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]
The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s... more The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV are measured using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3:1 AE 0:3 pb À1 . Integrated over the rapidity range jyj < 2, we find the product of the Çð1SÞ production cross section and branching fraction to dimuons to be ðpp ! Çð1SÞXÞ Á BðÇð1SÞ ! þ À Þ ¼ 7:37 AE 0:13 þ0:61 À0:42 AE 0:81 nb, where the first uncertainty is statistical, the second is systematic, and the third is associated with the estimation of the integrated luminosity of the data sample. This cross section is obtained assuming unpolarized Çð1SÞ production. With the assumption of fully transverse or fully longitudinal production polarization, the measured cross section changes by about 20%. We also report the measurement of the Çð1SÞ, Çð2SÞ, and Çð3SÞ differential cross sections as a function of transverse momentum and rapidity.
Measurement of energy flow at large pseudorapidities in pp collisions at $ \sqrt {s} = 0.{9} $ and 7 TeV
Journal of High Energy Physics, 2011
... and √ s = 7 TeV data samples, respectively. 3.2 Dijet Events The jets were reconstructed usin... more ... and √ s = 7 TeV data samples, respectively. 3.2 Dijet Events The jets were reconstructed using the anti-kT jet clustering algorithm [16], with a distance parameter of 0.5. Particle flow objects [17] that combine information from all the CMS sub-detectors were used as input. ...
Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data ... more Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 pb −1 . Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
Search for a W boson decaying to a muon and a neutrino in pp collisions at √ s = 7 TeV ✩ .CMS Col... more Search for a W boson decaying to a muon and a neutrino in pp collisions at √ s = 7 TeV ✩ .CMS Collaboration CERN, Geneva, Switzerland a r t i c l e i n f o a b s t
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]
The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s... more The Çð1SÞ, Çð2SÞ, and Çð3SÞ production cross sections in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV are measured using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3:1 AE 0:3 pb À1 . Integrated over the rapidity range jyj < 2, we find the product of the Çð1SÞ production cross section and branching fraction to dimuons to be ðpp ! Çð1SÞXÞ Á BðÇð1SÞ ! þ À Þ ¼ 7:37 AE 0:13 þ0:61 À0:42 AE 0:81 nb, where the first uncertainty is statistical, the second is systematic, and the third is associated with the estimation of the integrated luminosity of the data sample. This cross section is obtained assuming unpolarized Çð1SÞ production. With the assumption of fully transverse or fully longitudinal production polarization, the measured cross section changes by about 20%. We also report the measurement of the Çð1SÞ, Çð2SÞ, and Çð3SÞ differential cross sections as a function of transverse momentum and rapidity.
Measurement of energy flow at large pseudorapidities in pp collisions at $ \sqrt {s} = 0.{9} $ and 7 TeV
Journal of High Energy Physics, 2011
... and √ s = 7 TeV data samples, respectively. 3.2 Dijet Events The jets were reconstructed usin... more ... and √ s = 7 TeV data samples, respectively. 3.2 Dijet Events The jets were reconstructed using the anti-kT jet clustering algorithm [16], with a distance parameter of 0.5. Particle flow objects [17] that combine information from all the CMS sub-detectors were used as input. ...
Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data ... more Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 pb −1 . Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
Search for a W boson decaying to a muon and a neutrino in pp collisions at √ s = 7 TeV ✩ .CMS Col... more Search for a W boson decaying to a muon and a neutrino in pp collisions at √ s = 7 TeV ✩ .CMS Collaboration CERN, Geneva, Switzerland a r t i c l e i n f o a b s t
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