The PHENIX Experiment at RHIC

The physics emphases of the PHENIX collaboration and the design and current status of the PHENIX detector are discussed. The plan of the collaboration for making the most effective use of the available luminosity in the first years of RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program available at http://www.rhic.bnl.gov/phenix

Quarkonium production from d+Au to Au+Au collisions

M. Rosati on behalf of the PHENIX Collaboration EIThe PHENIX experiment measured J/$\psi$ production in pp, d+Au and Au+Au reactions at \sqrt{^sNN}$= 200 GeV over a wide range of rapidity and transverse momentum. The nuclear modification factor obtained by comparing the d+Au and pp cross sections as a function of rapidity, is consistent with shadowing of the gluon distribution functions. J/$\psi$ production in Au+Au collisions was compared to the production in pp collisions and it was found to be inconsistent with models that predict strong enhancement relative to binary collision scaling

Low mass dilepton production at RHIC energies

EIRecent results on low mass dilepton measurements from the PHENIX experiment are reported. Invariant mass spectra of $\phi-> e+e-$ are measured for the first time in Au-Au collisions at $\sqrt{^{S}NN} = 200 GeV$ in Run2. In d-Au collisions, the yields and MT slopes of both $\phi ->e+e-$ and $\phi-> K+K-$ are measured. Both results are consistent with each other within errors. In the future, a Hadron Blind Detector will be installed in PHENIX which will enhance our capabilities of rejecting external photon conversions and Dalitz pairs, that will result in a significant reduction of the large combinatorial background

Heavy flavor production in PHENIX

O. Drapier on behalf of the PHENIX Collaboration, EIThe PHENIX experiment at RHIC measured single electron spectra in p + p, d + Au and Au + Au collisions at $\sqrt{s_{NN}} = 200$ GeV, and in Au + Au collisions at $\sqrt{s_{NN}} = 62.4$ GeV. In these spectra, electrons from semi-leptonic decays of charmed particles are the dominant contribution after subtraction of all 'photonic' sources (photon conversions, Dalitz decays, decays of light vector mesons). The p + p open charm production cross-section is found to be in good agreement with pQCD NLO calculations. The shape of the distributions obtained for p + p interactions is compared with those observed for nucleus-nucleus collisions. From p + p to d + Au and Au + Au interactions, open charm production is found to scale with the number of binary collisions $N_{\rm coll}$ . Au + Au data at $\sqrt{s_{NN}} = 62.4$ GeV is compatible with the ISR p + p results scaled by $N_{\rm coll}$ . The elliptic flow parameter v2 of heavy flavor electrons has also been measured, and is found to be non-zero in the intermediate pT range

Differential probes of medium-induced energy loss

B. Cole on behalf of the PHENIX Collaboration -EIResults from the PHENIX experiment of measurements of high- $p_{\rm T}$ particle production presented at the Hard Probes 2004 Conference are summarized. This paper focuses on a sub-set of the measurements presented at the conference, namely the suppression of $\pi^0$ production at moderate to high $p_{\rm T}$ as a function of angle with respect to the collision reaction plane, $\Delta\phi$ , for different collision centralities. The data are presented in the form of nuclear modification factor as a function of angle with respect to the reaction plane, $R_{AA} (\Delta \phi)$ . The data are analyzed using empirical estimates of the medium-induced energy loss obtained from the $R_{AA} (\Delta \phi)$ values. A geometric analysis is performed with the goal of understanding the simultaneous dependence of RAA on $\Delta\phi$ and centrality. We find that the centrality and $\Delta\phi$ dependence of the $\pi^0$ suppression can be made approximately consistent using an admittedly over-simplistic description of the geometry of the jet propagation in the medium but only if the energy loss is effectively reduced for short parton path lengths in the medium. We find that with a more "canonical" treatment of the quenching geometry, the $\pi^0$ suppression varies more rapidly with $\Delta\phi$ than would be expected from the centrality dependence of the suppression

Medium effects on high ¶T\P_{T} particle production measured with the PHENIX experiment

EITransverse momentum $\P_{T}$ spectra measured by the PHENIX experiment at RHIC in Au + Au, d + Au and pp collisions at $\sqrt {^S{NN}} = 200 GeV$ and in Au + Au collisions at $\sqrt {^S{NN}} = 62.4 GeV$ are presented. A suppression of the yield of high $\P_{T}$ hadrons in central Au + Au collisions by a factor 4-5 at $\P_{T}>5$ is found relative to the pp reference scaled by the nuclear overlap function (\T_{AB}) . In contrast, direct photons are not suppressed in central Au + Au collisions and no suppression of high $\P_{T}$ particles can be seen in d + Au collisions. This leads to the conclusion that the dense medium formed in central Au + Au collisions is responsible for the suppression

Can ϕ\phi mesons give an answer to the baryon puzzle at RHIC?

EIInternational audienceThe PHENIX experiment at RHIC has observed a large enhancement of baryon and anti-baryon production at ~ 2-5 GeV/c, compared to expectations from jet fragmentation. While a number of theoretical interpretations of the data are available, there is not yet a definitive answer to the “baryon puzzle”. We investigate the centrality dependence of -meson production at mid-rapidity in Au + Au collisions with $sqrt {^{s}NN}=200 GeV$. Comparison with the proton and anti-proton spectra reveal similar shapes, as expected for soft production described by hydrodynamics. However, the absolute yields show a different centrality dependence. The nuclear modification factors for $\phi$ are similar to those of pions, rather than (anti)protons that have similar mass. At intermediate , baryon/meson effects seem to be more important than the mass effects, in support of recombination models