Abstract
Results are reported from a search for new physics beyond the standard model in proton-proton collisions in final states with a single lepton; multiple jets, including at least one jet tagged as originating from the hadronization of a bottom quark; and large missing transverse momentum. The search uses a sample of proton-proton collision data at $\sqrt{s} =$ 13 TeV, corresponding to 137 fb$^{-1}$, recorded by the CMS experiment at the LHC. The signal region is divided into categories characterized by the total number of jets, the number of bottom quark jets, the missing transverse momentum, and the sum of masses of large-radius jets. The observed event yields in the signal regions are consistent with estimates of standard model backgrounds based on event yields in the control regions. The results are interpreted in the context of simplified models of supersymmetry involving gluino pair production in which each gluino decays into a top quark-antiquark pair and a stable, unobserved neutralino, which generates missing transverse momentum in the event. Scenarios with gluino masses up to about 2150 GeV are excluded at 95% confidence level (or more) for neutralino masses up to 700 GeV. The highest excluded neutralino mass is about 1250 GeV, which holds for gluino masses around 1850 GeV.
Highlights
ESTIMATION METHODThe method for estimating the background yields in each of the signal bins takes advantage of the fact that the MJ and mT distributions of background events with a significant amount of Initial-state radiation (ISR) are largely uncorrelated and that there are background-dominated control samples that can be used to test the method and establish systematic uncertainties
The dominant contribution to this type of background arises from tt events with two leptonic W boson decays, including W decays involving τ leptons, which can themselves decay into hadrons, electrons, or muons
The approximate independence of MJ and mT is a consequence of two key features of the data, namely, that the high-mT sample is composed primarily of dilepton tt events and that the MJ spectra of tt events with one and two leptons become highly similar in the presence of ISR jets
Summary
‘The physics program of the CMS experiment at the CERN LHC [1] is designed to explore the TeV energy scale and to search for new particles and phenomena beyond the standard model (SM), for example, those predicted by supersymmetry (SUSY) [2,3,4,5,6,7,8,9]. The signature used here to search for the processes shown in Fig. 1 is characterized by the presence of an isolated high transverse momentum (pT) lepton, multiple jets, at least one b-tagged jet, and large pmT iss, and by additional kinematic variables The first of these is mT, defined as the transverse mass of the system consisting of the lepton and the p⃗ mT iss in the event. Because of the effectiveness of the mT variable in helping to suppress the single-lepton tt background, the residual background in the signal regions arises predominantly from a single SM process, dilepton tt production In such background events, both W bosons from the t → bW decays produce leptons, but only one of the two leptons satisfies the lepton-identification criteria, as well as the requirements on the pT, pseudorapidity (η), and isolation from other energetic particles in the event.
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