Measurement of Transverse Energy-energy Correlations in Multi-jet Events in Pp Collisions at [arrow]"

Measurement of Transverse Energy-energy Correlations in Multi-jet Events in Pp Collisions at [arrow]
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Total Pages: 21
Release: 2015
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High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy-energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb-1. The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. The strong coupling constant given at the Z boson mass is determined to be [alpha]s(mZ)=0.1173"0.0010 (exp.) -0.0026+0.0065 (theo.).

Measurement of Transverse Energy{u2013}energy Correlations in Multi-jet Events in Pp Collisions at {u221A}s

Measurement of Transverse Energy{u2013}energy Correlations in Multi-jet Events in Pp Collisions at {u221A}s
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Total Pages: 21
Release: 2015
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High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy–energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb–1. The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. The strong coupling constant given at the Z boson mass is determined to be ?s(mZ)=0.1173±0.0010 (exp.) –0.0026+0.0065 (theo.).

Study of Hadronic Event-shape Variables in Multijet Final States in Pp Collisions at [arrow]"

Study of Hadronic Event-shape Variables in Multijet Final States in Pp Collisions at [arrow]
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Release: 2014
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Event-shape variables, which are sensitive to perturbative and nonperturbative aspects of quantum chromodynamic (QCD) interactions, are studied in multijet events recorded in proton-proton collisions at [arrow]" = 7 TeV. Events are selected with at least one jet with transverse momentum pT> 110 GeV and pseudorapidity.

Measurement of Dijet Azimuthal Decorrelation in Pp Collisions at $\sqrt{s}$

Measurement of Dijet Azimuthal Decorrelation in Pp Collisions at $\sqrt{s}$
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Release: 2016
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A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2 TeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.

Measurement of Transverse Momentum Relative to Dijet Systems in PbPb and $pp$ Collisions at $\sqrt{s_{NN}}

Measurement of Transverse Momentum Relative to Dijet Systems in PbPb and $pp$ Collisions at $\sqrt{s_{NN}}
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Total Pages: 48
Release: 2015
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An analysis of dijet events in PbPb and pp collisions is performed to explore the properties of energy loss by partons traveling in a quark-gluon plasma. Data are collected at a nucleon-nucleon center-of-mass energy of 2.76 TeV at the LHC. The distribution of transverse momentum (pT) surrounding dijet systems is measured by selecting charged particles in different ranges of pT and at different angular cones of pseudorapidity and azimuth. The measurement is performed as a function of centrality of the PbPb collisions, the pT asymmetry of the jets in the dijet pair, and the distance parameter R used in the anti-kT jet clustering algorithm. In events with unbalanced dijets, PbPb collisions show an enhanced multiplicity in the hemisphere of the subleading jet, with the pT imbalance compensated by an excess of low-pT particles at large angles from the jet axes.

Measurement of the T T-bar Production Cross Section in Pp Collisions at 7 TeV in Lepton + Jets Events Using B-quark Jet Identification

Measurement of the T T-bar Production Cross Section in Pp Collisions at 7 TeV in Lepton + Jets Events Using B-quark Jet Identification
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Total Pages: 39
Release: 2011
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A new measurement of the inclusive production cross section for pp to t t-bar is performed at a center-of-mass energy of 7 TeV using data collected by the CMS experiment at the LHC. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns, and is based on the final state with one isolated, high transverse momentum muon or electron, missing transverse energy, and hadronic jets. The ttbar content of the selected events is enhanced by requiring the presence of at least one jet consistent with b-quark hadronization. The measured cross section is 150 +/- 9 (stat.) +/- 17 syst.) +/- 6 (lumi.) pb and is in agreement with higher-order QCD calculations. The combination of this measurement with a previous CMS result based on dileptons gives 154 +/- 17 (stat.+syst.) +/- 6 (lumi.) pb.

Measurement of the Jet Mass in Highly Boosted T-tbar Events from Pp Collisions at $\sqrt{s}$

Measurement of the Jet Mass in Highly Boosted T-tbar Events from Pp Collisions at $\sqrt{s}$
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Release: 2017
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The first measurement of the jet mass m[jet] of top quark jets produced in t t-bar events from pp collisions at sqrt(s) = 8 TeV is reported for the jet with the largest transverse momentum pt in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7 inverse femtobarns. The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay t to bW with W to l nu where l is an electron or muon, are used to select t t-bar events with large Lorentz boosts. The products of the fully hadronic decay t to bW with W to q q'-bar are reconstructed using a single Cambridge-Aachen jet with distance parameter R=1.2, and pt>400 GeV. The t t-bar cross section as a function of m[jet] is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the m[jet] distribution is sensitive to the top quark mass m[t], and the data are used to extract a value of m[t] to assess this sensitivity.

Jet Energy Scale and Resolution in the CMS Experiment in Pp Collisions at 8 TeV.

Jet Energy Scale and Resolution in the CMS Experiment in Pp Collisions at 8 TeV.
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Release: 2016
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Improved jet energy scale corrections, based on a data sample corresponding to an integrated luminosity of 19.7 inverse-femtobarns collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 8 TeV, are presented. The corrections as a function of pseudorapidity eta and transverse momentum pT are extracted from data and simulated events combining several channels and methods. They account successively for the effects of pileup, uniformity of the detector response, and residual data-simulation jet energy scale differences. Further corrections, depending on the jet flavor and distance parameter (jet size) R, are also presented. The jet energy resolution is measured in data and simulated events and is studied as a function of pileup, jet size, and jet flavor. Typical jet energy resolutions at the central rapidities are 15-20% at 30 GeV, about 10% at 100 GeV, and 5% at 1 TeV. The studies exploit events with dijet topology, as well as photon+jet, Z+jet and multijet events. Several new techniques are used to account for the various sources of jet energy scale corrections, and a full set of uncertainties, and their correlations, are provided. The final uncertainties on the jet energy scale are below 3% across the phase space considered by most analyses (pT> 30 GeV and abs(eta) 5.0). In the barrel region (abs(eta)

Search for a Dijet Resonance in Events with Jets and Missing Transverse Energy in Pp[over ̄] Collisions at Sqrt[s]

Search for a Dijet Resonance in Events with Jets and Missing Transverse Energy in Pp[over ̄] Collisions at Sqrt[s]
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Release: 2013
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We report on a search for a dijet resonance in events with only two or three jets and large imbalance in the total event transverse momentum. This search is sensitive to the possible production of a new particle in association with a W or Z boson, where the boson decays leptonically with one or more neutrinos in the final state. We use the full data set collected by the CDF II detector at the Tevatron collider at a proton-antiproton center-of-mass energy of 1.96 TeV. These data correspond to an integrated luminosity of 9.1 fb{̂-1}. We study the invariant mass distribution of the two jets with highest transverse energy. We find good agreement between data and standard model background expectations and measure the combined cross section for WW, WZ, and ZZ production to be 13.8{̂+3.0}_{-2.7} pb. No significant anomalies are observed in the mass spectrum and 95% credibility level upper limits are set on the production rates of a potential new particle in association with a W or Z boson.