Search for Long-Lived Heavy Neutrinos in the Decays of B Mesons Produced in Proton-Proton Collisions at √s=13 Tev

Abstract

A search for long-lived heavy neutrinos (N) in the decays of B mesons produced in proton-proton collisions at root s = 13 TeV is presented. The data sample corresponds to an integrated luminosity of 41.6 fb(-1) collected 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 < m(N) < 3 GeV and decay lengths in the range 10(-2) < c tau(N) < 10(4) mm, where tau(N) is the N proper mean lifetime. Signal events are defined by the signature B -> l(B)NX; N -> l(+/-)pi(-/+), where the leptons l(B) and l can 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 the l(+/-)pi(-/+) invariant mass distributions. Limits at 95% confidence level on the sum of the squares of the mixing amplitudes between heavy and light neutrinos, vertical bar V-N vertical bar(2), and on c tau(N) are obtained in different mixing scenarios for both Majorana and Dirac-like N particles. The most stringent upper limit vertical bar V-N vertical bar(2) < 2.0 x 10(-5) is obtained at m(N) = 1.95 GeV for the Majorana case where N mixes exclusively with muon neutrinos. The limits on vertical bar V-N vertical bar(2) for masses 1 < m(N) < 1.7 GeV are the most stringent from a collider experiment to date.