Fixed target Drell-Yan data and NNLO QCD fits of parton distribution functions

TL;DR

This paper assesses the impact of fixed-target Drell-Yan data on NNLO QCD parton distribution functions by testing DIS-DY consistency and performing a combined DIS/DY fit. It identifies a representative, consistent DY data subset (E605 and E866 cross-section ratios) to include with DIS data and shows that NNLO DY corrections are essential for precision. The resulting NNLO DIS/DY PDFs significantly improve sea quark constraints at large x, while gluons are largely unchanged, and the fit achieves good quality with chi2/NDP ~ 1.13. The work also highlights phenomenological implications for alpha_s, NuTeV related ratios, and W/Z production predictions at the Tevatron, demonstrating robust, high-precision PDFs for collider phenomenology.

Abstract

We discuss the influence of fixed target Drell-Yan data on the extraction of parton distribution functions at next-to-next-to-leading order (NNLO) in QCD. When used in a parton distribution fit, the Drell-Yan (DY) data constrain sea quark distributions at large values of Bjorken x. We find that not all available DY data are useful for improving the precision of parton distribution functions (PDFs) obtained from a fit to the deep inelastic scattering (DIS) data. In particular, some inconsistencies between DIS-based parton distribution functions and DY data for large values of dilepton rapidity are found. However, by selecting a sample of the DY data that is both representative and consistent with the DIS data, we are able to perform a combined PDF fit that significantly improves the precision of non-strange quark distributions at large values of x. The NNLO QCD corrections to the DY process are crucial for improving the precision. They reduce the uncertainty of the theoretical prediction, making it comparable to the experimental uncertainty in DY cross-sections over a broad range of x.

Figures (9)

• Figure 1: The NLO (dashes) and NNLO (solid) dilepton rapidity distributions for proton-copper collisions, calculated with the DIS PDFs of Ref. alekhin, in comparison with the E-605 data at zero rapidity. The NNLO $1\sigma$ uncertainty band due to PDF errors is displayed by the dotted curves. The relation between $x_1$ and $x_2$ for data points in the upper panel is shown in the lower panel.
• Figure 2: The same as in Fig. \ref{['e605Y0']} for the E-866 proton (upper panels) and deuteron (middle panels) data for dilepton masses $M=5.45~{\rm GeV}$ (left panels) and $M = 8.45~{\rm GeV}$ (right panels).
• Figure 3: Te same as in Fig. \ref{['e605Y0']} for the E-772 deuterium data and for the dimuon invariant mass $M=4.75~{\rm GeV}$.
• Figure 4: The same as in Fig. \ref{['e605Y0']} for the deuteron to proton cross-section ratio measured by the E-886 experiment. Larger values of $x_2$ correspond to larger dimuon invariant masses.
• Figure 5: Data points used in the DIS/DY fit vs. predictions based on fitted PDFs. The bands reflect the $1\sigma$ uncertainty of fitted PDFs.