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
Authors: Abratenko P. , Alterkait O. , Andrade Aldana D. , Arellano L. , Asaadi J. , Ashkenazi A. , Balasubramanian S. , Baller B. , Barr G. , Barrow D. , Barrow J. , Basque V. , Benevides Rodrigues O. , Berkman S. , Bhanderi A. , Bhat A. , Bhattacharya M. , Bishai M. , Blake A. , Bogart B. , Bolton T. , Book J.Y. , Camilleri L. , Cao Y. , Caratelli D. , Caro Terrazas I. , Cavanna F. , Cerati G. , Chen Y. , Conrad J.M. , Convery M. , Cooper-Troendle L. , Crespo-Anadón J.I. , Cross R. , Del Tutto M. , Dennis S.R. , Detje P. , Devitt A. , Diurba R. , Djurcic Z. , Dorrill R. , Duffy K. , Dytman S. , Eberly B. , Englezos P. , Ereditato A. , Evans J.J. , Fine R. , Finnerud O.G. , Fleming B.T. , Foreman W. , Foppiani N. , Franco D. , Furmanski A.P. , Garcia-Gamez D. , Gardiner S. , Ge G. , Gollapinni S. , Goodwin O. , Gramellini E. , Green P. , Greenlee H. , Gu W. , Guenette R. , Guzowski P. , Hagaman L. , Hen O. , Hicks R. , Hilgenberg C. , Horton-Smith G.A. , Imani Z. , Irwin B. , Itay R. , James C. , Ji X. , Jiang L. , Jo J.H. , Johnson R.A. , Jwa Y.-J. , Kalra D. , Kamp N. , Karagiorgi G. , Ketchum W. , Kirby M. , Kobilarcik T. , Kreslo I. , Lepetic I. , Li J.-Y. , Li K. , Li Y. , Lin K. , Littlejohn B.R. , Liu H. , Louis W.C. , Luo X. , Mariani C. , Marsden D. , Marshall J. , Martinez N. , Martinez Caicedo D.A. , Martynenko S. , Mastbaum A. , McConkey N. , Meddage V. , Micallef J. , Miller K. , Mogan A. , Mohayai T. , Mooney M. , Moor A.F. , Moore C.D. , Mora Lepin L. , Moudgalya M.M. , Mulleriababu S. , Naples D. , Navrer-Agasson A. , Nayak N. , Nebot-Guinot M. , Nowak J. , Oza N. , Palamara O. , Pallat N. , Paolone V. , Papadopoulou A. , Papavassiliou V. , Parkinson H.B. , Pate S.F. , Patel N. , Pavlovic Z. , Piasetzky E. , Ponce-Pinto I.D. , Pophale I. , Qian X. , Raaf J.L. , Radeka V. , Rafique A. , Reggiani-Guzzo M. , Ren L. , Rochester L. , Rodriguez Rondon J. , Rosenberg M. , Ross-Lonergan M. , Rudolf von Rohr C. , Safa I. , Scanavini G. , Schmitz D.W. , Schukraft A. , Seligman W. , Shaevitz M.H. , Sharankova R. , Shi J. , Snider E.L. , Soderberg M. , Söldner-Rembold S. , Spitz J. , Stancari M. , John J.St. , Strauss T. , Szelc A.M. , Tang W. , Taniuchi N. , Terao K. , Thorpe C. , Torbunov D. , Totani D. , Toups M. , Tsai Y.-T. , Tyler J. , Uchida M.A. , Usher T. , Viren B. , Weber M. , Wei H. , White A.J. , Wolbers S. , Wongjirad T. , Wospakrik M. , Wresilo K. , Wright N. , Wu W. , Yandel E. , Yang T. , Yates L.E. , Yu H.W. , Zeller G.P. , Zennamo J. , Zhang C. ,   The MicroBooNE collaboration
Published: July 2024

Abstract
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.