We report on mid-rapidity mass spectrum of di-electrons and cross sections of pseudoscalar and vector mesons via $e^{+}e^{-}$ decays, from $\sqrt{s} = 200$ GeV $p+p$ collisions, measured by the large acceptance experiment STAR at RHIC. The ratio of the di-electron continuum to the combinatorial background is larger than 10% over the entire mass range. Simulations of di-electrons from light-meson decays and heavy-flavor decays (charmonium and open charm correlation) are found to describe the data. The extracted $\omega\rightarrow e^{+}e^{-}$ invariant yields are consistent with previous measurements. The mid-rapidity yields ($dN/dy$) of $\phi$ and $J/\psi$ are extracted through their di-electron decay channels and are consistent with the previous measurements of $\phi\rightarrow K^{+}K^{-}$ and $J/\psi\rightarrow e^{+}e^{-}$. Our results suggest a new upper limit of the branching ratio of the $\eta \rightarrow e^{+}e^{-}$ of $1.7\times10^{-5}$ at 90% confidence level.
The electron-pair invariant mass distri- butions for unlike-sign pairs in minimum-bias p + p collisions.
The electron-pair invariant mass distributions for like-sign pairs in minimum-bias p + p collisions.
The electron-pair invariant mass distributions for mix-event pairs in minimum-bias p + p collisions.
We present measured J/psi production rates in d+Au collisions at sqrt(s_NN) = 200 GeV over a broad range of transverse momentum (p_T=0-14 GeV/c) and rapidity (-2.2<y<2.2). We construct the nuclear-modification factor R_dAu for these kinematics and as a function of collision centrality (related to impact parameter for the R_dAu collision). We find that the modification is largest for collisions with small impact parameters, and observe a suppression (R_dAu<1) for p_T<4 GeV/c at positive rapidities. At negative rapidity we observe a suppression for p_T<2 GeV/c then an enhancement (R_dAu>1) for p_T>2 GeV/c. The observed enhancement at negative rapidity has implications for the observed modification in heavy-ion collisions at high p_T.
$J/\psi$ invariant yield as a function of $p_T$ for $p+p$ and 0–100% centrality integrated $d$+Au collisions. The type C systematic uncertainty for each distribution is given as a percentage in the legend. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
$J/\psi$ invariant yield as a function of $p_T$ for $p+p$ and 0–100% centrality integrated $d$+Au collisions. The type C systematic uncertainty for each distribution is given as a percentage in the legend. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
$J/\psi$ invariant yield as a function of $p_T$ for $p+p$ and 0–100% centrality integrated $d$+Au collisions. The type C systematic uncertainty for each distribution is given as a percentage in the legend.Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Background: Heavy-flavor production in p+p collisions tests perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p+p results, quantified with the nuclear-modification factor (R_AA), provides information on both cold- and hot-nuclear-matter effects. Purpose: Determine transverse-momentum, pt, spectra and the corresponding R_AA for muons from heavy-flavor mesons decay in p+p and Cu+Cu collisions at sqrt(s_NN)=200 GeV and y=1.65. Method: Results are obtained using the semi-leptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the p_T spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte-Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted. Results: The charm-production cross section in p+p collisions at sqrt{s}=200 GeV, integrated over pt and in the rapidity range 1.4<y<1.9 is found to be dsigma_ccbar/dy = 0.139 +/- 0.029 (stat) ^{+0.051}_{-0.058} (syst) mb. This result is consistent with calculations and with expectations based on the corresponding midrapidity charm-production cross section measured earlier by PHENIX. The R_AA for heavy-flavor muons in Cu+Cu collisions is measured in three centrality intervals for 1<pt<4 GeV/c. Suppression relative to binary-collision scaling (R_AA<1) increases with centrality. Conclusions: Within experimental and theoretical uncertainties, the measured heavy-flavor yield in p+p collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu+Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.
Production cross section of negative muons from heavy-flavor mesons decay as a function of $p_T$ in $p$+$p$ collisions at $\sqrt{s}=200$ GeV.
Invariant production yields of negative muons from heavy-flavor-mesons decay as a function $p_T$ in Cu+Cu collisions for three different centrality intervals (40-94%, 20-40%, and 0-20%), scaled by powers of ten for clarity. The solid line associated to each set of points corresponds to a fit to the $p$+$p$ invariant yield distribution described in the text, scaled by the appropriate number of binary collisions $N_{coll}$ when comparing to the Cu+Cu measurements.
Invariant production yields of negative muons from heavy-flavor-mesons decay as a function $p_T$ in $p$+$p$ collisions at $\sqrt{s}=200$ GeV. The solid line associated to each set of points corresponds to a fit to the $p$+$p$ invariant yield distribution described in the text, scaled by the appropriate number of binary collisions $N_{coll}$ when comparing to the Cu+Cu measurements.
The anisotropy of the azimuthal distributions of charged particles produced in PbPb collisions with a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, two- and four-particle cumulants, and Lee--Yang zeros. The anisotropy is presented as a function of transverse momentum (pt), pseudorapidity (eta) over a broad kinematic range: 0.3 < pt < 20 GeV, abs(eta) < 2.4, and in 12 classes of collision centrality from 0 to 80%. The results are compared to those obtained at lower center-of-mass energies, and various scaling behaviors are examined. When scaled by the geometric eccentricity of the collision zone, the elliptic anisotropy is found to obey a universal scaling with the transverse particle density for different collision systems and center-of-mass energies.
Measurements of the elliptic anisotropy parameter using the event-plane method, V2(EP) v PT for the centrality range 0-5%.
Measurements of the elliptic anisotropy parameter using the event-plane method, V2(EP) v PT for the centrality range 5-10%.
Measurements of the elliptic anisotropy parameter using the event-plane method, V2(EP) v PT for the centrality range 10-15%.
The diffractive process ep \rightarrow eXY, where Y denotes a proton or its low mass excitation with MY < 1.6 GeV, is studied with the H1 experiment at HERA. The analysis is restricted to the phase space region of the photon virtuality 3 \leq Q2 \leq 1600 GeV2, the square of the four-momentum transfer at the proton vertex |t| < 1.0 GeV2 and the longitudinal momentum fraction of the incident proton carried by the colourless exchange xIP < 0.05. Triple differential cross sections are measured as a function of xIP, Q2 and beta = x/xIP where x is the Bjorken scaling variable. These measurements are made after selecting diffractive events by demanding a large empty rapidity interval separating the final state hadronic systems X and Y . High statistics measurements covering the data taking periods 1999-2000 and 2004-2007 are combined with previously published results in order to provide a single set of diffractive cross sections from the H1 experiment using the large rapidity gap selection method. The combined data represent a factor between three and thirty increase in statistics with respect to the previously published results. The measurements are compared with predictions from NLO QCD calculations based on diffractive parton densities and from a dipole model. The proton vertex factorisation hypothesis is tested.
The reduced diffractive cross section multiplied by X_Pomeron at XP=0.0003 and Q^2=3.5 GeV^2 . The first (sys) error is the uncorrelated systematic error and the second is the correlated systematic error.
The reduced diffractive cross section multiplied by X_Pomeron at XP=0.0003 and Q^2=5.0 GeV^2 . The first (sys) error is the uncorrelated systematic error and the second is the correlated systematic error.
The reduced diffractive cross section multiplied by X_Pomeron at XP=0.0003 and Q^2=6.5 GeV^2 . The first (sys) error is the uncorrelated systematic error and the second is the correlated systematic error.
We present measurements of the differential cross section dsigma/dpT_gamma for the inclusive production of a photon in association with a b-quark jet for photons with rapidities |y_gamma|< 1.0 and 30<pT_gamma <300 GeV, as well as for photons with 1.5<|y_gamma|< 2.5 and 30< pT_gamma <200 GeV, where pT_gamma is the photon transverse momentum. The b-quark jets are required to have pT>15 GeV and rapidity |y_jet| < 1.5. The results are based on data corresponding to an integrated luminosity of 8.7 fb^-1, recorded with the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. The measured cross sections are compared with next-to-leading order perturbative QCD calculations using different sets of parton distribution functions as well as to predictions based on the kT-factorization QCD approach, and those from the Sherpa and Pythia Monte Carlo event generators.
The differential cross section as a function of PT for the production of GAMMA + B-JET in the photon |rapidity/ region < 1.0.
The differential cross section as a function of PT for the production of GAMMA + B-JET in the photon |rapidity| region 1.5-2.5.
The ALICE Collaboration has measured inclusive J/psi production in pp collisions at a center of mass energy sqrt(s)=2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges |y|<0.9 and 2.5<y<4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are L^e_int=1.1 nb^-1 and L^mu_int=19.9 nb^-1, and the corresponding signal statistics are N_J/psi^e+e-=59 +/- 14 and N_J/psi^mu+mu-=1364 +/- 53. We present dsigma_J/psi/dy for the two rapidity regions under study and, for the forward-y range, d^2sigma_J/psi/dydp_t in the transverse momentum domain 0<p_t<8 GeV/c. The results are compared with previously published results at sqrt(s)=7 TeV and with theoretical calculations.
Double differential J/$\psi$ production cross section at $\sqrt{s}=2.76$ TeV. The first uncertainty is statistical, the second one is $p_{\rm T}$-coorelated, the third one is uncorrelated. Polarization-related uncertainties are not included.
The $\sqrt{s}$-dependence of $\langle p_{\rm T}\rangle$ for inclusive J/$\psi$ production (forward rapidity).
the $\sqrt{s}$-dependence of $\langle p_{\rm T}\rangle$ for inclusive J/$\psi$ production (forward rapidity).
A measurement of the inclusive cross section for the process pp to b b-bar X to muon muon X' at sqrt(s) = 7 TeV is presented, based on a data sample corresponding to an integrated luminosity of 27.9 inverse picobarns collected by the CMS experiment at the LHC. By selecting pairs of muons each with pseudorapidity abs(eta)<2.1, the value of the cross section for pp to b b-bar X to muon muon X' is found to be 26.4 +/- 0.1 (stat.) +/- 2.4 (syst.) +/- 1.1 (lumi.) nb is obtained for muons with transverse momentum greater than 4 GeV, and 5.12 +/- 0.03 (stat.) +/- 0.48 (syst.) +/- 0.20 (lumi.) nb for transverse momenta greater than 6 GeV. These results are compared to QCD predictions at leading and next-to-leading orders.
The measured integrated cross sections. The second systematic error is due to the luminosity uncertainty.
Measurements of the anisotropy parameter v_2 of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p_T, and transverse kinetic energy KE_T at midrapidity (|\eta|<0.35) in Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. Pions and protons are identified up to p_T = 6 GeV/c, and kaons up to p_T = 4 GeV/c, by combining information from time-of-flight and aerogel Cherenkov detectors in the PHENIX Experiment. The scaling of v_2 with the number of valence quarks (n_q) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KE_T/n_q in noncentral Au+Au collisions (20--60%), but this scaling remains valid in central collisions (0--10%).
Identified hadron $v_2$ in central (0–20% centrality, left panels) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Panels (a) and (b) show $v_2$ as a function of transverse momentum $p_T$. The $v_2$ of all species for centrality 0–20% has been scaled up by a factor of 1.6 for better comparison with results of 20–60% centrality. The error bars (shaded boxes) represent the statistical (systematic) uncertainties. The systematic uncertainties shown are type A and B only.
Identified hadron $v_2$ in central (0–20% centrality, left panels) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Panels (a) and (b) show $v_2$ as a function of transverse momentum $p_T$. The $v_2$ of all species for centrality 0–20% has been scaled up by a factor of 1.6 for better comparison with results of 20–60% centrality. The error bars (shaded boxes) represent the statistical (systematic) uncertainties. The systematic uncertainties shown are type A and B only.
Identified hadron $v_2$ in central (0–20% centrality, left panels) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Panels (a) and (b) show $v_2$ as a function of transverse momentum $p_T$. The $v_2$ of all species for centrality 0–20% has been scaled up by a factor of 1.6 for better comparison with results of 20–60% centrality. The error bars (shaded boxes) represent the statistical (systematic) uncertainties. The systematic uncertainties shown are type A and B only.
A search for quark compositeness using dijet angular distributions from pp collisions at sqrt(s) = 7 TeV is presented. The search has been carried out using a data sample corresponding to an integrated luminosity of 2.2 inverse femtobarns, recorded by the CMS experiment at the LHC. Normalized dijet angular distributions have been measured for dijet invariant masses from 0.4 TeV to above 3 TeV and compared with a variety of contact interaction models, including those which take into account the effects of next-to-leading-order QCD corrections. The data are found to be in agreement with the predictions of perturbative QCD, and lower limits are obtained on the contact interaction scale, ranging from 7.5 up to 14.5 TeV at 95% confidence level.
Normalized dijet angular distributions for |yboost| < 1.11 and Mjj > 3.0 TeV.
Normalized dijet angular distributions for yboost < 1.11 and 2.4 < Mjj < 3.0 TeV.
Normalized dijet angular distributions for yboost < 1.11 and 1.9 < Mjj < 2.4 TeV.
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