PoS(ICRC2021)514 1 International th 12–23 July 2021 July 12–23 37 SICS CONFERENCE SICS CONFERENCE Berlin | Germany Berlin Berlin | Germany Cosmic Ray Conference Ray Cosmic 1 ICRC 2021 THE ASTROPARTICLE PHY ICRC 2021 THEASTROPARTICLE PHY A. Sobkow, https://pos.sissa.it/ 3 M. Kasztelan, can be investigated 3 2 for Spin Independent J. Puputti, 2 ONLINE 1 cm 6,ℎ -46 J. Joutsenvaara, 1 J. Orzechowski, 5 and T. E. Ward 2 . If our interpretation is correct, the expected cross section for Spin Dependent and 10 2 K. K. Loo, 2 0 K. Jedrzejczak, I. Usoskin 0 cm 1 -42 T. Enqvist, ∗ P. Kuusiniemi, 0, J. Szabelski, 3 4 [email protected] International Cosmic Ray Conference (ICRC 2021) Presenter ∗ th Preliminary results from a 349-day run (live time) with ameasurement 565 kg are Pb target and presented. a 166-day background Three minormultiplicity anomalies spectra. were detected The in multiplicities of muon-suppressedsimilar these neutron but small excesses independent match measurement. theprinciple, outcome they of The may an be nature earlier, a of(WIMP) signature with the of a mass self-annihilation anomalies around of 10 remains a GeV/c would unclear, Weakly Interacting be but, Massive of in Particle theinteractions. order Analysis of of 10 the eventsection rate, limits based for Dark on Matter the (DM) mass statistical rangewith uncertainty, of an indicates approximately 3-40 upgraded that GeV/c NEMESIS cross- setup. Office of Nuclear Energy, DOE 1000 IndependenceTechSource, Santa Ave., Fe, SW, NM, Washington, D.C., United States 20585, United States E-mail: Department of Physics, University of Jyväskylä, P.O.Cosmic Box Ray 35, Laboratory, FI-40014 National University of Centre for Jyväskylä,28 Finland Nuclear Pułku Research (NCBJ), Strzelców Kaniowskich 69, 90-558 Łódź,University of Poland Oulu, Sodankylä Geophysical Observatory, P.O.University Box of 3000, Oulu, FIN-99600 Kerttu Sodankylä, Saalasti Finland Institute, PajatieHelsinki 5, Institute 85500 of Nivala, Physics Finland (HIP), P.O. BoxInstitut 64, für 00014 Physik University (IPH), of Johannes Helsinki, Gutenberg-Universität Finland Staudingerweg Mainz 7, (JGU), 55128 Mainz, Germany Copyright owned by the author(s) under the terms of the Creative Commons 4 2 6 ℎ 0 1 3 5 37 July 12th – 23rd, 2021 Online – Berlin, Germany © Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). M. Slupecki, O. Kotavaara, W. H. Trzaska, New NEMESIS Results PoS(ICRC2021)514 for WIMP 2 mass range. W. H. Trzaska 2 cm -39 self-annihilates on a Pb target, 2 2 mass range, meaningful searches could also be conducted on a 2 [3]. To go beyond these impressive results, even larger setups and 2 mass range. An auxiliary shield of charged-particle detectors would be [1]. For Spin Independent (SI) interactions, the corresponding limits 2 2 cm -47 Search for Dark Matter (DM) attracts significant theoretical and experimental effort. Some of Scattering is not the only feasible interaction mode for WIMPs. If they exist, they are also For WIMPs in the GeV/c Simulations are an integral part of every design study. Nevertheless, the actual data from a In addition to serving as a feasibility demonstrator for the full-size NEMESIS Dark Matter NEMESIS reuses the measuring stations2), (Fig. computer network, and some of the detectors the latest results in theoff direct nuclei search come for from Weakly XENON1T Interacting collaborationDependent Massive [1–3]. (SD) Particles The scattering (WIMPs) new of recoiling cross nonbaryonic section cold upper limit DM for is Spin- now of the order of 10 New NEMESIS Results 1. Introduction expected to self-annihilate into detectablephotons. Standard Model Such indirect (SM) searches particles, areCherenkov including conducted, telescopes high-energy for looking instance, by at H.E.S.S.,galaxies dense of MAGIC the and astronomical Milky VERITAS Way objects [4]. like These searches the are sensitive dwarf to spheroidal WIMPs in satellite the TeV/c masses around 100 GeV/c longer exposure times are needed [1]. are of the order of 10 working prototype is essential totions, optimize and the justify detection funding technology, for verify a full-scale thein experiment.1, background Fig. condi- has The NEMESIS been setup, collecting depictedmine data schematically [8] at in a Finland depth since of November 2019. 210 m.w.e. in the Callioexperiment, Lab NEMESIS also [7] collects at muon-induced neutron the spectra. Pyhäsalmi tracking The results with will combine position-sensitive muon neutronlateral detection distributions of providing high-multiplicity neutron precision events induced by cosmic yields, muonsThese on multiplicities, lead data, and copper. and summarised elsewhere inMonte these Carlo proceedings simulation [9], packages provide empiricalevaluation [10, of present input/database11]. and for future deep-underground experiments, They, includingneutrino-less searches in for double Dark turn, beta Matter, decay are studies, the etc. primary tool for background of the EMMA experiment [6]. The setup consists of 5 layers of SC16 muon counters [6], two large- smaller scale. For instance, if athe WIMP emerging SM with particles a would mass cause of aspallation a chain with of few GeV/c emission interactions resembling of proton- multiple or secondary muon-induced neutrons.a few An tonnes array of of target neutron material counters wouldof surrounding provide XENON1T adequate in means the of GeV/c detection to surpassneeded the to suppress sensitivity the cosmic muon induced backgroundleptons and serve from as a WIMP trigger for self-annihilation energetic charged [5].to design, The long-term build goal andIncluding of operate neutronS) the reflects such NEMESIS the Collaboration a is factEMMA setup. experiment that [6]. we The are reusing name infrastructure NEMESIS and (New components Emma from MEasurementS the 2. NEMESIS setup PoS(ICRC2021)514 ) 3 cm 5 × 10 × W. H. Trzaska 20 He proportional counters in 3 The yellow inset, superim- He neutron detectors were used 3 Figure 2: posed on the actual photo,size and shows position the of NEMESIS detec- tors inside one of the EMMAing measur- stations. The surroundingis tunnel approximately 5 meters wide andmeters 5 tall. 3 , with a common time output and hit-pattern informa- 3 cm 0 . He counters (pink) 3 3 × 5 . 12 × 5 . 12 ), amplitude-sensitive scintillators, and fourteen 2 cm 100 × Front (left) and side (right) view of the essential 100 For historical reasons, NEMESIS utilises a dual data acquisition system (DAQ). The SC16 Usually, DM measurements are performed deep underground to minimise the ambient muon are surrounded by PE moderator (red).(ochre) and MAZE SC16 scintillators scintillators (blue) are also shown. area ( polyethylene (PE) casting used for16 neutron individual pixels, detection. Each of the 46 SC16 modules comprises Figure 1: elements of the NEMESISmillimetres. setup. The Pb All target,lead dimensions bricks, consisting is are of depicted 50 in in standard-size darkfourteen grey. 50 The cm active long, volumes of 2.5 cm diameter tion [12]. Thesereliable detectors operation were and designed satisfactory tracking for capabilities extended [13]. use The underground and have demonstrated New NEMESIS Results extensively in the background conditionwithin studies the of ILIAS European and BSUIN underground projects laboratories [14].the conducted MAZE The outreach large-area plastic project scintillator [15]. detectors The were 565 part kg of target consists of fifty standard-size ( modules, responsible for muon tracking, relyflux on EMMA measurements DAQ. [13] It was at previously LSCthe used in two in the top Canfranc, muon layers Spain. anddetectors one The and of DAQ the the is two two triggered large-size bottomif scintillators when SC16 at use at layers least the least have one MAZE registered one neutron anneutron DAQ. of tube It thermalization event. was is time, fired. 2 The configured ms neutron to All longneutron collect waveforms signals event. from data are The the synchronisation digitised large of scintillators using the are FADCs. EMMA stored and with To MAZE each account DAQ systems for takes the place3. offline. Overburden and the ambient muon flux flux and the related background events.tracking Since capabilities, NEMESIS it is can a dual-purposefact, yield setup since meaningful with corrections results good for muon also thechallenges, at the muon-induced operation a of background moderate a demonstrator and depth at detectionIt a of allows site for efficiencies with 210 efficient an tuning are m.w.e. adequate of the number the of DAQ electronicsfor main In events and is data the beneficial. development quality of software checking. and procedures A statistically significant data sample, both with and without a target, Pb bricks. The bricks are removable toconfiguration. allow for background measurements in the same geometrical PoS(ICRC2021)514 W. H. Trzaska -suppressed), as µ , there is only a 17% difference 1 = < is the registered neutron multiplicity, < efficiency is a reasonable approximation. 2% ± 4 8 muon flux at the EMMA level [6]. Having the setup just is the actual and -1 s " -2 ) m 06 . , where 0 ± 29 . 1 Efficiency / < = Top panel: neutron multiplicity spectra obtained with Pb target (All events and . < " 13 The first striking feature, visible in3, Fig. is the clear background (measurement without Pb Preliminary results from a 349-day run (live time) with a 565 kg Pb target and a 166-day The extracted neutron multiplicities, shown in3, Fig. are not yet corrected for efficiency. ' " target) separation for multiplicities higher than one. While for Since Figure 3: well as without a target (Background). Bottom panel: statistical significance of thecan observed be excess events. collected within a few months.infrastructure2), (Fig. The accessibility, other and a advantages well-known of muon the flux. chosenhave Three location verified independent are measurements the the available ( background measurement are shown into3. Fig. match The the background acquisition countsDecember time on 2020, of the when plot the the were background Pb adjusted runintend run. to started. start It measuring The will with Pb be a ongoing copper data until target. were August 2021 taken4.1 when from we November Neutron multiplicity 2019 till Hence, the horizontal axis showsemitted the neutrons. registered number Neutron of detection neutrons efficiencyrelevant and simulations is not and a the analysis function are actual of complex numberHowever, both for and of energy simplified will and be evaluations, multiplicity. summarised a in The constant a dedicated publication. a short drive from theexisting surface facilities and lab detectors allows significantly for lowers the prompt costs and and unscheduled installation interventions. time. Reusing4. the Results and analysis New NEMESIS Results PoS(ICRC2021)514 km/s ) 3 ± 233 W. H. Trzaska ( = c E > 2 data yielded three and < 3 ) GeV/cm . It is unlikely that this agreement is 17 .
, the background events are suppressed ) 0 2 7 ( ± = > 6. A fit to the 9 . 55 < 2 . < 0 = 5 % ) 2 ( 8 / % ) , the largest registered background multiplicity, the suppression 2 ( 5 2 . = 23 < , is plotted in the lower panel of3. Fig. The position along the neutron He neutron detectors and a muon shield. The 271-day measurement, σ 3 Considering the amount of rock surrounding the relatively small 565 kg target, such a clear There is no doubt that neutrons from cosmic-ray (CR) muon interactions dominate the mul- The 2020 Review of Particle Physics [18] lists ( In 2001-2002, a group of Russian and US scientists performed a similar search [16, 17] Extensive simulations would be needed for a reliable comparison of NEMESIS with the 2002 -suppressed’ in3. Fig. Rejection of events related to transient muons reduced eight-fold the µ background separation could not have been takenand for granted. floor Fortunately, the are cavern walls, atreduce ceiling least the neutron 2 flux meters fromof from the neutron rock, absorbing the material a target (e.g., waterthis and PE(B)) tank on time. could the the be neutron sides More placed and information detectorsproceedings under above on the [9]. 2). (Fig. the the setup. station neutron None and multiplicity To of bricks measurements it further was is used given4.2 elsewhere in DM the candidates tiplicity spectra shown inconstitute3. Fig. a tiny addition to If thefor WIMP registered evidence events. self-annihilation of In small events principle, peaks are withthe at huge also visibility high statistics, of one present, multiplicities. DM might candidates, they look However, one thisdone will needs is to by not suppress requiring the muon-induced the events. case absence here. Withwe of NEMESIS, a expect it To improve is track the in emission SC16 ofvalid arrays signal an (no either traversing from energetic muons). the lepton top In or from’ the addition, the bottom since MAZE self-annihilation scintillator. event The [5], resulting spectrum we is request labelled a factor is 1 to 193. total number of counts exposing three structures at New NEMESIS Results between the target and background counts,by already one at order of magnitude. At Gaussian peaks on the dominantof exponential the tail. standard deviation The significance of the excess counts, in units accidental. 4.4 Cross section estimates as the updated local DM density and the circular rotation speed, respectively. Using these values, multiplicity axis and the statistical significance of the peaks are4.3 listed in1. Tab. Comparison with previous measurements for WIMP self-annihilation signalsMultiplicity in Detector System the (NMDS) designed Pyhäsalmi and constructed mine inSt. the in Khloplin Petersburg, Radium Finland. Russia. Institute in NMDS consisted They oflong, a employed 300 1.55 Neutron kg cubical cm Pb target diameter surroundedconducted by at sixty, 583 28.5 m.w.e. cm depth, yielded noanomalies conclusive discerned results. in However, there the were data, three corresponding one-sigma to neutron multiplicities 23, 33,NMDS and results. 471). (Tab. Nevertheless, the similarity betweenis the observed evident. anomalies, summarised The in multiplicity1, Tab. ratioratio for of all the three peaks two is experiments constant and close to the neutron efficiency PoS(ICRC2021)514 ) ) 2 0 & j 2 ( &, 3.02 ratio 2.9(7) 3.0(2) 3.4(3) & ( Multiplicity Efficiency ratio W. H. Trzaska and annihilation and gravitational ) ) ] 2 − 0 G= 13 18 23 = ∼ ∼ ∼ → c [GeV/c WIMP mass  ( # + c ( , strong for SI interactions. 102(26) 146(36) 185(46) ) Deduced ± 2 1 cm = c 46 NEMESIS . The composite neutral DM particle − ) ( 8(2)% efficiency 7.7(3) 11.0(6) 14.0(4) Neutron multiplicity 10 & Measured 6 6 . Taking 8% for the NEMESIS neutron detection ) #, , the average DM flux in the solar system is of the 2 2 f # , the Higgs pseudoscalar field, the mesons ) a 3.6 1.5 1.8 for SD and g, a 2 nificance ( Statistical sig- cm `, g 42 − ] 4, ` 2 4 10 12 18 25 = × gauge boson identified as Dark Matter, a massive neutral gauge particle upon contact with a Pb nucleus can weakly interact via the neutral near ∼ ∼ ∼ ; 5 ) ) ; [GeV/c + 0 ( WIMP mass 2 j ( strongly coupled to the massless graviton. = ) c 2 c , respectively. The energy deposited by each of the hadronic and baryonic reactions ( / ) NMDS 99(4) DM particles per second per cm 140(9) 202(13) G= Deduced radiation gauge boson field mixing with Yang–Mills (Y–M) fields. The model has 6 ) → 10 8 GeV 23.2(2)% efficiency + Properties of anomalous peaks in neutron multiplicity spectra detected by NMDS and NEMESIS. 2  ≈ # = We expect the annihilation of a DM particle within a Pb target to produce a large spallation-like In 2002 Ward presented [19] an extended Standard Model isospin symmetry breaking (ISB) The DM particle structure is extracted from RGM ISB matrix analysis. Such a WIMP is + 33(2) 47(3) 23(1) DM c Neutron multiplicity Measured # < Table 1: ( ( ( massless neutrino tunnelling out ofnucleon. the Following deep the (8 interaction, GeV)baryonic the DM parts DM potential which particle and undergo annihilates interacting into cascade with its a spallation constituent target in hadronic the and target wavefunction is found toby be the composed RGM of ISB 54% matrixneutral lepton, particle interactions DM 23% of the meson massive and radiation 23% gauge baryon bosons generated and Y–M fields. A order of efficiency, 40% as the total (intrinsic andmass geometrical) of efficiency of the the Pb MAZEWIMP scintillators, target 565 would and be kg around one-year measurement, the estimated detection limit for a 10 GeV/c and gravitational field, the scalar baryons ( and assuming WIMP mass around 10 GeV/c emission of neutrons. Like inand spallation, the we number assume of a emitted linear neutrons.to correlation extract However, DM neutron between mass. multiplicity the spectra Additional WIMP information alone or mass for are assumptions an are not needed. unambiguous sufficient link One between needs a the specific number model of observed neutrons and WIMPmodel mass. of massive spin-dependent electroweak (EW) New NEMESIS Results 4.5 DM mass estimates composed of ordinary matter,gravitational, quarks and and Y–M fields. leptons generatedscheme, There rather by are ordinary the no forces exotic combination such interactionsthe of as or WIMP the EW, exotic decay W-boson dark Higgs, in propagator propagators an of inlepton interaction the this scalar of weak DM particles interaction particle central with to nuclei. The Y–M EW field introduces the recently been improved by theGauge addition Model of (RGM). Radiation A Gaugeresidual Theory result tensor [20] of and the renamed spin Radiation dependent Y–M RGM ISB matrices was a massive PoS(ICRC2021)514 W. H. Trzaska mass for DM, the average 2 . We welcome new collaborators to the 2 for SI interactions. 7 2 cm 3.5 GeV lepton adds about 0.8 GeV in nucleon recoil to -46 ∼ . In the case of SD interactions, the expected cross section 2 for SD and 10 2 cm -42 level. That requires ten times more data. Encouraged by the prototype’s success, σ range. 2 Convincing argument indicating that these one-sigma anomalies are not just a statistical fluke is The strongest argument against the WIMP interpretation is the lack of evidence from other DM The best way to test if the observed anomalies are real is to increase the statistical significance This work has been supported in part by the EU INTERREG for the Baltic Sea programme The interaction of protons, neutrons or pions with a Pb nucleus will produce comparable, Two similar but completely independent experiments conducted two decades apart report small we are making plans formore a neutron larger detectors, version and of betterstatistical the scintillator analysis NEMESIS of coverage. setup. the Taking event anDM rate It cross-section upper in would limits3 limit Fig. have inindicates of a the that 1 bigger mass a count target, range NEMESIS-like in of setup 3-40 the can GeV/c investigate the exact multiplicity match between the two measurements.that This fact these also diminishes events the possibility are causedrock by above very the energetic setup. secondarytrigger particles Such only from the particles top muon would scintillator. interactions indeed Thisselective in is enhancement produce the not of many the only neutrons specific case multiplicities. here. in Further, the there Pb is target no apparent and experiments. reason for No such a events were reportedmay so far be by due the to HALO Collaboration the [23].results challenges for and This, however, the delays in direct the detectionannihilation data are events analysis directly still would and probably less interpretations. require sensitive significantmight changes in The to be the XENON1T the non-trivial XENON1T relevant to setup mass implement. that range. To register self- of all peaks to 5 within the BSUIN project, and by the Polish Ministry of Science and Higher Education (Grant no. New NEMESIS Results is approximately 1.88 GeV. The escaping project. 6. Acknowledgements would be around 10 energy-dependent spallation and neutron multiplicities.tracted from the The 800- relevant and numericalinteraction 1600-MeV values and neutron were two multiplicity 1.88 ex- data GeV63.7 [21, interactions n/event22]. from from the the Assuming 5-cm WIMP one thick annihilation 0.8 NEMESIS decay target. GeV of Given DM, an we 8-GeV/c expect but consistent anomalies in the neutronThe multiplicity anomalies spectra become from visible a only Pb whenof target the the located CR anomalies underground. muon-related remains events unclear, are but,a suppressed. in WIMP with principle, The a they nature mass may close be to a 10 signature GeV/c of self-annihilation of the energy causing spallation of the target nucleus. neutron multiplicity is 8 n/GeV. Corrected for thethe 8(2)% mass neutron of detection efficiency WIMP of particles NEMESIS, GeV/c responsible for the anomalies listed in1 Tab. would be in5. the 10-30 Discussion and conclusions PoS(ICRC2021)514 , , , , Phys. , 136:042077, Phys. Rev. Lett. AIP Conf. Proc. Phys. Rev. Lett. , 103(6):063028, W. H. Trzaska , 79(8):721, 2019, . , 610:419–422, 2009, Phys. Rev. D , 151:293–304, 11 2005. J. Phys. Conf. Ser. Eur. Phys. J. C , 196:429–432, 2009. , 82:10–18, 2015. Joint International , 835:186–225, 2016. Nucl. Instrum. Meth. A 8 Annals of Nuclear Energy Nucl. Phys. B Proc. Suppl. , 2020(8):083C01, 2020. Nucl. Instrum. Meth. A , 102(6):062001, 2020, 2008.00688. https://meetings.aps.org/Meeting/APR19/Session/G17.1 PTEP . IOP publishing, Bristol and Philadelphia, 2003. Phys. Rev. D . Accessed: 2021-06-22. https://www.lip.pt/events/2006/ecrs/proc/ecrs06-s0-92.pdf , 102:67–76, 2018. Beyond the Desert 2002 https://callio.info , 65:044621, 2002, nucl-ex/0112003. 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