Construction of Angular Observables Sensitive to New Physics in $\bar B\to D^\tau^-\bar \nu_\tau$ Decays and Measurements of Differential Cross Sections of $\bar B\to D^\ell^-\bar\nu_\ell$ Decays with Hadronic Tagging at Belle

Authors	Thomas Kuhr, Kilian Lieret
Non-Belle II authors	Martin Jung, Gerhard Buchalla
Date	Jan. 1, 2018
Belle II Number	BELLE2-MTHESIS-2021-069
Abstract	Recent measurements of $\bar B\to D^{()}\ell^-\bar\nu_\ell$ cross sections at Belle, BaBar, and LHCb challenge lepton universality and thus the Standard Model at a combined confidence level close to four standard deviations. New measurements of differential decay rates could contribute to the understanding of these anomalies. The differential cross section of the decay $\bar{B} \longrightarrow D^{}(\rightarrow D \pi) l^{-} \bar{\nu}_{l}$ is parametrized according to different dependencies on the three decay angles and the coupling constants of potential new physics contributions. Observables using binned measurements of the differential cross section are characterized and explicitly constructed. Based on an estimate for the obtainable sensitivity, optimal binnings for such measurements are discussed. The discriminatory power of the thus constructed observables is discussed based on a basis of dimension six operators with renormalizable couplings contributing to $\bar{B} \longrightarrow D^{} l^{-} \bar{\nu}_{l}$. Furthermore, continuing work on an analysis of the $\bar{B} \longrightarrow D^{}(\rightarrow D \pi) \ell^{-} \bar{\nu}_{\ell}$ decay channel for $\ell=e, \mu$ using data from the Belle detector at KEKB is presented. The events are selected from 772 million $e^{+} e^{-} \rightarrow \Upsilon(4 S) \rightarrow B \bar{B}$ events, where one $B$ meson is fully reconstructed in hadronic modes. Unfolded differential decay rates in four kinematic variables are presented separately for $\ell=e, \ell=\mu$ and a combined fit, allowing for precise calculations of $V_{c b}$ and $B \longrightarrow D^{}$ form factors. The new lepton flavor specific results are also expected to impact the discussion about potential light lepton flavor universality violations prompted by measurements of $B \longrightarrow K^{()} \ell \ell$ decays.
Conference	Munich

Authors

Thomas Kuhr, Kilian Lieret

Non-Belle II authors

Martin Jung, Gerhard Buchalla

Date

Jan. 1, 2018

Belle II Number

BELLE2-MTHESIS-2021-069

Abstract

Recent measurements of $\bar B\to D^{(*)}\ell^-\bar\nu_\ell$ cross sections at Belle, BaBar, and LHCb challenge lepton universality and thus the Standard Model at a combined confidence level close to four standard deviations. New measurements of differential decay rates could contribute to the understanding of these anomalies. The differential cross section of the decay $\bar{B} \longrightarrow D^{*}(\rightarrow D \pi) l^{-} \bar{\nu}_{l}$ is parametrized according to different dependencies on the three decay angles and the coupling constants of potential new physics contributions. Observables using binned measurements of the differential cross section are characterized and explicitly constructed. Based on an estimate for the obtainable sensitivity, optimal binnings for such measurements are discussed. The discriminatory power of the thus constructed observables is discussed based on a basis of dimension six operators with renormalizable couplings contributing to $\bar{B} \longrightarrow D^{*} l^{-} \bar{\nu}_{l}$. Furthermore, continuing work on an analysis of the $\bar{B} \longrightarrow D^{*}(\rightarrow D \pi) \ell^{-} \bar{\nu}_{\ell}$ decay channel for $\ell=e, \mu$ using data from the Belle detector at KEKB is presented. The events are selected from 772 million $e^{+} e^{-} \rightarrow \Upsilon(4 S) \rightarrow B \bar{B}$ events, where one $B$ meson is fully reconstructed in hadronic modes. Unfolded differential decay rates in four kinematic variables are presented separately for $\ell=e, \ell=\mu$ and a combined fit, allowing for precise calculations of $V_{c b}$ and $B \longrightarrow D^{*}$ form factors. The new lepton flavor specific results are also expected to impact the discussion about potential light lepton flavor universality violations prompted by measurements of $B \longrightarrow K^{(*)} \ell \ell$ decays.

Conference

Munich

Construction of Angular Observables Sensitive to New Physics in $\bar B\to D^*\tau^-\bar \nu_\tau$ Decays and Measurements of Differential Cross Sections of $\bar B\to D^*\ell^-\bar\nu_\ell$ Decays with Hadronic Tagging at Belle

Files

Construction of Angular Observables Sensitive to New Physics in $\bar B\to D^\tau^-\bar \nu_\tau$ Decays and Measurements of Differential Cross Sections of $\bar B\to D^\ell^-\bar\nu_\ell$ Decays with Hadronic Tagging at Belle