Session S16: Supersymmetry Searches and Models

Jet Finding Efficiencies for Single and Multiple Matched Partons

One of the primary goals of the second Run of the LHC is to search for supersymmetric (SUSY) particles. One particular SUSY model is where supersymmetric tops, stops, are produced by violating the symmetry of R-parity. SUSY searches with a final state of jets are promising search channels for stop searches, and for heavy stops can decay to a final state of partons that become merged into a single jet with some substructure. The merged jet can be studied by making smaller subjets corresponding to smaller parton showers. I looked at the optimal jet cone size for different jet algorithms with different generators to simulate the fragmentation of the partons. This technique provides an alternative to using substructure variables to discriminate merged jets from those that come from a single parton. A potential advantage of such a technique is the reduction of pile up included in the jet.   

A Stop Decay Search Using Jet Substructure

A possible extension of the Standard Model is Supersymmetry, which partners every Standard Model particle with a Supersymmetric particle. Should such partner particles exist, experiment and theory indicate that the Large Hadron Collider at CERN will have the capability to produce them when it begins its second major data collection run at a 13 TeV center-of-mass energy. A possible method of detection is through the production and decay of the top quark's Supersymmetric partner, the stop squark. Simulations of a heavy stop decay to a light stop and a Higgs boson are performed. A likely decay of the Higgs boson is to two W bosons. A feature of this process is a high number of cascades of particles known as jets. Due to an anticipated heavy stop mass of upwards of 1 TeV, the lighter decay products become relativistically boosted, leading to closely clustered bursts of particles that may become merged into a single jet within the CMS detector by typical reconstruction techniques. Simulated data is analyzed to determine the efficacy of variables that discriminate between jets with substructure and background jets produced by normal quark-gluon interactions. Further, the jets originating from the stop decay should possess masses very nearly the mass of the particles from which they have decayed. Background particles from other interactions, called pileup, blur these masses, and techniques are explored to remove these extraneous particles from the final analysis.   

Identifying Boosted New Physics With Non-Isolated Leptons

We demonstrate the utility of leptons which fail standard isolation criteria in searches for new physics at the LHC. These leptons could arise in a highly boosted signal decaying to both leptons and quarks, and have been missed by current search strategies. We offer an alternate signal-background discernment to the standard isolation variables, showing through a proof-of-principle search for R-parity violating supersymmetry both the experimental reach attained by including non-isolated leptons in this search and the utility of this new substructure variable over the existing techniques.   

A Search for Supersymmetry at CMS in Events with Two Photons and Missing Transverse Energy

We present a search for supersymmetry with gauge-mediated breaking (GMSB). This search was performed in pp-collisions with two photons collected by the CMS experiment at the LHC. The missing transverse energy distribution of these selected events is compared to the Standard Model background predictions, determined using a data-driven technique. The results are then interpreted using the simplified models.   

Supersymmetry discovery potential in future LHC and HL-LHC running with the CMS detector

The search for supersymmetry (SUSY) is a major goal of the LHC physics program. The number of SUSY scenarios is large, and both high luminosity data samples and the full set of CMS detector capabilities are required to provide sensitivity to the broad range of signatures, cross sections, and decay branching fractions that can arise. If evidence for a spectrum of new particles is discovered, an extensive program of measurements will be required to determine its properties. In this talk, results are presented from a set of studies that address key questions related to the anticipated program of SUSY searches, assuming integrated luminosities from 300 $fb^{-1}$ (LHC Run 2+3) to 3000 $fb^{-1}$ (High Luminosity LHC). Three full-spectrum natural SUSY scenarios are considered in detail, as well as two compressed mass spectra. Using these complementary approaches, results are presented on the sensitivities of measurements with a varying number of jets, b-tagged jets, and leptons, and with a variety of different kinematic variables. These studies, together with results from previous investigations, demonstrate the tremendous potential for discovering and elucidating SUSY with the CMS detector in future LHC running.   

Search for Natural GMSB in Top Quark Pair + Photons Events

We present a search for Gauge Mediated Supersymmetry Breaking (GMSB) with the stop squark as the lightest squark/gluino and the gravitino as the lightest supersymmetric particle. The strong production of pairs of stop squarks and their decays would produce events with top quark pairs and pairs of neutralinos, each decaying to photons and gravitinos. This search is performed in 19.7 $fb^{-1}$ of proton-proton collision data at $\sqrt{s} = 8$ TeV in the electron+jets and muon+jets channel. We compare the missing transverse energy of these events against the expected spectrum of Standard Model processes.   

A search for new physics with multilepton final states by the CMS experiment at the Large Hadron Collider

Many models of physics beyond the standard model predict events that contain three or more leptons with or without extra jets, missing energy, accompanying b-quarks, etc. Supersymmetry is the most well-known source of such multilepton events, but other new physics theories such as the see-saw mechanism, two Higgs Doublet models, flavor-changing decays of the top quark to the higgs and charm final states, etc, can also yield multileptons. This presentation describes an inclusive search for new physics with multileptons carried out by the CMS experiment using 2012 proton-proton collision data from the Large Hadron Collider.   

A search for SUSY with Razor kinematic variables in proton-proton collisions at $\sqrt{s}$=8 TeV with the ATLAS detector at the LHC

The experimental signature for our search is jets and missing energy. The Razor variables are built using two mega-jets and are designed to discriminate against QCD multi-jets background. Contributions from dominant background sources (Z+jets, W+jets, $t\bar{t}$, and QCD) are estimated using control regions in data. The result is interpreted in the context of the simplified models of squark-pair production.   

Search for $h\to $\textit{aa }decays in the NMSSM in the $\mu \mu \tau \tau $ channel using 20.3 /fb of pp collisions at $\surd $s $=$ 8 TeV using the ATLAS detector

We present a search for the exotic decay of the SM-like Higgs boson ($h)$, or the production of a second CP-even Higgs boson ($H)$ decaying to a pair of neutral pseudoscalar Higgs bosons ($a)$, in the next-to-minimal supersymmetric standard model (NMSSM), in events with two muons from the decay of one $a$ boson, with the ATLAS detector in 20.3 /fb of $\surd $s $=$ 8 TeV pp collisions.~ Events are further required to have an additional muon or an electron, with nearby tracks, consistent with decay of the second $a$ boson to two taus.~An upper limit on the production rate of $h\to $\textit{aa,} relative to the SM production, is set~as a function $m_{a}$ in the range 3.7 to 50 GeV.~ An upper limit is also placed on the production rate of $H\to $\textit{aa }for $m_{a}=$ 5 GeV and $m_{H} $ranging from 100 to 500 GeV.