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Register a new userJet-Hadron Correlations in sqrt{s_{NN}} = 200 GeV p+p and Central Au+Au Collisions
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Azimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in Au+Au and p+p collisions at $sqrt{s_{text{NN}}} = 200 text{GeV}$ in STAR are presented. The trigger jet population in Au+Au collisions is biased towards jets that have not interacted with the medium, allowing easier matching of jet energies between Au+Au and p+p collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum ($p_{text{T}}^{text{assoc}}$) and enhanced at low $p_{text{T}}^{text{assoc}}$ in 0-20% central Au+Au collisions compared to p+p collisions, which is indicative of medium-induced parton energy loss in ultrarelativistic heavy-ion collisions.
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We report the measurements of $Sigma (1385)$ and $Lambda (1520)$ production in $p+p$ and $Au+Au$ collisions at $sqrt{s_{NN}} = 200$ GeV from the STAR collaboration. The yields and the $p_{T}$ spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central $Au+Au$ collisions. Our results indicate that there may be a time-span between chemical and thermal freeze-out during which elastic hadronic interactions occur.
We report $e^pm-mu^mp$ pair yield from charm decay measured between midrapidity electrons ($|eta|<0.35$ and $p_T>0.5$ GeV/$c$) and forward rapidity muons ($1.4<eta<2.1$ and $p_T>1.0$ GeV/$c$) as a function of $Deltaphi$ in both $p$$+$$p$ and in $d$+Au collisions at $sqrt{s_{_{NN}}}=200$ GeV. Comparing the $p$$+$$p$ results with several different models, we find the results are consistent with a total charm cross section $sigma_{cbar{c}} =$ 538 $pm$ 46 (stat) $pm$ 197 (data syst) $pm$ 174 (model syst) $mu$b. These generators also indicate that the back-to-back peak at $Deltaphi = pi$ is dominantly from the leading order contributions (gluon fusion), while higher order processes (flavor excitation and gluon splitting) contribute to the yield at all $Deltaphi$. We observe a suppression in the pair yield per collision in $d$+Au. We find the pair yield suppression factor for $2.7<Deltaphi<3.2$ rad is $J_{dA}$ = 0.433 $pm$ 0.087 (stat) $pm$ 0.135 (syst), indicating cold nuclear matter modification of $cbar{c}$ pairs.
Yields, correlation shapes, and mean transverse momenta pt{} of charged particles associated with intermediate to high-pt{} trigger particles ($2.5 < pt < 10$ GeVc) in d+Au and Au+Au collisions at $snn=200$ GeV are presented. For associated particles at higher $pt gtrsim 2.5$ GeVc, narrow correlation peaks are seen in d+Au and Au+Au, indicating that the main production mechanism is jet fragmentation. At lower associated particle $pt < 2$ GeVc, a large enhancement of the near- ($dphi sim 0$) and away-side ($dphi sim pi$) associated yields is found, together with a strong broadening of the away-side azimuthal distributions in Au+Au collisions compared to d+Au measurements, suggesting that other particle production mechanisms play a role. This is further supported by the observed significant softening of the away-side associated particle yield distribution at $dphi sim pi$ in central Au+Au collisions.
The sum of charm and beauty in Au+Au collisions at 200 GeV measured through nonphotonic electrons, show similar suppression at high pT as light hadrons, in contrast to expectations based on the dead cone effect. To understand this observation, it is important to separate the charm and beauty components. Non-photonic electron-D0 and electron-hadron azimuthal angular correlations are used to disentangle the contributions from charm and beauty decays. The beauty contribution in p+p collisions at 200 GeV is found to be comparable to charm at pT 5.5 GeV, indicating that beauty may contribute significantly to the non photonic electrons from heavy flavour decays in Au+Au data at high pT. Furthermore, in Au+Au collisions we present the status of D0 meson reconstruction using microvertexing techniques made possible with the addition of the silicon detectors.
We report $J/psi$ spectra for transverse momenta $p_T$> 5 GeV/$c$ at mid-rapidity in p+p and Au+Au collisions at sqrt(s_{NN}) = 200 GeV.The inclusive $J/psi$ spectrum and the extracted $B$-hadron feed-down are compared to models incorporating different production mechanisms. We observe significant suppression of the $J/psi$ yields for $p_T$> 5 GeV/$c$ in 0-30% Au+Au collisions relative to the p+p yield scaled by the number of binary nucleon-nucleon collisions in Au+Au collisions. In 30-60% collisions, no such suppression is observed.The level of suppression is consistently less than that of high-$p_T$ $pi^{pm}$ and low-$p_T$ $J/psi$.
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