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Publications (61)19.62 Total impact

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    B. Bilin, for the CMS Collaboration
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    ABSTRACT: The measurement of differential cross section of a Z boson produced in association with jets is presented. The cross section is presented with respect to various jet kinematic variables where the Z bosons are reconstructed from opposite sign lepton pairs. The analysis is based on data of proton proton collisions with the centre of mass energy of 8 TeV collected in 2012 by the CMS experiment at LHC corresponding to 19.8 /fb of integrated luminosity. Obtained results are compared with different generators and are shown to be consistent with the Standard Model predictions.
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    Bugra Bilin, for the CMS Collaboration
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    ABSTRACT: Measurements of Vector Boson production in association with jets are presented, using p-p collision data at sqrt{s} = 7 TeV. The measurements presented include Z + jets azimuthal correlations, event shapes, vector boson + jets differential cross section measurements, hard double-parton scattering using W + jets events and electroweak Z + forward - backward jet production.
    The European Physical Journal Conferences 10/2014; 71. DOI:10.1051/epjconf/20147100016
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    Gustavo G. da Silveira, for the CMS Collaboration
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    ABSTRACT: We report the results on the search for exclusive production of $W$ pairs in the LHC with data collected by the Compact Muon Solenoid detector in proton-proton collisions at $\sqrt{s}$ = 7 TeV. The analysis comprises the two-photon production of a $W$ pairs, ${pp\to p\,W^{+}W^{-}\,p\to p\,\nu e^{\pm}\nu\mu^{\mp}\,p}$. Two events are observed in data for $p_{\textrm{\footnotesize T}}(\ell)>$ 4 GeV, $|\eta(\ell)|<$ 2.4 and $m(\mu^{\pm}e^{\mp})>$ 20 GeV, in agreement with the standard model prediction of 2.2 $\pm$ 0.4 signal events with 0.84 $\pm$ 0.15 background events. Moreover, a study of the tail of the lepton pair transverse momentum distribution is performed to search for an evidence of anomalous quartic gauge couplings in the $\gamma\gamma\to W^{+}W^{-}$ vertex. As no events are observed in data, it results in a model-independent upper limits for the anomalous quartic gauge couplings $a^{W}_{0,C}/\Lambda^{2}$, which are of the order of 10$^{-4}$.
    The European Physical Journal Conferences 01/2014; DOI:10.1051/epjconf/20147100032
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    Aruna Kumar Nayak, for the CMS Collaboration
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    ABSTRACT: A search for neutral Higgs bosons in the minimal supersymmetric extension of the Standard Model (MSSM) decaying to a pair of b quarks or a pair of tau leptons, using events recorded by the CMS experiment at the LHC in 2011 and 2012 at the centre-of-mass energy of 7 TeV and 8 TeV respectively, is presented. The result is also presented for a search for the charged Higgs boson that can be produced in the top quark decay with subsequent decay of H+ in tau and neutrino. Results are also reported from a search for non-standard-model Higgs boson decays to pairs of new light bosons, each of which decays into the di-muon final state.
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    Aruna Kumar Nayak, for the CMS Collaboration
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    ABSTRACT: The reconstruction and identification of physics objects in the CMS detector, in the context of the charged Higgs boson search analysis, are presented. The reconstruction algorithms and their performance in 7 TeV and 8 TeV LHC data are discussed. The identification of tau hadronic decays, the reconstruction of hadronic jets and missing transverse energy and the identification of b jets are described in detail.
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    Gustavo G. da Silveira, for the CMS Collaboration
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    ABSTRACT: We report the results on the searches of exclusive production of low- and high-mass pairs with the Compact Muon Solenoid (CMS) detector in proton-proton collisions at $\sqrt{s}$ = 7 TeV. The analyses comprise the central exclusive $\gamma\gamma$ production, the exclusive two-photon production of dileptons, $e^{+}e^{-}$ and $\mu^{+}\mu^{-}$, and the exclusive two-photon production of $W$ pairs in the asymmetric $e^{\pm}\mu^{\mp}$ decay channel. No diphotons candidates are observed in data and an upper limit on the cross section is set to 1.18 pb with 95% confidence level for $E_{T}(\gamma)>$ 5.5 GeV and $|\eta(\gamma)|<$ 2.5. In the measurement of exclusive dilepton production, seventeen $e^{+}e^{-}$ candidates are observed in data with $E_{T}(e)>$ 5.5 GeV and $|\eta(e)|<$ 2.5, and the cross section for the exclusive dimuon production is set to $\sigma(pp\to p\,\mu^{+}\mu^{-}\,p)=3.38^{+0.58}_{-0.55}$ (stat.) $\pm$ 0.16 (syst.) $\pm$ 0.14 (lumi.) pb for $m(\mu^{+}\mu^{-})>$ 11.5 GeV, $p_{\textrm{T}}(\mu)>$ 4 GeV and $|\eta(\mu)|<$ 2.1, both in agreement with the theoretical predictions. For high-mass systems, two events are observed in data for the exclusive two-photon production of $W$ pairs for $p_{\textrm{T}}(\mu)>$ 4 GeV, $|\eta(\mu)|<$ 2.4 and $m(e^{\pm}\mu^{\mp})>$ 20 GeV. Moreover, the study of the tail of the dilepton transverse momentum distribution resulted in model-independent upper limits for the anomalous quartic gauge couplings, which are of the order of 10$^{-4}$.
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    Carl Vuosalo, for the CMS Collaboration
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    ABSTRACT: A variety of new physics models predict heavy resonances that decay to multiple hadronic jets. These models include axigluons, colorons, diquarks, excited quarks, Randall-Sundrum gravitons, string resonances, and Z' models, among others. Other models make the prediction that high-pT jets will be suppressed, resulting in jet extinction. Using the data collected in 2012 at a center-of-mass energy of 8 TeV, the CMS Collaboration has made a baseline inclusive jet cross section measurement for comparison with new-physics searches, and then performed searches for jet extinction and resonances that decay to two hadronic jets. The results of these searches will be presented. No evidence of new physics has been observed, and these results set new limits on the parameters of these models.
    The European Physical Journal Conferences 07/2013; 60. DOI:10.1051/epjconf/20136017001
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    Carl Vuosalo, for the CMS Collaboration
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    ABSTRACT: A variety of models of physics beyond the standard model predict new particles that decay to leptons, jets, or both together. These models include axigluons, colorons, diquarks, excited quarks, heavy long-lived charged particles, leptoquarks, Randall-Sundrum gravitons, string resonances, and new vector bosons (right-handed W and Z'). Using the data collected in 2011 and 2012 at center-of-mass energies of 7 and 8 TeV, the CMS collaboration has performed searches for these new particles in channels with leptons and jets. The results of these searches will be presented. No evidence of new physics has been observed, and these results set new limits on the parameters of these models.
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    ABSTRACT: Recent measurements of top quark pair and single top production are presented. The results include inclusive cross sections as well as studies of differential distributions. Evidence for single top quark production in association with a W-boson in the final state is reported for the first time. Calculations in perturbative QCD up to approximate next-to-next-to-leading order show very good agreement with the data.
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    Petra Van Mulders, for the CMS Collaboration, for the ATLAS Collaboration
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    ABSTRACT: The high center-of-mass energy at the LHC provides the opportunity to test the predictions of some of the beyond the standard model theories. We provide an overview of a selected number of searches for new fermions and new bosons with the ATLAS and CMS experiments. No evidence for the existence of new particles was found and therefore limits are obtained on the parameters of the models under consideration.
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    ABSTRACT: The heaviest known elementary particle today, the top quark, has been discovered in 1995 by the CDF and D0 collaborations at the Tevatron proton antiproton collider at Fermilab. Recently, the CDF and D0 collaborations have studied the forward-backward asymmetry in ttbar events, resulting in measured values larger than the standard model prediction. With the start of the LHC at CERN in 2010, a new top quark factory has opened and asymmetry measurements in ttbar have also been performed in a proton proton environment with higher collision energy. No deviations from the standard model have been noticed so far in the measurements of ATLAS and CMS. This article discusses recent results of asymmetry measurements in ttbar events of the ATLAS, CDF, CMS and D0 collaborations.
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    Matthew Nguyen, for the CMS Collaboration
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    ABSTRACT: The flavor dependence of jet quenching is a powerful handle to discriminate between models of parton energy loss in heavy-ion collisions. We demonstrate the capacity of CMS to identify jets initiated by bottom quarks using displaced vertices reconstructed in the silicon tracking system. The b-jet to inclusive jet ratio is measured in PbPb collisions and compared to pp collisions and simulations at the same center-of-mass energy.
    Nuclear Physics A 11/2012; 904. DOI:10.1016/j.nuclphysa.2013.02.112 · 2.50 Impact Factor
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    Gavin Hesketh, for the ATLAS Collaboration, for the CMS Collaboration
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    ABSTRACT: This paper summarises results on W and Z plus jet production in pp collisions at $\sqrt{s} = 7$ TeV at the CERN Large Hadron Collider, from both the ATLAS and CMS experiments. Based on the 2010 and 2011 datasets, measurements have been made of numerous cross sections providing excellent tests of the latest predictions from QCD calculations and event generators.
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    Yvonne Peters, for the Collaboration
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    ABSTRACT: The heaviest known elementary particle today, the top quark, has been discovered in 1995 by the CDF and D0 collaborations at the Tevatron collider at Fermilab. Its high mass and short lifetime, shorter than the timescale for hadronization, makes the top quark a special particle to study. Due to the short lifetime, the top quark's spin information is preserved in the decay products. In this article we discuss the studies of ttbar spin correlations at D0, testing the full chain from production to decay. In particular, we present a measurement using angular information and an analysis using a matrix-element based technique. The application of the matrix-element based technique to the ttbar dilepton and semileponic final state resulted in the first evidence for non-vanishing ttbar spin correlations.
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    Torsten Dahms, for the CMS Collaboration
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    ABSTRACT: The Compact Muon Solenoid (CMS) has measured numerous quarkonium states via their decays into muon pairs in pp and PbPb collisions at sqrt(s_NN) = 2.76 TeV. Quarkonia are especially relevant for studying the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. Non-prompt J/psi from b-hadron decays show a strong suppression in the transverse momentum range (6.5 < p_T < 30 GeV/c) when compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. This suppression is related to the in-medium b-quark energy loss. In the same kinematic region, for prompt J/psi, a strong, centrality-dependent suppression is observed in PbPb collisions. Such strong suppression at high p_T has previously not been observed at RHIC. At midrapidity (|y| < 1.6) and the same p_T region, inclusive psi(2S) are even stronger suppressed than J/psi, whereas psi(2S) at forward rapidity (1.6 < |y| < 2.4) and lower p_T (3 < p_T < 30 GeV/c) appear to be less suppressed than J/psi, however, with large uncertainties that prevent a conclusion. Furthermore, low-p_T Y(2S) and Y(3S) mesons are strongly suppressed in PbPb collisions. The suppression of the Y(1S) state is smaller than the suppression of the excited states and consistent with the suppression of the feed-down contribution only.
    Nuclear Physics A 09/2012; 910. DOI:10.1016/j.nuclphysa.2012.12.017 · 2.50 Impact Factor
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    Andrew Chisholm, for the ATLAS Collaboration, for the CMS Collaboration
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    ABSTRACT: Two recent observations of new b hadrons in pp collisions at \sqrt{s} = 7 TeV at the Large Hadron Collider (LHC) are presented. The ATLAS collaboration has observed a new state in radiative transitions to \Upsilon(1S) and \Upsilon(2S) and interprets this as the first observation of the \chi_b(3P) states. The CMS collaboration has observed a new b baryon decaying to \Xi_b-\pi+ (plus charge conjugates). This is interpreted as a neutral J^P = 3/2^+ \Xi_b* baryon.
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    Pedro Silva, for the ATLAS Collaboration, for the CMS Collaboration
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    ABSTRACT: An overview of the most recent results on top quark physics obtained using proton-proton collision data collected with the ATLAS and the CMS experiments at 7 TeV center-of-mass energy is given. Measurements for inclusive and differential top quark pair or single top quark production in different final states are reviewed. Top properties such as W helicity in top decays, electric charge, charge asymmetry and spin correlations of top quark pairs, among others have also been measured by the LHC experiments. All the measurements are found to be consistent with the Standard Model predictions with a good level of accuracy. The latest results in the measurement of the top quark mass at the LHC are also presented and discussed.
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    A. A. Paramonov, for the ATLAS Collaboration, for the CMS Collaboration
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    ABSTRACT: The ATLAS and CMS experiments at the LHC conduct an extensive program to study production of events with a W or Z boson and particle jets. Dedicated studies focus on final states with the jets containing decays of heavy-flavor hadrons (b-tagged jets). The results are obtained using data from proton-proton collisions at sqrt{s}=7 TeV from the LHC at CERN. The set of measurements constitute a stringent test of the perturbative QCD calculations.
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    Marco Pieri, for the CMS Collaboration
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    ABSTRACT: We searched for the standard model Higgs boson in many different channels using approximately 5 fb-1 of 7 TeV pp collisions data collected with the CMS detector at LHC. Combining the results of the different searches we exclude at 95% confidence level a standard model Higgs boson with mass between 127.5 and 600 GeV. The expected 95% confidence level exclusion if the Higgs boson is not present is from 114.5 and 543 GeV. The observed exclusion is weaker than expected at low mass because of some excess that is observed below about 128 GeV. The most significant excess is found at 125 GeV with a local significance of 2.8 sigma. It has a global significance of 0.8 sigma when evaluated in the full search range and of 2.1 sigma when evaluated in the range 110-145 GeV. The excess is consistent both with background fluctuation and a standard model Higgs boson with mass of about 125 GeV, and more data are needed to investigate its origin.
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    Tommaso Dorigo, for the CMS Collaboration
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    ABSTRACT: The CMS collaboration has recently produced results of a number of searches for new physics processes using data collected during the 2011 run of the Large Hadron Collider. Up to 5 inverse femtobarns of proton-proton collisions at 7 TeV centre-of-mass energy have been used to search for the standard model Higgs boson in five different decay modes, divided in 42 independent sub-channels. The combination of the results has allowed CMS to set 95% confidence-level limits on the Higgs boson mass, constraining it to lay in the region 114.4<M(H)<127 GeV or M(H)>600 GeV. An excess of events with a local significance of 3.1 standard deviations is observed for M(H)=124 GeV; the global significance of observing such an effect anywhere in the search range 110-600 GeV is estimated to be 1.5 standard deviations. A number of signatures of supersymmetric particles have also been investigated, significantly restricting the parameter space of natural low-scale theories. A search for the rare decays of neutral bottom mesons to muon pairs, Bs to mu mu and Bd to mu mu, has achieved the tightest limits to date, and is approaching the sensitivity to measure the standard model branching ratios. As it happens, though, the highly informative results extracted from 2011 data produce more questions than answers; this doubles expectations for the 2012 run of LHC, which will conclusively answer several of them.
    The European Physical Journal Conferences 04/2012; 70. DOI:10.1051/epjconf/20147000021