109 research outputs found

    RPC monitoring tools in the CMS experiment

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    Resistive Plate Chambers have been used in the CMS experiment to build up a dedicated muon detector system which covers the whole geometric acceptance up to a pseudorapidity of 1.6 with a total of 480 chambers in the barrel and 432 in the endcaps. In order to guarantee the quality of the data collected and to monitor online the detector performance, a set of common tools has been developed in CMS and they are in particular heavily used in the RPC system: the Web Based Monitoring tools and the Data Quality Monitor system. The first ones are a set of templates available on the web which allow the user to check the hardware performance during data taking with distributions and plots of all the parameters. The Data Quality Monitoring service is composed by a set of algorithms which can work both during data taking and offline, running on stored data, to check the quality of reconstructed physical variables. Both these monitoring systems will be described here with a particular emphasys on their structure, functionalities and performance

    Jet momentum dependence of jet quenching in PbPb collisions at sqrt(sNN)=2.76 TeV.

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    Dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 150 inverse microbarns is analyzed. Jets are reconstructed using combined information from tracking and calorimetry. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the same collision energy is found, while more central collisions show a strong imbalance of leading and subleading jet transverse momenta attributed to the jet-quenching effect. The dijet momentum imbalance in central collisions is found to persist for leading jet transverse momenta up to the highest values studied

    Measurement of the Production Cross Section for Pairs of Isolated Photons in pp collisions at sqrt(s) = 7 TeV

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    The integrated and differential cross sections for the production of pairs of isolated photons is measured in proton-proton collisions at a centre-of-mass energy of 7 TeV with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 36 inverse picobarns is analysed. A next-to-leading-order perturbative QCD calculation is compared to the measurements. A discrepancy is observed for regions of the phase space where the two photons have an azimuthal angle difference, Delta(phi), less than approximately 2.8

    Measurement of the charge asymmetry in top-quark pair production in proton-proton collisions at sqrt(s) = 7 TeV.

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    The difference in angular distributions between top quarks and antiquarks, commonly referred to as the charge asymmetry, is measured in pp collisions at the LHC with the CMS experiment. The data sample corresponds to an integrated luminosity of 1.09 fb−1 at a centre-of-mass energy of 7 TeV. Top-quark pairs are selected in the final state with an electron or muon and four or more jets. At least one jet is identified as originating from b-quark hadronization. The charge asymmetry is measured in two variables, one based on the pseudorapidities (η) of the top quarks and the other on their rapidities (y). The results and are consistent within uncertainties with the standard-model predictions

    Search for quark compositeness in dijet angular distributions from pp collisions at sqrt(s) = 7 TeV.

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    A search for quark compositeness using dijet angular distributions from pp collisions at sqrt(s) = 7 TeV is presented. The search has been carried out using a data sample corresponding to an integrated luminosity of 2.2 inverse femtobarns, recorded by the CMS experiment at the LHC. Normalized dijet angular distributions have been measured for dijet invariant masses from 0.4 TeV to above 3 TeV and compared with a variety of contact interaction models, including those which take into account the effects of next-to-leading-order QCD corrections. The data are found to be in agreement with the predictions of perturbative QCD, and lower limits are obtained on the contact interaction scale, ranging from 7.5 up to 14.5 TeV at 95% confidence level