The Subjet Multiplicity in Quark and Gluon Jets

Abstract

We calculate the mean number of subjets in quark and gluon jets in the final state of e^+e^- annihilation. Since `quark' and `gluon' jets are scheme-dependent objects, we stress the importance of using the same definition as in experimental analyses. We define the jets using the k_perp algorithm at a coarse scale y_1, and the subjets using a finer scale y_0, in the same algorithm. Gluon jets are anti-tagged by the presence of heavy quarks in both other jets. Our result is exact to leading order in alpha_s, and resums leading and next-to-leading logarithmic terms in the ratio y_1/y_0 to all orders in alpha_s.

arXiv comment11 pages, 6 figures included using the latex2e graphics package. A postscript version of this paper can be obtained from http://surya11.cern.ch/users/seymour/pubs/subjet.ps.Z

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