Charm counting and B semileptonic branching fraction.pdf

a r X i v : h e p - p h / 9 9 1 2 3 0 8 v 1 1 0 D e c 1 9 9 9 Heavy Flavours 8, Southampton, UK, 1999 HEAVY FLAVOURS8 PROCEEDINGS Charm counting and B semileptonic branching fraction Hitoshi Yamamoto University of Hawaii , 2505 Correa Rd., Honolulu HI 96822 USA E-mail: hitoshi@phys.hawaii.edu Abstract: We review recent measurements as well as phenomenological background ofthe semilep- tonic branching fraction of b hadrons and number of charm produced per decay of b hadrons. 1. Introduction The puzzle of inclusive non-leptonic B decay was first pointed out in around 1994 [1, 2] when the theoretical prediction was considered to be diffi- cult to accommodate 12% or less for the semilep- tonic branching ratio Bs.l. of B meson while the measurement published by the CLEO collabora- tion was [3] Bs.l. = 10.49± 0.46% (Υ(4S)). (1.1) The discrepancy was particularly stark when viewed in the two-dimensional plane of nc vs Bs.l., where nc is the average number of charm or anticharm created per B decay [1, 2, 5]. The experimental value of nc was [4] nc = 1.10± 0.05 . (1.2) while the naive expectation was around 1.16. This was because when the uncertainties of the the- ory, in particular the charm quark mass, were tweaked to reduce Bs.l., it increased the inclu- sive non-leptonic decay rates which resulted in too large a value for nc compared to measure- ment. We have now new measurements related to this subjects which we will review below to- gether with phenomenological background. 2. Definitions By Bs.l., we mean the average branching frac- tion for direct electron production. The aver- age is taken over the hadrons containing b quark produced in a given environment. It is usually assumed that the electronic branching fraction is the same as the muonic branching fraction. In reality Bs.l. is average over weakly-decaying hadrons containing one b quark. In the case of experiments running on the Υ(4S) resonance, the average is over B+ and B0 and their charge con- jugate hadr