Differential elliptic flow (v_2) for phi mesons and (anti)deuterons (d^bar)d is measured for Au+Au collisions at sqrt(s_NN) = 200 GeV. The v_2 for phi mesons follows the trend of lighter pi^+/- and K^+/- mesons, suggesting that ordinary hadrons interacting with standard hadronic cross sections are not the primary driver for elliptic flow development. The v_2 values for (d^bar)d suggest that elliptic flow is additive for composite particles. This further validation of the universal scaling of v_2 per constituent quark for baryons and mesons suggests that partonic collectivity dominates the transverse expansion dynamics.
$m_{inv}$ distributions for foreground and background $K^+ K^-$ pairs for 20-60% central Au+Au collisions.
$m_{inv}$ distributions
$<cos(2(\varphi^{pair}-\Phi_2))>$ vs. $m_{inv}$.
The PHENIX experiment presents results from the RHIC 2005 run with polarized proton collisions at sqrt(s)=200 GeV, for inclusive \pi^0 production at mid-rapidity. Unpolarized cross section results are given for transverse momenta p_T=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p_T. The cross section is described well for p_T < 1 GeV/c by an exponential in p_T, and, for p_T > 2 GeV/c, by perturbative QCD. Double helicity asymmetries A_LL are presented based on a factor of five improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton, and exclude maximal values for the gluon polarization.
The neutral pion production cross section at $\sqrt{s}$ = 200 GeV as a function of $p_T$ and the results of NLO pQCD calculations for theory scales $\mu$ = $p_T$/2, $p_T$, and $2p_T$. Additional 9.7% normalization uncertainty is not included.
The double helicity asymmetry ($A_{LL}$) for neutral pion production at $\sqrt{s}$ = 200 GeV as a function of $p_T$ (GeV/$c$). Not included in the figure/table: the correlated for all points scale systematic uncertainty of 9.4% (scales both the values and stat. uncertainties by the same factor).
The single helicity asymmetry ($A_L$) for neutral pion production at $\sqrt{s}$ = 200 GeV as a function of $p_T$ (GeV/$c$). Systematic uncertainties are negligible.
Longitudinal density correlations of produced matter in Au+Au collisions at sqrt(s_NN)=200 GeV have been measured from the inclusive charged particle distributions as a function of pseudorapidity window sizes. The extracted \alpha \xi parameter, related to the susceptibility of the density fluctuations in the long wavelength limit, exhibits a non-monotonic behavior as a function of the number of participant nucleons, N_part. A local maximum is seen at N_part ~ 90, with corresponding energy density based on the Bjorken picture of \epsilon_Bj \tau ~ 2.4 GeV/(fm^2 c) with a transverse area size of 60 fm^2. This behavior may suggest a critical phase boundary based on the Ginzburg-Landau framework.
Weighted mean of corrected NBD $k$, $<k_c>$ as a function of pseudorapidity window size. The dominant sources systematic correlate with dead maps (corr.sys.(dead)) and two-track seperation cuts (corr.sys.(fake)). The total systematic error (uncorr.sys.) is the quadratic sum over all errors.
Weighted mean of corrected NBD $k$, $<k_c>$ as a function of pseudorapidity window size. The dominant sources systematic correlate with dead maps (corr.sys.(dead)) and two-track seperation cuts (corr.sys.(fake)). The total systematic error (uncorr.sys.) is the quadratic sum over all errors.
Fit results based on $k(\delta_{\eta})$=$1/{{2\alpha\xi}/{\delta_{\eta}}}$ ($\xi << \delta_{\eta}$).
We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV utilizing 425 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. We consider the final state of the top quark pair containing one high-pT electron or muon and at least four jets. We exploit specific kinematic features of ttbar events to extract the cross section. For a top quark mass of 175 GeV, we measure sigma_ttbar = 6.4 +1.3-1.2(stat} +/- 0.7(syst)+/- 0.4(lum) pb in good agreement with the standard model prediction.
TOP TOPBAR production cross section.
We present a study of eegamma and mumugamma events using over 1 fb-1 of data collected with the D0 detector at the Fermilab Tevatron ppbar Collider at sqrt(s) = 1.96 TeV. Having observed 453 (515) candidates in the eegamma (mumugamma) final state, we measure the Zgamma production cross section for a photon with transverse energy ET > 7 GeV, separation between the photon and leptons Delta R(lgamma} > 0.7, and invariant mass of the di-lepton pair M(ll) > 30 GeV, to be 4.96 +/- 0.30(stat. + syst.) +/- 0.30(lumi.) pb, in agreement with the standard model prediction of 4.74 +/- 0.22 pb. This is the most precise Zgamma cross section measurement at a hadron collider. We set limits on anomalous trilinear Zgammagamma and ZZgamma gauge boson couplings of -0.085 < h(30)^(gamma) < 0.084, -0.0053 < h(40)^(gamma) < 0.0054 and -0.083 < h(30)^(Z) < 0.082, -0.0053 < h(40)^(Z) < 0.0054 at the 95% C.L. for the form-factor scale Lambda = 1.2 TeV.
Measured cross section for Z0 GAMMA production. Error contains both statistics and systematics (excluding luminosity uncertainty).
Azimuthal angle \Delta\phi correlations are presented for charged hadrons from dijets for 0.4 < p_T < 10 GeV/c in Au+Au collisions at sqrt(s_NN) = 200 GeV. With increasing p_T, the away-side distribution evolves from a broad to a concave shape, then to a convex shape. Comparisons to p+p data suggest that the away-side can be divided into a partially suppressed 'head' region centered at Delta\phi ~ \pi, and an enhanced 'shoulder' region centered at Delta\phi ~ \pi +/- 1.1. The p_T spectrum for the 'head' region softens toward central collisions, consistent with the onset of jet quenching. The spectral slope for the 'shoulder' region is independent of centrality and trigger p_T, which offers constraints on energy transport mechanisms and suggests that the 'shoulder' region contains the medium response to energetic jets.
<p>Per-trigger yield versus $\Delta\phi$ for various trigger and partner $p_T$ ($p_T^A$ $\otimes$ $p_T^B$), in $p$+$p$ and 0-20% Au+Au collisions.</p> <p><i>The systematic errors on $v_2$ are represented by "sys. corr." and are dominated by the reaction plane resolution. The fit that accounts for the overlap of the near- and away-side Gaussians at $\Delta\phi_{min}$ gives systematically lower $b_0$ values that that for ZYAM, and is assigned as the differences as one-sided systematic errors on $b_0$ represented by "sys. uncorr.".
<p>Per-trigger yield versus $\Delta\phi$ for various trigger and partner $p_T$ ($p_T^A$ $\otimes$ $p_T^B$), in $p$+$p$ and 0-20% Au+Au collisions.</p> <p><i>The systematic errors on $v_2$ are represented by "sys. corr." and are dominated by the reaction plane resolution. The fit that accounts for the overlap of the near- and away-side Gaussians at $\Delta\phi_{min}$ gives systematically lower $b_0$ values that that for ZYAM, and is assigned as the differences as one-sided systematic errors on $b_0$ represented by "sys. uncorr.".</p></i>
<p>$R_{HS}$ versus $p_T^B$ for $p$+$p$ and Au+Au collisions for four trigger selections.</p> <p><i>The systematic errors on $v_2$ are represented by "sys. corr." and are dominated by the reaction plane resolution. The fit that accounts for the overlap of the near- and away-side Gaussians at $\Delta\phi_{min}$ gives systematically lower $b_0$ values that that for ZYAM, and is assigned as the differences as one-sided systematic errors on $b_0$ represented by "sys. uncorr.".</p></i>
We present a measurement of the ttbar pair production cross section in ppbar collisions at sqrt(s) = 1.96 TeV utilizing approximately 425 pb-1 of data collected with the D0 detector. We consider decay channels containing two high pT charged leptons (either e or \mu) from leptonic decays of both top-daughter W bosons. These were gathered using four sets of selection criteria, three of which required that a pair of fully identified leptons (i.e., e\mu, ee, or \mu\mu) be found. The fourth approach imposed less restrictive criteria on one of the lepton candidates and required that at least one hadronic jet in each event be tagged as containing a b quark. For a top quark mass of 175 GeV, the measured cross section is 7.4 +/-1.4(stat} +/- 1.0(syst) pb.
TOP TOPBAR production cross section for top quark mass 175 GeV.
TOP TOPBAR production cross section for the current Tevatron average top quark mass 170.9 GeV.. Error contains both statistics and systematics.
We present transverse momentum (p_T) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at \sqrts = 200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, \nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that the yield per nucleon-nucleon collision saturates with \nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p_T.
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
We present measurements of the process $p\bar{p} \to WZ+X \to \ell^{\prime} \nu_{\ell^{\prime}} \ell \bar{\ell}$ at $\sqrt{s}=1.96$ TeV, where $\ell$ and $\ell^{\prime}$ are electrons or muons. Using 1 fb$^{-1}$ of data from the D0 experiment, we observe 13 candidates with an expected background of $4.5\pm0.6$ events and measure a cross section $\sigma(WZ)=2.7^{+1.7}_{-1.3}$ pb. From the number of observed events and the $Z$ boson transverse momentum distribution, we limit the trilinear $WWZ$ gauge couplings to $-0.17 \le \lambda_Z \le 0.21$ $(\Delta \kappa_Z = 0)$ at the 95% C.L. for a form factor scale $\Lambda=2$ TeV. Further, assuming that $\Delta g^Z_1 = \Delta\kappa_Z$, we find $-0.12 \le \Delta\kappa_Z \le 0.29$ $(\lambda_Z=0)$ at the 95% C.L. These are the most restrictive limits on the $WWZ$ couplings available to date.
Measured WZ cross section.
We present the first model-independent measurement of the helicity of $W$ bosons produced in top quark decays, based on a 1 fb$^{-1}$ sample of candidate $t\bar{t}$ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. We reconstruct the angle $\theta^*$ between the momenta of the down-type fermion and the top quark in the $W$ boson rest frame for each top quark decay. A fit of the resulting \costheta distribution finds that the fraction of longitudinal $W$ bosons $f_0 = 0.425 \pm 0.166 \hbox{(stat.)} \pm 0.102 \hbox{(syst.)}$ and the fraction of right-handed $W$ bosons $f_+ = 0.119 \pm 0.090 \hbox{(stat.)} \pm 0.053 \hbox{(syst.)}$, which is consistent at the 30% C.L. with the standard model.
COS(THETA*) distribution for leptonic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for hadronic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for W decay in dilepton events.. Data are read from plots and errors are statistcial (sqrt(N)).
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