在LHC上光子引发双轻子末态的产生：截面与前后向不对称性研究
Photon-initiated production of a di-lepton final state at the LHC: cross section versus forward-backward asymmetry studies
摘要：
本文研究了在大型强子对撞机环境中光子诱导双轻子末态产生的效应。利用QED部分子分布函数（PDF）集，我们可以将光子看作质子内部的实部分子，并将它们的产额直接与Drell-Yan（DY）过程的产额进行比较。特别是，我们集中在两个机制的误差分析。为了做到这一点，我们使用NNPDF集，它带有一组副本来估计系统PDF误差。一方面，我们发现，PI的贡献成为占主导地位的DY以上的双轻子不变质量为3 TeV。另一方面，PI预测受到来自QED PDF的大误差的影响，远高于影响DY模式的误差。我们通过微分截面和前后不对称（AFB）观测量作为双轻子不变质量的函数，在共振和非共振搜索中性大质量矢量玻色子（Z '）的背景下评估这些不确定性的影响。虽然前者受到上述显著的残余误差的影响，但后者显示出即使在存在PI贡献的情况下也预期的系统误差消除（回想AFB是截面的比率），使得最近强调的AFB作为共振和非共振模式中的Z'发现和解释的有效工具所发挥的关键作用进一步得到巩固。
英文摘要：
We explore the effects of Photon Induced (PI) production of a dilepton final state in the Large Hadron Collider environment. Using QED Parton Distribution Function (PDF) sets we can treat the photons as real partons inside the protons and compare their yield directly to that of the Drell-Yan (DY) process. In particular, we concentrate on an error analysis of the two mechanisms. In order to do so, we use the NNPDF set, which comes with a set of replicas to estimate the systematic PDF error. On the one hand, we find that the PI contribution becomes dominant over DY above a dilepton invariant mass of 3 TeV. On the other hand, the PI predictions are affected by a large error coming from the QED PDFs, well above the one affecting the DY mode. We assess the impact of these uncertainties in the context of resonant and non-resonant searches for a neutral massive vector boson (Z') through the differential cross section and Forward-Backward Asymmetry (AFB) observables as a function of the dilepton invariant mass. While the former is subject to the aforementioned significant residual errors the latter shows the systematic error cancellation expected (recall that AFB is a ratio of cross sections) even in presence of PI contributions, so that the recently emphasized key role played by AFB as a valid tool for both Z' discovery and interpretation in both resonant and non-resonant mode is further consolidated.
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