A Study of the Fragmentation of Quarks in $e^-p$ Collisions at HERA

TL;DR

This paper analyzes quark fragmentation in electron-proton collisions at HERA, comparing it with electron-positron data to understand similarities in quark behavior and the role of coherence effects in parton showers.

Contribution

It provides the first detailed comparison of quark fragmentation functions between ep and ee collisions, highlighting the universality and kinematic evolution of quark fragmentation.

Findings

Quark fragmentation functions in ep are similar to those in ee.

The evolution variable is the invariant four-momentum transfer squared.

Evidence for coherence effects in parton showers is discussed.

Abstract

Deep inelastic scattering (DIS) events, selected from 1993 data taken by the H1 experiment at HERA, are studied in the Breit frame of reference. The fragmentation function of the quark is compared with those of \ee data. It is shown that certain aspects of the quarks emerging from within the proton in \ep interactions are essentially the same as those of quarks pair-created from the vacuum in \ee annihilation. The measured area, peak position and widthof the fragmentation function show that the kinematic evolution variable, equivalent to the \ee squared centre of mass energy, is in the Breit frame the invariant square of the four-momentum transfer. We comment on the extent to which we have evidence for coherence effects in parton showers.