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A<sc>bstract</sc> A search for long-lived heavy neutrinos (N) in the decays of B mesons produced in proton-proton collisions at$$ \sqrt{s} $$ = 13 TeV is presented. The data sample corresponds to an integrated luminosity of 41.6 fb−1collected in 2018 by the CMS experiment at the CERN LHC, using a dedicated data stream that enhances the number of recorded events containing B mesons. The search probes heavy neutrinos with masses in the range 1 <mN< 3 GeV and decay lengths in the range 10−2<cτN< 104mm, where τNis the N proper mean lifetime. Signal events are defined by the signature B →ℓBNX; N →ℓ±π∓, where the leptonsℓBandℓcan be either a muon or an electron, provided that at least one of them is a muon. The hadronic recoil system, X, is treated inclusively and is not reconstructed. No significant excess of events over the standard model background is observed in any of theℓ±π∓invariant mass distributions. Limits at 95% confidence level on the sum of the squares of the mixing amplitudes between heavy and light neutrinos, |VN|2, and oncτNare obtained in different mixing scenarios for both Majorana and Dirac-like N particles. The most stringent upper limit|VN|2< 2.0×10−5is obtained atmN= 1.95 GeV for the Majorana case where N mixes exclusively with muon neutrinos. The limits on|VN|2for masses 1 <mN< 1.7 GeV are the most stringent from a collider experiment to date.
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This content will become publicly available on July 1, 2025
First application of a liquid argon time projection chamber for the search for intranuclear neutron-antineutron transitions and annihilation in 40 Ar using the MicroBooNE detector
Abstract We present a novel methodology to search for intranuclear neutron-antineutron transition (n⟶n̅) followed byn̅-nucleon annihilation within an40Ar nucleus, using the MicroBooNE liquid argon time projection chamber (LArTPC) detector. A discovery of n⟶n̅transition 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⟶n̅events 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 ×1026neutron-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⟶n̅lifetime in40Ar of τm≳ 1.1×1026years, and on the free n⟶n̅transition time of τn⟶n̅≳ 2.6×105s, 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.
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- PAR ID:
- 10556456
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- Journal of Instrumentation
- Volume:
- 19
- Issue:
- 07
- ISSN:
- 1748-0221
- Page Range / eLocation ID:
- P07032
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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