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arXiv 1406.1689hep-ph
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在LHC上用孤立光子探测p+Pb碰撞中小- $x$核胶子的正向快度分布

Probing the small-$x$ nuclear gluon distributions with isolated photons at forward rapidities in p+Pb collisions at the LHC

Ilkka Helenius, Kari J. Eskola, Hannu Paukkunen

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15 pages, 17 figures
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摘要：

在非线性光学微扰QCD中研究了LHC中p+Pb碰撞中的直接光子产生。我们的目的是量化的优势$x$地区探测在不同的速度，并确定最佳的条件下测试的核胶子部分子分布函数（nPDF）在小$x$。与包含性π介子产生的比较表明，从这两个过程中，光子对小- $x$部分子具有更高的灵敏度，并且通过对光子事件施加隔离切割可以进一步增加这种灵敏度。然而，分离标准的细节似乎仅对研究的$x$灵敏度产生微小差异，并且对预期的核修饰几乎没有影响。我们还考虑了前向和后向快速性之间的产量不对称性，这可以用于探测nPDF，而不管是否有准确的p+p基线。

英文摘要：

Inclusive direct photon production in p+Pb collisions at the LHC is studied within the NLO perturbative QCD. Our aim is to quantify the dominant $x$ regions probed at different rapidities and to identify the best conditions for testing the nuclear gluon parton distribution functions (nPDFs) at small $x$. A comparison to the inclusive pion production reveals that from these two processes the photons carry more sensitivity to the small-$x$ partons and that this sensitivity can be further increased by imposing an isolation cut for the photon events. The details of the isolation criteria, however, seem to make only a small difference to the studied $x$ sensitivity and have practically no effect on the expected nuclear modifications. We consider also the yield asymmetry between forward and backward rapidities which can be used to probe the nPDFs irrespectively of whether an accurate p+p baseline is available.

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