Elastic rho production at HERA

TL;DR

This paper reports on the measurement of elastic rho meson electroproduction at HERA, analyzing cross sections, mass distributions, and spin density matrix elements across various energies and photon virtualities.

Contribution

It provides new detailed measurements of rho meson production, including cross sections, mass distributions, and polarization states, expanding understanding of vector meson electroproduction.

Findings

Cross section dependence on Q^2, W, and t is characterized.

The rho mass distribution shape is analyzed.

The ratio of longitudinal to transverse cross sections R is determined.

Abstract

Results on elastic electroproduction of rho mesons are presented for a photon virtuality in the range 1 < Q^2 < 60 GeV^2 and for a hadronic centre of mass energy in the range 30 < W < 140 GeV. The shape of the (pi pi) mass distribution is discussed and measurements of the cross section dependences on Q^2, W and t (the four-momentum transfer squared to the proton) are presented. The full set of rho spin density matrix elements is measured, providing information on the rho meson and on the photon polarisation states. In particular, the ratio R of longitudinal to transverse gamma^*p cross section is determined.