First application of a liquid argon time projection chamber for the search for intranuclear neutron-antineutron transitions and annihilation in 40Ar using the MicroBooNE detector Abratenko, P. García Gámez, Diego Microboone Collaboration Data Analysis Image processing Noble liquid detectors (scintillation, ionization, double-phase) Time projection Chambers (TPC) Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359. MicroBooNE is supported by the following: the U.S. Department of Energy, Office of Science, Offices of High Energy Physics and Nuclear Physics; the U.S. National Science Foundation; the Swiss National Science Foundation; the Science and Technology Facilities Council (STFC), part of the United Kingdom Research and Innovation; the Royal Society (United Kingdom); the U.K. Research and Innovation (UKRI) Future Leaders Fellowship; and the NSF AI Institute for Artificial Intelligence and Fundamental Interactions. Additional support for the laser calibration system and cosmic ray tagger was provided by the Albert Einstein Center for Fundamental Physics, Bern, Switzerland. We present a novel methodology to search for intranuclear neutron-antineutron transition (n⟶n̅) followed by n̅-nucleon annihilation within an 40Ar nucleus, using the MicroBooNE liquid argon time projection chamber (LArTPC) detector. A discovery of n⟶n̅ transition or a new best limit on the lifetime of this process would either constitute physics beyond the Standard Model or greatly constrain theories of baryogenesis, respectively. The approach presented in this paper makes use of deep learning methods to select n⟶n̅ events based on their unique features and differentiate them from cosmogenic backgrounds. The achieved signal and background efficiencies are (70.22 ± 6.04)% and (0.0020 ± 0.0003)%, respectively. A demonstration of a search is performed with a data set corresponding to an exposure of 3.32 ×1026 neutron-years, and where the background rate is constrained through direct measurement, assuming the presence of a negligible signal. With this approach, no excess of events over the background prediction is observed, setting a demonstrative lower bound on the n⟶n̅ lifetime in 40Ar of τm ≳ 1.1×1026 years, and on the free n⟶n̅ transition time of τn⟶n̅ ≳ 2.6×105 s, each at the 90% confidence level. This analysis represents a first-ever proof-of-principle demonstration of the ability to search for this rare process in LArTPCs with high efficiency and low background. 2025-02-19T11:52:16Z 2025-02-19T11:52:16Z 2024-07-29 journal article P. Abratenko et al. 2024 JINST 19 P07032. DOI: 10.1088/1748-0221/19/07/P07032 https://hdl.handle.net/10481/102502 10.1088/1748-0221/19/07/P07032 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional IOPScience