Inclusive transverse momentum distributions of charged particles in diffractive and non--diffractive photoproduction at HERA

TL;DR

This paper measures inclusive transverse momentum distributions of charged particles in diffractive and non-diffractive photoproduction at HERA, revealing exponential behavior at low pT and a high pT tail, and compares results with theoretical models.

Contribution

It provides detailed measurements of pT spectra in diffractive and non-diffractive photoproduction, including photon dissociation, and compares these with QCD calculations and lower energy data.

Findings

Low pT spectra fall exponentially.

Non-diffractive spectra show a high pT tail.

Data agree with next-to-leading order QCD predictions.

Abstract

Inclusive transverse momentum spectra of charged particles in photoproduction events in the laboratory pseudorapidity range $-1.2<\eta<1.4$ have been measured up to $p_{T}=8\GeV $ using the ZEUS detector. Diffractive and non--diffractive reactions have been selected with an average $\gamma p$ centre of mass (c.m.) energy of $\langle W \rangle = 180\GeV$. For diffractive reactions, the $p_{T}$ spectra of the photon dissociation events have been measured in two intervals of the dissociated photon mass with mean values $\langle M_{X} \rangle = 5$ GeV and $10$ GeV. The inclusive transverse momentum spectra fall exponentially in the low $p_{T}$ region. The non--diffractive data show a pronounced high $p_{T}$ tail departing from the exponential shape. The $p_{T}$ distributions are compared to lower energy photoproduction data and to hadron--hadron collisions at a similar c.m. energy. The data are also compared to the results of a next--to--leading order QCD calculation.