Event shapes in e+e− annihilation

We present a complete set of rotationally invariant observables (Hl) which characterizes the ‘shapes’ of final states in e+e− annihilation. They are infrared stable when calculated in QCD perturbation theory. We compare the ‘shapes’ of final states from the processes e+e− → qq, e+e− → qq(G) and from the three-gluon decays of heavy vector mesons. We also consider the production and decay of heavy quarks and leptons. Using a realistic model for the development of hadron jets, we find that for c.m. energies above about 10 GeV, these processes may be clearly distinguished by their distributions in the Hl. We indicate how our analysis may be extended to deep inelastic lepton-hadron interactions and hadron-hadron collisions involving large transverse momenta.

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