This paper presents a measurement of the W^+W^- production cross section in pp collisions at sqrt{s}=7 TeV. The leptonic decay channels are analyzed using data corresponding to an integrated 4.6 fb-1 collected with the ATLAS detector at the Large Hadron Collider. The W^+W^- production cross section sigma(pp -> W^+W^-+X) is measured to be 51.9 +- 2.0 (stat) +- 3.9 (syst) +- 2.0 (lumi) pb, compatible with the Standard Model prediction of 44.7 +2.1 -1.9 pb. A measurement of the normalized fiducial cross section as a function of the leading lepton transverse momentum is also presented. The reconstructed transverse momentum distribution of the leading lepton is used to extract limits on anomalous WWZ and WWgamma couplings.
Measurements of differential cross sections are presented for the production of a Z boson and at least one hadronic jet in proton-proton collisions at sqrt(s) = 7 TeV, recorded by the CMS detector, using a data sample corresponding to an integrated luminosity of 4.9 inverse femtobarns. The jet multiplicity distribution is measured for up to six jets. The differential cross sections are measured as a function of jet transverse momentum and pseudorapidity for the four highest transverse momentum jets. The distribution of the scalar sum of jet transverse momenta is also measured as a function of the jet multiplicity. The measurements are compared with theoretical predictions at leading and next-to-leading order in perturbative QCD.
Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pt) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 inverse femtobarns. The measured cross sections are compared to predictions from Monte Carlo generators, MADGRAPH + PYTHIA and SHERPA, and to next-to-leading-order calculations from BLACKHAT + SHERPA. The differential cross sections are found to be in agreement with the predictions, apart from the pt distributions of the leading jets at high pt values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.
Measurements of the differential cross sections for the production of exactly four jets in proton-proton collisions are presented as a function of the transverse momentum pt and pseudorapidity eta, together with the correlations in azimuthal angle and the pt balance among the jets. The data sample was collected in 2010 at a center-of-mass energy of 7 TeV with the CMS detector at the LHC, with an integrated luminosity of 36 inverse picobarns. The cross section for a final state with a pair of hard jets with pt > 50 GeV and another pair with pt > 20 GeV within abs(eta) < 4.7 is measured to be sigma = 330 +- 5 (stat.) +- 45 (syst.) nb. It is found that fixed-order matrix element calculations including parton showers describe the measured differential cross sections in some regions of phase space only, and that adding contributions from double parton scattering brings the Monte Carlo predictions closer to the data.
Measurements are presented of the associated production of a W boson and a charm-quark jet (W + c) in pp collisions at a center-of-mass energy of 7 TeV. The analysis is conducted with a data sample corresponding to a total integrated luminosity of 5 inverse femtobarns, collected by the CMS detector at the LHC. W boson candidates are identified by their decay into a charged lepton (muon or electron) and a neutrino. The W + c measurements are performed for charm-quark jets in the kinematic region $p_T^{jet} \gt$ 25 GeV, $|\eta^{jet}| \lt$ 2.5, for two different thresholds for the transverse momentum of the lepton from the W-boson decay, and in the pseudorapidity range $|\eta^{\ell}| \lt$ 2.1. Hadronic and inclusive semileptonic decays of charm hadrons are used to measure the following total cross sections: $\sigma(pp \to W + c + X) \times B(W \to \ell \nu)$ = 107.7 +/- 3.3 (stat.) +/- 6.9 (syst.) pb ($p_T^{\ell} \gt$ 25 GeV) and $\sigma(pp \to W + c + X) \times B(W \to \ell \nu)$ = 84.1 +/- 2.0 (stat.) +/- 4.9 (syst.) pb ($p_T^{\ell} \gt$ 35 GeV), and the cross section ratios $\sigma(pp \to W^+ + \bar{c} + X)/\sigma(pp \to W^- + c + X)$ = 0.954 +/- 0.025 (stat.) +/- 0.004 (syst.) ($p_T^{\ell} \gt$ 25 GeV) and $\sigma(pp \to W^+ + \bar{c} + X)\sigma(pp \to W^- + c + X)$ = 0.938 +/- 0.019 (stat.) +/- 0.006 (syst.) ($p_T^{\ell} \gt$ 35 GeV). Cross sections and cross section ratios are also measured differentially with respect to the absolute value of the pseudorapidity of the lepton from the W-boson decay. These are the first measurements from the LHC directly sensitive to the strange quark and antiquark content of the proton. Results are compared with theoretical predictions and are consistent with the predictions based on global fits of parton distribution functions.
Measurements of the differential and double-differential Drell-Yan cross sections are presented using an integrated luminosity of 4.5(4.8) inverse femtobarns in the dimuon (dielectron) channel of proton-proton collision data recorded with the CMS detector at the LHC at $\sqrt{s}$ = 7 TeV. The measured inclusive cross section in the Z-peak region (60-120 GeV) is $\sigma(\ell \ell)$ = 986.4 +/- 0.6 (stat.) +/- 5.9 (exp. syst.) +/- 21.7 (th. syst.) +/- 21.7 (lum.) pb for the combination of the dimuon and dielectron channels. Differential cross sections $d\sigma/dm$ for the dimuon, dielectron, and combined channels are measured in the mass range 15 to 1500 GeV and corrected to the full phase space. Results are also presented for the measurement of the double-differential cross section $d^2\sigma/dm d |y|$ in the dimuon channel over the mass range 20 to 1500 GeV and absolute dimuon rapidity from 0 to 2.4. These measurements are compared to the predictions of perturbative QCD calculations at next-to-leading and next-to-next-to-leading orders using various sets of parton distribution functions.
A measurement of the b-hadron production cross section in proton-proton collisions at sqrt(s)=7 TeV is presented. The dataset, corresponding to 85 inverse nanobarns, was recorded with the CMS experiment at the LHC using a low-threshold single-muon trigger. Events are selected by the presence of a muon with transverse momentum greater than 6 GeV with respect to the beam direction and pseudorapidity less than 2.1. The transverse momentum of the muon with respect to the closest jet discriminates events containing b hadrons from background. The inclusive b-hadron production cross section is presented as a function of muon transverse momentum and pseudorapidity. The measured total cross section in the kinematic acceptance is sigma(pp to b+X to mu + X') =1.32 +/- 0.01 (stat) +/- 0.30 (syst) +/- 0.15 (lumi) microbarns.
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.
The production of the X(3872) is studied in pp collisions at sqrt(s) = 7 TeV, using decays to J/psi pi pi, where the J/psi decays to two muons. The data were recorded by the CMS experiment and correspond to an integrated luminosity of 4.8 inverse femtobarns. The measurements are performed in a kinematic range in which the X(3872) candidates have a transverse momentum 10 < pt < 50 GeV and rapidity abs(y) < 1.2. The ratio of the X(3872) and psi(2S) cross sections times their branching fractions into J/psi pi pi is measured as a function of pt. In addition, the fraction of X(3872) originating from B decays is determined. From these measurements the prompt X(3872) differential cross section times branching fraction as a function of pt is extracted. The pi pi mass spectrum of the J/psi pi pi system in the X(3872) decays is also investigated.
The inclusive b-jet production cross section in pp collisions at a center-of-mass energy of 7 TeV is measured using data collected by the CMS experiment at the LHC. The cross section is presented as a function of the jet transverse momentum in the range 18 < pT < 200 GeV for several rapidity intervals. The results are also given as the ratio of the b-jet production cross section to the inclusive jet production cross section. The measurement is performed with two different analyses, which differ in their trigger selection and b-jet identification: a jet analysis that selects events with a b jet using a sample corresponding to an integrated luminosity of 34 inverse picobarns, and a muon analysis requiring a b jet with a muon based on an integrated luminosity of 3 inverse picobarns. In both approaches the b jets are identified by requiring a secondary vertex. The results from the two methods are in agreement with each other and with next-to-leading order calculations, as well as with predictions based on the PYTHIA event generator.
Forum