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

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

A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-1) collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 GeV

Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at root s=13 TeV

Peer reviewe

Measurements of Higgs boson production cross sections and couplings in the diphoton decay channel at root s=13 TeV

Measurements of Higgs boson production cross sections and couplings in events where the Higgs boson decays into a pair of photons are reported. Events are selected from a sample of proton-proton collisions at root s = 13TeV collected by the CMS detector at the LHC from 2016 to 2018, corresponding to an integrated luminosity of 137 fb(-1). Analysis categories enriched in Higgs boson events produced via gluon fusion, vector boson fusion, vector boson associated production, and production associated with top quarks are constructed. The total Higgs boson signal strength, relative to the standard model (SM) prediction, is measured to be 1.12 +/- 0.09. Other properties of the Higgs boson are measured, including SM signal strength modifiers, production cross sections, and its couplings to other particles. These include the most precise measurements of gluon fusion and vector boson fusion Higgs boson production in several different kinematic regions, the first measurement of Higgs boson production in association with a top quark pair in five regions of the Higgs boson transverse momentum, and an upper limit on the rate of Higgs boson production in association with a single top quark. All results are found to be in agreement with the SM expectations.Peer reviewe

Observation of tW production in the single-lepton channel in pp collisions at root s=13 TeV

A measurement of the cross section of the associated production of a single top quark and a W boson in final states with a muon or electron and jets in proton-proton collisions at root s = 13 TeV is presented. The data correspond to an integrated luminosity of 36 fb(-1) collected with the CMS detector at the CERN LHC in 2016. A boosted decision tree is used to separate the tW signal from the dominant t (t) over bar background, whilst the subleading W+jets and multijet backgrounds are constrained using data-based estimates. This result is the first observation of the tW process in final states containing a muon or electron and jets, with a significance exceeding 5 standard deviations. The cross section is determined to be 89 +/- 4 (stat) +/- 12 (syst) pb, consistent with the standard model.Peer reviewe

Measurement of the top quark mass using events with a single reconstructed top quark in pp collisions at root s=13 TeV

Abstract:A measurement of the top quark mass is performed using a data sample en-riched with single top quark events produced in thetchannel. The study is based on proton-proton collision data, corresponding to an integrated luminosity of 35.9 fb−1, recorded at√s= 13TeV by the CMS experiment at the LHC in 2016. Candidate events are selectedby requiring an isolated high-momentum lepton (muon or electron) and exactly two jets,of which one is identified as originating from a bottom quark. Multivariate discriminantsare designed to separate the signal from the background. Optimized thresholds are placedon the discriminant outputs to obtain an event sample with high signal purity. The topquark mass is found to be172.13+0.76−0.77GeV, where the uncertainty includes both the sta-tistical and systematic components, reaching sub-GeV precision for the first time in thisevent topology. The masses of the top quark and antiquark are also determined separatelyusing the lepton charge in the final state, from which the mass ratio and difference aredetermined to be0.9952+0.0079−0.0104and0.83+1.79−1.35GeV, respectively. The results are consistentwithCPTinvariance

Searches for an extended Higgs boson sector at CMS

The existence of the final building block of the Standard Model (SM) was confirmed by the discovery of the Higgs boson by the CMS and the ATLAS detectors in 2012. This discovery ultimately crowned the SM as the most successful explanation of particle physics ever to be achieved, but this theory still falls short of providing a unified description of the fundamental interactions. To remedy the incompleteness of the SM, many scenarios of physics Beyond the Standrd Model (BSM) were proposed of particular interest to better understand the behavior of nature at high energies, in the hope of finding hints of what may lie ahead of the standard model. This report, is a brief overview of the most recent full run 2 CMS searches in the context of an extended Higgs boson sector

Search for 2HDM neutral Higgs bosons through ℓ+ℓ−bb final states at CMS in run 2 LHC data

With the discovery of the Higgs boson, the Standard Model (SM) of particle physics can now be considered complete. Still, it is far from being able to answer all the questions that arise when looking at the world around us. To gain deeper insights into nature's behavior at high energies, numerous scenarios Beyond the Standard Model (BSM) have been proposed to extend or modify the SM in the pursuit of a more complete and unified theory of fundamental particles and forces. Since there is no requirement for the Higgs sector to be minimal, one of the remaining unanswered questions is whether the newly discovered Higgs boson is part of an extended scalar sector or not. The Two-Higgs-doublet models (2HDM) are considered to be among the simplest extensions of SM. The addition of the second Higgs doublet leads to a richer phenomenology as there are five physical scalar states predicted in this theory: two neutral scalars - h and H - a pseudo-scalar A, and a pair of charged Higgs bosons H±. To confirm or disprove this possibility, an investigation would involve precision measurements of the properties and couplings of the discovered Higgs boson, as well as searches for the other predicted Higgs bosons in the extended scalar sector. This thesis addresses the search for the new H and A bosons through H/A → Z A/H → ℓ+ℓ− bb signatures within the LHC using CMS full run 2 data. This search extends the reach of the 2HDM type-II scenario to intermediate and high tan values for two production mechanisms, gluon-gluon fusion, and b-associated production. It also probes regions of the mass plane that have been overlooked before, such as the boosted regime, where the difference in mass between the heavy Higgs and the pseudo-scalar causes the production of the daughter particle to be produced with a large boost, resulting in close b jets often reconstructed as a single fat-jet. The reported analysis pushes the boundaries of conventional analysis methods employed in previous search strategies by using machine learning and other advanced techniques in the hope of finding hints of new physics beyond the standard model.(SC - Sciences) -- UCL, 202

Search for 2HDM neutral Higgs bosons through ℓ+ℓ−bbˉ\ell^{+}\ell^{-} b\bar{b} final states at CMS in run 2 LHC data.

With the discovery of the Higgs boson, the Standard Model (SM) of particle physics can now be considered complete. Still, it is far from being able to answer all the questions that arise when looking at the world around us. To gain deeper insights into nature's behavior at high energies, numerous scenarios Beyond the Standard Model (BSM) have been proposed to extend or modify the SM in the pursuit of a more complete and unified theory of fundamental particles and forces. Since there is no requirement for the Higgs sector to be minimal, one of the remaining unanswered questions is whether the newly discovered Higgs boson is part of an extended scalar sector or not. The Two-Higgs-doublet models (2HDM) are considered to be among the simplest extensions of SM. The addition of the second Higgs doublet leads to a richer phenomenology as there are five physical scalar states predicted in this theory: two neutral scalars - h and H - a pseudo-scalar A, and a pair of charged Higgs bosons $H^{\pm}$. To confirm or disprove this possibility, an investigation would involve precision measurements of the properties and couplings of the discovered Higgs boson, as well as searches for the other predicted Higgs bosons in the extended scalar sector. This thesis addresses the search for the new H and A bosons through $H/A \rightarrow Z A/H \rightarrow \ell^{+}\ell^{-} b\bar{b}$ signatures within the LHC using CMS full run 2 data. This search extends the reach of the 2HDM type-II scenario to intermediate and high $\tan\beta$ values for two production mechanisms, gluon-gluon fusion, and b-associated production. It also probes regions of the mass plane that have been overlooked before, such as the boosted regime, where the difference in mass between the heavy Higgs and the pseudo-scalar causes the production of the daughter particle to be produced with a large boost, resulting in close b jets often reconstructed as a single fat-jet. The reported analysis pushes the boundaries of conventional analysis methods employed in previous search strategies by using machine learning and other advanced techniques in the hope of finding hints of new physics beyond the standard model

Measurement of the double-differential inclusive jet cross section in proton-proton collisions at s\sqrt{s} = 5.02 TeV

International audienceThe inclusive jet cross section is measured as a function of jet transverse momentum $p_\mathrm{T}$ and rapidity $y$. The measurement is performed using proton-proton collision data at $\sqrt{s}$ = 5.02 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 27.4 pb$^{-1}$. The jets are reconstructed with the anti-$k_\mathrm{T}$ algorithm using a distance parameter of $R$ = 0.4, within the rapidity interval $\lvert y\rvert$$\lt$ 2, and across the kinematic range 0.06 $\lt$$p_\mathrm{T}$$\lt$ 1 TeV. The jet cross section is unfolded from detector to particle level using the determined jet response and resolution. The results are compared to predictions of perturbative quantum chromodynamics, calculated at both next-to-leading order and next-to-next-to-leading order. The predictions are corrected for nonperturbative effects, and presented for a variety of parton distribution functions and choices of the renormalization/factorization scales and the strong coupling $\alpha_\mathrm{S}$