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Particle Production, Transport, and Identification in the Regime of 1−7 Gev=C

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Particle Production, Transport, and Identification in the Regime of 1−7 Gev=C PHYSICAL REVIEW ACCELERATORS AND BEAMS 22, 061003 (2019) Particle production, transport, and identification in the regime of 1−7 GeV=c A. C. Booth,1 N. Charitonidis,2,* P. Chatzidaki,2,3,4 Y. Karyotakis,5 E. Nowak,2,6 I. Ortega-Ruiz,2 M. Rosenthal,2 and P. Sala2,7 1University of Sussex, Brighton BN1 9RH, United Kingdom 2CERN, 1211 Geneva 23, Switzerland 3National Technical University of Athens, School of Applied Physics, GR-157 80 Zografos, Attiki, Greece 4Heidelberg University, Kirchhoff-Institute for Physics, Im Neuenheimer Feld 227 D-69120 Heidelberg, Germany 5LAPP, Lab. d’Annecy-le-Vieux de Physique de Particules, Universit´e Grenoble Alpes, Universit´e Savoie Mont Blanc, CNRS/IN2P3, F-74941 Annecy, France 6AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Krakow, Poland 7INFN, Via G. Celoria, 16 IT-20133 Milan, Italy (Received 13 March 2019; published 21 June 2019) The recently constructed H4-VLE beam line, a tertiary extension branch of the existing H4 beam line in the CERN North Area, was commissioned in October 2018. The beam line was designed with the purpose of providing very low energy (VLE) hadrons and positrons to the NP-04 experiment, in the momentum range of 1–7 GeV=c. The production of these low-energy particles is achieved with a mixed hadron (pions, kaons, protons), 80 GeV=c secondary beam impinging on a thick target. The H4-VLE beam line has been instrumented with prototype scintillating fiber detectors providing the beam profile, intensity, and time-of- flight measurement of the beam particles, that, together with Cherenkov threshold counters, permit an event-by-event particle identification over the entire momentum spectrum. In this paper, we present detailed results of the beam line performance and the measured beam composition, as well as the comparison of these measurements with simulations performed during the design phase using FLUKA and GEANT-4-based Monte-Carlo codes. DOI: 10.1103/PhysRevAccelBeams.22.061003 I. INTRODUCTION H. Atherton et al. [2] measured the exact composition of secondary particles emitted from the CERN North Area The production of secondary hadron or lepton beams via beryllium targets, for different production angles, using the the interaction of a primary beam impinging on a target H2 beam line. The lowest secondary momentum point material is the most common technique worldwide for reported by Atherton et al. is 60 GeV=c, in both positive providing experiments or facilities with particle beams of and negative polarities. The work, described in Ref. [2], different intensities, compositions and momenta. A promi- was subsequently supplemented by the NA-56/SPY experi- nent example of a facility that provides mixed particle ment [3], that performed measurements of secondary beams in the momentum range of 10 to 400 GeV=c is the particle production down to 7 GeV=c, starting this time CERN North Area Secondary Beam facility (see for from 450 GeV=c primary protons and impinging on example, Ref. [1]), where the primary beam from the beryllium targets of different lengths. However, data for CERN Super Proton Synchroton (SPS) accelerator secondary particle production below 7 GeV=c starting impinges on a beryllium target and produces the secondary from medium-to-high momenta (in the multi-GeV/c range) particles. During the 1980s, in a landmark article, and for target materials different than beryllium are, to the authors’ best knowledge, quite scarce and difficult to find in *Corresponding author. the literature. [email protected] The recently commissioned NP-04 (Single-Phase ProtoDUNE) experiment [4], located in an extension of Published by the American Physical Society under the terms of the CERN North Area EHN1 facility designated “CERN the Creative Commons Attribution 4.0 International license. Neutrino Platform Facility” [5], is a large-sized prototype Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, detector based on Liquid Argon Time Projection Chamber and DOI. (LAr–TPC) technology. As described in the experiment’s 2469-9888=19=22(6)=061003(12) 061003-1 Published by the American Physical Society A. C. BOOTH et al. PHYS. REV. ACCEL. BEAMS 22, 061003 (2019) FIG. 1. A schematic layout of EHN1, the largest experimental hall of SPS secondary beam facilities. As explained in the text, the primary beam from SPS is slowly extracted on the primary (T2) target. Subsequently, the secondary 80 GeV=c beam is momentum- selected and transported to the newly constructed secondary targets, in order to produce the low energy particles. The newly designed H2-VLE and H4-VLE beam lines select and transport these low energy particles to NP-02 and NP-04 experiments. scientific proposal, and also justified in detail in the DUNE sufficient rate for the experiment. The initial optics con- technical design report [6], the hadrons produced by figuration (“v0”) discussed in the reference above, was neutrino interactions with matter are expected to be in chosen as a first estimate, using the first-order optics the range between 0.5 and 10 GeV=c. In order to satisfy calculation code TRANSPORT [8]. Despite the broad use these requirements, a new tertiary branch of the existing H4 of this code in the experimental areas of CERN and beam line was designed during 2017 with the installation elsewhere since the 1970s, it presents a few intrinsic and commissioning to take place in 2018. The layout limitations: (a) It is not possible to restrict the minimum and optics design principles of these new beam lines have and maximum value of any fit parameter (b) The fitting been reported elsewhere [7]. The conceptual design of the algorithm is not optimal, thus leading to an important beam line involves a medium-energy, medium-intensity dependence of the possible solution on the initial value (106 particles per 4.8 seconds spill) secondary beam of used for the fit. This fact allows only families of optics 80 GeV=c produced in the T2 “primary” target and trans- solutions to be found without offering the ability to easily ported to impinge on a “secondary” target. The new H4- explore large parameter phase-space domains. (c) Since the VLE beam line accepts, momentum-selects and transports spatial and momentum coordinates of the produced par- the third generation (“tertiary”) low-energy particles to the ticles are highly correlated, tracking through the magnetic NP-04 experiment. A layout of the EHN1 facility showing elements with a realistic phase space as input was deemed the existing and the new beam lines can be seen in Fig. 1. necessary. This option is not offered by TRANSPORT or its In this paper, we present in detail the methodology for associated tracking tool, DECAY TURTLE [9]. Additionally, the optimization of this low energy beam line in terms of there is no possibility of communication of variables beam optics, target material choices as well as radiation between the optics and the tracking programs. (d) The shielding. The transverse dynamics studies were performed results processing, in terms of the output file format in with various beam optics and tracking codes, while the conjunction with the various intrinsic limitations of particles’ interactions with matter were studied using well FORTRAN (for example, in character manipulation), can established Monte-Carlo codes. Furthermore, we discuss become inconvenient especially in the cases that a large the instrumentation and particle identification systems parameter variation is necessary. chosen. We finally report on measurements of the particle In order to overcome these challenges and at the same production rates and relative abundance in the momentum time explore the possibilities that modern optics and regime of interest of 1–7 GeV=c, along with a comparison Monte-Carlo programs offer for matter-dominated beam to Monte-Carlo simulations. lines, the following strategy was employed: (a) The preexisting H4 beam line and the H4-VLE part II. OPTIMIZATION SIMULATIONS were modeled in the GEANT-4 based Monte-Carlo program G4beamline [10]. The model included a detailed description A. Optics and target optimization of the magnetic elements’ geometrical features and materi- As discussed in Ref. [7], low energy particles are als, while for the crucial H4-VLE part, their magnetic fields produced via a secondary beam with a momentum of (inside the magnets’ gap, the iron yokes as well as the 80 GeV=c, which is generated in the existing T2 target and fringe fields), were modeled via explicitly calculated field transported for ∼600 m through the H4 beam line towards a maps. All the collimators and most of the detectors of the secondary target. The design of the tertiary beam line after upstream, high-energy beam line were also modeled, along this target had to satisfy the following stringent require- with all the relevant part of the shielding. All the detectors, ments: (a) relatively short length (to limit the amount of vacuum windows, and material present in the particles’ pion and kaon decays upstream of the experiment) (b) large trajectories were modeled precisely in the H4-VLE low- bending angles (to avoid the high-energy background energy part. reaching the experiment), and (c) large angular acceptance (b) The expected secondary beam composition at (at least in the order of 50 mm mrad), in order to assure 80 GeV=c, as predicted by the “Atherton formula” 061003-2 PARTICLE PRODUCTION, TRANSPORT, AND … PHYS. REV. ACCEL. BEAMS 22, 061003 (2019) 100 C (graphite) - 15 cm length Pb-15 cm length W-15 cm length W-30 cm length Cu-30 cm length 10 1 Relative Composition (%) 0.1 FIG. 3. Bending plane beam size in H4-VLE near the detector e- mu- pi+ K+ p e+ mu+ entrance for a 7 GeV=c beam, as simulated via PTC.
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