No Arabic abstract
I will present an overview of identified particle spectra at high $p_T$ ($p_T{}^{>}_{sim}$ 5 GeV/$c$) in both p+p collisions and AA collisions at RHIC. In p+p collisions, summary of particle ratios of K, $eta$, $omega$, $rho$, $phi$, $p$, $bar{p}$, $Lambda$ and heavy-flavor (open charm, $J/Psi$) to $pi$ at high-pt will be compiled and compared to the ratios of integrated yields. The spectra are used in $x_t$ scaling study and compared to pQCD calculations. These will help us establish particle composition in jets and the quark and gluon contributions to hadron production at high $p_T$. Similar jet chemistry has been extracted in Au+Au data in search for a quantitative measure of color charge dependence of jet energy loss.
We report recent results of high-pt measurements in Pb--Pb collisions at $sqrt{s_{NN}}=2.76$ TeV by the ALICE experiment and discuss the implications in terms of energy loss of energetic partons in the strongly interaction medium formed in the collisions.
We report the recent results of proton and anti-proton yields as a function of centrality and p_T in Au+Au collisions at sqrt(s_NN) = 200 GeV, measured by the PHENIX experiment at RHIC. In central collisions at intermediate transverse momenta (1.5 < p_T < 4.5 GeV/c) a significant fraction of all produced particles is protons and anti-protons. They show a different scaling behavior from that of pions. The pbar/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.
Identified charged particle spectra of $pi^{pm}$, $K^{pm}$, $p$ and $pbar$ at mid-rapidity ($|y|<0.1$) measured by the $dedx$ method in the STAR-TPC are reported for $pp$ and d+Au collisions at $snn = 200$ GeV and for Au+Au collisions at 62.4 GeV, 130 GeV, and 200 GeV. ... [Shortened for arXiv list. Full abstract in manuscript.]
The transverse momentum ($p_{mathrm T}$) spectra for identified charged pions, protons and anti-protons from $p$+$p$ and $d$+Au collisions are measured around midrapidity ($mid$y$mid$ $<$ 0.5) over the range of 0.3 $<$ $p_{mathrm T}$ $<$ 10 GeV/$c$ at $sqrt{s_{mathrm {NN}}}$ = 200 GeV. The charged pion and proton+anti-proton spectra at high p_{T} in p+p collisions have been compared with the next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations with a specific fragmentation scheme. The p/pi^{+} and pbar/pi^{-}has been studied at high p_{T}. The nuclear modification factor (R_{dAu}) shows that the identified particle Cronin effects around midrapidity are significantly non-zero for charged pions and to be even larger for protons at intermediate p_{T} (2 < p_{T} < 5 GeV/c).
We report new results on identified (anti)proton and charged pion spectra at large transverse momenta (3<$p_{T}$<10 GeV/c) from Cu+Cu collisions at $sqrt{s_{NN}}$=200 GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). This study explores the system size dependence of two novel features observed at RHIC with heavy ions: the hadron suppression at high-$p_{T}$ and the anomalous baryon to meson enhancement at intermediate transverse momenta. Both phenomena could be attributed to the creation of a new form of QCD matter. The results presented here bridge the system size gap between the available pp and Au+Au data, and allow the detailed exploration for the on-set of the novel features. Comparative analysis of all available 200 GeV data indicates that the system size is a major factor determining both the magnitude of the hadron spectra suppression at large transverse momenta and the relative baryon to meson enhancement.