First Measurement of the Inclusive Charmless B Decay Branching Ratio and Determination of the B ! C Cs Rate Delphi Collaboration Delphi Collaboration Measurement of the Inclusive Charmless and Double Charm B Decay Branching Ratios with the B-tagging Probability Technique

A measurement of the inclusive B decay branching ratios into charmless and double charmed nal states has been performed, using the data collected by the DELPHI experiment at LEP from 1992 to 1995, by mean of two diierent techniques that are presented in two diierent notes. In the rst analysis, the results are extracted from a t to the b-tagging probability distribution based on the precise impact parameter measured by the Micro Vertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm as c c states, is measured to be 0.044 0.025, the B branching ratio into two charmed particles is 0.163 0.046 and the number of charmed particles per B decay is 1.163 0.045. A second method is based on identiied kaons in the RICH. Using partially reconstructed charm particles in combination with a kaon, the B decay branching ratio into two charmed particles BR(B ! D DX) has been determined to be 0.170 0.047. In addition an upper limit is obtained for the yield of the b ! sg process by a t to the transverse momentum distribution of identiied secondary kaons. The combination of these results, discussed at the end of the paper, gives an accurate determination of the B ! D DX decay rate and constrains models predicting enhanced contribution to the charmless B decay branching ratio from new physics. Abstract A measurement of the inclusive charmless B decay branching ratio, the B branching ratio into two charmed particles, and the total number of charmed particles in B decays has been performed by the DELPHI experiment at LEP, using the hadronic Z data taken between 1992 and 1994. The results are extracted from a t to the b-tagging probability distribution based on the precise impact parameter measurements by the microvertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm (c c), is measured to be 0:044 0:025. The B branching ratio into two open charmed particles is 0:1630:046. The mean number of charmed particles per B decay (including hidden charm) is 1:163 0:045. The charmless B branching ratio is compatible with the Standard Model expectation. Models that predict an additional contribution to the charmless B branching ratio of 0.045 or higher are excluded at 95% CL.