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

Testing lepton flavour universality and activities of phase-II upgrade in CMS

I carried out my research activities for the PhD in Physics within the Compact Muon Solenoid (CMS) experiment team at the University and INFN of Pisa. CMS is one of the two multipurpose detectors at the Large Hadron Collider (LHC), credited for the discovery of Higgs Boson in 2012. Within the CMS Pisa group, I am working in the Beyond Standard Model (BSM) physics searches, in particular, the study of Lepton Flavour Non-Universality (LFNU) in collaboration with other international groups. LFNU can be observed by investigating deviations from the Standard Model (SM) prediction of all the three charged leptons, that in the SM are supposed to have the same coupling constants for the electroweak interactions. For this investigation, I am looking at a specific decay channel of charmed B meson; We measure the ratio R(J/Psi), which is a ratio of decay of B charmed meson to Tau (signal channel) and muon (normalisation). I am studying this particular decay, since measurements of semi-leptonic decay of b hadron provide a direct handle to study the origin of LFNU and non-universal coupling. The analysis is ongoing and seems to converge soon. CMS Run3 data shall have some positive impact on the results but better statistical results are expected from high luminosity upgrades. The LHC is undergoing an upgrade to accomplish the transition to the high-luminosity phase (HL-LHC), foreseen from ~2027. To withstand this high radiation flux, CMS is having major upgrades. I have actively worked on the upgrade of the inner pixel tracker of the CMS, which is located closest to the interaction point and susceptible to the highest amount of radiation. I have performed TCAD simulation studies, to study the effect of these high doses of radiation on the silicon pixels. Since the present tracker will be completely replaced with a new and high radiation resistant sub-detector, extensive R&D is ongoing. As part of this R & D, I am pursuing the studies of planar and 3D silicon pixels of varying dimensions for the innermost layer of the tracker. Modules are being irradiated at high fluences and beam test studies are being done before and after irradiation for evaluating the performances in realistic conditions

Testing lepton flavour universality and activities of phase-II upgrade in CMS

I carried out my research activities for the PhD in Physics within the Compact Muon Solenoid (CMS) experiment team at the University and INFN of Pisa. CMS is one of the two multipurpose detectors at the Large Hadron Collider (LHC), credited for the discovery of Higgs Boson in 2012. Within the CMS Pisa group, I am working in the Beyond Standard Model (BSM) physics searches, in particular, the study of Lepton Flavour Non-Universality (LFNU) in collaboration with other international groups. LFNU can be observed by investigating deviations from the Standard Model (SM) prediction of all the three charged leptons, that in the SM are supposed to have the same coupling constants for the electroweak interactions. For this investigation, I am looking at a specific decay channel Bc+ → J/Ψτ+ντ; To measure the ratio R(J/Ψ), where: R(J/Ψ)=B(Bc+→J/Ψτ+ντ)/B ( B c+ → J / Ψ μ + ν μ). I am studying this particular decay since measurements of semi-leptonic decay of b hadron provide a direct handle to study the origin of LFNU and non-universal coupling. The analysis is ongoing and seems to converge soon. CMS Run3 data shall have some positive impact on the results but better statistical results are expected from high luminosity upgrades. The LHC is undergoing an upgrade to accomplish the transition to the high-luminosity phase (HL-LHC), foreseen from ∼2027. To withstand this high radiation flux, CMS is having major upgrades. I have actively worked on the upgrade of the inner pixel tracker of the CMS, which is located closest to the interaction point and susceptible to the highest amount of radiation. I have performed TCAD simulation studies, to study the effect of these high doses of radiation on the silicon pixels. Since the present tracker will be completely replaced with a new and high radiation resistant sub-detector, extensive R&D is ongoing. As part of this R & D, I am pursuing the studies of planar and 3D silicon pixels of varying dimensions for the innermost layer of the tracker. Modules are being irradiated at high fluences and beam test studies are being done before and after irradiation for evaluating the performances in realistic conditions

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 $\alpha_\mathrm{S}$

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 $\alpha_\mathrm{S}$