Study of Leading Hadrons in Gluon and Quark Fragmentation.pdf

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN–PH-EP/2006-015 10 May 2006 Study of Leading Hadrons in Gluon 6 and Quark Fragmentation 0 0 2 t DELPHI Collaboration c O 1 1 1 v 1 Abstract 3 0 + − 0 The study of quark jets in e e reactions at LEP has demonstrated that the 1 hadronisation process is reproduced well by the Lund string model. However, 6 our understanding of gluon fragmentation is less complete. In this study en- 0 / riched quark and gluon jet samples of different purities are selected in three-jet x e events from hadronic decays of the Z collected by the DELPHI experiment in - the LEP runs during 1994 and 1995. The leading systems of the two kinds of p e jets are defined by requiring a rapidity gap and their sum of charges is studied. h An excess of leading systems with total charge zero is found for gluon jets in : v all cases, when compared to Monte Carlo Simulations with JETSET (with and i X without Bose-Einstein correlations included) and ARIADNE. The correspond- r ing leading systems of quark jets do not exhibit such an excess. The influence of a the gap size and of the gluon purity on the effect is studied and a concentration 2 of the excess of neutral leading systems at low invariant masses ( 2 GeV/c ) is observed, indicating that gluon jets might have an additional hitherto unde- tected fragmentation mode via a two-glu