657 research outputs found

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

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    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^{-1} recorded by the CMS experiment at the Large Hadron Collider at CERN. The cross section is measured using anti-kTk_\text{T} jets with radius parameters of R = 0.4 and R = 0.8 as a function of the dijet rapidity separation y∗y^{*} , the total boost of the dijet system yby_\text{b} , and either the average transverse momentum ⟹pT⟩1,2\langle p_\text{T}\rangle_{1,2} or the invariant mass mjjm_\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

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    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 αs(MZ)\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 αs(MZ)\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 αs(MZ)\alpha _{\text {s}} (M_{\text {Z}}) αs(MZ) at next-to-next-to-leading order

    Measurement of b jet shapes in proton-proton collisions at root s=5.02 TeV

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    We present the first study of charged-hadron production associated with jets originating from b quarks in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data sample used in this study was collected with the CMS detector at the CERN LHC and corresponds to an integrated luminosity of 27.4 pb(-1). To characterize the jet substructure, the differential jet shapes, defined as the normalized transverse momentum distribution of charged hadrons as a function of angular distance from the jet axis, are measured for b jets. In addition to the jet shapes, the per-jet yields of charged particles associated with b jets are also quantified, again as a function of the angular distance with respect to the jet axis. Extracted jet shape and particle yield distributions for b jets are compared with results for inclusive jets, as well as with the predictions from the pythia and herwig++ event generators.Peer reviewe

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