Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at √ s... more Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at √ s NN = 2.76 TeV by the CMS collaboration, using data from the 2011 LHC heavy-ion run. The data set includes a sample of ultra-central (0-0.2% centrality) PbPb events collected using a trigger based on total transverse energy in the hadron forward calorimeters and the total multiplicity of pixel clusters in the silicon pixel tracker. A total of about 1.8 million ultra-central events were recorded, corresponding to an integrated luminosity of 120 µb −1 . The observed correlations in ultra-central PbPb events are expected to be particularly sensitive to initial-state fluctuations. The single-particle anisotropy Fourier harmonics, from v 2 to v 6 , are extracted as a function of particle transverse momentum. At higher transverse momentum, the v 2 harmonic becomes significantly smaller than the higher-order v n (n ≥ 3). The p T -averaged v 2 and v 3 are found to be equal within 2%, while higher-order v n decrease as n increases. The breakdown of factorization of dihadron correlations into single-particle azimuthal anisotropies is observed. This effect is found to be most prominent in the ultra-central PbPb collisions, where the initial-state fluctuations play a dominant role. A comparison of the factorization data to hydrodynamic predictions with event-byevent fluctuating initial conditions is also presented. Submitted to the Journal of High Energy Physics c 2013 CERN for the benefit of the CMS Collaboration. CC-BY-3.0 license arXiv:1312.1845v1 [nucl-ex]
Search for exotic resonances decaying into WZ/ZZ in pp collisions at $ \sqrt{s}=7 $ TeV
Journal of High Energy Physics, 2013
Abstract A search for new exotic particles decaying to the VZ final state is performed, where V i... more Abstract A search for new exotic particles decaying to the VZ final state is performed, where V is either a W or a Z boson decaying into two overlapping jets and the Z decays into a pair of electrons, muons or neutrinos. The analysis uses a data sample of pp collisions ...
A search for supersymmetry is presented using a sample of events with b jets and missing transver... more A search for supersymmetry is presented using a sample of events with b jets and missing transverse momentum. The search uses a data sample of proton-proton collisions at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 35 pb −1 , collected with the CMS detector. A total of 0.33 +0.43 −0.33 (stat.) ± 0.13 (syst.) events is predicted, using control samples in the data, to arise from standard model processes, and one event is observed in the data. Upper limits are set at the 95% confidence level on the cross sections of benchmark supersymmetric models.
Transverse-Momentum and Pseudorapidity Distributions of Charged Hadrons in pp Collisions at sqrt[s]=7 TeV
Physical Review Letters, 2010
ABSTRACT Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton col... more ABSTRACT Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at square root of s = 7 TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity dN(ch)/dη|(|η|<0.5) = 5.78 ± 0.01(stat) ± 0.23(syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from square root of s = 0.9 to 7 TeV is [66.1 ± 1.0(stat) ± 4.2(syst)]%. The mean transverse momentum is measured to be 0.545 ± 0.005(stat) ± 0.015(syst) GeV/c. The results are compared with similar measurements at lower energies.
95 , T. Signal 95 , J.C. Williams 95 , M. Ahmad 96 , I. Ahmed 96 , M.I. Asghar 96 , H.R. Hoorani ... more 95 , T. Signal 95 , J.C. Williams 95 , M. Ahmad 96 , I. Ahmed 96 , M.I. Asghar 96 , H.R. Hoorani 96 , W.A. Khan 96 , T. Khurshid 96 , S. Qazi 96 , M. Cwiok 97 , W. Dominik 97 , K. Doroba 97 , M. Konecki 97 , J. Krolikowski 97 , T. Frueboes 98 , R. Gokieli 98 , M. Górski 98 , M. Kazana 98 , K. Nawrocki 98 , M. Szleper 98 , G. Wrochna 98 , P. Zalewski 98 , N. Almeida 99 , A. David 99 , P. Faccioli 99 , P.G. Ferreira Parracho 99 , M. Gallinaro 99 , P. Martins 99 , G. Mini 99 , P. Musella 99 , A. Nayak 99 , L. Raposo 99 , P.Q. Ribeiro 99 , J. Seixas 99 , P. Silva 99 ,
We have measured the spin structure functions g p 2 and g d 2 and the virtual photon asymmetries ... more We have measured the spin structure functions g p 2 and g d 2 and the virtual photon asymmetries A p 2 and A d 2 over the kinematic range 0.02 ≤ x ≤ 0.8 and 0.7 ≤ Q 2 ≤ 20 GeV 2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and 6 LiD targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d p 2 and d n 2 are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x → 0. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A2 is significantly smaller than the A2 < R(1 + A1)/2 limit.
Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at √ s... more Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at √ s NN = 2.76 TeV by the CMS collaboration, using data from the 2011 LHC heavy-ion run. The data set includes a sample of ultra-central (0-0.2% centrality) PbPb events collected using a trigger based on total transverse energy in the hadron forward calorimeters and the total multiplicity of pixel clusters in the silicon pixel tracker. A total of about 1.8 million ultra-central events were recorded, corresponding to an integrated luminosity of 120 µb −1 . The observed correlations in ultra-central PbPb events are expected to be particularly sensitive to initial-state fluctuations. The single-particle anisotropy Fourier harmonics, from v 2 to v 6 , are extracted as a function of particle transverse momentum. At higher transverse momentum, the v 2 harmonic becomes significantly smaller than the higher-order v n (n ≥ 3). The p T -averaged v 2 and v 3 are found to be equal within 2%, while higher-order v n decrease as n increases. The breakdown of factorization of dihadron correlations into single-particle azimuthal anisotropies is observed. This effect is found to be most prominent in the ultra-central PbPb collisions, where the initial-state fluctuations play a dominant role. A comparison of the factorization data to hydrodynamic predictions with event-byevent fluctuating initial conditions is also presented. Submitted to the Journal of High Energy Physics c 2013 CERN for the benefit of the CMS Collaboration. CC-BY-3.0 license arXiv:1312.1845v1 [nucl-ex]
Search for exotic resonances decaying into WZ/ZZ in pp collisions at $ \sqrt{s}=7 $ TeV
Journal of High Energy Physics, 2013
Abstract A search for new exotic particles decaying to the VZ final state is performed, where V i... more Abstract A search for new exotic particles decaying to the VZ final state is performed, where V is either a W or a Z boson decaying into two overlapping jets and the Z decays into a pair of electrons, muons or neutrinos. The analysis uses a data sample of pp collisions ...
A search for supersymmetry is presented using a sample of events with b jets and missing transver... more A search for supersymmetry is presented using a sample of events with b jets and missing transverse momentum. The search uses a data sample of proton-proton collisions at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 35 pb −1 , collected with the CMS detector. A total of 0.33 +0.43 −0.33 (stat.) ± 0.13 (syst.) events is predicted, using control samples in the data, to arise from standard model processes, and one event is observed in the data. Upper limits are set at the 95% confidence level on the cross sections of benchmark supersymmetric models.
Transverse-Momentum and Pseudorapidity Distributions of Charged Hadrons in pp Collisions at sqrt[s]=7 TeV
Physical Review Letters, 2010
ABSTRACT Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton col... more ABSTRACT Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at square root of s = 7 TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity dN(ch)/dη|(|η|&amp;lt;0.5) = 5.78 ± 0.01(stat) ± 0.23(syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from square root of s = 0.9 to 7 TeV is [66.1 ± 1.0(stat) ± 4.2(syst)]%. The mean transverse momentum is measured to be 0.545 ± 0.005(stat) ± 0.015(syst) GeV/c. The results are compared with similar measurements at lower energies.
95 , T. Signal 95 , J.C. Williams 95 , M. Ahmad 96 , I. Ahmed 96 , M.I. Asghar 96 , H.R. Hoorani ... more 95 , T. Signal 95 , J.C. Williams 95 , M. Ahmad 96 , I. Ahmed 96 , M.I. Asghar 96 , H.R. Hoorani 96 , W.A. Khan 96 , T. Khurshid 96 , S. Qazi 96 , M. Cwiok 97 , W. Dominik 97 , K. Doroba 97 , M. Konecki 97 , J. Krolikowski 97 , T. Frueboes 98 , R. Gokieli 98 , M. Górski 98 , M. Kazana 98 , K. Nawrocki 98 , M. Szleper 98 , G. Wrochna 98 , P. Zalewski 98 , N. Almeida 99 , A. David 99 , P. Faccioli 99 , P.G. Ferreira Parracho 99 , M. Gallinaro 99 , P. Martins 99 , G. Mini 99 , P. Musella 99 , A. Nayak 99 , L. Raposo 99 , P.Q. Ribeiro 99 , J. Seixas 99 , P. Silva 99 ,
We have measured the spin structure functions g p 2 and g d 2 and the virtual photon asymmetries ... more We have measured the spin structure functions g p 2 and g d 2 and the virtual photon asymmetries A p 2 and A d 2 over the kinematic range 0.02 ≤ x ≤ 0.8 and 0.7 ≤ Q 2 ≤ 20 GeV 2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and 6 LiD targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d p 2 and d n 2 are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x → 0. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A2 is significantly smaller than the A2 < R(1 + A1)/2 limit.
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