Study of HERA ep Data at Low Q^2 and Low x_Bj and the Need for Higher-Twist Corrections to Standard pQCD Fits

TL;DR

This paper compares HERA low-$x$, low-$Q^2$ data with standard pQCD predictions and finds that including higher-twist corrections significantly improves the fit, indicating the need for further corrections below 2 GeV$^2$.

Contribution

It introduces an additional higher-twist term to the standard DGLAP evolution to better describe low-$Q^2$, low-$x$ data, highlighting the limitations of current pQCD models.

Findings

Higher-twist corrections improve fit to HERA data

Standard DGLAP evolution is inadequate at low $Q^2$

Further corrections needed below 2 GeV$^2$

Abstract

A detailed comparison of HERA data at low Bjorken-$x$ and low four-momentum-transfer squared, $Q^2$, with predictions based on $\ln{Q^2}$ evolution (DGLAP) in perturbative Quantum Chromo Dynamics suggests inadequacies of this framework. The standard DGLAP evolution was augmented by including an additional higher-twist term in the description of the longitudinal structure function, $F_{\rm L}$. This additional term, $F_{\rm L}~A_{\rm L}^{\rm HT}/Q^2$, improves the description of the reduced cross sections significantly. The resulting predictions for $F_{\rm L}$ suggest that further corrections are required for $Q^2$ less than about 2 GeV$^2$.