CMS SUS Jamboree 2015 Results

Search for Supersymmetry

CMS has performed a broad range of searches for particles predicted by theories of supersymmetry (SUSY), which can in principle explain the astrophysical dark matter and the low observed value of the Higgs-boson mass. Because of the many possible theoretical scenarios, the program of CMS SUSY searches is designed to be as generic as possible. Early Run 2 searches are designed to be inclusive, but they focus especially on the pair production of gluinos, for which the production cross section for the mass range of interest has the largest increase from 8 TeV (Run 1) to 13 TeV (Run 2). In SUSY scenarios motivated by the gauge hierarchy problem, the gluino typically decays either into a third-generation squark-anti-quark pair; decays to a generic first- or second-generation squark-anti-quark pair are considered as well. Many of these scenarios produce multiple b quarks, together with the characteristic large missing transverse momentum associated with the lightest supersymmetric particle (LSP), assumed to be a neutralino.
	Figure 1. Simplified-model diagrams for gluino pair production with three-body gluino decays into a quark, and anti-quark, and a neutralino.
Figure 1 shows simplified-model diagrams for gluino pair production with three-body gluino decays into a quark (either a light quark, a bottom quark or a top quark), its corresponding anti-quark, and a neutralino. Searches for these processes have been performed in all-hadronic (jets + missing transverse momentum), single-lepton (jets +e/ $\mu$ + missing transverse momentum), and like-sign dilepton channels (jets + like sign, same or opposite flavor leptons + missing transverse momentum).

Figure 2. Exclusion regions in the plane mass of the lighest neutralino versus mass of the gluino.
Figure 2 shows that significant progress has already made in Run 2 for the exclusion limits in the plane of gluino mass (x-axis) vs. neutralino mass (y-axis). The value of the gluino mass determines the cross section, with a very rapid, approximately power-law falloff that limits all analyses at some high gluino mass value. The value of the neutralino mass, in particular its splitting with respect to the gluino, determines the momentum spectrum of final state particles, as well as the missing transverse momentum, limiting the search sensitivity to some high LSP mass approaching the diagonal of the plot. Limits are first placed on the production cross section times branching fraction for each scenario; the displayed boundary curves are then obtained by assuming 100% branching fraction of the gluino to the given final state particles and comparing with the theoretical cross section. The excluded region from the combination of all CMS Run 1 searches (19.5 fb^-1) extends up to a gluino mass of about 1350 GeV (for low neutralino mass). This value has already been surpassed by most of the individual searches in Run 2, using only about 2.2 fb^-1. Typical SUSY searches look for broad excesses in the extreme tails of the distributions of missing transverse momentum and hadronic energy and therefore require excellent detector performance, a detailed understanding of the background shapes in these tails. The most important background contributions are measured from data in control regions. Four searches are performed in the all-hadronic channel, based on complementary approaches using the kinematic variables MHT (missing HT), MT2, the razor variables, and alphaT. These searches are also binned in a several variables, such as HT, the number of jets, and the number of b-jets. Hadronic searches are typically the most difficult, because they have the most complex background composition, with contributions from QCD, W+jets, Z+jets, and ttbar. The variables MT2 and alphaT are particularly powerful in suppressing the QCD background. The Z + jets background is important in search bins with no b-jets; this contribution is often determined using a combination of (Z->ll) + jets and photon + jets control samples. The single lepton SUSY search, in contrast, was designed to have a simple background composition dominated by dilepton ttbar events. This analysis uses MET, MT, and MJ, the sum of the masses of large-radius jets. Finally, the same-sign dilepton search has very strong suppression of SM backgrounds and requires a very careful evaluation of the contribution of leptons from non-prompt sources. In Run1, CMS observed a small excess in the opposite-sign dilepton channel. This search as been performed again in Run 2 and no excess has been observed.

CMS-SUS-15-002	Search for supersymmetry in the multijet and missing transverse momentum channel in pp collisions at 13 TeV	Submitted to PLB
CMS-PAS-SUS-15-003	Search for new physics in the all-hadronic final state with the $M_{\mathrm{T2}}$ variable
CMS-PAS-SUS-15-005	Search for new physics in final states with jets and missing transverse momentum in $\sqrt{s} =$ 13 TeV pp collisions with the $\alpha_{\text{T}}$ variable
CMS-PAS-SUS-15-004	Inclusive search for supersymmetry using the razor variables at $\sqrt{s} =$ 13 TeV
CMS-PAS-SUS-15-007	Search for supersymmetry in pp collisions at $\sqrt s =$ 13 TeV in the single-lepton final state using the sum of masses of large radius jets
CMS-PAS-SUS-15-008	Search for SUSY in same-sign dilepton events at $\sqrt{s} =$ 13 TeV
CMS-PAS-SUS-15-011	Search for new physics in final states with two opposite-sign same-flavor leptons, jets and $E_{ \mathrm{T} }^{ \text{miss} }$ in pp collisions at $\sqrt{s} =$ 13 TeV

Compact Muon Solenoid
LHC, CERN