Tests of Lepton Flavour Universality with Semileptonic Decays at LHCb

Abstract

The observable $\mathcal{R}\left(D^{(\ast )}\right)=\mathcal{B}\left(B^0\to D^{(\ast )-}{\tau }^{+}{\nu }_{\tau }\right)/\mathcal{B}\left(B^0\to D^{(\ast )-}{\mu }^{+}{\nu }_{\mu }\right)$ is a probe for Lepton Universality violation, so it is sensitive to New Physics processes. The current combination of the measurements of $\mathcal{R}\left(D^{(\ast )}\right)$ differs from Standard Model predictions with a $4\sigma$ significance. A measurement of $\mathcal{R}(D^{\ast })$ using three-prong $\tau$ decays has been performed at LHCb, resulting in $\mathcal{R}(D^{\ast })=0.285\pm 0.019(\text{stat})\pm 0.025(\text{syst})\pm 0.014(\text{ext})$. This value, combined with the LHCb result obtained with $\tau \to \mu {\nu }_{\tau }{\bar{\nu }}_{\mu }$ decays, gives $\mathcal{R}(D^{\ast })=0.306\pm 0.016(\text{stat})\pm 0.022(\text{syst})$, consistent with the world average and 2.1 standard deviations above the SM prediction.

References in corpus (6)

• Measurement of the branching ratio of $\bar{B}\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$ relative to $\bar{B}\to D^{(\ast )}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with hadronic tagging at Belle
• Measurement of the ratio of branching fractions $\mathcal{B}({\overline{B}}^0\to D^{\ast +}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}({\overline{B}}^0\to D^{\ast +}{\mu }^{-}{\overline{\nu }}_{\mu })$
• Measurement of the $\tau$ lepton polarization and $R(D^{\ast })$ in the decay $\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau }$
• On the B to D* tau nu Sensitivity to New Physics
• Measurement of the branching ratio of ${\bar{B}}^0\to D^{\ast +}{\tau }^{-}{\bar{\nu }}_{\tau }$ relative to ${\bar{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with a semileptonic tagging method
• Measurement of the ratio of the $B^0\to D^{\ast -}{\tau }^{+}{\nu }_{\tau }$ and $B^0\to D^{\ast -}{\mu }^{+}{\nu }_{\mu }$ branching fractions using three-prong $\tau$-lepton decays