Tau properties in $B\to D\tau \nu$ from visible final-state kinematics

Abstract

In semi-leptonic $B$ decays with a tau lepton, features of the production process are imprinted on the tau helicity states. Since the tau momentum cannot be fully reconstructed experimentally, the available information on the tau properties is encoded in its visible decay products. Focusing on the process $B\to D\tau \nu$, we find explicit relations between the tau properties and the kinematics of the charged particles in the decays $\tau \to \pi \nu$, $\tau \to \rho \nu$, and $\tau \to \ell \nu \bar{\nu }$. In particular, we show that the perpendicular polarization, $P_{\perp }$, and the forward-backward asymmetry, $A_{\tau }$, of the tau lepton can simultaneously be extracted from an angular asymmetry of the charged particle against the $D$ meson. For the most sensitive decay channel, $\tau \to \pi \nu$, we expect a relative statistical precision of about $10\%$ for $P_{\perp }$ and $A_{\tau }$ in a measurement based on $50$ab${}^{-1}$ of data at BELLE II.

11 pages, 4 figures, 1 table

References in corpus (7)

• 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
• The lifetime of the $B_c^{-}$ meson and the anomalies in $B\to D^{(\ast )}\tau \nu$
• New physics in the weak interaction of $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$
• Charged-Higgs effects in a new B -> D tau nu differential decay distribution
• New Physics in the Visible Final States of $B\to D^{(\ast )}\tau \nu$
• Probing new physics in ${\bar{B}}^0\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau }$ using the longitudinal, transverse, and normal polarization components of the tau lepton
• CP violation in $B\to D\tau {\nu }_{\tau }$ using multi-pion tau decays

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