Abstract
We confront the recent improved measurements of the D(s) (semi-)leptonic decays with Lattice QCD (LQCD) with nf=3 flavours and QCD spectral sum rules (QSSR) predictions. D→μνμ leptonic width data compared with theoretical determinations of fD, leads to the value of the CKM mixing angle: |Vcd|=0.230(10)exp(9)th. Measured ratio of the D semi-leptonic widths combined with LQCD and QSSR predictions leads to the average |Vcd|/|Vcs|=0.2175(88), and then to |Vcs|=1.068(47). We consider the previous determinations as improvements of the existing estimates. Using the average data of the Ds→μνμ (respectively Ds→τντ) branching ratios, one obtains: |Vcs|fDsμ=(259±12) MeV (respectively |Vcs|fDsτ=(274±13) MeV), which can be compared with the average of the Standard Model (SM) values from LQCD and QSSR fDs=(240±7) MeV. If one uses the present determination of |Vcs|, there is an agreement with the SM prediction within 1σ. If instead, we impose the unitarity constraint |Vcs|⩽1, or assume (as frequently done) |Vcs|=|Vud|, we would obtain a deviation from the SM expectations ranging from 1.5 to 3σ, therefore, signaling some New Physics beyond the SM.
Highlights
Good experimental and theoretical controls of the leptonic decay constants fP of charmed D(s) and beautiful B(s)scalar mesons are of prime importance for understanding the dynamics of the heavy light quark systems in QCD.Many efforts have been devoted to this study both theoretically and experimentally 2
GF is the Fermi constant and |Vcq| is the CKM matrix element controlling the weak coupling of the c and q quarks. fDq is the leptonic decay constant normalized like fπ = (130.4 ± 0.2) MeV as: 0|qγ5c|Dq = fDq MD2 q
In order to use this data, we update the value of the ratio of form factors from QSSR [16] by using the recent value ms(2 GeV) = (96.3 ± 17.5) MeV [17] instead of the one ms(2 GeV) = 115.7 MeV used in the original paper
Summary
Good experimental and theoretical controls of the leptonic decay constants fP (analogue to fπ) of charmed D(s) and beautiful B(s) (pseudo)scalar mesons are of prime importance for understanding the dynamics of the heavy light quark systems (overlap of the wavefunctions, heavy quark mass-behaviour,...) in QCD. FDq is the leptonic decay constant normalized like fπ = (130.4 ± 0.2) MeV as:. While the electron mode is tiny due to strong helicity suppression, the measurement of the τ mode involves the detection of additionnal neutrinos, such that, the muon mode is experimentally the cleanest and most accessible one. The extraction of |Vus| from Kl3 is affected by the uncertainties on the value of the K-form factor, while τ -decay data give a slightly different (though consistent) value [4].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
