Limit on a right-handed admixture to the weakb→ccurrent from semileptonic decays

Abstract

We determine an upper bound for a possible right-handed $b\ensuremath{\rightarrow}c$ quark current admixture in semileptonic $\overline{B}\ensuremath{\rightarrow}{X}_{c}{\ensuremath{\ell}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$ decays from a simultaneous fit to moments of the lepton-energy and hadronic-mass distribution measured as a function of the lower limit on the lepton energy, using data measured by the BABAR detector. The right-handed admixture is parametrized by a new parameter ${c}_{R}$ as coefficient of computed moments with right-handed quark current. For the standard-model part we use the prediction of the heavy-quark expansion up to order $1/{m}_{b}^{3}$ and perturbative corrections and for the right-handed contribution only up to order $1/{m}_{b}^{2}$ and perturbative corrections. We find ${c}_{R}^{\ensuremath{'}}={0.05}_{\ensuremath{-}0.50}^{+0.33}$ in agreement with the standard-model prediction of zero. Additionally, we give a constraint on a possible right-handed admixture from exclusive decays, which is with a value of ${c}_{R}^{\ensuremath{'}}=0.01\ifmmode\pm\else\textpm\fi{}0.03$ more restrictive than our value from the inclusive fit. The difference in $|{V}_{cb}|$ between the inclusive and exclusive extraction is only slightly reduced when allowing for a right-handed admixture in the range of ${c}_{R}^{\ensuremath{'}}=0.01\ifmmode\pm\else\textpm\fi{}0.03$.