental data obtained with the NA61/SHINE apparatus. An example of the resulting advantages for a phenomenological analysis is shown in Fig. 29 (left and central panels) where the proton and neutron data from NA49 - the predecessor of NA61/SHINE- build the full non-strange baryon experimental distribution in proton-proton collisions, and in proton-carbon reactions in which the projectile proton collides with more than one nucleon from the carbon target. Thanks to the detailed character, precision and very broad coverage of the NA49 proton and neutron data [95, 96], the Dual Parton Model - DPM [97] - analysis performed by the authors does not suffer from the grave uncertainties characteristic of earlier existing studies of baryon stopping. As a consequence, the latter analysis demonstrates in great detail the inability of the standard mechanism of softening of the projectile di-quark [97, 98] to describe the strength of baryon stopping in the multiple proton-nucleon collision process. This brings the conclusion that the di-quark cannot remain intact in more than ∼60%, and must be disintegrated in about 40% of such processes. The process of transport of the incoming baryon energy into the ﬁnal state has a fundamental importance for the totality of nowadays heavy ion physics, as it is connected to the energy density necessary for quark-gluon plasma formation [99, 100]. In this context, the state of the art knowledge on this process appears surprisingly limited, in particular also in the LHC regime, and not exempt of spectacular controversies [101]. New experimental data at the CERN SPS give a unique chance to signiﬁcantly improve this situation as their completeness, high coverage, as well as isospin-independence obtained by means of neutron measurements give a far better insight into the fate of quarks in the collision, including such fundamental elements√ as the survival or disintegration of di-quarks addressed above. The collision energy of sNN > 15 GeV, well available at the SPS, is optimal for the collection of such data as it allows for the experimental coverage of the complete projectile hemisphere, while at the same time it fully belongs to the ultra-relativistic, high energy regime. A dedicated research program of baryon transport studies with NA61/SHINE is supposed to bring

43 _ _ pp > B−B X pC > B−B X, 0.6 multiple collisions p dn/dy model 0.4 model

0.2 single diquark model x 0.6 A 0 0 1 2 3 0 1 2 3 y y

Figure√ 29: Left: distribution of net non-strange baryons measured in proton-proton collisions at sNN=17.3 GeV (data points), put together with the result of the DPM model calculation drawn as a solid line. Central: same distribution obtained for proton-carbon reactions in which the projectile proton undergoes multiple collisions with carbon target nucleons (data points), put together with the DPM model result drawn as a solid line; the same model result scaled by 0.6 is also shown. Right: diagram of annihilation of the negative baryon number from the anti-proton on multiple nucleons from the nuclear target. The left and central panels come from Ref. [93]. a considerable improvement of the baryon stopping process, at the price of a manpower/- financial effort which is close to negligible with respect to the overall working effort of the heavy ion field. Measurements with anti-proton beams have long been recognized as a component of key importance for such a research program [98, 102, 103]. This is because they offer new possibilities of studying the properties of the non-perturbative strong process by the presence of baryon number annihilation. As an example, Fig. 29 (right panel) illustrates a very specific diagram of the annihilation of negative baryon number from the anti-proton over multiple nucleons, the appearance of which is a direct consequence of the disintegration of the diquark postulated in Ref. [93]. As it is evident from the figure, the cross section for such annihilation processes will be strongly sensitive to the underlying dynamics governing the fate of quarks in the collision. Therefore, a comparative analysis of baryon stopping in proton- and anti-proton-induced reactions as a function of target atomic number will constitute the most efficient experimental tool in order to probe the different theoretical scenarios. The research program of p+p and p+A (A = 9, 12, 40, 208) measurements, and comparative studies with corresponding p+p and p+A reactions, is presently under consideration by the NA61/SHINE Collaboration.

7.3 Measurements for physics of neutrinos and cosmic-rays

NA61/SHINE will continue to support the needs of the neutrino and cosmic ray community after LS3. The most critical measurements in this time frame are likely to be measurements of hadron yields off of LBNF and Hyper-Kamiokande replica targets. Additional thin target

44 measurements are also likely to be needed, as the designs and simulations of these beam lines are further reﬁned. A clear area of need for ﬂux predictions at neutrino experiments is data using low-energy hadron beams, where existing hadron production data is extremely sparse. The future NA61/SHINE neutrino and cosmic-rays program is therefore likely to include data collected in the low energy beam described in Section6.

45 8 Summary

This NA61/SHINE annual report brieﬂy presents the status and plans of the NA61/SHINE experiment [1] at the CERN SPS. The report refers to the period October 2019 – October 2020. The summary of this report is as follows:

(i) New physics results, final and preliminary, were released (see Section2). They include results relevant for the NA61/SHINE study of the onsets of deconfinement and fireball and search for the critical point: (a) Final results concerning p+p interactions and onset of deconfinement [5]. (b) Final results on π− production in Be+Be [2]. (c) Final results on fluctuations of identified particles in inelastic p+p interactions [24]. (d) Preliminary results on higher order moments of multiplicity and net-charge in central Be+Be collisions at 150A GeV/c [37]. (e) Higher-statistics preliminary results on intermittency analysis in central Ar+Sc collisions at 150A GeV/c [41]. (f) Preliminary results on intermittency analysis using cumulative variables in central Ar+Sc collisions at 150A GeV/c. + (g) Final results on Ξ− and Ξ production in inelastic p+p interactions at 158 GeV/c [43].

Further new physics results within the strong interaction programme concern: (a) Final results on search for pentaquarks in inelastic p+p interactions at 158 GeV/c [58]. (b) Final results on φ meson production in inelastic p+p interactions at 40–158 GeV/c [60]. (c) Final results on K∗(892)0 production in inelastic p+p interactions at 158 GeV/c.[61]. (d) Final results on two-particle correlations in azimuthal angle and pseudorapidity in Be+Be collisions at 20A-150A GeV/c [69]. (e) Preliminary results on electromagnetic effects in Ar+Sc collisions at 40A GeV/c.

The results obtained within the NA61/SHINE reference measurements for long-baseline neutrino oscillation experiments at J-PARC and Fermilab as well as cosmic-ray experiments (CR-A, CR-G) include: (a) Preliminary results on production cross section of p+C interactions at 31 GeV/c for T2K (J-PARC). (b) Final results on hadron spectra in π++Be and π++C interactions at 60 GeV/c (FNAL) [71]. (c) Preliminary results on hadron spectra in p interactions at 60GeV/c (FNAL). (d) Preliminary results on fragmentation cross section of C on p to B at 13A GeV/c [79].

46 (ii) Software and calibration modiﬁcations (see Section3), in particular, include: (a) The NA61/SHINE software infrastructure changes follow the CERN IT infrastructure development. Numerous upgrades of the SHINE framework have been done. (b) The native SHINE Monte Carlo software is used for the simulated data production. (c) The native SHINE reconstruction software is under detailed tests. (d) The native SHINE dE/dx calibration software was developed and it is under tests. (e) The data calibration and reconstruction is progressing well.

(iii) Detector upgrade progress and plans are reported in Section4: (a) The upgrade conducted during the Long Shutdown 2 (2019-2021) concerns several major components of the NA61/SHINE experiment: Vertex Detector, readout electronics of the Time Projection Chambers, trigger and data acquisition systems, Projectile Spectator Detectors and Time-of-Flight detectors. Work on the upgrade follows the schedule and no obstacles are seen to complete the upgrade by summer 2021. (b) The ﬁnancial resources needed for the upgrade have been secured.

(iv) The beam request for 2021 already recommended by the SPSC and approved by the Research Board is presented in Section 5.1. It includes ﬁve weeks of hadron beams for detector commissioning and calibration, ﬁve weeks of proton beam at 31 GeV/c for measurements needed by T2K in Japan and four weeks of lead beams at 150A GeV/c and 13A GeV/c for the measurement within the NA61/SHINE open charm programme and the measurement for the fragmentation of intermediate-mass nuclei relevant for the propagation of cosmic rays in the Galaxy.

(v) Request for measurements in 2022-2024 which the SPSC already recognized as being of the broad physics interest is summarized in Section 5.2. Physics motivation and experimental performance were detailed in 2018 Addendum [81]. The requested measurements are a continuation of the 2021 measurements and include measurements with lead beams: (a) 2022: four weeks of Pb beam at 150A GeV/c for charm hadron measurements in Pb+Pb collisions, 2022: two weeks of a secondary light-ion beam at 13A GeV/c for nuclear fragmentation cross-section measurements for cosmic-ray physics, (b) 2023: six weeks of Pb beam at 150A GeV/c for charm hadron measurements in Pb+Pb collisions, (c) 2024: six weeks of Pb beam at 40A GeV/c for charm hadron measurements in Pb+Pb collisions.

as well as measurements with secondary hadron beams:

47 (i) 2022: four weeks of K+ beam at 60 GeV/c for thin-target graphite cross-section measurements, 2022: four weeks of 120 GeV/c proton beam at 120 GeV/c for thin-target titanium cross-section measurements, (ii) 2023: four weeks of 120 GeV/c proton beam for measurements on a LBNF/DUNE prototype target.

NA61/SHINE requests the SPSC recommendation of the measurements planned for 2022-2024

(vi) NA61/SHINE in collaboration with EN-EA experts is developing a design of a very low energy (VLE) 1-20 GeV beamline, Sec.6. Data from this beamline would serve a variety of purposes, including providing important constraints on low energy hadron interactions that impact the neutrino ﬂux predictions of T2K, Hyper-Kamiokande, and DUNE. Feasibility and design studies are underway now, and collaboration is compos- ing an addendum that describes the physics case for this beamline and makes a formal beam request. In order to make best use of this data, the beamline would ideally be ready for data taking in 2023.

(vii) Ideas for measurements after LS3 are presented in Section7: (a) Recent NA61/SHINE results on the onset of ﬁreball indicate a need to perform systematic measurements of the effect by conducting a detailed two dimensional scan with low and intermediate mass nuclei at the CERN SPS. This programme would require a signiﬁcant improvement of the quality of ion beams at the NA61/ SHINE target. Two options are under studies: improvement of the H2 beamline discussed with EN-EA and BE-OP, and installation of beam focusing optics based on Gabor lenses. (b) The research program based on measurements of p+p and p+A interactions is presently under consideration by the Collaboration. (c) There is an obvious need for continuation of the NA61/SHINE support of the neutrino and cosmic ray community after LS3. The most critical measurements in this time frame are likely to be measurements of hadron yields off of LBNF and Hyper- Kamiokande replica targets.

48 Acknowledgments

We would like to thank the CERN EP, BE, HSE and EN Departments for the strong support of NA61/SHINE. This work was supported by the Hungarian Scientific Research Fund (grant NKFIH 123842/ 123959), the Polish Ministry of Science and Higher Education (grants 667/N-CERN/2010/0, NN 202 48 4339 and NN 202 23 1837), the National Science Centre Poland(grants 2014/14/E/ ST2/00018, 2014/15/B/ST2 / 02537 and 2015/18/M/ST2/00125, 2015/19/N/ST2 /01689, 2016/23/B/ST2/00692, DIR/WK/ 2016/2017/ 10-1, 2017/ 25/N/ ST2/ 02575, 2018/30/ A/ST2/00226, 2018/31/G/ST2/03910), the Russian Science Foundation, grant 16-12-10176 and 17-72-20045, the Russian Academy of Science and the Russian Foundation for Basic Re- search (grants 08-02-00018, 09-02-00664 and 12-02-91503-CERN), the Russian Foundation for Basic Research (RFBR) funding within the research project no. 18-02-40086, the National Research Nuclear University MEPhI in the framework of the Russian Academic Excellence Project (contract No. 02.a03.21.0005, 27.08.2013), the Ministry of Science and Higher Edu- cation of the Russian Federation, Project "Fundamental properties of elementary particles and cosmology" No 0723-2020-0041, the European Union’s Horizon 2020 research and in- novation programme under grant agreement No. 871072, the Ministry of Education, Cul- ture, Sports, Science and Technology, Japan, Grant-in-Aid for Scientific Research (grants 18071005, 19034011, 19740162, 20740160 and 20039012), the German Research Foundation (grant GA 1480/8-1), the Bulgarian Nuclear Regulatory Agency and the Joint Institute for Nuclear Research, Dubna (bilateral contract No. 4799-1-18/20), Bulgarian National Science Fund (grant DN08/11), Ministry of Education and Science of the Republic of Serbia (grant OI171002), Swiss Nationalfonds Foundation (grant 200020117913/1), ETH Research Grant TH-01 07-3 and the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359 and the IN2P3-CNRS (France).

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