The invariant differential cross section for inclusive neutral-pion production in p+p collisions at roots=200 GeV has been measured at midrapidity (eta<0.35) over the range 1<p(T)less than or similar ...to14 GeV/c by the PHENIX experiment at the Relativistic Heavy Ion Collider. Predictions of next-to-leading order perturbative QCD calculations are consistent with these measurements. The precision of our result is sufficient to differentiate between prevailing gluon-to-pion fragmentation functions.
Proton and deuteron production has been observed in S+S and S+Pb collisions at 200 A\(\cdot\)GeV and in Pb+Pb reactions at 158 A\(\cdot\)GeV at the CERN SPS accelerator. For Pb+Pb triton production ...was also measured. The p and d spectra as well as the p and t spectra were observed in similar rapidity ranges and over similar ranges of transverse momenta per nucleon, making it possible to interpret the cross sections of the composite particles in terms of coalescence mechanisms. Volumes of homogeneity were extracted and compared to pion-pair HBT interferometry results. Special attention is given to the dependence on transverse mass, centrality and rapidity.
Transverse single-spin asymmetries to probe the transverse-spin structure of the proton have been measured for neutral pions and nonidentified charged hadrons from polarized proton-proton collisions ...at midrapidity and root s = 200 GeV. The data cover a transverse momentum (pT) range 1.0-5.0 GeV/c for neutral pions and 0.5-5.0 GeV/c for charged hadrons, at a Feynman-x value of approximately zero. The asymmetries seen in this previously unexplored kinematic region are consistent with zero within errors of a few percent. In addition, the inclusive charged hadron cross section at midrapidity from 0.5 < P-T < 7.0 GeV/c is presented and compared to next-to-leading order perturbative QCD ( pQCD) calculations. Successful description of the unpolarized cross section above similar to 2 GeV/c suggests that pQCD is applicable in the interpretation of the asymmetry results in the relevant kinematic range.
Bose-Einstein correlations of identically charged pion pairs were measured by the PHENIX experiment at midrapidity in Au+Au collisions at roots(NN)=200 GeV. The Bertsch-Pratt radius parameters were ...determined as a function of the transverse momentum of the pair and as a function of the centrality of the collision. Using the standard core-halo partial Coulomb fits, and a new parametrization which constrains the Coulomb fraction as determined from the unlike-sign pion correlation, the ratio R-out/R-side is within 0.8-1.1 for 0.25<<k(T)><1.2 GeV/c. The centrality dependence of all radii is well described by a linear scaling in N-part(1/3), and R-out/R-side for <k(T)>similar to0.45 GeV/c is approximately constant at unity as a function of centrality.
Measurements of neutral pion (pi(0)) production at midrapidity in root s(NN)=200 GeV Au+Au collisions as a function of transverse momentum, p(T), collision centrality, and angle with respect to ...reaction plane are presented. The data represent the final pi(0) results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of 3 increase in statistics over previously published results for p(T)>6 GeV/c. We evaluate the suppression in the yield of high-p(T) pi(0)'s relative to pointlike scaling expectations using the nuclear modification factor R-AA. We present the p(T) dependence of R-AA for nine bins in collision centrality. We separately integrate R-AA over larger p(T) bins to show more precisely the centrality dependence of the high-p(T) suppression. We then evaluate the dependence of the high-p(T) suppression on the emission angle Delta phi of the pions with respect to event reaction plane for seven bins in collision centrality. We show that the yields of high-p(T) pi(0)'s vary strongly with Delta phi, consistent with prior measurements 1,2. We show that this variation persists in the most peripheral bin accessible in this analysis. For the peripheral bins we observe no suppression for neutral pions produced aligned with the reaction plane, whereas the yield of pi(0)'s produced perpendicular to the reaction plane is suppressed by a factor of similar to 2. We analyze the combined centrality and Delta phi dependence of the pi(0) suppression in different p(T) bins using different possible descriptions of parton energy loss dependence on jet path-length averages to determine whether a single geometric picture can explain the observed suppression pattern.
We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at rootS(NN)=200 GeV measured at midrapidity by the PHENIX experiment at ...the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta (1.5<p(T)<4.5 GeV/c) a significant fraction of all produced particles are protons and antiprotons. They show a centrality-scaling behavior different from that of pions. The (p) over bar/pi and p/pi ratios are enhanced compared to peripheral Au+Au, p+p, and e(+)e(-) collisions. This enhancement is limited to p(T)<5 GeV/c as deduced from the ratio of charged hadrons to pi(0) measured in the range 1.5<p(T)<9 GeV/c.
Proton distributions at midrapidity have been measured for 158A·GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. A high degree of nuclear stopping is found in the truly ...heavy ion collisions. Systematic results of single particle transverse momentum distributions of pions, kaons, and protons, of 200A·GeV S+S and 158A·GeV Pb+Pb central collisions will be addressed within the context of thermalization. By comparing these data with thermal and transport models, freeze-out parameters such as the temperature parameter
T
fo
and mean collective flow velocity 〈β〉 are extracted. Preliminary results of the particle ratios of
K
−
K
+
and
p
p
are discussed in the context of cascade models of RQMD and VENUS.
Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at sqrts(NN)=130 GeV for transverse momenta up to 6 GeV/c, where ...hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T)<2 GeV/c is consistent with collective hydrodynamical flow calculations. At p(T)>3 GeV/c, a saturation of v(2) is observed which persists up to p(T)=6 GeV/c.
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