We determine the SU(3)-breaking effects in the overlineB/D → Kl overlinev decays from the ratio of the overlineB/D → Kl overlinev over the overlineB/D → πl overlinev semileptonic form factors using a semi-analytic expression based on QCD spectral sum rules. We obtain ƒ +overlineB→K (0)/ƒ +overlineB→π (0) = 1.007 ± 0.020 and ƒ +D→K(0)/ƒ +E→π(0) = 1.102 ±0.007 which combined with the present CLEO data, leads to Vcd/ Vcs = 0.323±0.058 and then, to: | Vcs| = 0.72±0.10. The prediction on the ration of mixing angle is (surprisingly) much higher than the value 0.226±0.004 derived from the unitarity constraint on the CKM matrix, while the corresponding value of Vcs is lower. These results can open a window for new physics, though a stringent conclusion needs data with much higher statistics (from, e.g., tau-charm factory) or/and alternative QCD-based estimates of the ratio of the semileptonic form factors.
Physics Letters B
- Pub Date:
- October 1994
- High Energy Physics - Phenomenology;
- High Energy Physics - Lattice
- 8 pages in latex file + 3 figures in PS-files available on requests. CERN-TH 7309/94 (1994) (to appear as Phys. Lett. B)