We report results for the virtual photon asymmetry $A_1$ on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton ($^{15}$NH$_3$) and deuteron ($^{15}$ND$_3$) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present paper, we concentrate on our results for $A_1(x,Q^2)$ and the related ratio $g_1/F_1(x,Q^2)$ in the resonance and the deep inelastic regions for our lowest and highest beam energies, covering a range in momentum transfer $Q^2$ from 0.05 to 5.0 GeV$^2$ and in final-state invariant mass $W$ up to about 3 GeV. Our data show detailed structure in the resonance region, which leads to a strong $Q^2$--dependence of $A_1(x,Q^2)$ for $W$ below 2 GeV. At higher $W$, a smooth approach to the scaling limit, established by earlier experiments, can be seen, but $A_1(x,Q^2)$ is not strictly $Q^2$--independent. We add significantly to the world data set at high $x$, up to $x = 0.6$. Our data exceed the SU(6)-symmetric quark model expectation for both the proton and the deuteron while being consistent with a negative $d$-quark polarization up to our highest $x$. This data setshould improve next-to-leading order (NLO) pQCD fits of the parton polarization distributions.
A1 and g1/F1 for the P target at incident energy 1.6000 GeV and W = 1.1300 GeV.
A1 and g1/F1 for the P target at incident energy 1.6000 GeV and W = 1.1500 GeV.
A1 and g1/F1 for the P target at incident energy 1.6000 GeV and W = 1.1700 GeV.
We present the directed flow ($v_1$) measured in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 62.4 GeV in the mid-pseudorapidity region $|\eta|<1.3$ and in the forward pseudorapidity region $2.5 < |\eta| < 4.0$. The results are obtained using the three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the Relativistic Heavy Ion Collider (RHIC), the standard method with the event plane reconstructed from spectator neutrons. Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle directed flow is in the direction opposite to that of fragmentation neutrons.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
We present results for two-particle transverse momentum correlations, <dpt,i dpt,j>, as a function of event centrality for Au+Au collisions at sqrt(sNN) = 20, 62, 130, and 200 GeV at the Relativistic Heavy Ion Collider. We observe correlations decreasing with centrality that are similar at all four incident energies. The correlations multiplied by the multiplicity density increase with incident energy and the centrality dependence may show evidence of processes such as thermalization, minijet production, or the saturation of transverse flow. The square root of the correlations divided by the event-wise average transverse momentum per event shows little or no beam energy dependence and generally agrees with previous measurements at the Super Proton Synchrotron.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 20 GeV for the 5% most central collisions.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 62 GeV for the 5% most central collisions.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 130 GeV for the 5% most central collisions.
We report on the first measurement of elliptic flow $v_2(p_T)$ of multi-strange baryons $\Xi+\bar{Xi}$ and $\Omega+\bar{Omega} in heavy-ion collisions. In minimum bias Au+Au collisions at sqrt(s_NN) = 200 GeV, a significant amount of elliptic flow, comparable to other non-strange baryons, is observed for multi-strange baryons which are expected to be particularly sensitive to the dynamics of the partonic stage of heavy-ion collisions. The $p_T$ dependence of $v_2$ of the multi-strange baryons confirms the number of constituent quark scaling previously observed for lighter hadrons. These results support the idea that a substantial fraction of the observed collective motion is developed at the early partonic stage in ultra-relativistic nuclear collisions at RHIC.
$\Xi^{-} + \Xi^{+}$ invariant mass distribution from minimum bias (0–80%) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
$\Omega^{-} + \Omega^{+}$ invariant mass distribution from minimum bias (0–80%) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Azimuthal distributions with respect to the event plane of the $\Xi^{-} + \Xi^{+}$ and $\Omega^{-} + \Omega^{+}$ raw yields.
The PHENIX experiment has measured mid-rapidity transverse momentum spectra (0.4 < p_T < 4.0 GeV/c) of single electrons as a function of centrality in Au+Au collisions at sqrt(s_NN) = 200 GeV. Contributions to the raw spectra from photon conversions and Dalitz decays of light neutral mesons are measured by introducing a thin (1.7% X_0) converter into the PHENIX acceptance and are statistically removed. The subtracted ``non-photonic'' electron spectra are primarily due to the semi-leptonic decays of hadrons containing heavy quarks (charm and bottom). For all centralities, charm production is found to scale with the nuclear overlap function, T_AA. For minimum-bias collisions the charm cross section per binary collision is N_cc^bar/T_AA = 622 +/- 57 (stat.) +/- 160 (sys.) microbarns.
Value of the Alpha power as used in a fit of dN/dy versus Ncoll of the form A*Ncoll^Alpha, where N is the non photonic electron yield and Ncoll the number of p+p collisions This value only includes data from Au+Au collisions The value of Alpha = 1 is the expectation in the absence of medium effects.
Value of the Alpha power as used in a fit of dN/dy versus Ncoll, of the form A*Ncoll^Alpha, where N is the non photonic electron yield and Ncoll the number of p+p collisions This value is calculated including previous data of p+p collisions, measured by PHENIX, in addition of the Au+Au data The value of Alpha = 1 is the expectation in the absence of medium effects.
Spectrum in transverse momentum of electrons created in open heavy flavor decays, for minimum bias events.
The pseudorapidity asymmetry and centrality dependence of charged hadron spectra in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV are presented. The charged particle density at mid-rapidity, its pseudorapidity asymmetry and centrality dependence are reasonably reproduced by a Multi-Phase Transport model, by HIJING, and by the latest calculations in a saturation model. Ratios of transverse momentum spectra between backward and forward pseudorapidity are above unity for \pT below 5 GeV/$c$. The ratio of central to peripheral spectra in d+Au collisions shows enhancement at 2 $<$ \pT $<$ 6 GeV/$c$, with a larger effect at backward rapidity than forward rapidity. Our measurements are in qualitative agreement with gluon saturation and in contrast to calculations based on incoherent multiple partonic scatterings.
The p$_T$ spectra of charged hadrons for various centrality classes.
The pseudorapidity dependence of charged particle densities for various centrality classes.
The ratio of charged hadron spectra in the backward rapidity to forward rapidity region for minimum bias and ZDC-d neutron-tagged events.
Mid-rapidity open charm spectra from direct reconstruction of $D^{0}$($\bar{D^0}$)$\to K^{\mp}\pi^{\pm}$ in d+Au collisions and indirect electron/positron measurements via charm semileptonic decays in p+p and d+Au collisions at \srt = 200 GeV are reported. The $D^{0}$($\bar{D^0}$) spectrum covers a transverse momentum ($p_T$) range of 0.1 $<p_T<$ 3 \GeVc whereas the electron spectra cover a range of 1 $<p_T<$ 4 GeV/$c$. The electron spectra show approximate binary collision scaling between p+p and d+Au collisions. From these two independent analyses, the differential cross section per nucleon-nucleon binary interaction at mid-rapidity for open charm production from d+Au collisions at RHIC is $d\sigma^{NN}_{c\bar{c}}/dy$=0.30$\pm$0.04 (stat.)$\pm$0.09(syst.) mb. The results are compared to theoretical calculations. Implications for charmoniumm results in A+A collisions are discussed.
Inclusive electrons yield versus transverse momentum in D+AU collisions Data points at PT = 2.2, 2.7 and 3.5 GeV/c was obtained using only the TPC (Time Projection Chamber) and cover a pseudo-rapidity range of -1<eta<1, while other points were obtained using both a prototypeTime-of-Flight System and the TPC and cover a pseudo-rapidity range of -1<eta<0.
Inclusive electrons yield versus transverse momentum in P+P collisions.
D0 yield versus transverse momentum in D+AU collisions.
Double-polarization asymmetries for inclusive $ep$ scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH$_3$ target in the CLAS detector. The polarized structure function $g_1(x,Q^2)$ was extracted throughout the nucleon resonance region and into the deep inelastic regime, for $Q^2 = 0.15 -1.64 $GeV$^2$. The contributions to the first moment $\Gamma_1(Q^2) = \int g_1(x,Q^2)dx$ were determined up to $Q^2=1.2$ GeV$^2$. Using a parametrization for $g_1$ in the unmeasured low $x$ regions, the complete first moment was estimated over this $Q^2$ region. A rapid change in $\Gamma_1$ is observed for $Q^2 < 1 $GeV$^2$, with a sign change near $Q^2 = 0.3 $GeV$^2$, indicating dominant contributions from the resonance region. At $Q^2=1.2$ GeV$^2$ our data are below the pQCD evolved scaling value.
The measured photon asymmetry (A1+ETA*A2) for the Q**2 region 0.15 to 0.22 GeV**2 obtained with a beam energy of 2.6 GeV.
The measured photon asymmetry (A1+ETA*A2) for the Q**2 region 0.6 to 1.10 GeV**2 obtained with a beam energy of 4.3 GeV.
The polarized structure function G1 as a function of Bjorken X for the Q**2range 0.15 to 0.27 GeV.
First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of J/Psi's measured in the PHENIX experiment via electron-positron decay pairs at mid-rapidity for Au-Au reactions at sqrt(s_NN) = 200 GeV are analyzed as a function of collision centrality. For this analysis we have studied 49.3 million minimum bias Au-Au reactions. We present the J/Psi invariant yield dN/dy for peripheral and mid-central reactions. For the most central collisions where we observe no signal above background, we quote 90% confidence level upper limits. We compare these results with our J/Psi measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.
Measured invariant differential yield at mid-rapidity of J/PSI, as a function of centratility, times branching ratio Be+e-, for three bins of centrality : 0-20%, 20-40% and 40-90% of Au-Au cross-section. The 90% confidence level upper limit (CLUL) for the yield is also given.
Measured differential yield of J/PSI per binary collisions,at mid rapidity, as a function of the centrality, times branching ratio Be+e-.The 90% confidence level upper limit (CLUL) for J/PSI differential yield is also given. The values of the number of participants for each centrality bins are calculated for general information.
Identified pi^[+/-] K^[+/-], p and p-bar transverse momentum spectra at mid-rapidity in sqrt(s_NN)=130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. The multiplicity densities scale faster than the number of participating nucleons. Kaon and nucleon yields per participant increase faster than the pion yields. In central collisions at high transverse momenta (p_T greater than 2 GeV/c), anti-proton and proton yields are comparable to the pion yields.
Transverse momentum spectra for PI+ in the midrapidity range for the centrality region 0 to 5 PCT. Errors are combined statistical and systematics.
Transverse momentum spectra for PI- in the midrapidity range for the centrality region 0 to 5 PCT. Errors are combined statistical and systematics.
Transverse momentum spectra for K+ in the midrapidity range for the centrality region 0 to 5 PCT. Errors are combined statistical and systematics.
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