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Register a new userB-meson production at forward and backward rapidity in $p$+$p$ and Cu+Au collisions at $sqrt{s_{_{NN}}}$=200 GeV
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The fraction of $J/psi$ mesons which come from B-meson decay, $textrm{F}_{B{rightarrow}J/psi}$, is measured for J/$psi$ rapidity mbox{$1.2<|y|<2.2$} and $p_T>0$ in $p$+$p$ and Cu+Au collisions at $sqrt{s_{_{NN}}}$=200 GeV with the PHENIX detector. The extracted fraction is $textrm{F}_{B{rightarrow}J/psi}$ = 0.025 $pm$ 0.006(stat) $pm$ 0.010(syst) for $p$+$p$ collisions. For Cu+Au collisions, $textrm{F}_{B{rightarrow}J/psi}$ is 0.094 $pm$ 0.028(stat) $pm$ 0.037(syst) in the Au-going direction ($-2.2<y<-1.2$) and 0.089 $pm$ 0.026(stat) $pm$ 0.040(syst) in the Cu-going direction ($1.2<y<2.2$). The nuclear modification factor, $R_{rm CuAu}$, of B mesons in Cu+Au collisions is consistent with binary scaling of measured yields in $p$+$p$ at both forward and backward rapidity.
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The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured $phi$ meson production and its nuclear modification in asymmetric Cu$+$Au heavy-ion collisions at $sqrt{s_{NN}}=200$ GeV at both forward Cu-going direction ($1.2<y<2.2$) and backward Au-going direction ($-2.2<y<-1.2$), rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0%--20% centrality, the $phi$ meson yield integrated over $1<p_T<5$ GeV/$c$ prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Additionally, the nuclear-modification factor in Cu$+$Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in $d$$+$Au collisions for these rapidities.
The PHENIX experiment has studied nuclear effects in $p$$+$Al and $p$$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV on charged hadron production at forward rapidity ($1.4<eta<2.4$, $p$-going direction) and backward rapidity ($-2.2<eta<-1.2$, $A$-going direction). Such effects are quantified by measuring nuclear modification factors as a function of transverse momentum and pseudorapidity in various collision multiplicity selections. In central $p$$+$Al and $p$$+$Au collisions, a suppression (enhancement) is observed at forward (backward) rapidity compared to the binary scaled yields in $p$+$p$ collisions. The magnitude of enhancement at backward rapidity is larger in $p$$+$Au collisions than in $p$$+$Al collisions, which have a smaller number of participating nucleons. However, the results at forward rapidity show a similar suppression within uncertainties. The results in the integrated centrality are compared with calculations using nuclear parton distribution functions, which show a reasonable agreement at the forward rapidity but fail to describe the backward rapidity enhancement.
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-$p_T$ $J/psi$.
Event-by-event fluctuations of the ratio of inclusive charged to photon multiplicities at forward rapidity in Au+Au collision at $sqrt{s_{NN}}$=200 GeV have been studied. Dominant contribution to such fluctuations is expected to come from correlated production of charged and neutral pions. We search for evidences of dynamical fluctuations of different physical origins. Observables constructed out of moments of multiplicities are used as measures of fluctuations. Mixed events and model calculations are used as baselines. Results are compared to the dynamical net-charge fluctuations measured in the same acceptance. A non-zero statistically significant signal of dynamical fluctuations is observed in excess to the model prediction when charged particles and photons are measured in the same acceptance. We find that, unlike dynamical net-charge fluctuation, charge-neutral fluctuation is not dominated by correlation due to particle decay. Results are compared to the expectations based on the generic production mechanism of pions due to isospin symmetry, for which no significant (<1%) deviation is observed.
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.
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