Three-jet event

Abstract: The study of the dierences of the fragmentation of quarks and gluons to jets of hadrons gives insight into the fundamental structure of QCD. Results from dierent approaches to properties of quarks and gluons are shown. The colour factor ratio CA=CF is measured in agreement with the QCD prediction. Identied particles in quark and gluon jets are investigated, revealing no overproduction of isoscalar 0 and (1020) in gluon jets, but an excess of protons. processes described by these vertices: The radiation of a gluon by a quark (q ! qg) or by another gluon (g ! gg) and the splitting of a gluon into a quark-antiquark pair (g ! q q). The probability of these processes is given by the splitting kernels which take the kinematics into account and are propor- tional to the colour factors CF , CA and TF respectively. The colour factors are the structure constants of the SU(3) colour symmetry group of QCD, vividly speaking, they take care of the bookkeeping of undetermined colour flows in these processes. As the main contribution to particle production in hadronic events is due to the radiation of gluons, it is to be expected that the dierences of the properties of jets initiated by quarks to those of jets initiated by gluons are in terms of the ratio CA=CF . The assumption of local parton-hadron duality (LPHD) gives rise to the hope that these perturbatively calculated dierences can be observed in the hadronic nal state. 2 Experimental access To get information about gluons, events with three jets are used, as they contain exactly one gluon jet. The jets of a hadronic three jet event are numbered according to their energy with jet 1 being the most energetic one while angles between jets are numbered according to the jet opposite of the angle. There are three dierent ways of getting information about quarks and gluons out of hadronic three jet events presented here. In the jet analysis 2;5

Abstract: We discuss the orientation of e+e- -> q qbar g events in terms of the polar and azimuthal angles of the event plane w.r.t. the electron beam direction. We define an asymmetry of the azimuthal-angle distribution, which, along with the left-right forward-backward polar-angle asymmetry, is sensitive to parity-violating effects in three-jet events; these have yet to be explored experimentally. We have evaluated these observables at O(alpha_s) in perturbative QCD and present their dependence on longitudinal beam polarisation and c.m. energy. We also define a moments analysis in terms of the orientation angles that allows a new and more detailed test of QCD by isolating the six independent helicity cross-sections.

Abstract: The properties of three-jet events in data of integrated luminosity 86±4 pb-1 from CDF Run 1b with a trigger on total ∑ ET > 175 GeV have been analyzed and compared to predictions from a next-to-leading order perturbative QCD calculation. Special emphasis has been placed on analysis of the Dalitz variables.