|V_{cd}|, |V_{cs}| and f_{D_s} from (semi) leptonic $D_{(s)}$-decays : signals of New Physics ?
Abstract
Description
We confront the recent improved measurements of the D_{(s)} (semi) leptonic decays with lattice QCD (LQCD) with n_f=3 flavours and QCD spectral sum rules (QSSR) predictions. D\toμν_μleptonic width data compared with theoretical determinations of f_D, leads to the value of the CKM mixing angle : |V_cd|= 0.230 (10)_exp (9)_th. Measured ratio of the D semi-leptonic widths combined with LQCD and QSSR predictions leads to the average |V_cd|/|V_cs|= 0.2175(88), and then to |V_cs|= 1.068(47). We consider the previous determinations as improvements of the existing estimates. Using the average data of the D_s\to μν_μ(resp. D_s\to τν_τ) branching ratios, one obtains : |V_cs|f_{D_s}^μ= (259 +- 12) {MeV} (resp) |V_cs|f_{D_s}^τ= (274 +- 13) {MeV}, which can be compared with the average of the Standard Model (SM) values from LQCD and QSSR f_{D_s}=(240 +- 7) MeV. If one uses the present determination of |V_cs|, there is an agreement with the SM prediction within 1σ. If instead, we impose the unitarity constraint |V_cs|< 1, or assume (as frequently done) |V_cs|=|V_ud|, we would obtain a deviation from the SM expectations ranging from 1.5 to 3 σ, eventually signaling some New Physics beyond the SM.
5 pages, 5 tables, no figure, slight changes, version to appear in PLB
5 pages, 5 tables, no figure, slight changes, version to appear in PLB