Abstract
Long-lived particles decaying to {e ^pm } {mu ^mp } {nu } , with masses between 7 and 50 ,text {GeV/}c^2 and lifetimes between 2 and 50 ,text {ps} , are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using 5.4 ,text {fb} ^{-1} of p p collisions collected with the LHCb detector at a centre-of-mass energy of sqrt{s} = 13 ,text {TeV} . Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of 125 ,text {GeV/}c^2 , and the charged current production from an on-shell W boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.
Highlights
Supersymmetry [14], and with right-handed neutrinos [15]
The study presented in this paper focuses on the search for decays of neutral long-lived particles (LLP) using three production mechanisms: direct pair production (DPP), pair production from the decay of a Standard Model (SM)-like Higgs boson with a mass of 125 GeV/c2 (HIG), and from charged current (CC) processes
Upper limits at 95% confidence level (CL) on the production cross-sections times branching fraction are computed for each production mechanism, σDPP = σ × B(χ10 → e±μ∓ν), σHIG = σ × B(h → χ10χ10) × B(χ10 → e±μ∓ν), and σCC = σ (W → l N ) × B(N → e±μ∓ν), for each pair of masses of the LLP (mLLP) and τLLP values using the CLs approach [46]
Summary
The LHCb detector [19,20] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The tracking system provides a measurement of momentum, p, of charged particles with a relative uncertainty that varies from 0.5% at low momentum to 1.0% at 200 GeV/c. Electrons and hadrons are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter (ECAL) and a hadronic calorimeter (HCAL). The online event selection is performed by a trigger, which consists of a hardware stage based on information from the calorimeter and muon systems, followed by a software stage that carries out a full event reconstruction. Events from pp collisions fulfilling the muon or electron trigger are studied. At the hardware level the muon trigger requires a muon track identified by matching hits in the muon stations, for the electron trigger a cluster in the ECAL with large transverse energy deposit is required. At the software level the muon trigger selects muons with a minimum pT of 10 GeV/c, the electron trigger selects electrons with a minimum pT of 15 GeV/c
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