2026/07/27 by BESIII Collaboration, M. Ablikim, M. N. Achasov +773
#hep-ex
The branching fractions of D0→ π-e+νe, D0→ π-μ+νμ, D+→ π0e+νe, and D+→ π0μ+νμ are precisely measured, using 20.3 fb-1 of e+e- collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The ratios of the decay widths between muon and positron channels are examined in full, across several four-momentum transfer ranges of ℓ+νℓ. No lepton flavor universality violation is found in the current data. From a simultaneous fit to the precisely measured partial decay rates and the first measured forward-backward asymmetries of these four decays, the product of the hadronic transition form factor, fD→π+(0), and the modulus of the c→ d quark mixing element, |Vcd|, is measured with unprecedented precision to be fD→π+(0)|Vcd|=0.1425±0.0005\rm stat.±0.0003\rm syst.. Taking the value of |Vcd| from the standard model global fit and fD→π+(0) derived by the lattice quantum chromodynamics calculation as input, we obtain fD→π+(0)=0.1425±0.0005\rm stat.±0.0003\rm syst. and |Vcd|=0.2262±0.0008\rm stat.±0.0005\rm syst.±0.0018\rm LQCD., respectively. The precision of each result is a factor of 2-3 better than the previous best measurements. Additionally, the real and imaginary parts of the scalar current contribution in the c→ d ℓ+νℓ transition are measured for the first time to be Re (CSμ)= 0.022 ± 0.023\rm stat.± 0.003\rm syst. and |Im (CSμ)|=0.000 ± 0.038\rm stat.± 0.012\rm syst..