First Measurement of the Ratio of Branching Fractions BR(LAMBDAB to Lambdac Mu Nu)/BR(LAMBDAB to Lambdac Pi) at CDF II

摘要

We present the first measurement of the ratio of branching fractionsBR(LAMBDAB TO LAMBDAC MU NU)/BR(LAMBDAB to LAMBDAC PI) based on 171.5 pb-1 ofppbar collisions at the center of mass energy 1.96 TeV taken with the CDF-IIdetector. In addition, we present measurements of BR(B0 TO DSTAR MU NU)/BR(B0TO DSTAR PI) and BR(B0 TO D MU NU)/BR(B0 TO D PI), which serve as controlsamples to understand the data and Monte Carlo used for the Lambdab analysis.We find the relative branching fractions of the control samples are consistentwith the ratios obtained by the Particle Data Group at the 0.7 and 1.1 sigmalevel, respectively. Finally, we obtain the relative Lambdab branching fractionto be: BR(LAMBDAB TO LAMBDAC MU NU)/BR(LAMBDAB to LAMBDAC PI)=20.0 +- 3.0(stat) +- 1.2 (syst) + 0.7 -2.1 (BR) +- 0.5 (UBR). The uncertainties of thethree relative branching fractions are from statistics, CDF internalsystematics, external measured branching ratios and unmeasured branchingratios, respectively. We present a method to derive BR(LAMBDAB TO LAMBDAC PI)using previous CDF measurements and obtain BR(LAMBDAB TO LAMBDAC PI) = (0.41 +-0.19 (stat + syst) + 0.06 -0.08 (pt))%, where the last uncertainty is due tothe measured Lambdab pt spectrum. Combining with our result, we determine theexclusive semileptonic branching fraction for the Lambdab= (8.1 +- 1.2 (stat) +1.1 -1.6 (syst) +- 4.3 (BR(LAMBDAB TO LAMDAC PI)))%