Measurement of the Proton Structure Function ${F_2}$ at low ${x}$ and low ${Q^2}$ at HERA

TL;DR

This paper presents measurements of the proton structure function F_2 at very low x and Q^2 at HERA, confirming the rise of F_2 with decreasing x and consistency with perturbative QCD in this regime.

Contribution

It provides new experimental data on F_2 at lower x and Q^2 than previous measurements, extending the understanding of proton structure in this kinematic region.

Findings

F_2 increases as x decreases at low Q^2

F_2 evolution aligns with perturbative QCD predictions

Results extend the kinematic range of previous measurements

Abstract

We report on a measurement of the proton structure function $F_2$ in the range $3.5\times10^{-5}\leq x \leq 4\times10^{-3}$ and 1.5 ${\rm GeV^2} \leq Q^2 \leq15$ ${\rm GeV^2}$ at the $ep$ collider HERA operating at a centre-of-mass energy of $\sqrt{s} = 300$ ${\rm GeV}$. The rise of $F_2$ with decreasing $x$ observed in the previous HERA measurements persists in this lower $x$ and $Q^2$ range. The $Q^2$ evolution of $F_2$, even at the lowest $Q^2$ and $x$ measured, is consistent with perturbative QCD.