Lifetime of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msubsup><mml:mi>B</mml:mi><mml:mi>c</mml:mi><mml:mo>−</mml:mo></mml:msubsup></mml:math> Mesons Constrains Explanations for Anomalies in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mi>D</mml:mi><mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mo>*</mml:mo><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:msup><mml:mi>τ</mml:mi><mml:mi>ν</mml:mi></mml:math> 论文

摘要

We investigate a new constraint on new-physics interpretations of the anomalies observed in $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\ensuremath{\nu}$ decays making use of the lifetime of the ${B}_{c}^{\ensuremath{-}}$ meson. A constraint is obtained by demanding that the rate for ${B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$ does not exceed the fraction of the total width that is allowed by the calculation of the lifetime in the standard model. This leads to a very strong bound on new-physics scenarios involving scalar operators since they lift the slight, but not negligible, chiral suppression of the ${B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$ amplitude in the standard model. The new constraint renders a scalar interpretation of the enhancement measured in ${R}_{{D}^{*}}$ implausible, including explanations implementing extra Higgs doublets or certain classes of leptoquarks. We also discuss the complementarity of ${R}_{{D}^{(*)}}$ and a measurement of the longitudinal polarization of the $\ensuremath{\tau}$ in the $B\ensuremath{\rightarrow}{D}^{*}\ensuremath{\tau}\ensuremath{\nu}$ decay in light of our findings.