Searches for New Physics in Top-Antitop Associated Production Processes and Mechanical Design and Thermal Performance of the CMS Inner Tracker Endcap Pixel Upgrade

Three analyses in top-antitop associated production processes are presented. The measurements are based on data collected in proton-proton collisions at √s = 13TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 138 fb−1. The first measurement is a search for new physics in producing one or more top quarks with additional leptons, jets, and b jets in the context of Effective Field Theory (EFT). EFT effects are incorporated into the event weights of the simulated samples, allowing detector-level predictions that account for correlations and interference effects among EFT operators and between EFT operators and Standard Model (SM) processes. The Wilson Coefficients (WCs) corresponding to 26 EFT operators were simultaneously fit to the data. In all cases, the data is found to be consistent with the SM expectations. Also, a measurement of the Charge-Parity (CP) structure of the Yukawa coupling between the Higgs (H) boson and top quarks at tree level, when the H boson is produced in association with one (tH) or two (t¯tH) top quarks, is presented. The analysis targets events where the H boson decays to leptons and the top quark(s) decay either leptonically or hadronically. CP-even is separated from CP-odd scenarios by applying machine learning techniques to final states characterized by the presence of at least two leptons. No significant CP-odd contribution is observed, and the results are compatible with predictions for the SM H boson. In addition, the first differential measurement of the production of H bosons in association with either one (tH) or two (t¯tH) top quarks in final states with electrons, muons, and taus are performed. The sensitivity of the analysis is improved by using machine learning methods to separate the signal from the background. The H boson transverse momentum and the mass of the t¯tH system are reconstructed, and differential cross sections for t¯tH production are calculated at the particle level, assuming a lack of new physics effects. The measurement is performed in terms of the H boson pT as well as in terms of the mass of the t¯tH system. Also, a measurement of the H trilinear coupling is performed. At the moment of publishing, this analysis is undergoing the internal review process of the CMS experiment; as such, the plots are marked as ’Work in Progress,’ and the data, numbers, and discussions presented here may differ from the paper’s final version. Lastly, the TEPX section of the inner tracker of the CMS experiment for the high-luminosity LHC is presented, and studies on the current development of said part are discussed. Several design choices surrounding the mechanical and thermal design were tested and their optimal configuration was selected

Hunting for B+→K+τ+τ−B^+\to K^+ \tau^+\tau^- imprints on the B+→K+μ+μ−B^+ \to K^+ \mu^+\mu^- dimuon spectrum

We investigate the possibility of indirectly constraining the $B^{+}\to K^{+}\tau^+\tau^-$ decay rate using precise data on the $B^{+}\to K^{+}\mu^+\mu^-$ dimuon spectrum. To this end, we estimate the distortion of the spectrum induced by the $B^{+}\to K^{+}\tau^+\tau^-\to K^{+} \mu^+\mu^-$ re-scattering process, and propose a method to simultaneously constrain this (non-standard) contribution and the long-distance effects associated to hadronic intermediate states. The latter are constrained using the analytic properties of the amplitude combined with data and perturbative calculations. Finally, we estimate the sensitivity expected at the LHCb experiment with present and future datasets. We find that constraints on the branching fraction of $O(10^{-3})$, competitive with current direct bounds, can be achieved with the current dataset, while bounds of $O(10^{-4})$ could be obtained with the LHCb upgrade-II luminosity.Comment: 13 pages, 3 figures, 1 table, v2: more references, less typo

Search for resonances decaying to three W bosons in proton-proton collisions at s\sqrt{s} =13 TeV

A search for charged leptons with large impact parameters using 139  fb−1 of √s=13  TeV pp collision data from the ATLAS detector at the LHC is presented, addressing a long-standing gap in coverage of possible new physics signatures. Results are consistent with the background prediction. This search provides unique sensitivity to long-lived scalar supersymmetric lepton partners (sleptons). For lifetimes of 0.1 ns, selectron, smuon, and stau masses up to 720, 680, and 340  GeV, respectively, are excluded at 95% confidence level, drastically improving on the previous best limits from LEP

Search for long-lived particles decaying into muon pairs in proton-proton collisions at s\sqrt{s} =13 TeV collected with a dedicated high-rate data stream

A search for long-lived particles decaying into muon pairs is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2017 and 2018, corresponding to an integrated luminosity of 101 fb−1. The data sets used in this search were collected with a dedicated dimuon trigger stream with low transverse momentum thresholds, recorded at high rate by retaining a reduced amount of information, in order to explore otherwise inaccessible phase space at low dimuon mass and nonzero displacement from the primary interaction vertex. No significant excess of events beyond the standard model expectation is found. Upper limits on branching fractions at 95% confidence level are set on a wide range of mass and lifetime hypotheses in beyond the standard model frameworks with the Higgs boson decaying into a pair of long-lived dark photons, or with a long-lived scalar resonance arising from a decay of a b hadron. The limits are the most stringent to date for substantial regions of the parameter space. These results can be also used to constrain models of displaced dimuons that are not explicitly considered in this paper

Measurement of W/pmγW^{/pm}\gamma differential cross sections in proton-proton collisions at s\sqrt{s} =13 TeV and effective field theory constraints

Differential cross section measurements of W±γ production in proton-proton collisions at √s=13  TeV are presented. The data set used in this study was collected with the CMS detector at the CERN LHC in 2016–2018 with an integrated luminosity of 138  fb−1. Candidate events containing an electron or muon, a photon, and missing transverse momentum are selected. The measurements are compared with standard model predictions computed at next-to-leading and next-to-next-to-leading orders in perturbative quantum chromodynamics. Constraints on the presence of TeV-scale new physics affecting the WWγ vertex are determined within an effective field theory framework, focusing on the O3W operator. A simultaneous measurement of the photon transverse momentum and the azimuthal angle of the charged lepton in a special reference frame is performed. This two-dimensional approach provides up to a factor of ten more sensitivity to the interference between the standard model and the O3W contribution than using the transverse momentum alone