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arXiv 2008.03853hep-ex
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在ATLAS实验中测量弱混合角的PDF不确定度的减小

Reduction of PDF uncertainty in the measurement of the weak mixing angle at the ATLAS experiment

Yao Fu, Siqi Yang, Minghui Liu, Liang Han, Tie-Jiun Hou, Carl Schmidt, Chen Wang, C. -P. Yuan

备注：
submitted to Chinese Physics C
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摘要：

研究了在欧洲核子研究中心（CERN）大型强子对撞机（LHC）上测量有效弱混合角$\sin^2θ_{\text{eff}}^{\ell}$时部分子分布函数（PDF）的不确定性。由于稀释效应，LHC质子-质子碰撞中PDF引起的不确定性很大。在大型强子对撞机上对Drell-Yan前后不对称性（$A_{FB}$）的测量可以用来减少$\sin^2θ_{\text{eff}}^{\ell}$测量中的PDF不确定性。然而，当在$A_{FB}$数据分析中包括轻子对的全部质量范围时，PDF更新程序和$\sin^2θ_{\text{eff}}^{\ell}$提取之间的相关性导致在所获得的$\sin^2θ_{\text{eff}}^{\ell}$值中存在相当大的偏差。从我们的研究中，我们发现，偏差可以显着减少通过删除Drell-Yan事件周围的$Z$极区域不变的质量，而在减少PDF的不确定性的大部分敏感性仍然存在。此外，$W$玻色子事件中的轻子电荷不对称性作为带电轻子的快度$A_\pm(η_\ell)$的函数，已知是另一个可观察的，其可用于减少$\sin^2θ_{\text{eff}}^{\ell}$测量中的PDF不确定性。来自$A_\pm(η_\ell)$的约束与来自$A_{FB}$的约束互补，因此没有偏倚影响$\sin^2θ_{\text{eff}}^{\ell}$提取。使用基于Hessian更新方法的错误PDF更新方法包（{ \sc ePump}）进行研究。本文以CT 14 HERA 2 PDF集为例。

英文摘要：

We investigate the parton distribution function (PDF) uncertainty in the measurement of the effective weak mixing angle $\sin^2θ_{\text{eff}}^{\ell}$ at the CERN Large Hadron Collider (LHC). The PDF-induced uncertainty is large in the proton-proton collisions at the LHC due to the dilution effect. The measurement of the Drell-Yan forward-backward asymmetry ($A_{FB}$) at the LHC can be used to reduce the PDF uncertainty in the $\sin^2θ_{\text{eff}}^{\ell}$ measurement. However, when including the full mass range of lepton pairs in the $A_{FB}$ data analysis, the correlation between the PDF updating procedure and the $\sin^2θ_{\text{eff}}^{\ell}$ extraction leads to a sizable bias in the obtained $\sin^2θ_{\text{eff}}^{\ell}$ value. From our studies, we find that the bias can be significantly reduced by removing Drell-Yan events with invariant mass around the $Z$ pole region, while most of the sensitivity in reducing the PDF uncertainty remains. Furthermore, the lepton charge asymmetry in the $W$ boson events as a function of the rapidity of the charged leptons, $A_\pm(η_\ell)$, is known to be another observable which can be used to reduce the PDF uncertainty in the $\sin^2θ_{\text{eff}}^{\ell}$ measurement. The constraint from $A_\pm(η_\ell)$ is complementary to that from the $A_{FB}$, thus no bias affects the $\sin^2θ_{\text{eff}}^{\ell}$ extraction. The studies are performed using the Error PDF Updating Method Package ({\sc ePump}), which is based on the Hessian updating methods. In this article, the CT14HERA2 PDF set is used as an example.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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