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利用直接光子和带电粒子方位角关联研究重离子碰撞中的部分子能量损失

Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations

The STAR Collaboration, B. I. Abelev

备注：
submitted to Phys. Rev. Lett, 6 pages, 4 figures
发表信息：
Phys.Rev.C82:034909,2010
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摘要：

用RHIC的STAR探测器测量了质心能量为$\sqrt{s_{_{NN}}}=200$ GeV的$p$ + $p$和Au+Au碰撞中与直接光子（$γ_{dir} $）和$π^0$有关的带电粒子谱。一个hower-shape分析用于部分地区分$γ_{dir}$和$π^0$。假设在$γ_{dir}$方向（近侧）上没有缔合带电粒子并且来自碎裂光子（$γ_{frag}$）的贡献很小，则提取与$γ_{dir}$（远侧）相反的缔合带电粒子产率。在中心Au+Au碰撞中的中快度（$|η|<0.9$）下，与$p$ + $p$碰撞相比，在高横动量（$8< p_{T}^{trig}<16$ GeV/ $c$）下与$γ_{dir}$和$π^0$相关的带电粒子产额被抑制3-5倍。在运动学范围$|η|<1$和$3< p_{T}^{assoc} < 16$ GeV/ $c$内，观测到的相关带电粒子的抑制对于$γ_{dir}$和$π^0$是相似的，并且在不确定性内与$γ_{dir}$能量无关。这些测量结果表明，部分子的能量损失，在所覆盖的运动学范围内，是不敏感的部分子路径长度。

英文摘要：

Charged-particle spectra associated with direct photon ($γ_{dir} $) and $π^0$ are measured in $p$+$p$ and Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$ GeV with the STAR detector at RHIC. A hower-shape analysis is used to partially discriminate between $γ_{dir}$ and $π^0$. Assuming no associated charged particles in the $γ_{dir}$ direction (near side) and small contribution from fragmentation photons ($γ_{frag}$), the associated charged-particle yields opposite to $γ_{dir}$ (away side) are extracted. At mid-rapidity ($|η|<0.9$) in central Au+Au collisions, charged-particle yields associated with $γ_{dir}$ and $π^0$ at high transverse momentum ($8< p_{T}^{trig}<16$ GeV/$c$) are suppressed by a factor of 3-5 compared with $p$ + $p$ collisions. The observed suppression of the associated charged particles, in the kinematic range $|η|<1$ and $3< p_{T}^{assoc} < 16$ GeV/$c$, is similar for $γ_{dir}$ and $π^0$, and independent of the $γ_{dir}$ energy within uncertainties. These measurements indicate that the parton energy loss, in the covered kinematic range, is insensitive to the parton path length.

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