Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for pp, d+Au, and Au+Au collisions at 200 GeV by the STAR experiment. The acoplanarities in pp and d+Au indicate initial state kT broadening. Larger acoplanarity is observed in Au+Au collisions. The central Au+Au data show an additional effect signaling conical emission of correlated charged hadrons.
Projections of away-side three-particle correlations along the diagonal $\Sigma$ within 0 < $\Delta$ < 0.35 (squares) and along the off-diagonal $\Delta$ within |$\Sigma$| < 0.35 (points) in (a) d+Au and (b) 12% central Au+Au collisions. The shaded areas indicate systematic uncertainties on the off-diagonal projections. The histogram in (a) is the near-side off-diagonal projection. The histogram in (b) is the away-side off-diagonal projection of our result with a = b = 1. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi mesons are observed to be similar in yield and shape for Cu+Cu and Au+Au colliding systems with similar average numbers of participating nucleons. The \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.
Upper panel. The ratio of the yields of $K^{−}$, $\phi$, $\bar{\Lambda}$ and $\Xi+\bar{\Xi}$ normalized to $N_{\scriptsize{\mbox{part}}}$ in nucleus-nucleus collisions to corresponding yields in inelastic $p+p$ collisions as a function of $N_{\scriptsize{\mbox{part}}}$ at 200 GeV. Lower panel. Same as above for $\phi$ mesons in $Cu+Cu$ collisions at 200 and 62.4 GeV. The $p+p$ collision data at 200 GeV are from STAR [5] and at 62.4 GeV from ISR [29]. The error bars shown represent the statistical and systematic errors added in quadrature.
We present results on strange and multi-strange particle production in Au+Au collisions at $\sqrt{s_{NN}}=62.4$ GeV as measured with the STAR detector at RHIC. Mid-rapidity transverse momentum spectra and integrated yields of $K^{0}_{S}$, $\Lambda$, $\Xi$, $\Omega$ and their anti-particles are presented for different centrality classes. The particle yields and ratios follow a smooth energy dependence. Chemical freeze-out parameters, temperature, baryon chemical potential and strangeness saturation factor obtained from the particle yields are presented. Intermediate transverse momentum ($p_T$) phenomena are discussed based on the ratio of the measured baryon-to-meson spectra and nuclear modification factor. The centrality dependence of various measurements presented show a similar behavior as seen in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
Temperature and baryon chemical potential obtained from thermal model fits as a function of √sNN (see Ref. [22]). The dashed lines correspond to the parametrizations given in Ref. [22]. The solid stars show the result for √sNN=62.4 and 200 GeV.
Temperature and baryon chemical potential obtained from thermal model fits as a function of √sNN (see Ref. [22]). The dashed lines correspond to the parametrizations given in Ref. [22]. The solid stars show the result for √sNN=62.4 and 200 GeV.
Temperature and baryon chemical potential obtained from thermal model fits as a function of √sNN (see Ref. [22]). The dashed lines correspond to the parametrizations given in Ref. [22]. The solid stars show the result for √sNN=62.4 and 200 GeV.
We present the first study of the energy dependence of $p_t$ angular correlations inferred from event-wise mean transverse momentum $<p_{t} >$ fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure suggests that the principal source of $p_t$ correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related $<p_{t}>$ fluctuations near 10 GeV.
Per-particle fluctuation dependence on pseudorapidity scale $\delta\eta$ in central collisions.
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