Charged particles and neutral kaons in photoproduced jets at HERA

TL;DR

This study analyzes charged particles and neutral kaons in photoproduced jets at HERA, comparing experimental data with PYTHIA simulations to understand particle distributions and fragmentation functions.

Contribution

It provides detailed measurements of particle distributions and fragmentation functions in photoproduced jets, and evaluates PYTHIA's modeling accuracy with specific parameter adjustments.

Findings

PYTHIA describes charged particles within jets well with standard settings.

Using multiparton interactions improves description outside jets.

Fragmentation functions agree with previous models and processes at high momenta.

Abstract

Charged particles ($h^\pm$) and \kz mesons have been studied in photoproduced events containing at least one jet of $E_T > 8$ GeV in a pseudorapidity interval (--0.5, 0.5) in the ZEUS laboratory frame. Distributions are presented in terms of transverse momentum, pseudorapidity and distance of the particle from the axis of a jet. The properties of \hpm within the jet are described well using the standard settings of PYTHIA, but the use of the multiparton interaction option improves the description outside the jets. A reasonable overall description of the \kz behaviour is possible with PYTHIA using a reduced value of the strangeness suppression parameter. The numbers of $h^\pm$ and \kz within a jet as defined above are measured to be $3.25\pm0.02\pm0.28$ and $0.431\pm0.013\pm0.088$ respectively. Fragmentation functions are presented for $h^\pm$ and \kz in photoproduced jets; agreement is found with calculations of Binnewies et al. and, at higher momenta, with $p\bar p$ scattering and with standard PYTHIA. Fragmentation functions in direct photoproduced events are extracted, and at higher momenta give good agreement with data from related processes in $e^+e^-$ annihilation and deep inelastic $ep$ scattering.