Jet Fragmentation in Vacuum and Medium with gamma-hadron Correlations in PHENIX

Jet fragmentation in p+p and Au+Au collisions is studied via back-to-back correlations of direct photons and charged hadrons. The direct photon correlations are obtained by statical subtraction of the background from decay photons. Results on the nuclear modification to the associated charged hadron yields are reviewed. Further studies of jet fragmentation in p+p using isolated direct photons are also presented. A kT-smeared LO pQCD calculation is used to interpret the data. The sensitivity of the data to the underlying fragmentation function is tested and the results are found to be compatible with expectations of a sample dominated by quark jet fragmentation.Comment: Talk presented at Hot Quarks 2010, June 21-26, La Londe Les Maures, France. To be published in Journal of Physics: Conference Series (JPCS

Study of Cronin effect and nuclear modification of strange particles in d-Au and Au-Au collisions at 200 GeV in PHENIX

Effects of strangeness on nuclear modification in d-Au and Au-Au collisions at 200 GeV are studied, in order to quantify the effects of quark content and mass. Measurements of ratios of the yields in central collisions to the yields in peripheral collisions are performed for lambda baryon and phi meson. Found results show little dependence of particle suppression or enhancement on mass and strange content, but rather prominent difference in nuclear modification between mesons and baryons.Comment: 4 pages, 4 figures, proceedings of the Seventeenth International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004

Stopping and Baryon Transport in Heavy Ion Reactions

In this report I will give an experimental overview on nuclear stopping in hadron collisions, and relate observations to understanding of baryon transport. Baryon number transport is not only evidenced via net-proton distributions but also by the enhancement of strange baryons near mid-rapidity. Although the focus is on high-energy data obtained from pp and heavy ions from RHIC, relevant data from SPS and ISR will be considered. A discussion how the available data at higher energy relates and gives information on baryon junction, quark-diquark breaking will be made.Comment: 8 pages, 7 figures. Invited plenary talk for the 5'th international conference on Physics and Astrophysics of Quark Gluon Plasma, February 8-12, 2005, Salt Lake City, Kolkata, Indi

Event anisotropy of identified π0\pi^{0}, photon and electron compared to charged π\pi, KK, pp and deuteron in sNN\sqrt{s_{NN}} = 200 GeV Au+Au at PHENIX

We report the recent results of event anisotropy analysis focused on $v_2$ in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at PHENIX.Comment: 4 pages, 3 figures, contribution to the proceedings of the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter, Oakland, January 11-17, 2004). To appear in the proceedings (Journal of Physics G

Hadron Production at Intermediate pTp_T at RHIC

Large proton and antiproton enhancement with respect to pions has been observed at intermediate transverse momentum $p_T \approx$ 2-5 GeV/$c$ in Au+Au collisions at RHIC. To investigate the possible source of this anomaly, the production of $\phi$ mesons and two particle angular correlations triggered by mid-$p_T$ baryons or mesons are studied. We also present the first measurement of proton and antiproton production at $\sqrt{s_{NN}} = 62.4$ GeV in Au+Au collisions, which aims to study the energy dependence of the observed baryon enhancement.Comment: 7 pages, 5 figures, proceedings of Hot Quarks 2004 workshop, Taos Valley, New Mexico, 18-24 Jul 2004,, to be published in J. Phys.

Baryonic Effect on chi_cJ Suppression in Au+Au Collisions at RHIC Energies

We predict that initially produced chi_cJ mesons at low transverse momentum in the central rapidity region are almost dissociated by nucleons and antinucleons in hadronic matter produced in central Au+Au collisions at RHIC energies sqrt {s_{NN}}= 130 and 200 GeV. In calculations the nucleon and antinucleon distributions in hadronic matter are results of evolution from their freeze-out distributions which well fit the experimental p_T spectra of proton and antiproton. Any measured chi_cJ mesons at low p_T are generated from deconfined matter and give an explicit proof of regeneration mechanism (recombination mechanism).Comment: 10 pages, 3 figures, Latex, a discussion added to the referenc

ϕ\phi meson production in d + Au collisions at sNN\sqrt{s_{NN}} = 200 GeV

We present the preliminary results on $\phi$ meson production in the $\phi \to K^{+}K^{-}$ and $\phi \to e^{+}e^{-}$ decay channels measured at mid-rapidity in $\sqrt{s}$ = 200 GeV d + Au collisions at RHIC by the PHENIX experiment. The transverse mass spectra were obtained in both channels. The extracted $\phi$ yields are found to be consistent with each other. The results are compared to the measurements in Au + Au collisions at the same center of mass energy.Comment: To appear in the proceedings of Hot Quarks 2004: Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions (HQ'04), Taos Valley, New Mexico, 18-24 Jul 2004. Submitted to J.Phys.

Centrality and sNNDependenceofthe\sqrt{s_{NN}} Dependence of the dE_{T}/d\etaand and dN_{ch}/d\eta$ in Heavy Ion Collisions at Mid-Rapidity

The PHENIX experiment at RHIC has measured transverse energy and charged particle multiplicity at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 19.6, 130, 62.4 and 200 GeV as a function of centrality. The presented results are compared to measurements from other RHIC experiments, and experiments at lower energies. The $\sqrt{s_{NN}}$ dependence of $dE_{T}/d\eta$ and $dN_{ch}/d\eta$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE_{T}/d\eta$ and $dN_{ch}/d\eta$ is similar at all measured incident energies. At RHIC energies the ratio of transverse energy per charged particle was found independent of centrality and growing slowly with $\sqrt{s_{NN}}$. A survey of comparisons between the data and available theoretical models is also presented.Comment: Proccedings of the Workshop: Focus on Multiplcity at Bari, Italy, June 17-19,2004. To be submitted to the Jornal of Physics, "Conference series". Includes: 20 Pages, 15 figures, 3 Tables, 80 Referencie

Systematics of mid-rapidity K-/pi ratio in heavy-ion collisions

It is observed that K-/pi in A+A and possibly p+p and pbar+p collisions follows an interesting systematic in omega, the pion transverse energy per unit of rapidity and transverse overlap area. The systematics show a linear increase of K-/pi with omega in the AGS and SPS energy regime and a saturation at RHIC energy. The systematics indicate that omega might be the relevant variable underlying K-/pi. At high energy, the omega variable is related to the gluon saturation scale in high density QCD, and perhaps to the initial energy density in the Bjorken picture.Comment: 4 pages, 3 figures. SQM-2001 proceeding

Neutral Pions with Large Transverse Momentum in d+Au and Au+Au Collisions

Measurements of transverse-momentum p_T spectra of neutral pions in Au+Au and d+Au collisions at sqrt{s_NN}=200 GeV and 62.4 GeV by the PHENIX experiment at RHIC in comparison to p+p reference spectra at the same sqrt{s_NN} are presented. In central Au+Au collisions at sqrt{s_NN}=200 GeV a factor 4-5 suppression for neutral pions and charged hadrons with p_T > 5 GeV/c is found relative to the p+p reference scaled by the nuclear overlap function . In contrast, such a suppression of high-p_T particles is absent in d+Au collisions independent of the centrality of the collision. To study the sqrt{s_NN} dependence of the suppression Au+Au collisions at sqrt{s_NN}=200 GeV and 62.4 GeV are compared.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N