Determination of f₊^π(0) and Extraction of |V_cd| from Semileptonic D Decays

2014/10/13 by G. Rong, Y. Fang, H. L. Ma +1
Physics and Astronomy · #hep-ex

paper · pdf · doi:10.1016/j.physletb.2015.02.049

arXiv admin note: substantial text overlap with arXiv:1409.8049

arxiv created 2014/10/13 · arxiv updated 2015/06/23

Abstract

By globally analyzing all existing measured branching fractions for D→ πe⁺ν_e decays, partial decay rates in different four momentum transfer-squared q² bins, as well as products of the decay form factor f₊^π(q²) and the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix element |V_cd|, we obtain f₊^π(0)|V_cd|=0.1428±0.0019. This product, in conjunction with |V_cd| from a global Standard Model fit, implies a value for the D→π semileptonic form factor f₊^π(0)=0.634±0.008±0.002, which is consistent within error with those calculated in theory based on QCD, but with higher precision than the most accurate f₊^π(0)_{\rm LQCD}=0.666±0.020±0.021 calculated in LQCD by a factor of 3.3. Alternately, using this product together with the most accurate form factor calculated in LQCD, we find |V_cd|^{D→ πe+ν_e}=0.2144±0.0029_{\rm exp}± 0.0093_{\rm LQCD}. Combining this |V_cd|^{D→ πe+ν_e} together with |V_cd|^{D+→μ+ν_μ}=0.2160±0.0049±0.0014 extracted from both the BESIII and CLEO-c measurements of D⁺→μ⁺ν_μ decays, we find the most precisely extracted |V_cd| to be |V_cd|=0.2157±0.0045 up to date, which improves the accuracy of the PDG'2014 value |V_cd|_{\rm PDG'2014}=0.225±0.008 by over 70%. Using this |V_cd| together with the PDG'2014 |V_ud| and |V_td|, we check for first column unitarity and find |V_ud|²+|V_cd|²+|V_td|²-1=-0.004±0.002, which deviates from unitarity by 2σ. In addition, we find the ratio of f₊^π(0) and D⁺ decay constant f_D⁺ to be f₊^π(0)/f_D⁺=(3.11±0.08) GeV^-1, which can be used to validate LQCD calculations for these two quantities.

Citations

• Determination of f₊^K(0) f + K ( 0 ) and extraction of |V_cs| | V c s | from semileptonic D D decays