PHENIX Results on Hadron Production in Large Collision Systems

Abstract

The paper presents recent PHENIX results on hadron production in heavy ion collisions. Comparison of light hadron ($\pi^{0}$, $\pi^{\pm}$, $K_{s}$, $K^{\pm}$, $K^{*}$, $(p+\bar{p})/2$, $\eta$, $\phi$, $\omega$) nuclear modification factors in Au $+$ Au, Cu $+$ Au collisions at $\sqrt{s_{NN}}=200$ GeV and U $+$ U collisions at $\sqrt{s_{NN}}=192$ GeV will be discussed.

1 INTRODUCTION

Studying of quark-gluon plasma (QGP) properties in heavy ion collisions is the main part of PHENIX [1] experiment physics program. One of the common ways to study signatures of QGP formation in heavy-ion collisions is measurement of nuclear modification factors ($R_{AB}$)—a quantitive characteristic of difference in hadron production in proton-proton (p + p) and nuclei-nuclei (A + B) collisions [2]. The paper presents comparison of light hadron $R_{AB}$ in Cu + Au collisions at $\sqrt{s_{NN}}=200$ GeV.

2 RESULTS AND DISCUSSION

Figure 1 presents different light hadron ($\pi^{0}$, $\pi^{\pm}$, $K_{s},K^{\pm}$, $K^{*}$, $(p+\bar{p})/2$, $\eta$, $\phi$, $\omega$) $R_{AB}$ measured in Cu $+$ Au collisions at $\sqrt{s_{NN}}=200$ GeV. At intermediate transverse momentum (2 $<p_{T}<$ 5 GeV/c) the ordering can be seen: $R_{AB}^{\pi^{0},\eta,\omega}<R_{AB}^{K^{\pm},K^{*},\phi}<R_{AB}^{p}$. At high $p_{T}$ ($p_{T}>5$ GeV/c) $R_{AB}$ values of all measured mesons are equal within uncertainties and much lower, than unity ($R_{AB}\approx$ 0.5). Previously similar $R_{AB}$ patterns were observed in symmetric Au $+$ Au collision system and were interpreted as signatures of QGP formation (baryon enhancement [2], strangeness enhancement [3] and jet quenching [3]). Hadron $R_{AB}$ values in symmetric Au $+$ Au, asymmetric Cu $+$ Au collisions and collisions of deformed U $+$ U nuclei were found to be in agreement at the same number of participant nucleons ($N_{part}$). As representative example Fig. 2 presents comparison of proton $\langle R_{AB}\rangle$ as a function of $N_{part}$ in Cu $+$ Au, Au $+$ Au, and U $+$ U collisions.

Fig. 1

Comparison of light hadron ($\pi^{0}$, $\pi^{\pm}$, $K_{s}$, $K^{\pm}$, $K^{*}$, $(p+\bar{p})/2$, $\eta$, $\phi$, $\omega$) $R_{AB}$ values in Cu $+$ Au collisions at $\sqrt{s_{NN}}=200$ GeV.

Fig. 2

Comparison of proton $\langle R_{AB}\rangle$ in Au $+$ Au, Cu $+$ Au collisions at $\sqrt{s_{NN}}=200$ GeV and U $+$ U collisions at $\sqrt{s_{NN}}=192$ GeV.

3 CONCLUSIONS

Recent PHENIX results on hadron production in Cu $+$ Au collisions at $\sqrt{s_{NN}}=200$ GeV and U $+$ U collisions at $\sqrt{s_{NN}}=192$ GeV have been presented. Signatures of QGP formation (baryon enhancement, strangeness enhancement and jet quenching) have been observed and found to be similar to previous Au $+$ Au results at the same $N_{\textrm{part}}$ values. That might indicate that light hadron production scales with the average size of the nuclear overlap region and do not depend on the details of its shape.