A measurement of the electron charge asymmetry in inclusive pp to W + X to e nu + X production at sqrt(s) = 7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 840 inverse picobarns. The electron charge asymmetry reflects the unequal production of positive and negative W bosons in pp collisions. The electron charge asymmetry is measured in bins of absolute value of electron pseudorapidity in the range of abs(eta) < 2.4. The asymmetry rises from about 0.1 to 0.2 as a function of the pseudorapidity and is measured with a relative precision better than 7%. This measurement provides new stringent constraints for parton distribution functions.
The differential cross sections for the production of photons in Z to mu+ mu- gamma decays are presented as a function of the transverse energy of the photon and its separation from the nearest muon. The data for these measurements were collected with the CMS detector and correspond to an integrated luminosity of 4.7 inverse femtobarns of pp collisions at sqrt(s) = 7 TeV delivered by the CERN LHC. The cross sections are compared to simulations with POWHEG and PYTHIA, where PYTHIA is used to simulate parton showers and final-state photons. These simulations match the data to better than 5%.
Event-shape variables, which are sensitive to perturbative and nonperturbative aspects of quantum chromodynamic (QCD) interactions, are studied in multijet events recorded in proton-proton collisions at sqrt(s) = 7 TeV. Events are selected with at least one jet with transverse momentum pt > 110 GeV and pseudorapidity abs(eta) < 2.4, in a data sample corresponding to integrated luminosities of up to 5 inverse femtobarns. The distributions of five event-shape variables in various leading jet pt ranges are compared to predictions from different QCD Monte Carlo event generators.
The polarizations of prompt J/psi and psi(2S) mesons are measured in proton-proton collisions at sqrt(s) = 7 TeV, using a dimuon data sample collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The prompt J/psi and psi(2S) polarization parameters lambda[theta], lambda[phi], and lambda[theta,phi], as well as the frame-invariant quantity lambda(tilde), are measured from the dimuon decay angular distributions in three different polarization frames. The J/psi results are obtained in the transverse momentum range 14 < pt < 70 GeV, in the rapidity intervals abs(y) < 0.6 and 0.6 < abs(y) < 1.2. The corresponding psi(2S) results cover 14 < pt < 50 GeV and include a third rapidity bin, 1.2 < abs(y) < 1.5. No evidence of large transverse or longitudinal polarizations is seen in these kinematic regions, which extend much beyond those previously explored.
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 total and fiducial inclusive W and Z boson production cross sections in pp collisions at $\sqrt{s}$ = 8 TeV is presented. Electron and muon final states are analyzed in a data sample collected with the CMS detector corresponding to an integrated luminosity of 18.2 +/- 0.5 inverse-picobarns. The measured total inclusive cross sections times branching fractions are $\sigma(pp \to WX) \times B(W \to l\nu)$ = 12.21 +/- 0.03 (stat) +/- 0.24 (syst) +/- 0.32 (lum) nb, and $\sigma(pp \to ZX) \times B(Z \to l^{+}l^{-})$ = 1.15 +/- 0.01 (stat) +/- 0.02 (syst) +/- 0.03 (lum) nb, for the dilepton mass in the range of 60 to 120 GeV. The measured values agree with next-to-next-to-leading-order QCD cross section calculations. Ratios of cross sections are reported with a precision of 2%. This is the first measurement of inclusive W and Z boson production in proton-proton collisions at $\sqrt{s}$ = 8 TeV.
Rapidity distributions are presented for events containing either a Z boson or a photon with a single jet in proton-proton collisions produced at the CERN LHC. The data, collected with the CMS detector at $\sqrt{s}$ = 7 TeV, correspond to an integrated luminosity of 5.0 inverse femtobarns. The individual rapidity distributions of the boson and the jet are consistent within 5% with expectations from perturbative QCD. However, QCD predictions for the sum and the difference in rapidities of the two final-state objects show discrepancies with CMS data. In particular, next-to-leading-order QCD calculations, and two common Monte Carlo event generators using different methods to match matrix-element partons with parton showers, appear inconsistent with the data as well as with each other.
Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt(sNN) = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and laboratory rapidity abs(y) < 1 are identified via their energy loss in the silicon tracker. The average pt increases with particle mass and the charged multiplicity of the event. The increase of the average pt with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that EPOS LHC, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike HIJING and AMPT. The pt spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity.
A measurement of the multi-strange $\Xi^-$ and $\Omega^-$ baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic proton-proton collisions at centre of mass energy of 7 TeV. The transverse momentum ($p_{\rm T}$) distributions were studied at mid-rapidity (|y| < 0.5) in the range of 0.6 < $p_{\rm T}$ < 8.5 GeV/$c$ for $\Xi^-$ and $\Xi^+$ baryons, and in the range of 0.8 < $p_{\rm T}$ < 5 GeV/$c$ for $\Omega^-$ and $\Omega^+$. Baryons and antibaryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current LHC data has allowed us to measure a difference between the mean $p_{\rm T}$ of $\Xi^-$ ($\Xi^+$) and $\Omega^-$ ($\Omega^+$). Particle yields, mean $p_{\rm T}$, and the spectra in the intermediate $p_{\rm T}$ range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for $\Omega^-$ ($\Omega^+$). This PYTHIA tune approaches the $p_{\rm T}$ spectra of $\Xi^-$ and $\Xi^+$ baryons below $p_{\rm T}$ < 0.85 GeV/$c$ and describes the $\Xi^-$ and $\Xi^+$ spectra above $p_{\rm T}$ > 6.0 GeV/$c$. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of ($\Omega^{-}+\Omega^+)/(\Xi^-+\Xi^+)$ as a function of transverse mass.
We present the measurements of particle pair yields per trigger particle obtained from di-hadron azimuthal correlations in pp collisions at $\sqrt{s} = 0.9$, $2.76$, and $7$ TeV recorded with the ALICE detector. The yields are studied as a function of the charged particle multiplicity. Taken together with the single particle yields the pair yields provide information about parton fragmentation at low transverse momenta, as well as on the contribution of multiple parton interactions to particle production. Data are compared to calculations using the PYTHIA6, PYTHIA8, and PHOJET event generators.
Forum