Session H19: Searches for BSM Exotic States

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We describe a search for the production of a pair of Bottom-type ($B\bar{B}$) vector-like quarks (VLQ’s) with masses greater than 900 GeV in a di-lepton final state using data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS Experiment. The analysis is based on the detection of a di-lepton pair from the decay of a $Z$ boson and is sensitive to events in which one VLQ decays to a $b$ quark and a $Z$ boson and the other to a $b$ quark and either a $Z$ or a Higgs boson. Requiring that the event kinematics are consistent with a di-leptonic $Z$ decay, with either a $Z$ or Higgs decaying to jets and that the reconstructed VLQ’s have equal masses greatly reduces the background from Standard Model processes. We use a modified-$\chi^2$ procedure based on the Higgs or $Z$ mass and the equality of the two VLQ masses to select the correct combinations of jets. Since for a highly boosted Higgs or $Z$, the two jets resulting from the daughter quarks might be merged to a single jet, we carry out two independent analyses depending on the number of observed jets. We present the expected exclusion limits from the combined analyses corresponding to 137 fb$^{-1}$ of integrated luminosity collected by CMS during 2016, 2017, and 2018 run period.   

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The discovery of Higgs boson of mass 125 GeV in 2012 by the CMS and the ATLAS experiments at the LHC opens a whole new portal to physics beyond the Standard Model. Vector-like quarks (VLQs) are hypothetical spin-1/2 particles of the fourth generation that have left- and right-handed components transforming exactly same under $ SU(3)_C \times SU(2)_L \times U(1)_Y~$ group. They are postulated to solve the hierarchy problem and stabilize the Higgs mass, while escaping constraints on the Higgs cross section measurement. This talk will present the current status of the search for VLQs ((T$^\prime$) ) decaying to a top quark and a Higgs boson at the CMS experiment at the LHC. We will also discuss how jet substructure techniques can be used to identify the decays of top quarks and the Higgs bosons.   

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The talk presents a search for a new leptophilic vector boson Z' decaying into the four-muon final state using the data collected in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector in the year 2015-2018. A moderate excess of 4μ events with a μ+μ− pair is the experimental signature for this study. The gauge boson Z' is predicted by the highly motivated gauged Lμ−Lτ model, which is the simplest extension of the Standard Model (SM). The model addresses the observed g-2 of the muon anomalous magnetic dipole moment and the B physics anomalies. At the same time, the model probes physics and cosmology outstanding questions related to the dark matter and neutrino mass.   

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Vector-like quarks (VLQ) are predicted in many extensions to the Standard Model (SM), especially those aimed at solving the hierarchy problem. Their vector-like nature allows them to extend the SM while still being compatible with electroweak sector measurements. In many models, VLQs decay to a SM boson and to a third-generation quark. Pair production of VLQ provides a model-independent method of searching due to the quantum chromodynamics production of the particles. This talk presents a search for pair production of vector-like top quarks that each decays into a SM W boson and a bottom quark, with one W boson decaying leptonically and the other decaying hadronically. The analysis takes advantage of boosted boson identification and a data-driven correction of the dominant $t\bar{t}$ background prediction to improve sensitivity. Furthermore, this analysis extends the previous analysis sensitivity by including the full Run 2 ATLAS dataset.   

Live

We describe the extension and combination of previous searches for the production of a pair of bottom-type vector-like quarks (VLQs) for masses above the current exclusion limit of 900 GeV/c$^{2}$ in data gathered by the CMS detector during the 13 TeV runs in 2016, 2017, and 2018 of the Large Hadron Collider at CERN. We study hypothesized events where each VLQ decays to a bottom quark and Higgs/$Z$ boson or to a top quark and $W$ boson. We consider the cases where the Higgs/$Z$/$W$ boson decays into two quarks, which are typically resolved as two jets but can merge together as one jet when the Higgs/$Z$/$W$ boson has a high transverse momentum. In the decay to $tW$, we consider events where the top quark is resolved as one, two, or three jets. For decays to $bHbZ$ and $bZbZ$ we consider decays of the $Z$ boson to two leptons of the same flavor and opposite charge. Using a $\chi^{2}$ metric based on the reconstructed mass of the Higgs/$Z$/$W$ boson and top quark, as well as jet-level quark tagging, significantly reduces background from Standard Model processes. We present the expected exclusion limits set from the combination of the fully-hadronic and dileptonic analyses run over 137 fb$^{-1}$ of integrated luminosity data collected by the CMS detector during Run II.   

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Discovery of a Higgs Boson with mass near 125GeV in 2012 marked one of the most important milestones in particle physics. The low mass of Higgs with diverging loop corrections adds motivation to look for new physics Beyond the Standard Model. Several BSM theories introduced new heavy quark partners(vector-like quarks) with mass in TeV scale. In particular, the vector-like top quark(T) can cancel the largest correction due to top quark loop,which is one of the main contributions to the divergence,and stabilize the scalar Higgs mass. This analysis searches for pair production of vector-like T or B quark with charge 2e/3 and e/3 in proton-proton collisions at 13TeV at the LHC. We focus on events with final state of same-sign dilepton pair and multiple(3 or more) leptons. Data was collected by the CMS detector at the LHC in 2017 and 2018 with integrated luminosities of 41.5 and 59.7fb^{-1}. Besides Standard Model processes,lepton misidentification is a significant background source in both channels and charge mis-identification is a background for the SS dilepton channel. They are estimated by data-driven methods. With estimated backgrounds, data,and uncertainties,we calculate the upper limit on TT and BB production cross section for different branching ratios and masses of T and B.   

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We present the status of our all-hadronic analysis in search of pair-produced Vector-Like Quarks (VLQs) using the Boosted Event Shape Tagger (BEST) with the CMS detector using 137 $fb^-1$ of $\sqrt{s}$ = 13 TeV proton-proton collisions at the LHC. VLQs are motivated by models which predict compositeness of the scalar Higgs boson and avoid increasing constraints from Higgs measurements. In the all-hadronic channel, this analysis is sensitive to all possible VLQ decay modes: T(B)->t(b)H/t(b)Z/b(t)W, capturing the highest branching fraction of each process. The high mass of the VLQs produce highly boosted objects in the final state which can be reconstructed as anti-$k_{T}$ R=0.8 jets and identified as either QCD/b/W/Z/H/t using the BESTagger. The tagger boosts jet constituents into various rest frames and uses neural networks to find correlations between event shape variables, such as Fox-Wolfram moments and sphericity, to determine the category of identification. The HT (sum pT) of the event is scanned for an excess of signal. The analysis is in progress and plans to be completed by summer 2021.   

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We analyze the signals arising from production and subsequent decay of Kaluza-Klein (KK) graviton in the extended warped extra dimensional models at the LHC. In these models, the extra dimensional bulk is divided into two regions: (i) from the UV brane to an O(10 TeV) middle brane, and (ii) from the middle brane to an O(TeV) IR brane. The standard model (SM) fermions only propagate in region (i), while SM gauge bosons and gravity propagate in all the bulk. This structure suppresses flavor violation, while keeping gravitons and KK gauge bosons accessible at the LHC. We find that the signals from KK graviton are significantly different than in the standard warped model, as the usually dominant decay modes of KK graviton are suppressed. In particular, we analyze the following two channels: (1) KK graviton decaying into a pair of radions and then each radion decaying into a pair of jets, giving an overall 4-jet signal with “antler” topology (2) KK graviton decaying into a KK gluon and a gluon jet followed by the KK gluon decaying into a radion and a jet, and finally the radion decaying into a pair of jets. This also results in a 4-jet signal, but with a different “double-cascade” topology. We find that the HL-LHC has sensitivity to KK graviton of (up to) $\sim$4 TeV in both channels.   

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We analyze signals arising from KK gravitons at the LHC. The extended warped extra dimensional model predicts two 4-jet signals produced by KK graviton decay: (1) KK graviton decay to two radions, which each dominantly decay to two (SM gluon) jets, and (2) KK graviton decay to KK gluon and (SM gluon) jet, followed by KK gluon to radion and (SM gluon) jet, followed by radion to two (SM gluon) jets. We analyze two parts of the model's parameter space at 14 TeV HL-LHC specifications. First, when the KK gluon is heavy, the decay of KK graviton to KK gluon and SM gluon is negligible. Analysis cuts focus on the "antler" topology of channel (1), imposing two dijet resonances and the 4-jet resonance on the final state jets. Second, when the KK gluon is lighter, the analysis cuts focus on the "double cascade" topology of channel (2), imposing a dijet resonance nested in a trijet resonance and the 4-jet resonance. For the second part of the analysis, we find the contribution from channel (1) can be important. Multiple benchmark points for each signal are shown with at least $3\sigma$ significance with an integrated luminosity 3000 fb$^{-1}$.