Z玻色子横向动量重整化对部分子分布函数确定的影响
Impact of Z-boson transverse-momentum resummation on PDF determination
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中文总结 AI 辅助
研究中性流Drell-Yan轻子对产生的小横向动量重整化对PDFs确定的影响，通过LHC的测量数据，用NNPDF方法拟合，考虑理论不确定性，发现重整化改善数据描述，对PDF拟合一致性重要，影响适中，理论不确定性相关性处理有核心作用。
中文摘要 AI 辅助
我们研究了中性流Drell-Yan轻子对产生的小横向动量重整化对共线部分子分布函数（PDFs）确定的影响。聚焦于ATLAS和CMS在大型强子对撞机（LHC）质心能量8和13 TeV下对Z玻色子横向动量谱的测量，并将其纳入基于NNPDF方法的PDF拟合。理论预测在微扰量子色动力学中计算到次下一个领先阶（NNLO），并补充了用RadISH获得的次下一个下一个领先对数精度的小横向动量重整化修正。通过由重整化和因子化尺度变化构建的理论协方差矩阵考虑缺失的高阶不确定性。首先重新审视8 TeV数据的处理，用数值稳定的NNLO计算取代先前分析中使用的固定阶预测，并消除早期拟合中引入的额外数值不确定性。然后评估13 TeV测量、重整化修正以及逐步降低对双轻子横向动量的最小截断的影响。发现重整化改善了对Z玻色子横向动量数据的描述，对确保PDF拟合的整体一致性至关重要。不过，它并不支持将拟合运动学区域扩展到几十GeV以下的横向动量。重整化对PDFs的影响适中，主要导致在与LHC现象学相关的运动学区域中胶子PDF的稳定。最后，评论了理论不确定性之间相关性的处理在对具有百分之和亚百分之精度测量的PDF拟合中可能起核心作用这一事实。
英文摘要
We study the impact of small-transverse-momentum resummation for neutral-current Drell-Yan lepton-pair production on the determination of collinear parton distribution functions (PDFs). We focus on measurements of the Z-boson transverse-momentum spectrum performed by ATLAS and CMS at the LHC at centre-of-mass energies of 8 and 13 TeV, and include them in PDF fits based on the NNPDF methodology. Theoretical predictions are computed at next-to-next-to-leading order (NNLO) in perturbative QCD and are supplemented with small-transverse-momentum resummation corrections at next-to-next-to-next-to-leading logarithmic accuracy obtained with RadISH. Missing higher-order uncertainties are accounted for through a theory covariance matrix constructed from renormalisation- and factorisation-scale variations. We first revisit the treatment of the 8 TeV data, replacing the fixed-order predictions used in previous analyses with numerically stable NNLO calculations, and removing the additional numerical uncertainties introduced in earlier fits. We then assess the impact of the 13 TeV measurements, of resummation corrections, and of progressively lowering the minimum cut on the dilepton transverse momentum. We find that resummation improves the description of the Z boson transverse-momentum data and is essential for ensuring the overall consistency of the PDF fits. Nevertheless, it does not conclusively support extending the fitted kinematic region to transverse momenta below a few tens of GeV. The impact of resummation on PDFs is moderate, leading primarily to a stabilisation of the gluon PDF in a kinematic region of relevance for LHC phenomenology. Finally, we comment on the fact that the treatment of correlations among theoretical uncertainties may play a central role in PDF fits to measurements with percent- and sub-percent-level precision.
