A recent analysis from the PHENIX collaboration of available direct photon measurement results in collisions of various systems such as Au+Au, Cu+Cu, and Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a universal, within experimental uncertainties, multiplicity scaling, in which direct photon \(p_{T}\)-spectra for transverse momenta up to 2 GeV/c are scaled with charged hadron pseudorapidity density at midrapidity raised to power \(\alpha =1.25\). On the other hand, those direct photon \(p_{T}\)-spectra also exhibit geometrical scaling in the similar \(p_{T}\) range. Assuming power-law dependence of the scaled photon spectra for both scaling laws, we formulate two independent conditions for the power \(\alpha \), which overshoot experimental data by \(\sim 10\%\) on average. We discuss possible sources that might improve this estimate.

中文翻译：

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重离子碰撞中直接光子产量的缩放性质

与PHENIX合作进行的最新分析表明，在39至2760 GeV的不同电子束能量下，各种系统（例如Au + Au，Cu + Cu和Pb + Pb）的碰撞在可用的直接光子测量中发生了碰撞，实验不确定性，多重度缩放，其中横向动量的直接光子\（p_ {T} \）-光谱高达2 GeV / c，并在带电的强子伪快速密度增加的情况下按比例缩放，功率提高到功率\（\ alpha = 1.25 \）。另一方面，那些直接光子\（p_ {T} \）-光谱也表现出相似的\（p_ {T} \）几何比例缩放范围。假设两个定标定律都依赖于定标光子光谱的幂定律依赖性，我们为功率\（\ alpha \）制定了两个独立条件，它们平均使实验数据超出\（\ sim 10 \％\）。我们讨论了可能改善这一估计的可能来源。