We report the measurement of the final-state products of negative pion and muon nuclear capture at rest on argon by the LArIAT experiment at the Fermilab Test Beam Facility. We measure a population of isolated MeV-scale energy depositions, or blips, in 296 LArIAT events containing tracks from stopping low-momentum pions and muons. The average numbers of visible blips are measured to be 0.74±0.19 and 1.86±0.17 near muon and pion track endpoints, respectively. The 3.6σ statistically significant difference in blip content between muons and pions provides the first demonstration of a new method of pion-muon discrimination in neutrino liquid argon time projection chamber experiments. LArIAT Monte Carlo simulations predict substantially higher average blip counts for negative muon (1.22±0.08) and pion (2.34±0.09) nuclear captures. We attribute this difference to geant4's inaccurate simulation of the nuclear capture process.

We present the first measurement of the negative pion total hadronic cross section on argon, which we performed at the Liquid Argon In A Testbeam (LArIAT) experiment. All hadronic reaction channels, as well as hadronic elastic interactions with scattering angle greater than 5~degrees are included. The pions have a kinetic energies in the range 100-700~MeV and are produced by a beam of charged particles impinging on a solid target at the Fermilab Test Beam Facility. LArIAT employs a 0.24~ton active mass Liquid Argon Time Projection Chamber (LArTPC) to measure the pion hadronic interactions. For this measurement, LArIAT has developed the ``thin slice method", a new technique to measure cross sections with LArTPCs. While generally higher than the prediction, our measurement of the ($\pi^-$,Ar) total hadronic cross section is in agreement with the prediction of the Geant4 model when considering a model uncertainty of $\sim$5.1\%.

E. Gramellini, † J. Ho, ‡ R. Acciarri, C. Adams, J. Asaadi, M. Backfish, W. Badgett, B. Baller, V. Basque, O. Benevides Rodrigues, 17 F. d. M. Blaszczyk, R. Bouabid, C. Bromberg, R. Carey, R. Castillo Fernandez, F. Cavanna, 22 J. I. Cevallos Aleman, A. Chatterjee, P. Dedin, M. V. dos Santos, D. Edmunds, C. Escobar, J. Esquivel, † J. J. Evans, A. Falcone, W. Flanagan, B. T. Fleming, W. Foreman, § D. Garcia-Gamez, ¶ D. Gastler, T. Ghosh, R. A. Gomes, R. Gran, D. R. Gratieri, P. Guzowski, A. Hahn, P. Hamilton, C. Hill, A. Holin, J. Hugon, E. Iwai, D. Jensen, R. A. Johnson, H. Kawai, E. Kearns, E. Kemp, M. Kirby, T. Kobilarcik, M. Kordosky, P. Kryczyński, ‖ K. Lang, R. Linehan, S. Lockwitz, X. Luo, A. A. B. Machado, A. Marchionni, T. Maruyama, L. Mendes Santos, W. Metcalf, C. A. Moura, R. Nichol, I. Nutini, ∗∗ A. Olivier, †† O. Palamara, 22 J. Paley, I. Parmaksiz, B. Passarelli Gelli, L. Paulucci, D. Phan, G. Pulliam, J. L. Raaf, B. Rebel, ‡‡ M. Reggiani Guzzo, M. Ross-Lonergan, §§ D. W. Schmitz, E. Segreto, D. Shooltz, D. Smith, M. Soares Nunes, ¶¶ M. Soderberg, B. Soubasis, ∗∗∗ F. Spagliardi, ††† J. M. St. John, † M. Stancari, D. Stefan, M. Stephens, R. Sulej, A. M. Szelc, M. Tabata, D. Totani, M. Tzanov, D. Walker, H. Wenzel, Z. Williams, T. Yang, J. Yu, S. Zhang, and J. Zhu Universidade Federal do ABC, Santo André, SP 09210-580, Brasil Universidade Federal de Alfenas, Poços de Caldas, MG 37715-400, Brasil Boston University, Boston, MA 02215, USA Universidade Estadual de Campinas, Campinas, SP 13083-859, Brasil Chiba University, Chiba 260, Japan University of Chicago, Chicago, IL 60637, USA University of Cincinnati, Cincinnati, OH 45221, USA University of Edinburgh, Edinburgh EH9 3FD, UK Fermi National Accelerator Laboratory, Batavia, IL 60510, USA Universidade Federal de Goiás, Goiás, CEP 74690-900, Brasil High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan Louisiana State University, Baton Rouge, LA 70803, USA University of Manchester, Manchester M13 9PL, UK Michigan State University, East Lansing, MI 48824, USA University of Minnesota, Duluth, Duluth, MN 55812, USA National Centre for Nuclear Research (NCBJ), Otwock 05-400, Poland Syracuse University, Syracuse, NY 13244, USA University of Texas at Arlington, Arlington, TX 76019, USA University of Texas at Austin, Austin, TX 78712, USA University College London, London WC1E 6BT, UK William & Mary, Williamsburg, VA 23187, USA Yale University, New Haven, CT 06520, USA

The LArIAT liquid argon time projection chamber, placed in a tertiary beam of charged particles at the Fermilab Test Beam Facility, has collected large samples of pions, muons, electrons, protons, and kaons in the momentum range 300-1400 MeV/c. This paper describes the main aspects of the detector and beamline, and also reports on calibrations performed for the detector and beamline components.

Liquid Argon Time Projection Chambers (LArTPCs) are ideal detectors for precision neutrino physics. These detectors, when located deep underground, can also be used for measurements of proton decay, and astrophysical neutrinos. The technology must be completely developed, up to very large mass scales, and fully mastered to construct and operate these detectors for this physics program. As part of an integrated plan of developing these detectors, accurate measurements in LArTPC of known particle species in the relevant energy ranges are now deemed as necessary. The LArIAT program aims to directly achieve these goals by deploying LArTPC detectors in a dedicated calibration test beam line at Fermilab. The set of measurements envisaged here are significant for both the short-baseline (SBN) and long-baseline (LBN) neutrino oscillation programs in the US, starting with MicroBooNE in the near term and with the adjoint near and far liquid argon detectors in the Booster beam line at Fermilab envisioned in the mid-term, and moving towards deep underground physics such as with the long-baseline neutrino facility (LBNF) in the longer term.