Abstract
A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of 19.5 inverse femtobarns of proton-proton collisions with center-of-mass energy sqrt(s) = 8 TeV, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying tau leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson (t to c H), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, lambda[H, tc] and lambda[H, ct], respectively, of sqrt(abs(lambda[H, tc])^2 + abs(lambda[H, ct])^2) < 0.21.
Highlights
The recent discovery of a Higgs boson [1,2,3] at the relatively low mass of about 125 GeV implies that physics beyond the standard model (BSM) may be observable at energy scales of around 1 TeV
Supersymmetry (SUSY) is a prominent candidate for BSM physics because it provides a solution to the hierarchy problem, predicts gauge-coupling unification, and contains a “natural” candidate for dark matter [4,5,6]
In R-parity [7] conserving SUSY models, supersymmetric particles are created in pairs, and the lightest supersymmetric particle (LSP) is stable
Summary
The recent discovery of a Higgs boson [1,2,3] at the relatively low mass of about 125 GeV implies that physics beyond the standard model (BSM) may be observable at energy scales of around 1 TeV. Direct pair production of the superpartners of the electron and muon (selectron and smuon, respectively) can yield a multilepton state dominated by τ leptons should the superpartner of the τ lepton (stau) be substantially lighter than the selectron and smuon, as is expected in some models. Another path to a multileptonic final state arises from top-squark production in which the top squark decays to leptonically decaying third-generation quarks and to a Z boson that yields an opposite-sign sameflavor (OSSF) lepton pair In these latter events, bottomquark jets (b jets) might be present.
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