Search for new physics in events with same-sign dileptons and jets in pp collisions at $ \sqrt{s} $ = 8 TeV

Abstract

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 fb −1 . In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and bquark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models. 8 Limits on models of new physics and on rare SM processes 109 Information for additional model testing 19 Summary 22The CMS collaboration 27 IntroductionIn the standard model (SM), proton-proton collision events having a final state with isolated leptons of the same sign are extremely rare. Searches for anomalous production of same-sign dileptons can therefore be very sensitive to new physics processes that produce this signature copiously. These include supersymmetry (SUSY) [1][2][3], universal extra dimensions [4], pair production of T 5/3 particles (fermionic partners of the top quark) [5], heavy Majorana neutrinos [6], and same-sign top-quark pair production [7,8]. In SUSY, for example, same-sign dileptons occur naturally with the production of gluino pairs, when each gluino decays to a top quark and a top anti-squark, with the anti-squark further decaying into a top anti-quark and a neutralino. In this paper we describe searches for new physics with same-sign dileptons (ee, eµ, and µµ) and hadronic jets, with or without accompanying missing transverse energy (E miss T ). Our choice of signatures is driven by the following considerations. New physics signals with large cross sections are likely to be produced by strong interactions, and we thus expect significant hadronic activity in conjunction with the two leptons. Astrophysical evidence for dark matter [9] suggests considering SUSY models with R-parity conservation, which provides an excellent dark matter candidate -a stable lightest supersymmetric particle -1 -JHEP01(2014)163 JHEP01 (2014)163 (LSP) that escapes detection. Therefore, a search for this signature involves sizable E miss T due to undetected LSPs. Nevertheless, we also consider signatures without significant E miss T in order to be sensitive to SUSY models with R-parity violation (RPV) [10] which imply an unstable LSP. Beyond these general guiding principles, the choice of signatures is made independently of any particular physics model and, as a result, these signatures can be applied also to probe non-supersymmetric ex...

The inverse seesaw in conformal electro-weak symmetry breaking and phenomenological consequences

“…The number of events produced by this interaction is expected to be small due to the off-shell W boson. Furthermore, due to suppressed lepton number violation it is clear within the CISS why no corresponding excess in the same-sign dilepton channel has been observed [83], as is expected in the case of a decaying W R . If this pattern was confirmed in the next run of the LHC, it would be a strong point in favour of the CISS.…”

Sbottoms of natural NMSSM at the LHC

“…In this regime, it is, however, important to study how the these latter BRs are shared among b-LSP (χ 0 1 ; singlino-like) and bχ 0 2,3 (higgsino-like) since these rates determine which kind of experimental constraints on sbottom mass would be pertinent. It can be noted here that sbottoms are searched for at the LHC assuming their three pure modes of decays, viz.,b 1 → bχ 0 1 ,b 1 → bχ 0 2 followed by χ 0 2 → hχ 0 1 and [26,28]. For sbottom mass below the top-chargino threshold the last decay mode simply does not exist.…”

“…On the other hand, a relatively light R-type sbottom can be present while the other sbottom and both stops are relatively heavy. 1 It is somewhat interesting to note that various possible decay modes of the sbottom have recently been explored rigorously for the first time by the experimental searches at the LHC [1,2,[26][27][28]. These result in lower bounds on mb 1 roughly ranging between 500-750 GeV.…”

Naturalness confronts nature: searches for supersymmetry with the CMS detector in pp collisions at √s = 8 and $13$ TeV

“…At the LHC, previous searches from ATLAS [97,98,99,100,101] and CMS [102,103,104,105,106] at √ s = 8 TeV excluded top squarks up to 700 GeV, and gluinos up to 1.4 TeV. In each case, search results were interpreted within simplified models with only one SUSY particle decay mode considered at a time.…”

“…3.8 [94]. Previous searches for natural SUSY by CMS [102,103,104,105,106] and ATLAS [97,98,99,100,101] at √ s = 7 and 8 TeV have probed gluino masses up to 1.3 TeV and top squark masses up to 700 GeV under the assumptions of specific decay modes for the SUSY particles. One important feature that sets this search apart is that the SUSY parameter space of gluino and top squark branching ratios is explored for the first time at the LHC [94].…”