Inclusive Charged Particle Distributions in Deep Inelastic Scattering Events at HERA

TL;DR

This paper measures inclusive charged particle distributions in deep inelastic electron-proton scattering at HERA, comparing results with models and lower energy experiments to understand QCD effects and the impact of rapidity gaps.

Contribution

It provides detailed measurements of charged particle distributions in DIS events, including differences between events with and without rapidity gaps, and compares these with theoretical models and previous experiments.

Findings

Higher order QCD processes are significant in modeling particle distributions.

Distinct differences are observed between rapidity gap and non-gap events.

The transverse momentum squared in gap events aligns with fixed target experiment results.

Abstract

A measurement of inclusive charged particle distributions in deep inelastic $ep$ scattering for $\gamma^* p$ centre-of-mass energies $75< W < 175$~GeV and momentum transfer squared $10< Q^2 < 160$~GeV$^2$ from the ZEUS detector at HERA is presented. The differential charged particle rates in the $\gamma^* p$ centre-of-mass system as a function of the scaled longitudinal momentum, $x_F$, and of the transverse momentum, $p_t^*$ and $<\!\!p_t^{*\,2}\!\!>\,\,$ , as a function of $x_F$, $W$ and $Q^2$ are given. Separate distributions are shown for events with (LRG) and without (NRG) a rapidity gap with respect to the proton direction. The data are compared with results from experiments at lower beam energies, with the naive quark parton model and with parton models including perturbative QCD corrections. The comparison shows the importance of the higher order QCD processes. Significant differences of the inclusive charged particle rates between NRG and LRG events at the same $W$ are observed. The value of $<\!\!p_t^{*\,2}\!\!>\,\,$ for LRG events with a hadronic mass $M_X$, which excludes the forward produced baryonic system, is similar to the $<\!\!p_t^{*\,2}\!\!>\,\,$ value observed in fixed target experiments at $W \approx M_X$.