Measurement of the branching fraction of leptonic decay D s + → τ + ν τ via τ + → π + π 0 ν ¯ τ

Résumé fourni par la source

By analyzing $6.32\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of ${e}^{+}{e}^{\ensuremath{-}}$ annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay ${D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\nu}}_{\ensuremath{\tau}}$, with ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$, to be ${\mathcal{B}}_{{D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\nu}}_{\ensuremath{\tau}}}=(5.29\ifmmode\pm\else\textpm\fi{}{0.25}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.20}_{\mathrm{syst}})%$. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element $|{V}_{cs}|$ and the ${D}_{s}^{+}$ decay constant ${f}_{{D}_{s}^{+}}$ to be ${f}_{{D}_{s}^{+}}|{V}_{cs}|=(244.8\ifmmode\pm\else\textpm\fi{}{5.8}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{4.8}_{\mathrm{syst}})\text{ }\text{ }\mathrm{MeV}$, using the known values of the ${\ensuremath{\tau}}^{+}$ and ${D}_{s}^{+}$ masses as well as the ${D}_{s}^{+}$ lifetime, together with our branching fraction measurement. Combining the value of $|{V}_{cs}|$ obtained from a global fit in the standard model and ${f}_{{D}_{s}^{+}}$ from lattice quantum chromodynamics, we obtain ${f}_{{D}_{s}^{+}}=(251.6\ifmmode\pm\else\textpm\fi{}{5.9}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{4.9}_{\mathrm{syst}})\text{ }\text{ }\mathrm{MeV}$ and $|{V}_{cs}|=0.980\ifmmode\pm\else\textpm\fi{}{0.023}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.019}_{\mathrm{syst}}$. Using the branching fraction of ${\mathcal{B}}_{{D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}}}=(5.35\ifmmode\pm\else\textpm\fi{}0.21)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, we obtain the ratio of the branching fractions ${\mathcal{B}}_{{D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\nu}}_{\ensuremath{\tau}}}/{\mathcal{B}}_{{D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}}}=9.89\ifmmode\pm\else\textpm\fi{}0.71$, which is consistent with the standard model prediction of lepton flavor universality.

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