The collimation C of a hadronic event in the e^+e^- annihilation is defined as the average of cosθ, C=<cosθ>, where θ is the angle of each hadron measured from the thrust axis, and the average is over all the hadrons produced in an event. It is an infrared-stable event-shape parameter. 1−Cˉ, the difference between the unity and the average collimation at a given energy, is proportional to the anomalous dimension of the hadron multiplicity at the leading order in MLLA. Its next-to-leading order corrections are calculated.
Cite
@article{arxiv.hep-ph/9705238,
title = {Collimation of the e^+e^- annihilation event},
author = {K. Kimura and K. Tesima},
journal= {arXiv preprint arXiv:hep-ph/9705238},
year = {2016}
}