Collisions between prolate uranium nuclei are used to study how particle production and azimuthal anisotropies depend on initial geometry in heavy-ion collisions. We report the two- and four-particle cumulants, $v_2\{2\}$ and $v_2\{4\}$, for charged hadrons from U+U collisions at $\sqrt{s_{\rm NN}}$ = 193 GeV and Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. Nearly fully overlapping collisions are selected based on the amount of energy deposited by spectators in the STAR Zero Degree Calorimeters (ZDCs). Within this sample, the observed dependence of $v_2\{2\}$ on multiplicity demonstrates that ZDC information combined with multiplicity can preferentially select different overlap configurations in U+U collisions. An initial-state model with gluon saturation describes the slope of $v_2\{2\}$ as a function of multiplicity in central collisions better than one based on Glauber with a two-component multiplicity model.
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We present results for the charged-particle multiplicity distribution at mid-rapidity in Au - Au collisions at sqrt(s_NN)=130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find $dN_{ch}/d\eta_{|\eta=0} = 622 \pm 1 (stat) \pm 41 (syst)$. The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.
130 GeV is sqrt(S) per nucleon-nucleon collision. N(C=N_NUCLEONS) and N(C=N_COLLISONS) are the number of participating nucleons and binary collisions. The statistical errors are negligible and only systematic errors are quoted. COL(NAME=CENTRALITY) is centrality.
We present the first measurement of charge-dependent directed flow in Cu+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The results are presented as a function of the particle transverse momentum and pseudorapidity for different centralities. A finite difference between the directed flow of positive and negative charged particles is observed that qualitatively agrees with the expectations from the effects of the initial strong electric field between two colliding ions with different nuclear charges. The measured difference in directed flow is much smaller than that obtained from the parton-hadron-string-dynamics (PHSD) model, which suggests that most of the electric charges, i.e. quarks and antiquarks, have not yet been created during the lifetime of the strong electric field, which is of the order of, or less than, 1fm/$c$.
$p_{\rm T}$ dependence of directed flow in centrality 10-20%.
$p_{\rm T}$ dependence of directed flow in centrality 20-30%.
$p_{\rm T}$ dependence of directed flow in centrality 30-40%.
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.
The 0-20% Au+Au jet-induced hadron-pair yield $\Delta\phi$ distributions calculated from the per-trigger yield using low-$p_T$ hadrons as triggers and high-$p_T$ hadrons as triggers. Data for 2 - 3 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 5-10 $\otimes$ 2-3, 4-5 $\otimes$ 4-5, 5-10 $\otimes$ 3-5, and 5-10 $\otimes$ 5-10 GeV/c.
The 0-20% Au+Au jet-induced hadron-pair yield $\Delta\phi$ distributions calculated from the per-trigger yield using low-$p_T$ hadrons as triggers and high-$p_T$ hadrons as triggers. Data for 3 - 4 GeV/$c$.
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.
The centrality dependence of transverse momentum distributions and yields for pi^+/-, K^+/-, p and p^bar in Au+Au collisions at sqrt(s_NN) = 200 GeV at mid-rapidity are measured by the PHENIX experiment at RHIC. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below ~ 2 GeV/c in p_T. Both mean transverse momenta and particle yields per participant pair increase from peripheral to mid-central and saturate at the most central collisions for all particle species. We also measure particle ratios of pi^-/pi^+, K^-/K^+, p^bar/p, K/pi, p/pi and p^bar/pi as a function of p_T and collision centrality. The ratios of equal mass particle yields are independent of p_T and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta ~ 1.5-4.5 GeV/c, proton and anti-proton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.
Centrality dependence of the $p_{T}$ distribution for $\pi^{+}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Errors are statistical only.
Centrality dependence of the $p_{T}$ distribution for $\pi^{-}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Errors are statistical only.
Centrality dependence of the $p_{T}$ distribution for $K^{+}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Errors are statistical only.
The first measurement of energy produced transverse to the beam direction at RHIC is presented. The mid-rapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that E_T / N_ch remains relatively constant as a function of centrality. The energy density calculated via Bjorken's prescription for the 2% most central Au+Au collisions at sqrt(s_NN)=130 GeV is at least epsilon_Bj = 4.6 GeV/fm^3 which is a factor of 1.6 larger than found at sqrt(s_NN)=17.2 GeV (Pb+Pb at CERN).
130 GeV is sqrt(S) per nucleon-nucleon collision. The statistical errors are negligible and only systematic errors are quoted. COL(NAME=CENTRALITY) is centrality.
We present measurements of azimuthal correlations of charged hadron pairs in $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions after subtracting an underlying event using a model that includes higher-order azimuthal anisotropy $v_2$, $v_3$, and $v_4$. After subtraction, the away-side ($\Delta\phi\sim\pi)$ of the highest transverse-momentum trigger ($p_T>4$ GeV/$c$) correlations is suppressed compared to that of correlations measured in $p$$+$$p$ collisions. At the lowest associated particle $p_T$, the away-side shape and yield are modified. These observations are consistent with the scenario of radiative-jet energy loss. For the lowest-$p_T$ trigger correlations, an away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle $\Psi_n$. The angular correlations show an asymmetry when selecting the sign of the trigger-particle azimuthal angle with respect to the $\Psi_2$ event plane. This asymmetry and the measured suppression of the pair yield out of plane is consistent with a path-length-dependent energy loss. No $\Psi_3$ dependence can be resolved within experimental uncertainties.
Higher-order flow harmonics for charged hadrons at midrapidity in Au$+$Au collisions at $\sqrt{s_{NN}}$ and their systematics: $v_2$, $v_3$, $v_4$, and $v_4\{\Psi_2\}$. The source of systematic uncertainties are difference among RXN event-planes, matching cut width for CNT hadron tracks, and difference between $v_n$ measured with RXN and BBC event planes .
Per-trigger yields $Y(\Delta\phi)$ of dihadrons pairs measured in Au$+$Au collisions at$\sqrt{s_{NN}}$ after subtracting the underlying event model with several $p_T$ selections and centralities. Systematic uncertainties are due to track matching and the $v_n$ and due to ZYAM.
Per-trigger yields $Y(\Delta\phi)$ of dihadron pairs measured in Au$+$Au collisions after subtracting the underlying event-model with several $p_T$ selections of the trigger and associated particles ($p_T^{t,a}$ and several centralities. Systematic uncertainties are due to track matching and the $v_n$ and due to ZYAM.
Flow coefficients v_n for n = 2, 3, 4, characterizing the anisotropic collective flow in Au+Au collisions at sqrt(s_NN) = 200 GeV, are measured relative to event planes Ψ_n determined at large rapidity. We report v_n as a function of transverse momentum and collision centrality, and study the correlations among the event planes of different order n. The v_n are well described by hydrodynamic models which employ a Glauber Monte Carlo initial state geometry with fluctuations, providing additional constraining power on the interplay between initial conditions and the effects of viscosity as the system evolves. This new constraint improves precision of the extracted viscosity to entropy density ratio eta/s.
Charged hadron azimuthal anisotropy $v_2$, $v_3$, and $v_4$ vs $p_T$ in 0-10% central Au+Au collisions at 200 GeV. The mean $<p_T>$ in each $p_T$ bins used for the $v_n$ measurement is shown in Fig.2.6.
Charged hadron azimuthal anisotropy $v_2$, $v_3$, and $v_4$ vs $p_T$ in 10-20% central Au+Au collisions at 200 GeV. The mean $<p_T>$ in each $p_T$ bins used for the $v_n$ measurement is shown in Fig.2.6.
Charged hadron azimuthal anisotropy $v_2$, $v_3$, and $v_4$ vs $p_T$ in 20-30% central Au+Au collisions at 200 GeV. The mean $<p_T>$ in each $p_T$ bins used for the $v_n$ measurement is shown in Fig.2.6.
The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the photon is an excellent approximation to the initial p_T of the jet and the ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_ AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z_T. The fragment yield at low z_T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.
Direct photon-hadron pair per-trigger yields vs Delta-phi (Au+Au and p+p)
Integrated per-trigger yields and I_AA vs xi
Integrated per-trigger yields and I_AA vs xi