Triple-Differential Measurement of the Dijet Cross Section at s\sqrt{s} = 13 TeV with the CMS Detector

In light of the large quantity of data collected during the second operational run of the Large Hadron Collider (LHC) at CERN, which has made it possible to perform measurements at unprecedented energies with a high degree of statistical precision, the necessity of understanding and constraining the systematic effects on such measurements has become increasingly important. Precision measurements of jet observables in proton-induced collisions have proven instrumental in constraining the parton distribution functions (PDFs) which describe the internal structure of protons, and which remain one of the largest sources of uncertainty in many analyses performed at hadron colliders. This thesis presents the first triple-differential measurement of the dijet production cross section performed in proton-proton collisions at a center-of-mass energy of 13 TeV, based on a data sample of 35.9 fb$^{-1}$ recorded by the CMS experiment at the Large Hadron Collider at CERN. The cross section is measured using anti-$k_\text{T}$ jets with radius parameters of R = 0.4 and R = 0.8 as a function of the dijet rapidity separation $y^{*}$ , the total boost of the dijet system $y_\text{b}$ , and either the average transverse momentum $\langle p_\text{T}\rangle_{1,2}$ or the invariant mass $m_\text{jj}$ of the dijet system as the third variable. This choice of rapidity variables exploits the topology of the dijet system to achieve an increased sensitivity to the proton PDFs. After accounting for detector-induced systematic effects in a three-dimensional unfolding procedure, the measured spectra are compared to fixed-order theory predictions at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics, obtained using several recent PDF sets. While the data are observed to be described by the theory within the experimental and theoretical uncertainties across a large portion of the phase space, potentially significant deviations are observed in areas where a heightened sensitivity to the PDFs is expected

Determination of the strong coupling constant using inclusive jet cross section data from multiple experiments

Abstract Inclusive jet cross section measurements from the ATLAS, CDF, CMS, D0, H1, STAR, and ZEUS experiments are explored for determinations of the strong coupling constant $$\alpha _{\text {s}} (M_{\text {Z}})$$ αs(MZ) . Various jet cross section data sets are reviewed, their consistency is examined, and the benefit of their simultaneous inclusion in the $$\alpha _{\text {s}} (M_{\text {Z}})$$ αs(MZ) determination is demonstrated. Different methods for the statistical analysis of these data are compared and one method is proposed for a coherent treatment of all data sets. While the presented studies are based on next-to-leading order in perturbative quantum chromodynamics (pQCD), they lay the groundwork for determinations of $$\alpha _{\text {s}} (M_{\text {Z}})$$ αs(MZ) at next-to-next-to-leading order

Search for dark photons in Higgs boson production via vector boson fusion in proton-proton collisions at √s = 13 TeV

A search is presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle and an isolated photon. The search is performed by the CMS collaboration at the LHC, using a data set corresponding to an integrated luminosity of 130 fb−1, recorded at a center-of-mass energy of 13 TeV in 2016–2018. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An upper limit is set on the product of the cross section for production via vector boson fusion and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a Higgs boson mass of 125 GeV, assuming the standard model production rates, the observed (expected) 95% confidence level upper limit on the branching fraction is 3.5 (2.8)%. This is the first search for such decays in the vector boson fusion channel. Combination with a previous search for Higgs bosons produced in association with a Z boson results in an observed (expected) upper limit on the branching fraction of 2.9 (2.1)% at 95% confidence level

Development and validation of HERWIG 7 tunes from CMS underlying-event measurements

This paper presents new sets of parameters (“tunes”) for the underlying-event model of the HERWIG7 event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in HERWIG7, and are obtained from a fit to minimum-bias data collected by the CMS experiment at s=0.9, 7, and 13Te. The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for event shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the dat

Measurement of the azimuthal anisotropy of Y(1S) and Y(2S) mesons in PbPb collisions at root s(NN)=5.02 TeV

The second-order Fourier coefficients (v(2)) characterizing the azimuthal distributions of Y(1S) and Y(2S) mesons produced in PbPb collisions at root s(NN) = 5.02 TeV are studied. The Y mesons are reconstructed in their dimuon decay channel, as measured by the CMS detector. The collected data set corresponds to an integrated luminosity of 1.7 nb(-1). The scalar product method is used to extract the v2 coefficients of the azimuthal distributions. Results are reported for the rapidity range vertical bar y vertical bar < 2.4, in the transverse momentum interval 0 < pT < 50 GeV/c, and in three centrality ranges of 10-30%, 30-50% and 50-90%. In contrast to the J/psi mesons, the measured v(2) values for the Y mesons are found to be consistent with zero. (C) 2021 The Author(s). Published by Elsevier B.V.Peer reviewe

Search for top squark pair production using dilepton final states in pp collision data collected at root s=13TeV

A search is presented for supersymmetric partners of the top quark (top squarks) in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from bquarks, and missing transverse momentum. The search uses data from proton-proton collisions at root s = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 137 fb(-1). Hypothetical signal events are efficiently separated from the dominant top quark pair production background with requirements on the significance of the missing transverse momentum and on transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced lightest top squarks. For top squarks decaying exclusively to a top quark and a lightest neutralino, lower limits are placed at 95% confidence level on the masses of the top squark and the neutralino up to 925 and 450 GeV, respectively. If the decay proceeds via an intermediate chargino, the corresponding lower limits on the mass of the lightest top squark are set up to 850 GeV for neutralino masses below 420 GeV. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1.4 TeV and 900 GeV respectively for the top squark and the lightest neutralino.Peer reviewe

Measurement of B-c(2S)(+) and B-c*(2S)(+) cross section ratios in proton-proton collisions at root s=13 TeV

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Measurement of the W gamma Production Cross Section in Proton-Proton Collisions at root s=13 TeV and Constraints on Effective Field Theory Coefficients

A fiducial cross section for W gamma production in proton-proton collisions is measured at a center-of-mass energy of 13 TeV in 137 fb(-1) of data collected using the CMS detector at the LHC. The W -> e nu and mu nu decay modes are used in a maximum-likelihood fit to the lepton-photon invariant mass distribution to extract the combined cross section. The measured cross section is compared with theoretical expectations at next-to-leading order in quantum chromodynamics. In addition, 95% confidence level intervals are reported for anomalous triple-gauge couplings within the framework of effective field theory.Peer reviewe

Measurement of the top quark Yukawa coupling from t(t)over-bar kinematic distributions in the dilepton final state in proton-proton collisions at root s=13 TeV

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