Study of Particle Production in Quark vs. Gluon Fragmentation at sqrt s ~ 10GeV

TL;DR

This study compares particle production in gluon versus quark fragmentation at around 10 GeV, revealing differences in baryon yields and challenging existing fragmentation models.

Contribution

It provides new measurements of particle enhancement ratios in gluon and quark fragmentation, especially for baryons, and tests predictions of the JETSET model.

Findings

Proton enhancement ratio is approximately 1.0 in gluon vs. quark fragmentation.

Lambda baryons show an enhancement of about 1.5 in gluon fragmentation.

Baryon production in two-gluon decays is smaller than in three-gluon decays of Upsilon(1S).

Abstract

Using data collected with the CLEO III detector at the Cornell Electron Storage Ring, we have compared proton, lambda (charged conjugate modes are implicit) and meson (phi and f2(1270)) production observed in gluon fragmentation vs. quark fragmentation. Two studies have been conducted: in the first, we corroborrate previous per-event particle yields in Upsilon(1S)->ggg vs. e+e- -> qqbar. In the second, we compare particle production in the photon-tagged process U(1S)->gggamma with that in e+e- -> qqbargamma events. For each particle, we determine the `enhancement' ratio, defined as the ratio of particle yields per gluon fragmentation event compared to quark fragmentation event. Thus defined, an enhancement of 1.0 implies equal per-event production in both gluon and quark fragmentation. In the photon-tagged analysis, we find an enhancement of order unity for protons and approximately 1.5 for lambda's. This measured proton enhancement rate is supported by a study of baryon production in chib(J=2)->proton+X relative to chib(J=1)->proton+X. The production of mesons having masses of order 1 GeV (phi and f2(1270)) are found to be also approximately the same in gggamma vs. qqbargamma fragmentation. Overall, per-event baryon production in two-gluon fragmentation is considerably smaller than that observed in three-gluon decays of the Upsilon(1S). Our results for baryon production are inconsistent with the predictions of the JETSET (7.4) fragmentation model.