Session J13: Beyond the Standard Model Searches at the LHC II

Live

A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above ∼2 TeV is presented. The data, corresponding to an integrated luminosity of 139 fb$^{-1}$, were recorded by the ATLAS experiment in proton--proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV during Run 2 of the Large Hadron Collider. The physics benchmark signature is $q\bar{q}\ell^+\ell^-$ contact-interactions, which would enhance the dilepton event rate at the TeV mass scale. To model the contribution from background processes a functional form is fit to the dilepton invariant-mass spectra in data. This is done in a low-mass control region, while the function is extrapolated to several high-mass signal regions where an enhancement of events is expected above the background processes. No significant deviation in data is observed above the background. A limit on the number of events in the signal regions is provided along with benchmark signal efficiencies. Upper limits are also placed on the visible cross-section times branching ratio in the signal regions. Lower limits on the contact-interaction scale, $\Lambda$, for several chirality hypotheses reach tens of TeV.   

Live

We describe a search for the pair production of Bottom-type ($B\overline{B}$) Vector-Like Quarks (VLQ's) with masses greater than 1000 GeV in a fully hadronic final state in proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS Experiment. The analysis is based on a final state consisting of jets resulting from the $b$ and $\overline{b}$ quarks produced in the VLQ decays. Requiring that the jets are consistent with the production of a pair of bosons, each of which can be either a Higgs or a $Z$, that the reconstructed VLQ's have equal masses, and that several of the jets are tagged as originating from the $b$ and $\overline{b}$ quarks greatly reduces the Standard Model background. We use a $\chi^2$ metric based on the masses of the bosons and the equality of the two VLQ masses to reconstruct the event. Since for a highly boosted Higgs or $Z$ the two jets resulting from the daughter quarks might be merged, we carry out independent analyses depending on the number of observed jets. We present expected exclusion limits as a function of the $B \rightarrow bH$ and $B \rightarrow bZ$ branching fractions using 137 fb$^{-1}$ of integrated luminosity collected by CMS during the 2016, 2017, and 2018 run periods.   

Live

We describe a search for the production of a pair of Bottom-type ($B\overline{B}$) Vector-Like Quarks (VLQ’s) with masses greater than 900 GeV in a di-leptonic final state in 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 $\chi^2$ metric 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, we carry out independent analyses depending on the number of observed jets. We present the expected exclusion limits using 137 fb$^{-1}$ of integrated luminosity collected by CMS during 2016, 2017 and 2018 run periods.   

Live

We describe a combination analysis of a fully hadronic and a di-leptonic search for the pair production of Bottom-type ($B\overline{B}$) Vector-Like Quarks (VLQ’s) with masses greater than 1000 GeV in proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS Experiment. In both searches, we detect events in which each VLQ decays to a $b$ quark and either a Higgs or a $Z$ boson. The fully hadronic search is based on events in which the Higgs and $Z$ bosons decay into quark anti-quark pairs while the di-leptonic search is based on events in which one or more $Z$ bosons decay to a lepton anti-lepton pair. In both cases, a $\chi^2$ metric based on the masses of the bosons and the equality of the two VLQ masses is used to reconstruct the event. We combine the results from the two analyses while ensuring that the two analyses are fully independent. We present the expected exclusion limits for the combination of the two analyses as a function of the $B \rightarrow bH$ and $B \rightarrow bZ$ branching fractions. The data analyzed corresponds to 137 fb$^{-1}$ of integrated luminosity collected by CMS during the 2016, 2017, and 2018 run periods.   

Live

Several theories beyond the Standard Model involve enhanced symmetry groups that introduce new heavy charged gauge bosons, typically denoted $W'$. This talk presents a search for $W'$ decaying to a top quark and a bottom quark. The analysis searches for both semi-leptonic and all-hadronic decays in data recorded with the ATLAS detector at a center-of-mass energy of 13 TeV.   

Live

This presentation describes a search for dark matter candidates produced in association with a Standard Model Higgs boson in the b$\bar{b}$ decay channel. The search utilises a dataset of $pp$ collisions at $\sqrt{s}=$ 13 TeV corresponding to an integrated luminosity of 139 fb$^{-1}$, recorded by the ATLAS detector. The results are interpreted in the context of the 2-Higgs doublet model with an extra vector or pseudoscalar mediator. The 2-Higgs doublet model is connected to the so-called Higgs portal models, in which dark matter particles interact with the SM particles only through their couplings with the Higgs sector of the theory.   

Live

The SuperCDMS Generation 2 dark matter experiment is currently being constructed at SNOLAB in Sudbury, Ontario to detect dark matter candidates less than 10 GeV/$c^{2}$ in mass using cryogenic germanium and silicon detectors. One major source of contamination for these detectors is gaseous radon progeny which can “plate-out” (stick) to detector components and limit sensitivity. Thus, it is imperative that steps be taken to minimize radon plate-out in these experiments. Many environmental factors can affect the rate of radon plate-out, including airflow from ventilation systems. To understand the role of airflow in radon plate-out rates, controlled plate-out tests were conducted inside an annular rectangular exposure chamber equipped with a variable speed fan, anemometer, and a copper plate. A Pylon radon flow-through source supplied a controlled concentration of radon-222 to the exposure chamber. Measurements of the surface activity of polonium-214 were used as a proxy for the number of atoms deposited on the copper plate. Data shows an increase in plate-out on the copper plate when airflow is present. Findings from this study can be used to aid in handling methods for ultra-sensitive detectors and can help develop models to predict how plate-out rates depend on airflow.   

On Demand

CP violation is studied in top quark pair production decaying into the dilepton channel(ee,mumu, and emu), collected by the CMS experiment at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb$^-1$. In this search two observables are probed, O1 and O3, which are the Levi-Civita tensors of the four-momenta of charged leptons, b quark jets, and top quarks. Asymmetries are obtained by these observables. The chromoelectric dipole moment (CEDM) of the top quark is extracted from the measured asymmetries and their uncertainties. Combination of three channels for the CEDM is also presented.   

On Demand

Experimentally, dark matter has not yet been observed, and there is not yet any evidence for non-gravitational interactions between dark matter and Standard Model particles. Since dark matter particles themselves do not produce signals in the Large Hardon Collider (LHC) detectors, one way to observe them is when they are produced in association with visible standard model particles such as muons, through a spin 1 mediator, e.g. a dark Z-like boson $Z_D$, that interacts with the Standard Model sector as well as the dark matter sector. Dark matter particles may have lifetimes that produce secondary decay vertices in collider experiments that are substantially displaced from the primary interaction vertex. We are preparing two models, involving dark scalars ($pp \rightarrow{Z_{D}}\rightarrow S_{D}\overline{S}_{D}$) and dark fermions ($pp \rightarrow{Z_{D}}\rightarrow F_{D_{1}}{F_{D_{1}}}\rightarrow F_{D_{2}}{F_{D_{2}}} \mathbin \mu^{+}\mu^{-}$), as reference models for a search for long-lived dark matter particles with the Compact Muon Solenoid (CMS) detector at the LHC. In this talk the status of Monte Carlo production and the kinematics of the generated events will be discussed. We will also outline our strategy for conducting this search using the full Run 2 CMS data set.