Abstracts for 2010 Hard Probe Meeting (Oct. 10-15, 2010, Eilat, Israel)

•  Wei Xie

Heavy quarks are unique probes to study the strongly coupled Quark-Gluon Plasma created at RHIC. Unlike light quarks, heavy quark masses come mostly from spontaneous symmetry breaking, which makes them ideal for studying the medium's QCD properties. Due to their large masses, they are produced early in the collisions and are expected to interact with the medium quite differently from that of light quarks. Detailed studies on the production of open heavy flavor mesons and heavy quarkonium in heavy-ion collisions and the baseline $p+p$ and $d+A$ collisions provide crucial information in understanding the medium's properties. With the large acceptance TPC, Time of Flight, EM Calorimeter and future Heavy-Flavor Tracker, STAR has the capabilities to study heavy quark production in the dense medium in all different directions. In this talk, we will review the current status as well as the future perspectives of heavy quark studies in STAR experiment.

• Zebo Tang

Title: $J/\psi$ production at high pT at STAR

The $c\bar{c}$ bound state $J/\psi$ provides a unique tool to probe the hot dense medium produced in heavy-ion collisions, but to date its production mechanism is not understood clearly neither in heavy-ion collisions nor in hadron hadron collisions. Measurement of $J/\psi$ production at high $p_T$ is particularly interesting since at high $p_T$
the various models give different predictions. More over some model calculations on $J/\psi$ production are only applicable at intermediate/high $p_T$. Besides, high $p_T$ particles are widely used to study the parton-medium interactions in heavy-ion collisions. In this talk, we will present the measurement of mid-rapidity (|y|<1) $J/\psi \rightarrow
e^+e^-$ production at high $p_T$ in p+p and Cu+Cu collisions at 200 GeV, that used a trigger on electron energy deposited in Electromagnetic Calorimeter. The $J/\psi$ $p_T$ spectra and nuclear modification factors will be compared to model calculations to understand its production mechanism and medium modifications. The $J/\psi$-hadron azimuthal angle correlation will be presented to disentangle $B$-mesons contributions to inclusive $J/\psi$. Progresses
from on-going analyses in p+p collisions at 200GeV taken in year 2009 high luminosity run will be also reported.

• Rosi Reed

Title: $\Upsilon$ production in p+p, d+Au, Au+Au collisions at $\sqrt{{S}_{NN }} = $ 200 GeV in STAR

Quarkonia is a good probe of the dense matter produced in heavy-ion collisions at RHIC because it is produced early in the collision and the production is theorized to be suppressed due to the Debye color screening of the potential between the heavy quarks. A model dependent measurement of the temperature of the Quark Gluon Plasma (QGP) can be determined by examining the ratio of the production of various quarkonia states in heavy ion collisions versus p+p collisions because lattice calculations indicate that the quarkonia states will be sequentially suppressed. Suppression is quantified by calculating ${R}_{AA}$, which is the ratio of the production in p+p scaled by the number of binary collisions to the production in Au+Au. The $\Upsilon$ states are of particular interest because at 200 GeV the effects of feed down and co-movers are smaller than for J/$\psi$, which decreases the systematic uncertainty of the ${R}_{AA} calculation. In addition to hadronic absorption, additional cold nuclear matter effects, such as shadowing of the PDFs, can be determined from d+Au collisions. We will present our results for mid-rapidity $\Upsilon$ production in p+p, as well as our preliminary results in d+Au and Au+Au at $\sqrt{{S}_{NN }}$ = 200 GeV. These results will then be compared with theoretical QCD calculations.

• Wei Li

Title: Non$-$Photonic Electron and Charged Hadron Azimuthal Correlation in 500 GeV p+p Collisionsions at RHIC

Due to the dead cone effect, heavy quarks were expected to lose less energy than light quarks since the current theory predicted that the dominant energy loss mechanism is gluon radiation for heavy quarks.  Whereas non-photonic electron from heavy quark decays show similar suppression as light hadrons at high $p_{T}$ in central Au+Au collisions.  It is important to separate the bottom contribution to non-photonic electron for the better understanding of heavy flavor
production and energy loss mechanism in ultra high energy heavy ion collisions. B decay contribution is approximately 50$\%$ at a transverse momentum of $p_{T}$$\geq$5 GeV/c in 200 GeV p+p collisions from STAR results. In this talk, we will present the azimuthal correlation analysis of non-photonic electrons with charged hadrons at $p_{T}$$\geq$6.5 GeV/c in p+p collisions at $\sqrt{s}$  = 500 GeV at RHIC. The results are compared to PYTHIA simulations to disentangle
charm and bottom contribution of semi-leptonic decays to non-photonic electrons.

• Gang Wang

Title: B/D Contribution to Non-Photonic Electrons and Status of Non-Photonic Electron $v_2$ at RHIC

In contrast to the expectations due to the dead cone effect, non-photonic electrons from decays of heavy quark carrying hadrons show a similar suppression as light hadrons at high $p_{T}$ in central 200 GeV Au+Au collisions at RHIC. It is important to separate the charm and bottom contributions to non-photonic electrons to better understand the heavy flavor production and energy loss mechanism in high energy heavy ion collisions. Heavy quark energy loss and heavy quark evolution in the QCD medium can also lead to an elliptic flow $v_2$ of heavy quarks which can be studied through $v_2$ of non-photonic electrons.

In this talk, we present the azimuthal correlation analysis of non-photonic electrons with charged hadrons at 1.5 GeV/c < $p_{T}$ < 9.5 GeV/c in p+p collisions at $\sqrt{s}$ = 200 GeV at RHIC, with the removal of J/$\Psi$ contribution to non-photonic electrons. The results are compared with PYTHIA simulations to disentangle charm and bottom contributions of semi-leptonic decays to non-photonic electrons. B decay contribution is approximately 50$\%$ at the electron transverse momentum of $p_{T}$ > 5 GeV/c in 200 GeV p+p collisions from STAR results. Incorporating the spectra and energy loss information of non-photonic electrons, we further estimate the spectra and energy loss of the electrons from B/D decays. Status of $v_2$ measurements for non-photonic electrons will also be discussed for 200 GeV Au+Au collisions with RHIC run2007 data.