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Reduction of Charm Quark Mass Scheme Dependence



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hep ph 0505068 CERN PH TH 2005 079 SLAC PUB 11177 Reduction of Charm Quark Mass Scheme Dependence in B Xs at the NNLL Level H M Asatriana C Greubb A Hovhannisyana T Hurth1c d and V Poghosyana a b Yerevan Physics Institute 375036 Yerevan Armenia Institute for Theoretical Physics University Berne CH 3012 Berne Switzerland c Theoretical Physics Division CERN CH 1211 Geneva 23 Switzerland d SLAC Stanford University Stanford CA 94309 USA Abstract The uncertainty of the theoretical prediction of the B Xs branching ratio at NLL level is dominated by the charm mass renormalization scheme ambiguity In this paper we calculate those NNLL terms which are related to the renormalization of mc in order to get an estimate of the corresponding uncertainty at the NNLL level We find that these terms significantly reduce by typically a factor of two the error on BR B Xs induced by the definition of mc Taking into account the experimental accuracy of around 10 and the future prospects of the B factories we conclude that a NNLL calculation would increase the sensitivity of the observable B Xs to possible new degrees of freedom beyond the SM significantly 1 Heisenberg Fellow Work supported in part by Department of Energy contract DE AC02 76SF00515 1 Introduction The branching ratio of B Xs is a very sensitive probe for new degrees of freedom beyond the standard model SM for a review see 1 Within supersymmetric extensions of the SM for example one can derive stringent bounds on the parameter space of these models 2 8 Clearly such bounds will be most valuable when the general nature of the new physics beyond the SM will be identified at the forthcoming LHC experiments Because of the heavy mass expansion that is valid for inclusive decay modes the decay rate of B Xs is dominated by the perturbatively calculable partonic decay rate b Xs QCD corrections to the latter due to hard gluon exchange are the most important perturbative contributions they were calculated in the past up to the next



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