Challenges with Large Transverse Momentum in Semi-Inclusive Deeply Inelastic Scattering

TL;DR

This paper reviews the challenges in accurately describing semi-inclusive deep inelastic scattering at large transverse momentum, highlighting discrepancies between experimental data and theoretical calculations.

Contribution

It provides a comprehensive survey of the phenomenological status and identifies significant disagreements between data and fixed order pQCD predictions at high transverse momentum.

Findings

Large discrepancies between HERMES and COMPASS data and theoretical calculations.

Breakdown of TMD factorization at high transverse momentum.

Potential need for improved theoretical models or understanding.

Abstract

We survey the current phenomenological status of semi-inclusive deep inelastic scattering at moderate hard scales and in the limit of very large transverse momentum. As the transverse momentum becomes comparable to or larger than the overall hard scale, the differential cross sections should be calculable with fixed order pQCD methods, while small transverse momentum (TMD factorization) approximations should eventually break down. We find large disagreement between HERMES and COMPASS data and fixed order calculations done with modern parton densities, even in regions of kinematics where such calculations should be expected to be very accurate. Possible interpretations are suggested.