DSpace collection: 期刊論文

Upsilon production cross section in pp collisions at root s=7 TeV

Mon, 11 Jun 2012 02:54:13 GMT

title: Upsilon production cross section in pp collisions at root s=7 TeV abstract: The Y(1S), Y(2S), and Y(3S) production cross sections in proton-proton collisions at root s = 7 TeV are measured using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3.1 +/- 0.3 pb(-1). Integrated over the rapidity range vertical bar y vertical bar < 2, we find the product of the Y(1S) production cross section and branching fraction to dimuons to be sigma(pp -> Y(1S)X) center dot B(Y(1S) -> mu(+)mu(-)) = 7.37 +/- 0.13(-0.42)(+0.61) +/- 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 Y(1S) 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 Y(1S), Y(2S), and Y(3S) differential cross sections as a function of transverse momentum and rapidity.

Study of Z Boson Production in PbPb Collisions at root s(NN)=2.76 TeV

Mon, 11 Jun 2012 02:54:11 GMT

title: Study of Z Boson Production in PbPb Collisions at root s(NN)=2.76 TeV abstract: A search for Z bosons in the mu(+)mu(-) decay channel has been performed in PbPb collisions at root s(NN) = 2.76 TeV with the CMS detector at the LHC, in a 7.2 mu b(-1) data sample. The number of opposite-sign muon pairs observed in the 60-120 GeV/c(2) invariant mass range is 39, corresponding to a yield per unit of rapidity (y) and per minimum bias event of [33.8 +/- 5.5(stat) +/- 4.4(syst)] x 10(-8), in the vertical bar y vertical bar < 2.0 range. Rapidity, transverse momentum, and centrality dependencies are also measured. The results agree with next-to-leading order QCD calculations, scaled by the number of incoherent nucleon-nucleon collisions.

Strange particle production in pp collisions at root s=0.9 and 7 TeV

Mon, 11 Jun 2012 02:54:09 GMT

title: Strange particle production in pp collisions at root s=0.9 and 7 TeV abstract: The spectra of strange hadrons are measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7TeV. The K(S)(0), A, and Xi(-) particles and their antiparticles are reconstructed from their decay topologies and the production rates are measured as functions of rapidity and transverse momentum, p(T). The results are compared to other experiments and to predictions of the PYTHIA Monte Carlo program. The p(T) distributions are found to differ substantially from the PYTHIA results and the production rates exceed the predictions by up to a factor of three.

Search for Supersymmetry in pp Collisions at root s=7 TeV in Events with Two Photons and Missing Transverse Energy

Mon, 11 Jun 2012 02:54:07 GMT

title: Search for Supersymmetry in pp Collisions at root s=7 TeV in Events with Two Photons and Missing Transverse Energy abstract: A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36 pb(-1) recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squark, gluino, and neutralino masses, excluding supersymmetry parameter space that was inaccessible to previous experiments.