标题： 高x部分子分布 显示英文标题

标题： Parton distributions at high x

摘要： 我们从NMC氘核和质子结构函数F_2(d)/F_2(p)的比值中提取了下（d）和上（u）部分子分布函数（PDF's）的比值，使用了对氘核中核结合效应的修正，这些修正是从SLAC F_2数据的核依赖性中提取的。标准PDF中对d夸克分布的显著修正是必要的，尤其是在高x区域。修正后的d/u比值与QCD在x=1时预测的0.2相一致。使用修正后的d/u比值的PDF来预测最近的CDF W不对称数据，在大快速度下给出了更好的一致性。使用更新的d/u比值和最新的alpha_s世界平均值，我们对所有DIS数据的F_2和R进行了NLO全局拟合，并使用重整子模型和经验模型估计了高阶扭曲贡献的大小。我们发现，随着alpha_s的更新值，高阶扭曲项的幅度是之前分析值的一半。在包含靶质量和高阶扭曲修正的情况下，具有更新d/u比值的标准NLO PDF能够描述到x=1.0的SLAC F_2数据。当在NNLO下重复分析时，我们发现额外的NNLO贡献在R中占了NLO拟合中提取的大部分高阶扭曲效应。NNLO下的分析表明，R、F_2和xF_3（例如GLS求和规则）中的高阶扭曲效应非常小。 显示英文摘要

摘要： We extract the ratio of the down (d) and up (u) parton distribution functions (PDF's) from the ratio of NMC deuteron and proton structure function F_2(d)/F_2(p), using corrections for nuclear binding effects in the deuteron, which are extracted from the nuclear dependence of SLAC F_2 data. Significant corrections to the d quark distribution in standard PDF's are required, especially at high x. The corrected d/u ratio is in agreement with the QCD prediction of 0.2 at x=1. The predictions for the recent CDF W asymmetry data using PDF's with the corrected d/u ratio give much better agreement at large rapidity. Using the updated d/u ratio and the most recent world average for alpha_s, we perform a NLO global fit to all DIS data for F_2 and R, and estimate the size of the higher twist contributions using both a renormalon model and an empirical model. We find that with the updated value of alpha_s, the magnitude of the higher twist terms is half the value of previous analysis. With the inclusion of target mass and higher twist corrections, the standard NLO PDF's with the updated d/u ratio describe the SLAC F_2 data up to x=1.0. When the analysis is repeated in NNLO, we find that the additional NNLO contributions to R account for most of the higher twist effects extracted in the NLO fit. The analysis in NNLO indicates that the higher twist effects in R, F_2 and xF_3 (e.g. GLS sum rule) are very small.