Thorne R S
Department of Physics and Astronomy, University College London, Gower Place, London , WC1E 6BT UK.
Eur Phys J C Part Fields. 2014;74(7):2958. doi: 10.1140/epjc/s10052-014-2958-4. Epub 2014 Jul 15.
I consider the effect on MSTW partons distribution functions (PDFs) due to changes in the choices of theoretical procedure used in the fit. I first consider using the 3-flavour fixed flavour number scheme instead of the standard general mass variable flavour number scheme used in the MSTW analysis. This results in the light quarks increasing at all relatively small [Formula: see text] values, the gluon distribution becoming smaller at high values of [Formula: see text] and larger at small [Formula: see text], the preferred value of the coupling constant [Formula: see text] falling, particularly at NNLO, and the fit quality deteriorates. I also consider lowering the kinematic cut on [Formula: see text] for DIS data and simultaneously introducing higher twist terms which are fit to data. This results in much smaller effects on both PDFs and [Formula: see text] than the scheme change, except for quarks at very high [Formula: see text]. I show that the structure function one obtains from a fixed input set of PDFs using the fixed flavour scheme and variable flavour scheme differ significantly for [Formula: see text] at high [Formula: see text], and that this is due to the fact that in the fixed flavour scheme there is a slow convergence of large logarithmic terms of the form [Formula: see text] relevant for this regime. I conclude that some of the most significant differences in PDF sets are largely due to the choice of flavour scheme used.
我考虑了因拟合中理论程序选择的变化而对MSTW部分子分布函数（PDFs）产生的影响。我首先考虑使用三味固定味数方案，而不是MSTW分析中使用的标准通用质量可变味数方案。这导致在所有相对较小的[公式：见原文]值下轻夸克增加，胶子分布在高[公式：见原文]值时变小而在低[公式：见原文]值时变大，耦合常数[公式：见原文]的优选值下降，特别是在NNLO时，并且拟合质量变差。我还考虑降低深度非弹性散射（DIS）数据中对[公式：见原文]的运动学截断，并同时引入与数据拟合的高阶扭转项。这对PDFs和[公式：见原文]产生的影响比方案变化小得多，除了在非常高的[公式：见原文]时的夸克。我表明，使用固定味方案和可变味方案从固定的PDF输入集获得的结构函数在高[公式：见原文]时对于[公式：见原文]有显著差异，并且这是由于在固定味方案中对于该区域相关的形式为[公式：见原文]的大对数项收敛缓慢。我得出结论，PDF集的一些最显著差异很大程度上归因于所使用的味方案的选择。
