arXiv 1412.09762014-12-02nucl-ex

基于硬过程产额与潜在事件活动的正相关计算$p$ +A碰撞的中心偏向因子

Calculation of centrality bias factors in $p$+A collisions based on a positive correlation of hard process yields with underlying event activity

Dennis V. Perepelitsa, Peter A. Steinberg

备注：: 7 pages, 3 figures

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摘要：

硬散射产率在中心选择质子-和氘-核（$p$ +A）碰撞一般比较核子-核子（$NN$）的横截面缩放到适当的部分子光度使用几何模型从最小偏差$p$ +A相互作用的分析。一般来说，这些模型假设硬过程速率和底层$NN$碰撞中的软事件活动的幅度是不相关的。当包含这些相关性时，这些相关性会影响名义中心性区间内的实测收益率，这种效应通常被称为“中心性偏差”。在这项工作中，硬散射产率和潜在的事件活动在个人$NN$碰撞之间的正相关性的影响进行了研究。ATLAS和PHENIX使用的中心性计算中包含了这种相关性，两者都基于类似的Monte Carlo Glauber方法，但每个碰撞或每个参与者事件活动的模型不同。结果发现，这种相关性的存在往往会增加在更中心的事件和减少它在周边事件测量的产量。计算了RHIC和LHC上$p$ +A碰撞的数值因子，以修正中心偏置效应的测量产额。合理的协议与以前的计算这些因素的PHENIX被发现，尽管在实施的基础偏差的差异。

英文摘要：

Hard scattering yields in centrality-selected proton-- and deuteron--nucleus ($p$+A) collisions are generally compared to nucleon--nucleon ($NN$) cross-sections scaled to the appropriate partonic luminosity using geometric models derived from an analysis of minimum bias $p$+A interactions. In general, these models assume that hard process rates and the magnitude of the soft event activity in the underlying $NN$ collisions is uncorrelated. When included, these correlations influence the measured yield in a nominal centrality interval, an effect typically referred to as a "centrality bias". In this work, the impact of a positive correlation between the hard scattering yield and the underlying event activity in individual $NN$ collisions is investigated. This correlation is incorporated into the centrality calculations used by ATLAS and PHENIX, both based on a similar Monte Carlo Glauber approach but with different models of the per-collision or per-participant event activity. It is found that the presence of this correlation tends to increase the yield measured in more central events and decrease it in peripheral events. Numerical factors to correct measured yields for the centrality bias effect are calculated for $p$+A collisions at RHIC and the LHC. Reasonable agreement with a previous calculation of these factors by PHENIX is found, despite differences in the implementation of the underlying bias.

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