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Hi all, since I would like to calculate precisely the ratio eps_t^u/eps_t^sl I used the cocktail and the generic MC with different levels of purities. This ratio can be calculated easily doing eps_t^u/eps_t^sl = N(Vub) / N(Vcb+Vub) * ratioBR_generated^-1 Assuming : ratioBR_B0(SP3) = 0.00888 ratioBR_B+(SP3) = 0.00978 ratioBR_B0(SP4) = 0.01287 ratioBR_B+(SP4) = 0.01281 (this is from the DECAY.DEC) I got Cocktail -------- (eps_t^u/eps_t^sl)_B0_SP3 = 0.92 +- 0.06 (eps_t^u/eps_t^sl)_B+_SP3 = 0.87 +- 0.05 (eps_t^u/eps_t^sl)_B0_SP4_run1 = 0.91 +- 0.08 (eps_t^u/eps_t^sl)_B+_SP4_run1 = 0.88 +- 0.07 (eps_t^u/eps_t^sl)_B0_SP4_run2 = 1.00 +- 0.09 (eps_t^u/eps_t^sl)_B+_SP4_run2 = 0.90 +- 0.09 As you see most of the results are below 1. The problem here is that I am not perfectly sure of the generated ratioBR since BR(b->ulnu) changed a lot in the releases 8.6, 8.8. ,10.- and part of the MC was produced with different releases even on SP3 or SP4. The fact that this ratio is not different from 1 (I can't understand why breco should be less efficient for b->ulnu events...) seems to be confirmed by the generic MC SP4 on run2 (eps_t^u/eps_t^sl)_B0_SP4_run2 = 1.00 +- 0.10 (eps_t^u/eps_t^sl)_B+_SP4_run2 = 0.96 +- 0.09 since this is probably the most coherent MC (generated with the same DECAY.DEC) Probably we need a different approach to calculate the value of this ratio on large statistics. MC truth from root files can't be used since it is biased by the Semiexcl selection. Any suggetion? Daniele