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Register a new userAn experimentalists guide to the semileptonic bottom to charm branching fractions
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Matthew Rudolph
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This work summarizes the current status of the measured semileptonic branching fractions $B^{0,+} to X_c mu u$. The sum of exclusive measurements is compared with the inclusive determination, accounting for isospin extrapolation. Further derived quantities are computed, taking into account different explanations for the unmeasured components of the total branching fraction. These quantities focus on the charge breakdown of the final states, and are designed for use as inputs or comparisons in future experimental measurements.
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Using the data accumulated in 2002-2004 with the DO detector in proton-antiproton collisions at the Fermilab Tevatron collider with centre-of-mass energy 1.96 TeV, the branching fractions of the decays B -> bar{D}_1^0(2420) mu^+ u_mu X and B -> bar{D}_2^{*0}(2460) mu^+ u_mu X and their ratio have been measured: BR(bar{b}->B) cdot BR(B-> bar{D}_1^0 mu^+ u_mu X) cdot BR(bar{D}_1^0 -> D*- pi+) = (0.087+-0.007(stat)+-0.014(syst))%; BR(bar{b}->B)cdot BR(B->D_2^{*0} mu^+ u_mu X) cdot BR(bar{D}_2^{*0} -> D*- pi^+) = (0.035+-0.007(stat)+-0.008(syst))%; and (BR(B -> bar{D}_2^{*0} mu^+ u_mu X)BR(D2*0->D*- pi+)) / (BR(B -> bar{D}_1^{0} mu^+ u_mu X)cdot BR(bar{D}_1^{0}->D*- pi^+)) = 0.39+-0.09(stat)+-0.12(syst), where the charge conjugated states are always implied.
We update the experimental moments for the charm quark as computed in arXiv:hep-ph/0702103. and used in arXiv:0907.2110 and arXiv:1010.6157 for the determination of the charm-quark mass. The new value for the MSbar charm-quark mass reads mc(3GeV)=0.993+/-0.008 GeV.
We present a new calculation of the $Dtopi$ and $D to K$ form factors from QCD light-cone sum rules. The $overline{MS}$ scheme for the $c$-quark mass is used and the input parameters are updated. The results are $f^+_{Dpi}(0)= 0.67^{+0.10}_{-0.07}$, $f^+_{DK}(0)=0.75^{+0.11}_{-0.08}$ and $f^+_{Dpi}(0)/f^+_{DK}(0)=0.88 pm 0.05$. Combining the calculated form factors with the latest CLEO data, we obtain $|V_{cd}|=0.225pm 0.005 pm 0.003 ^{+0.016}_{-0.012}$ and $|V_{cd}|/|V_{cs}|= 0.236pm 0.006pm 0.003pm 0.013$ where the first and second errors are of experimental origin and the third error is due to the estimated uncertainties of our calculation. We also evaluate the form factors $f^-_{Dpi}$ and $f^-_{DK}$ and predict the slope parameters at $q^2=0$. Furthermore, calculating the form factors from the sum rules at $q^2<0$, we fit them to various parameterizations. After analytic continuation, the shape of the $Dto pi,K $ form factors in the whole semileptonic region is reproduced, in a good agreement with experiment.
We present predictions for a variety of single-inclusive observables that stem from the production of charm and bottom quark pairs at the 7 TeV LHC. They are obtained within the FONLL semi-analytical framework, and with two Monte Carlo + NLO approaches, MC@NLO and POWHEG. Results are given for final states and acceptance cuts that are as close as possible to those used by experimental collaborations and, where feasible, are compared to LHC data.
The measurement of $B_s$-meson branching fractions is a fundamental tool to probe physics beyond the Standard Model. Every measurement of untagged time-integrated $B_s$-meson branching fractions is model-dependent due to the time dependence of the experimental efficiency and the large lifetime difference between the two $B_s$ mass eigenstates. In recent measurements, this effect is bundled in the systematics. We reappraise the potential numerical impact of this effect -- we find it to be close to 10% in real-life examples where new physics is a correction to dominantly Standard-Model dynamics. We therefore suggest that this model dependence be made explicit, i.e. that $B_s$ branching-fraction measurements be presented in a two-dimensional plane with the parameter that encodes the model dependence. We show that ignoring this effect can lead to over-constraining the couplings of new-physics models. In particular, we note that the effect also applies when setting upper limits on non-observed $B_s$ decay modes, such as those forbidden within the Standard Model.
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