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158 GeV/核子的Pb-Pb碰撞中相对于反应平面的J/psi方位各向异性

J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon

F. Prino

备注：
proceedings of HP08 conference corrected a typo in one equation
发表信息：
Eur.Phys.J.C61:853-858,2009
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摘要：

利用NA_（50）实验测量了158 GeV/核子的Pb-Pb碰撞中J/ $ψ$相对于反应面的方位角分布。在重离子碰撞中产生的介质中与粲偶素解离相关的各种物理机制预计将在SPS能量下所观察到的J/ $ψ$介子的方位角分布中引入各向异性。因此，测量J/ $ψ$椭圆各向异性，量化的傅立叶系数v $_2$的J/ $ψ$方位角分布相对于反应平面，是一个重要的工具，以约束理论模型，旨在解释异常J/ $ψ$抑制Pb-Pb碰撞中观察到的。我们提出了测量J/ $ψ$产量在不同的箱的方位角相对于反应平面，以及作为碰撞中心和J/ $ψ$横向动量的函数的傅立叶系数v $_{2}$的值。根据电磁量能计测得的中性横能的方位角分布估计了反应面。对分布在5个中心性或p $_{\rm T}$子样本中的约100 000个事件的数据样本进行了分析。对于非中心碰撞，提取的v $_{2}$值显著大于零，并且可以看出随着p $_{\rm T}$而增加。

英文摘要：

The J/$ψ$ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/$ψ$ mesons at SPS energies. Hence, the measurement of J/$ψ$ elliptic anisotropy, quantified by the Fourier coefficient v$_2$ of the J/$ψ$ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/$ψ$ suppression observed in Pb-Pb collisions. We present the measured J/$ψ$ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v$_{2}$ as a function of the collision centrality and of the J/$ψ$ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p$_{\rm T}$ sub-samples. The extracted v$_{2}$ values are significantly larger than zero for non-central collisions and are seen to increase with p$_{\rm T}$.

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