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Towards a global analysis of polarized parton distributions

M. Stratmann, W. Vogelsang

TL;DR

Addresses the challenge of incorporating exact NLO cross sections into global analyses of polarized parton distributions, crucial for extracting $\Delta g$ and flavor separation from upcoming polarized pp data and SIDIS measurements. Introduces a Mellin-moment framework that converts convolutions into products and allows precomputation of the hard-scattering pieces, enabling fast, precise NLO predictions during fits. Demonstrates the method with semi-inclusive DIS and high-$p_T$ prompt-photon production, including a toy analysis to illustrate future potential for RHIC data. Concludes that this approach makes fully NLO-accurate polarized PDF extractions feasible within reasonable computational costs, paving the way for robust global analyses of $\Delta g$ and sea-quark polarizations.

Abstract

We present a technique for implementing in a fast way, and without any approximations, higher-order calculations of partonic cross sections into global analyses of parton distribution functions. The approach, which is set up in Mellin-moment space, is particularly suited for analyses of future data from polarized proton-proton collisions, but not limited to this case. The usefulness and practicability of this method is demonstrated for the semi-inclusive production of hadrons in deep-inelastic scattering and the transverse momentum distribution of ``prompt'' photons in pp collisions, and a case study for a future global analysis of polarized parton densities is presented.

Towards a global analysis of polarized parton distributions

TL;DR

Addresses the challenge of incorporating exact NLO cross sections into global analyses of polarized parton distributions, crucial for extracting and flavor separation from upcoming polarized pp data and SIDIS measurements. Introduces a Mellin-moment framework that converts convolutions into products and allows precomputation of the hard-scattering pieces, enabling fast, precise NLO predictions during fits. Demonstrates the method with semi-inclusive DIS and high- prompt-photon production, including a toy analysis to illustrate future potential for RHIC data. Concludes that this approach makes fully NLO-accurate polarized PDF extractions feasible within reasonable computational costs, paving the way for robust global analyses of and sea-quark polarizations.

Abstract

We present a technique for implementing in a fast way, and without any approximations, higher-order calculations of partonic cross sections into global analyses of parton distribution functions. The approach, which is set up in Mellin-moment space, is particularly suited for analyses of future data from polarized proton-proton collisions, but not limited to this case. The usefulness and practicability of this method is demonstrated for the semi-inclusive production of hadrons in deep-inelastic scattering and the transverse momentum distribution of ``prompt'' photons in pp collisions, and a case study for a future global analysis of polarized parton densities is presented.

Paper Structure

This paper contains 3 sections, 16 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Hadronic Cross Sections and the Mellin Moment Technique
  3. Semi-Inclusive Deep-Inelastic Scattering

Figures (2)

  • Figure 1: Contours in complex Mellin-$n,m$ spaces for the calculation of the double Mellin inverse in Eq. (\ref{['eq8']}). $r_n$ and $r_m$ denote the rightmost poles of the integrand in $n$ and $m$, respectively, and the $c_i$ the intersections with the real axis.
  • Figure :