Exclusive $\rho^0$ production in deep inelastic electron-proton scattering at HERA

TL;DR

This study measures exclusive $ ho^0$ meson production in deep inelastic scattering at HERA, revealing a strong energy dependence linked to gluon density growth at low $x$, challenging soft pomeron models.

Contribution

It provides detailed cross section measurements for $ ho^0$ production at high $Q^2$ and energies, and compares results with perturbative QCD predictions, highlighting gluon density effects.

Findings

Cross section depends on $Q^2$ as $Q^{-4.2}$

Cross section increases with energy, inconsistent with soft pomeron exchange

Data align with gluon density growth at low $x$

Abstract

The exclusive production of $\rho^0$ mesons in deep inelastic electron-proton scattering has been studied using the ZEUS detector. Cross sections have been measured in the range $7 < Q^2 < 25$ GeV$^2$ for $\gamma^*p$ centre of mass (c.m.) energies from 40 to 130 GeV. The $\gamma^*p \to \rho^0 p$ cross section exhibits a $Q^{-(4.2 \pm 0.8 ^{+1.4}_{-0.5})}$ dependence and both longitudinally and transversely polarised $\rho^0$'s are observed. The $\gamma^*p \to \rho^0 p$ cross section rises strongly with increasing c.m. energy, when compared with NMC data at lower energy, which cannot be explained by production through soft pomeron exchange. The data are compared with perturbative QCD calculations where the rise in the cross section reflects the increase in the gluon density at low $x$. the gluon density at low $x$.