855 research outputs found

    Measurement of ttH(H→bb) production in the semi-leptonic tt decay channel at the CMS Experiment

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    A measurement of the production of a Higgs boson in association with a top quark-antiquark pair and the subsequent decay of the Higgs boson to a bottom quark-antiquark pair (ttˉH(H→bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{H}\rightarrow \text{b}\bar{\text{b}})) at a center-of-mass energy of 13 TeV13\,\text{TeV} is presented. The measurement focuses on the semileptonic decay channel of the top quark-antiquark pair and is based on proton-proton collision data recorded by the CMS Experiment in the years 2016 and 2017 corresponding to an integrated luminosity of 77.4 fb−177.4\,\text{fb}^{-1}. The cross section for the production of a Higgs boson in association with a top quark-antiquark pair (ttˉH\text{t}\bar{\text{t}}\text{H}) depends on the top-Higgs Yukawa coupling and a measurement of ttˉH\text{t}\bar{\text{t}}\text{H} production provides direct access to this important property of the standard model of particle physics. To achieve the measurement of this process, candidate ttˉH(H→bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{H}\rightarrow \text{b}\bar{\text{b}}) events are first selected from the analyzed data. Artificial neural networks are then used to construct observables that allow the discrimination between signal and background processes. To extract the signal contribution in data, standard model predictions for these observables are fit to data using a profile likelihood approach. This results in a best-fit value for the signal strength relative to the standard model prediction ÎŒ=σ/σSM\mu = \sigma/\sigma_{\text{SM}} of \begin{equation} \hat{\mu} = 1.22^{+0.41}_{-0.37}({\text{tot.}}) \left[{}^{+0.19}_{-0.19}({\text{stat.}}) {}^{+0.36}_{-0.32}({\text{syst.}}) \right]. \end{equation} This result is compatible with the standard model prediction and corresponds to an observed (expected) significance of 3.33.3 (2.72.7) standard deviations with respect to the background-only hypothesis. In addition, combined analyses performed by the CMS Collaboration are discussed, in which analyses of various production and decay modes of the Higgs boson were statistically combined. The presented anylsis of ttˉH(H→bbˉ)\text{t}\bar{\text{t}}\text{H}(\text{H}\rightarrow \text{b}\bar{\text{b}}) production in the semileptonic channel was an important contribution to theses combinations, which resulted in the observation of ttˉH\text{t}\bar{\text{t}}\text{H} production and of the H→bbˉ\text{H}\rightarrow \text{b}\bar{\text{b}} decay mode

    Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

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    A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

    Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV