The PHENIX experiement has measured the electron-positron pair mass spectrum from 0 to 8 GeV/c^2 in p+p collisions at sqrt(s)=200 GeV. The contributions from light meson decays to e^+e^- pairs have been determined based on measurements of hadron production cross sections by PHENIX. They account for nearly all e^+e^- pairs in the mass region below 1 GeV/c^2. The e^+e^- pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) \mu b, which is consistent with QCD calculations and measurements of single leptons by PHENIX.
Differential charm cross section at mid rapidity An additional +-39.5 microbarn error, due to the validity of the model used to extrapolate the data, is not included The contribution from beauty estimated to be 3.7 microbarn, has been subtracted. The c->e branching ratio used was 9.5 +-1.0%.
Total charm cross section An additional systemactic error of +- 200 microbarn, due to the validity of the model used to extrapolate the data, is not included. To obtain the total charm cross section, the differential charm cross section has been extrapolated to the whole rapidity range, using a HVQMNR rapidity distribution with aCTEQ5M PDF.
We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the llll channel, we observe three ZZ candidates with an expected background of 0.096^{+0.092}_{-0.063} events. In the llnunu channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of llll and llnunu channels, we observe an excess of events with a probability of $5.1\times 10^{-6}$ to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is sigma(ppbar -> ZZ) = 1.4^{+0.7}_{-0.6} (stat.+syst.) pb, consistent with the standard model expectation.
Measured cross section. Errors are combined statistics and systematics.
The PHENIX experiment has measured the suppression of semi-inclusive single high transverse momentum pi^0's in Au+Au collisions at sqrt(s_NN) = 200 GeV. The present understanding of this suppression is in terms of energy-loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dN^g/dy, the medium transport coefficient
$\pi^0$ $0-5\%$ centrality
Yields for J/psi production in Cu+Cu collisions at sqrt (s_NN)= 200 GeV have been measured by the PHENIX experiment over the rapidity range |y| < 2.2 at transverse momenta from 0 to beyond 5 GeV/c. The invariant yield is obtained as a function of rapidity, transverse momentum and collision centrality, and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data provide greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, providing a key constraint that is needed for disentangling cold and hot nuclear matter effects.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 0-20 centrality range. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 20-40 centrality range. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 40-60 centrality range. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
Azimuthal angle (Delta phi) correlations are presented for a broad range of transverse momentum (0.4 < pT < 10 GeV/c) and centrality (0-92%) selections for charged hadrons from di-jets in Au+Au collisions at sqrt(s_NN) = 200 GeV. With increasing pT, the away-side Delta phi distribution evolves from a broad and relatively flat shape to a concave shape, then to a convex shape. Comparisons to p+p data suggest that the away-side distribution can be divided into a partially suppressed head region centered at Delta phi ~ \pi, and an enhanced shoulder region centered at Delta phi ~ \pi \pm 1:1. The pT spectrum for the associated hadrons in the head region softens toward central collisions. The spectral slope for the shoulder region is independent of centrality and trigger pT . The properties of the near-side distributions are also modified relative to those in p + p collisions, reflected by the broadening of the jet shape in Delta phi and Delta eta, and an enhancement of the per-trigger yield. However, these modifications seem to be limited to pT < 4 GeV/c, above which both the dihadron pair shape and per-trigger yield become similar to p + p collisions. These observations suggest that both the away- and near-side distributions contain a jet fragmentation component which dominates for pT \ge 5GeV and a medium-induced component which is important for pT \le 4 GeV/c. We also quantify the role of jets at intermediate and low pT through the yield of jet-induced pairs in comparison to binary scaled p + p pair yield. The yield of jet-induced pairs is suppressed at high pair proxy energy (sum of the pT magnitudes of the two hadrons) and is enhanced at low pair proxy energy. The former is consistent with jet quenching/ the latter is consistent with the enhancement of soft hadron pairs due to transport of lost energy to lower pT.
Per-trigger yield versus $\Delta\phi$ for various trigger and partner $p_T$ ($p^a_T \otimes p^b_T$), arranged by increasing pair proxy energy (sum of $p^a_T$ and $p^b_T$), in p + p collisions for 5-10 $\otimes$ 2-3, 4-5 $\otimes$ 4-5, 5-10 $\otimes$ 3-5, and 5-10 $\otimes$ 5-10 GeV/c.
Per-trigger yield versus $\Delta\phi$ for various trigger and partner $p_T$ ($p^a_T \otimes p^b_T$), arranged by increasing pair proxy energy (sum of $p^a_T$ and $p^b_T$), in p + p collisions for 3-4 $\otimes$ 0.4-1, 3-4 $\otimes$ 1-2, 3-4 $\otimes$ 2-3, and 3-4 $\otimes$ 3-4 GeV/c.
Per-trigger yield versus $\Delta\phi$ for various trigger and partner $p_T$ ($p^a_T \otimes p^b_T$), arranged by increasing pair proxy energy (sum of $p^a_T$ and $p^b_T$), in Au + Au collisions for 3-4 $\otimes$ 0.4-1, 3-4 $\otimes$ 1-2, 3-4 $\otimes$ 2-3, and 3-4 $\otimes$ 3-4 GeV/c.
For Au + Au collisions at 200 GeV we measure neutral pion production with good statistics for transverse momentum, p_T, up to 20 GeV/c. A fivefold suppression is found, which is essentially constant for 5 < p_T < 20 GeV/c. Experimental uncertainties are small enough to constrain any model-dependent parameterization for the transport coefficient of the medium, e.g. \mean(q^hat) in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au+Au collisions/ instead, it increases proportional to the number of participating nucleons, as N_part^2/3.
$\pi^0$ invariant yields for different centralities. The bin range is not an uncertainty in the x-axis because the actual uncertainty by having the finite bin width is corrected for by the bin-shift correction. These bins were constructed using the corrected finite values as centers.
$\pi^0$ invariant yields for different centralities. The bin range is not an uncertainty in the x-axis because the actual uncertainty by having the finite bin width is corrected for by the bin-shift correction. These bins were constructed using the corrected finite values as centers.
$\pi^0$ invariant yields for different centralities. The bin range is not an uncertainty in the x-axis because the actual uncertainty by having the finite bin width is corrected for by the bin-shift correction. These bins were constructed using the corrected finite values as centers.
Neutral pion transverse momentum (pT) spectra at mid-rapidity (|y| < 0.35) were measured in Cu+Cu collisions at \sqrt s_NN = 22.4, 62.4, and 200 GeV. Relative to pi -zero yields in p+p collisions scaled by the number of inelastic nucleon-nucleon collisions (Ncoll) at the respective energies, the pi-zero yields for pT \ge 2 GeV/c in central Cu+Cu collisions at 62.4 and 200 GeV are suppressed, whereas an enhancement is observed at 22.4 GeV. A comparison with a jet quenching model suggests that final state parton energy loss dominates in central Cu+Cu collisions at 62.4 GeV and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.
Invariant $\pi^0$ yields in central Cu+Cu collisions and invariant $\pi^0$ cross sections in $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 22.4 GeV. The error (tot.) includes the quadratic sum of the statistical and total systematic uncertainties.
Invariant $\pi^0$ yields in central Cu+Cu collisions and invariant $\pi^0$ cross sections in $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 62.4 GeV. The error (tot.) includes the quadratic sum of the statistical and total systematic uncertainties.
Invariant $\pi^0$ yields in central Cu+Cu collisions and invariant $\pi^0$ cross sections in $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. The error (tot.) includes the quadratic sum of the statistical and total systematic uncertainties.
We present a measurement of the cross section for W-boson production in association with jets in pbarp collisions at sqrt(s)=1.96$ TeV. The analysis uses a data sample corresponding to an integrated luminosity of 320 pb^-1 collected with the CDF II detector. W bosons are identified in their electron decay channel and jets are reconstructed using a cone algorithm. For each W+>= n-jet sample ($n= 1 - 4$) we measure sigma(ppbar =>W+>=n$-jet)x BR(W => e nu) with respect to the transverse energy E_T of the n^th-highest E_T jet above 20 GeV, for a restricted W => e nu decay phase space. The cross sections, corrected for all detector effects, can be directly compared to particle level W+ jet(s) predictions. We present here comparisons to leading order and next-to-leading order predictions.
Measured ET differential cross section of the 1st jet in >= 1 JET plus W < E NU > events.
Measured ET differential cross section of the 2nd jet in >= 2 JET plus W < E NU > events.
Measured ET differential cross section of the 3rd jet in >= 3 JET plus W < E NU > events.
We present the first measurement of the production cross section of a W boson with a single charm quark (c) in p-pbar collisions at sqrt(s)=1.96 TeV, using soft muon tagging of c jets. In a data sample of ~1.8 fb-1, recorded with the CDF II detector at the Fermilab Tevatron, we select events with W+1 or 2 jets. We use the charge correlation between the W and the muon from the semileptonic decay of a charm hadron to extract the Wc signal. We measure sigma_{Wc}(p_{Tc}>20 GeV/c, |\eta_c|<1.5)\times BR(W->\ell\nu) = 9.8+/-3.2 pb, in agreement with theoretical expectations.
The measured cross section for leptonic decay of the W.
Inclusive jet cross sections in Z/gamma^* events, with Z/gamma^* decaying into an electron-positron pair, are measured as a function of jet transverse momentum and jet multiplicity in ppbar collisions at sqrt{s} = 1.96 TeV with the upgraded Collider Detector at Fermilab in Run II, based on an integrated luminosity of 1.7 fb^-1. The measurements cover the rapidity region | yjet | < 2.1 and the transverse momentum range ptjet > 30 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.
Total cross section for .GE.1JET.
Total cross section for .GE.2JET.
Total cross section for .GE.3JET.
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