The PHENIX experiment at RHIC has measured charged hadron yields at mid-rapidity over a wide range of transverse momentum (0.5 < p_T < 10 GeV/c) in Au+Au collisions at sqrt(s_NN)=200 GeV. The data are compared to pi^zero measurements from the same experiment. For both charged hadrons and neutral pions, the yields per nucleon-nucleon collision are significantly suppressed in central compared to peripheral and nucleon-nucleon collisions. The suppression sets in gradually and increases with increasing centrality of the collisions. Above 4-5 GeV/c in p_T, a constant and almost identical suppression of charged hadrons and pi^zeroes is observed. The p_T spectra are compared to published spectra from Au+Au at sqrt(s_NN)=130 in terms of x_t scaling. Central and peripheral pi^zero as well as peripheral charged spectra exhibit the same x_t scaling as observed in p+p data.
$p_T$ spectra of charged hadrons for minimum bias collisions along with spectra for 9 centrality classes derived from the pseudo-rapidity region $|\eta|$ < 0.18. Stat. stands for statistical error, syst. stands for the systematic errors and occ. stands for occupancy error.
$p_T$ spectra of charged hadrons for minimum bias collisions along with spectra for 9 centrality classes derived from the pseudo-rapidity region $|\eta|$ < 0.18. Stat. stands for statistical error, syst. stands for the systematic errors and occ. stands for occupancy error.
$p_T$ spectra of charged hadrons for minimum bias collisions along with spectra for 9 centrality classes derived from the pseudo-rapidity region $|\eta|$ < 0.18. Stat. stands for statistical error, syst. stands for the systematic errors and occ. stands for occupancy error.
Event-by-event fluctuations of the average transverse momentum of produced particles near mid-rapidity have been measured by the PHENIX Collaboration in sqrt(s_NN)=200 GeV Au+Au and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the transverse momentum window over which the average is calculated. Both the centrality and p_T dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard scattering processes.
Comparisons between the data and mixed event $M_{p_T}$ distributions for the representative 0-5% centrality classes. Also given are the residuals between the data and mixed events in units of standard deviations of the data points form the mixed event points.
Comparisons between the data and mixed event $M_{p_T}$ distributions for the representative 30-35% centrality classes. Also given are the residuals between the data and mixed events in units of standard deviations of the data points form the mixed event points.
$F_{p_T}$ (in percent, 0.2 GeV/$c$ < $p_T$ < 2.0 GeV/$c$) as a function of centrality, which is expressed in terms of the number of participants in the collision, $N_{part}$.
The transverse single-spin asymmetries of neutral pions and non-identified charged hadrons have been measured at mid-rapidity in polarized proton-proton collisions at sqrt(s) = 200 GeV. The data cover a transverse momentum (p_T) range 0.5-5.0 GeV/c for charged hadrons and 1.0-5.0 GeV/c for neutral pions, at a Feynman-x (x_F) value of approximately zero. The asymmetries seen in this previously unexplored kinematic region are consistent with zero within statistical errors of a few percent. In addition, the inclusive charged hadron cross section at mid-rapidity from 0.5 < p_T < 7.0 GeV/c is presented and compared to NLO pQCD calculations. Successful description of the unpolarized cross section above ~2 GeV/c using NLO pQCD suggests that pQCD is applicable in the interpretation of the asymmetry results in the relevant kinematic range.
Invariant cross section vs. $p_T$ for the production of charged hadrons at mid-rapidity.
Mid-rapidity neutral pion transverse single-spin asymmetry, $A_N$, vs. transverse momentum.
Mid-rapidity charged hadron transverse single-spin asymmetry, $A_N$, vs. transverse momentum.
PHENIX has measured the centrality dependence of mid-rapidity pion, kaon and proton transverse momentum distributions in d+Au and p+p collisions at sqrt(s_NN) = 200 GeV. The p+p data provide a reference for nuclear effects in d+Au and previously measured Au+Au collisions. Hadron production is enhanced in d+Au, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti) protons is larger than that for pions. The difference increases with centrality, but is not sufficient to account for the abundance of baryon production observed in central Au+Au collisions at RHIC. The centrality dependence in d+Au shows that the nuclear modification factor increases gradually with the number of collisions suffered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production.
Mean number of binary collisions, particpating nucleons from the Au nucleus, number of collisions per participating deuteron nucleon, and trigger bias corrections for the $d$+Au centrality bins.
Transverse momentum in GeV/$c$ for $\pi^{\pm}$.
Transverse momentum in GeV/$c$ for $\pi^{\pm}$.
The properties of jets produced in p+p collisions at sqrt(s)=200 GeV are measured using the method of two particle correlations. The trigger particle is a leading particle from a large transverse momentum jet while the associated particle comes from either the same jet or the away-side jet. Analysis of the angular width of the near-side peak in the correlation function determines the jet fragmentation transverse momentum j_T . The extracted value, sqrt(<j_T^2>)= 585 +/- 6(stat) +/- 15(sys) MeV/c, is constant with respect to the trigger particle transverse momentum, and comparable to the previous lower sqrt(s) measurements. The width of the away-side peak is shown to be a convolution of j_T with the fragmentation variable, z, and the partonic transverse momentum, k_T . The <z> is determined through a combined analysis of the measured pi^0 inclusive and associated spectra using jet fragmentation functions measured in e^+e^-. collisions. The final extracted values of k_T are then determined to also be independent of the trigger particle transverse momentum, over the range measured, with value of sqrt(<k_T^2>) = 2.68 +/- 0.07(stat) +/- 0.34(sys) GeV/c.
The $\chi^2(DOF)$ $\sigma_N$ and $\sqrt{<p^2_{out}>}$ values extracted for the correlation function in GeV/$c$.
The $\chi^2(DOF)$ $\sigma_N$ and $\sqrt{<p^2_{out}>}$ values extracted for the correlation function in GeV/$c$.
Measured widths of the near- and away-angle $\pi^0$ - $h^{\pm}$ correlation peaks for various trigger momenta.
The production of low mass e+e- pairs for m_{e+e-} < 300 MeV/c^2 and 1 < p_T <5 GeV/c is measured in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. Enhanced yield above hadronic sources is observed. Treating the excess as internal conversions, the invariant yield of direct photons is deduced. In central Au+Au collisions, the excess of direct photon yield over p+p is exponential in transverse momentum, with inverse slope T = 221 +/- 19 (stat) +/- 19 (syst) MeV. Hydrodynamical models with initial temperatures ranging from 300--600 MeV at times of ~ 0.6 - 0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at ~ 170 MeV.
Electron pair mass distribution for Au+Au events for 1.0 < $p_T$ < 1.5 GeV/$c$.
Electron pair mass distribution for Au+Au events for 1.0 < $p_T$ < 1.5 GeV/$c$.
Electron pair mass distribution for Au+Au events for 1.0 < $p_T$ < 1.5 GeV/$c$.
A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV, and Cu+Cu collisions sqrt(s_NN) = 22.5, 62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for non-dynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon p+p data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. An analysis of Negative Binomial Distribution fits to the multiplicity distributions demonstrates that the heavy ion data exhibit weak clustering properties.
Additional information containing number of events which were used to reconstruct the numvers matching to Figure 1 and 2.
Additional information containing number of events which were used to reconstruct the numvers matching to Figure 1 and 2.
Additional information containing number of events which were used to reconstruct the numvers matching to Figure 1 and 2.
It has been postulated that partonic orbital angular momentum can lead to a significant double-helicity dependence in the net transverse momentum of Drell-Yan dileptons produced in longitudinally polarized p+p collisions. Analogous effects are also expected for dijet production. If confirmed by experiment, this hypothesis, which is based on semi-classical arguments, could lead to a new approach for studying the contributions of orbital angular momentum to the proton spin. We report the first measurement of the double-helicity dependence of the dijet transverse momentum in longitudinally polarized p+p collisions at sqrt(s) = 200 GeV from data taken by the PHENIX experiment in 2005 and 2006. The analysis deduces the transverse momentum of the dijet from the widths of the near- and far-side peaks in the azimuthal correlation of the dihadrons. When averaged over the transverse momentum of the triggered particle, the difference of the root-mean-square of the dijet transverse momentum between like- and unlike-helicity collisions is found to be -37 +/- 88(stat) +/- 14(syst) MeV/c.
Values of derived $<z_T>$ and $\hat{x_h}$.
Helicity-averaged $\sqrt{<j^2_T>}$ and $\sqrt{<k^2_T>}$ for combined 2005 and 2006 data.
Difference in $\sqrt{<j^2_T>}$ and $\sqrt{<k^2_T>}$ for like- minus unlike-helicity combinations.
We report the measurement of the transverse momentum dependence of inclusive J/psi polarization in p+p collisions at sqrt(s)=200 GeV performed by the PHENIX Experiment at RHIC. The polarization is studied in the helicity, Gottfried-Jackson, and Collins-Soper frames for p_T < 5 GeV/c and |y| < 0.35. The J/psi polarization in the helicity and Gottfried-Jackson frames is consistent with zero for all transverse momenta, with a slight (1.8 sigma) trend towards longitudinal polarization for transverse momenta above 2 GeV/c. No conclusion is allowed due to the limited acceptance in the Collins-Soper frame and the uncertainties of the current data. The results are compared to observations for other collision systems and center of mass energies and to different quarkonia production models.
$J/\psi$ yield times dielectron branching ratio ($B$) after detector acceptance and efficiency corrections for the real data with $A$ = 28.7 $\pm$ 1.0 nb/GeV/$c$, $b$ = 3.41 $\pm$ 0.21 GeV/$c$, and $n$ = 4.6 $\pm$ 0.4.
$J/\psi$ polarization parameter ($\lambda_{J/\psi}$) versus transverse momentum ($p_T$).
$J/\psi$ polarization parameter ($\lambda_{J/\psi}$) versus transverse momentum ($p_T$).
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at sqrt(S_NN)=200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor R_AA for Au+Au and Cu+Cu, and R_dA for d+Au collisions, studied as a function of transverse momentum (1<p_T<7 GeV/c) and centrality. In central and mid-central Au+Au collisions, the R_AA of phi exhibits a suppression relative to expectations from binary scaled p+p results. The amount of suppression is smaller than that of the neutral pion and the eta meson in the intermediate p_T range (2--5 GeV/c); whereas at higher p_T the phi, pi^0, and eta show similar suppression. The baryon (protons and anti-protons) excess observed in central Au+Au collisions at intermediate p_T is not observed for the phi meson despite the similar mass of the proton and the phi. This suggests that the excess is linked to the number of constituent quarks rather than the hadron mass. The difference gradually disappears with decreasing centrality and for peripheral collisions the R_AA values for both particles are consistent with binary scaling. Cu+Cu collisions show the same yield and suppression as Au+Au collisions for the same number of N_part. The R_dA of phi shows no evidence for cold nuclear effects within uncertainties.
Invariant $p_T$ spectra of the $\phi$ meson for different centrality bins in Au+Au, Cu+Cu, $d$+Au, and $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV.
$R_{AA}$ vs. $p_T$ for $\phi$ in central Au+Au collisions, $R_{AA}$ vs. $p_T$ for $\phi$ and $\pi^0$ in 10-20% mid-central Au+Au collisions, and $R_{AA}$ vs. $p_T$ for $\phi$ and $p$+$\bar{p}$ in 60-92% and for $\pi^0$ in 80-92% peripheral Au+Au collisions. The global uncertainty of ~ 10% related to the $p$+$p$ reference normalization is not shown.
$R_{AA}$ vs. $p_T$ for $\phi$ for 30-40% centrality Au+Au and 0-10% centrality Cu+Cu collisions, and $R_{AA}$ vs. $p_T$ for $\phi$ and $\pi^0$ for 40-50% centrality Au+Au and 10-20% centrality Cu+Cu collisions. The global uncertainty of ~ 10% related to the $p$+$p$ reference normalization is not shown.
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