We report on charmonium measurements [J/psi(1S), psi'(2S), and chi_c(1P)] in p+p collisions at sqrt(s)=200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi_c in the midrapidity region ($|\eta|<0.35$) is 9.6+/-2.4% and 32+/-9%, respectively. We also report new, higher statistics p_T and rapidity dependencies of the J/psi yield via dielectron decay in the same midrapidity range and at forward rapidity (1.2<|eta|<2.4) via dimuon decay. These results are compared with measurements from other experiments and discussed in the context of current charmonium production models.
Foreground, background counts in the $J/\psi$ mass region, and the signal count.
Foreground, background counts in the $J/\psi$ mass region, and the signal count.
$\psi^{\prime}(J/\psi)$ dielectron yield ratio measured at $|y|$ < 0.35 followed by point-to-point uncorrelated (uncorr.) (statistical and uncorrelated systematic uncertainties) and correlated systematic (corr.) uncertainties.
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.
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.
The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV down to $p_T=0.4$ GeV/$c$. Photons are detected via photon conversions to $e^+e^-$ pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low $p_T$. We find an excess of direct photons above the $N_{\rm coll}$-scaled yield measured in $p$$+$$p$ collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/$c$ in the $p_T$ range from 0.6--2.0 GeV/$c$. While the shape of the $p_T$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $N_{\rm part}^\alpha$, where $\alpha=1.48{\pm}0.08({\rm stat}){\pm}0.04({\rm syst})$.
Ratio $R_{\gamma}$ as function of photon $p_T$ from the 2007 and 2010 data sets in minimum-bias Au+Au collisions, and the $R_{\gamma}$ in the combined 2007+2010 measurement.
Ratio $R_{\gamma}$ as function of photon $p_T$ for the combined 2007 and 2010 data sets in different centrality bins.
Direct photon $p_T$ spectra in different centrality bins.
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.
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, $N_{part}$.
Two particle correlations between identified meson and baryon trigger particles with 2.5 < p_T < 4.0 GeV/c and lower p_T charged hadrons have been measured at midrapidity by the PHENIX experiment at RHIC in p+p, d+Au and Au+Au collisions at sqrt(s_NN) = 200 GeV. The probability of finding a hadron near in azimuthal angle to the trigger particle is almost identical for leading mesons and baryons for non-central Au+Au. The yield for both trigger baryons and mesons is significantly higher in Au+Au than in p+p and d+Au, except for trigger baryons in central collisions. The baryon excess is likely to arise predominantly from hard scattering processes.
$\Delta\phi$ distributions for meson and baryon triggers with 2.5 < $p_T$ < 4.0 GeV/$c$ and associated charged hadrons with 1.7 < $p_T$ < 2.5 GeV/$c$ for five centralities in Au+Au collisions.
$\Delta\phi$ distributions for meson triggers with 2.5 < $p_T$ < 4.0 GeV/$c$ and associated charged hadrons with 1.7 < $p_T$ < 2.5 GeV/$c$ in $d$+Au collisions.
$\Delta\phi$ distributions unidentified triggers with 2.5 < $p_T$ < 4.0 GeV/$c$ and associated charged hadrons with 1.7 < $p_T$ < 2.5 GeV/$c$ in $p$+$p$ collisions.
We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central $d$$+$Au and minimum bias $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The charged hadron is measured at midrapidity $|\eta|<0.35$, and the energy is measured at large rapidity ($-3.7<\eta<-3.1$, Au-going direction). An enhanced near-side angular correlation across $|\Delta\eta| >$ 2.75 is observed in $d$$+$Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength $v_2$ for inclusive charged hadrons at midrapidity up to $p_T=4.5$ GeV/$c$. We also present the measurement of $v_2$ for identified $\pi^{\pm}$ and (anti)protons in central $d$$+$Au collisions, and observe a mass-ordering pattern similar to that seen in heavy ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from $p$$+$Pb at $\sqrt{s_{_{NN}}}=5.02$ TeV. The magnitude of the mass-ordering in $d$$+$Au is found to be smaller than that in $p$$+$Pb collisions, which may indicate smaller radial flow in lower energy $d$$+$Au collisions.
$c_2$ ($p_T$) for track lower-tower pairs from 0-5% $d$+Au collisions and $c_2$ ($p_T$) for pairs in minimum bias $p$+$p$ collisions times the dilution factor.
Measured $v_2$ for midrapidity charged tracks in 0-5% central $d$+Au at $\sqrt{s_{NN}}$ = 200 GeV using the event plane method.
Measured $v_2$ ($p_T$) for identified pions, each charged combined, 0-5% central $d$+Au collisions at RHIC.
We report on event structure and double helicity asymmetry ($A_LL$) of jet production in longitudinally polarized p+p collisions at $\sqrt{s}$=200 GeV. Photons and charged particles were measured at midrapidity $|\eta| < 0.35$ with the requirement of a high-momentum ($>2$ GeV/$c$) photon in each event. Measured event structure is compared with {\sc pythia} and {\sc geant} simulations. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet $A_{LL}$, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster $p_T$ sum ($p_T^{\rm reco}$). The effect of detector response and the underlying events on $p_T^{\rm reco}$ was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the NLO pQCD jet production cross section. For $4 < p_T^{\rm reco} < 12$ GeV/$c$ with an average beam polarization of $< P > = 49%$ we measured $A_{LL} = -0.0014 \pm 0.0037^{\rm stat}$ at the lowest $p_T^{\rm reco}$ bin (4-5 GeV/$c$) and $-0.0181 \pm 0.0282^{\rm stat}$ at the highest $p_T^{\rm reco}$ bin (10-12 GeV/$c$) with a beam polarization scale error of 9.4% and a $\pT$ scale error of 10%. Jets in the measured $p_T^{\rm reco}$ range arise primarily from hard-scattered gluons with momentum fraction $0.02 < x < 0.3$ according to {\sc pythia}. The measured $A_{LL}$ is compared with predictions that assume various $\Delta G(x)$ distributions based on the GRSV parameterization. The present result imposes the limit $-1.1 < \int_{0.02}^{0.3}dx \Delta G(x, \mu^2 = 1 {\rm GeV}^2) < 0.4$ at 95% confidence level or $\int_{0.02}^{0.3}dx \Delta G(x, \mu^2 = 1 {\rm GeV}^2) < 0.5$ at 99% confidence level.
The relative yields of $q$+$q$, $q$+$g$, and $g$+$g$ subprocesses in the PYTHIA+GEANT simulation.
The correction factor $\epsilon^j_{trig+acc}$ for high-$p_T$ photon trigger efficiency and acceptance effect.
Reconstructed-jet $A_{LL}$ as a function of $p_T^{reco}$.
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>
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