| V cb | from the semileptonic decay B → D ? ν ˉ ? and the properties of the D-meson distribution amplitude

摘要

The improved QCD light-cone sum rule (LCSR) provides an effective way to deal with the heavy-to-light transition form factors (TFFs). Firstly, we adopt the improved LCSR approach to deal with the B → D TFF f + ( q 2 ) up to twist-4 accuracy. Due to the elimination of the most uncertain twist-3 contribution and the large suppression of the twist-4 contribution, the obtained LCSR shall provide us a good platform for testing the D -meson leading-twist DA. For the purpose, we suggest a new model for the D -meson leading-twist DA ( ? 3 D ), whose longitudinal behavior is dominantly determined by a parameter B . Moreover, we find its second Gegenbauer moment a 2 D ～ B . Varying B within certain region, one can conveniently mimic the D -meson DA behavior suggested in the literature. Inversely, by comparing the estimations with the experimental data on the D -meson involved processes, one can get a possible range for the parameter B and a determined behavior for the D -meson DA. Secondly, we discuss the B → D TFF at the maximum recoil region and present a detailed comparison of it with the pQCD estimation and the experimental measurements. Thirdly, by applying the LCSR on f + ( q 2 ) , we study the CKM matrix element | V cb | together with its uncertainties by adopting two types of processes, i.e. the B 0 / B ˉ 0 -type and the B ± -type. It is noted that a smaller B ? 0.20 shows a better agreement with the experimental value on | V cb | . For example, for the case of B = 0.00 , we obtain | V c b | ( B 0 / B ˉ 0 ? type ) = ( 41.28 ? 4.82 + 5.68 ? 1.16 + 1.13 ) × 10 ? 3 and | V c b | ( B ± ? type ) = ( 40.44 ? 4.72 + 5.56 ? ? 1.00 + 0.98 ) × 10 ? 3 , whose first (second) uncertainty comes from the squared average of the mentioned theoretical (experimental) uncertainties.