Characteristics of Parton Energy Loss Studied with High-p_T Particle Spectra from PHENIX

In the first three years of the physics program at the Relativistic Heavy Ion Collider (RHIC) a picture was established in which the suppression of hadrons at high transverse momenta (p_T) in central Au+Au collisions is explained by energy loss of quark and gluon jets in a medium of high color-charge density. Measurements of single particle spectra for a smaller nucleus (Cu), for different center-of-mass energies and with higher statistics were performed in the subsequent years and are used to test predictions and assumptions of jet quenching models in more detail. The measurements presented here are consistent with a parton energy loss scenario so that these models can be used to relate the observed suppression to properties of the created medium.Comment: To appear in the proceedings of 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 04-10 Feb 200

Highlights from PHENIX - II

This contribution highlights recent results from the PHENIX Collaboration at RHIC with emphasis on those obtained through lepton and photon measurements in PHENIX.Comment: 9 pages, 13 figures, presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions - "Quark Matter 2008", Jaipur, India, February 4-10, 200

Recent PHENIX Results on Open Heavy Flavor

Throughout the history of the RHIC physics program, questions concerning the dynamics of heavy quarks have generated much experimental and theoretical investigation. A major focus of the PHENIX experiment is the measurement of these quarks through their semi-leptonic decay channels at mid and forward rapidity. Heavy quark measurements in $p+p$ collisions give information on the production of heavy flavor, without complications from medium effects. New measurements in $d+$Au and Cu+Cu indicate surprising cold nuclear matter effects on these quarks at midrapidity, and provide a new baseline for interpretation of the observed suppression in Au+Au collisions. When considered all together, these measurements present a detailed study of nuclear matter across a wide range of system size and temperature. Here we present preliminary PHENIX measurements of non-photonic electron spectra and their centrality dependence in $d$+Au and Cu+Cu, and discuss their implications on the current understanding of parton energy loss in the nuclear medium.Comment: 4 pages, 3 figures, to appear in the proceedings of Quark Matter 201

J/ψ\psi production in In-In and p-A collisions

The NA60 experiment studies dimuon production in In-In and p-A collisions at the CERN SPS. We report recent results on \jpsi production, measured through its muon pair decay. As a function of centrality, we show that in In-In the \jpsi yield is suppressed beyond expectations from nuclear absorption. We present also for the first time results on \jpsi production in p-A collisions at 158 GeV, the same energy of the nucleus-nucleus data. For both p-A and In-In we show preliminary results on \psip suppression. Finally, we have studied the kinematical distributions of the \jpsi produced in In-In collisions. We present results on transverse momentum and rapidity, as well as on the angular distribution of the \jpsi decay products.Comment: 8 pages, Quark Matter 2006 conference proceeding

Quarkonium production in ultra-relativistic nuclear collisions: suppression vs. enhancement

After a brief review of the various scenarios for quarkonium production in ultra-relativistic nucleus-nucleus collisions we focus on the ingredients and assumptions underlying the statistical hadronization model. We then confront model predictions for J/$\psi$ phase space distributions with the most recent data from the RHIC accelerator. Analysis of the rapidity dependence of the J/$\psi$ nuclear modification factor yields first evidence for the production of J/$\psi$ mesons at the phase boundary. We conclude with predictions for charmonium production at the LHC.Comment: 8 pages, 6 figures, invited paper, Quark Matter 2006 conference, Shanghai, submitted to J. Phys.

Heavy Quarkonia Production in p+p Collisions from the PHENIX Experiment

Quarkonia provide a sensitive probe of the properties of the hot dense medium created in high energy heavy ion collisions. Hard scattering processes result in the production of heavy quark pairs that interact with the collision medium during hadronization. These in-medium interactions convey information about the fundamental properties of the medium itself and can be used to examine the modification of the QCD confining potential in the collision environment. Baseline measurements from p+p and d+Au collision systems are used to distinguish cold nuclear matter effects while measurements from heavy ion collision systems are used to quantify in-medium effects. The PHENIX experiment has the capability of detecting heavy quarkonia at $1.2<|\eta|<2.2$ via the $\mu^+\mu^-$ decay channel and at $|\eta|<0.35$ via the $e^+e^-$ decay channel. Recent runs have resulted in the collection of high statistics p+p data sets that provide an essential baseline reference for heavy ion measurements and allow for further critical evaluation of heavy quarkonia production mechanisms. The latest PHENIX results for the production of the $J/\psi$ in p+p collisions are presented and future prospects for $\psi'$, $\chi_{c}$ and $\Upsilon$ measurements are discussed.Comment: 4 pages, 2 figures, Proceedings for Quark Matter 200

Measurement of two-particle correlations with respect to second- and third-order event planes in Au plus Au collisions at root s(NN)=200 GeV

We present measurements of azimuthal correlations of charged hadron pairs in root s(NN) = 200 GeV Au + Au collisions for the trigger and associated particle transverse-momentum ranges of 1 4 GeV/c) correlations is suppressed compared with that of correlations measured in p + p collisions. At the lowest associated particle p(T)(0.5 <p(T)(a) <1 GeV/c), the away-side shape and yield are modified relative to those in p + p collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-p(T) trigger correlations (2 <p(T)(t) <4 GeV/c), a finite 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(2) and Psi(3). The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and 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.Peer reviewe

Measurements of e(+)e(-) pairs from open heavy flavor in p plus p and d plus A collisions at root S-NN=200 GeV

We report a measurement of e(+)e(-) pairs from semileptonic heavy-flavor decays in p + p collisions at root S-NN = 200 GeV. The e(+)e(-) pair yield from b (b) over bar and c (c) over bar is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and p(T). We used three different event generators, PYTHIA, MC@NLO, and POWHEG, to simulate the e(+)e(-) spectra from c (c) over bar and b (b) over bar production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4 pi, significant differences are observed for the total cross section. These difference are less pronounced for b (b) over bar than for c (c) over bar. The same model dependence was observed in already published d + A data. The p + p data are also directly compared with d + A data in mass and p(T), and within the statistical accuracy no nuclear modification is seen.Peer reviewe

Low-momentum direct-photon measurement in Cu plus Cu collisions at root S-NN=200 GeV

We measured direct photons for p(T) <5 GeV/c in minimum bias and 0%-40% most-central events at midrapidity for Cu+Cu collisions at root S-NN = 200 GeV. The e(+)e(-) contribution from quasireal direct virtual photons has been determined as an excess over the known hadronic contributions in the e(+)e(-) mass distribution. A clear enhancement of photons over the binary scaled p+p fit is observed for p(T) <4 GeV/c in Cu+Cu data. The p(T) spectra are consistent with the Au+Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the p+p baseline are 285 +/- 53 (stat) +/- 57(syst) MeV/c and 333 +/- 72(stat) +/- 45(syst) MeV/c for minimum bias and 0%-40% most-central events, respectively. The rapidity density, dN / dy, of photons demonstrates the same power law as a function of dN(ch)/d eta observed in Au+Au at the same collision energy.Peer reviewe

The Future of Quark Matter at RHIC

Projected annual results for heavy particle and high-p_{T} correlation studies at future RHICII luminosities.Comment: 8 pages, 3 figures. Proceedings for Quark Matter 2006, Shanghai, Chin