Exploring the role of new physics in $b\to u\tau \bar{\nu }$ decays

Abstract

The recent measurements on $R_D$, $R_{D^{\ast }}$ and $R_{J/\psi }$ by three pioneering experiments, BaBar, Belle and LHCb, indicate that the notion of lepton flavour universality is violated in the weak charged-current processes, mediated through $b\to c\ell {\bar{\nu }}_{\ell }$ transitions. These intriguing results, which delineate a tension with their standard model predictions at the level of $(2-3)\sigma$ have triggered many new physics propositions in recent times, and are generally attributed to the possible implication of new physics in $b\to c\tau \bar{\nu }$ transition. This, in turn, opens up another avenue, i.e., $b\to u\tau \bar{\nu }$ processes, to look for new physics. Since these processes are doubly Cabibbo suppressed, the impact of new physics could be significant enough, leading to sizeable effects in some of the observables. In this work, we investigate in detail the role of new physics in $B\to (\pi ,\rho ,\omega )\tau \bar{\nu }$ and $B_s\to (K,K^{\ast })\tau \bar{\nu }$ processes considering a model independent approach. In particular, we focus on the standard observables like branching fraction, lepton flavour non-universality (LNU) parameter, forward-backward asymmetry and polarization asymmetries. We find significant deviations in some of these observables, which can be explored by the currently running experiments LHCb and Belle-II. We also briefly comment on the impact of scalar leptoquark $R_2(3,2,7/6)$ and vector leptoquark $U_1(3,1,2/3)$ on these decay modes.

arXiv comment23 pages, 7 figures, published version

References in corpus (31)

• Test of lepton universality using $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ decays
• Test of lepton universality with $B^0\to K^{\ast 0}{\ell }^{+}{\ell }^{-}$ decays
• 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 $\mathcal{B}({\overline{B}}^0\to D^{\ast +}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}({\overline{B}}^0\to D^{\ast +}{\mu }^{-}{\overline{\nu }}_{\mu })$
• $B\to V{\ell }^{+}{\ell }^{-}$ in the Standard Model from Light-Cone Sum Rules
• Measurement of the $\tau$ lepton polarization and $R(D^{\ast })$ in the decay $\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau }$
• Averages of $b$-hadron, $c$-hadron, and $\tau$-lepton properties as of 2018
• Search for lepton-universality violation in $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ decays
• Differential branching fractions and isospin asymmetries of $B\to K^{(\ast )}{\mu }^{+}{\mu }^{-}$ decays
• Model-independent description of $B\to \pi l\nu$ decays and a determination of $|V_{ub}|$
• Testing leptoquark models in $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$
• 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
• Angular analysis and differential branching fraction of the decay $B_s^0\to \varphi {\mu }^{+}{\mu }^{-}$
• Measurement of the ratio of branching fractions $\mathcal{B}(B_c^{+}\to J/\psi {\tau }^{+}{\nu }_{\tau })$/$\mathcal{B}(B_c^{+}\to J/\psi {\mu }^{+}{\nu }_{\mu })$
• Renormalization-group evolution of new physics contributions to (semi)leptonic meson decays
• Test of lepton-flavor universality in $B\to K^{\ast }{\ell }^{+}{\ell }^{-}$ decays at Belle
• Global fit to $b\to c\tau \nu$ transitions
• Test of lepton flavor universality and search for lepton flavor violation in $B\to K\ell \ell$ decays
• Impact of polarization observables and $B_c\to \tau \nu$ on new physics explanations of the $b\to c\tau \nu$ anomaly
• Explaining the $R_K$ and $R_{D^{(\ast )}}$ anomalies with vector leptoquarks
• $D^{\ast }$ polarization vs. $R_{D^{(\ast )}}$ anomalies in the leptoquark models
• $B\to \pi \ell \ell$ form factors for new-physics searches from lattice QCD
• $B_s\to K\ell \nu$ decay from lattice QCD
• Right-handed Neutrinos and $R(D^{(\ast )})$
• Solutions to $R_D$-$R_{D^{\ast }}$ in light of Belle 2019 data
• Inclusive semileptonic ${\Lambda }_b$ decays in the Standard Model and beyond
• Probing New Physics with $\bar{B}\to \rho (770){\ell }^{-}{\bar{\nu }}_{\ell }$ and $\bar{B}\to a_1(1260){\ell }^{-}{\bar{\nu }}_{\ell }$
• Model independent analysis of $B^{\ast }\to P\ell {\bar{\nu }}_{\ell }$ decay processes
• Impact of vector new physics couplings on $B_s\to (K,K^{\ast })\tau \nu$ and $B\to \pi \tau \nu$ decays
• Investigating the effect of $U_1$ vector leptoquark on $b\to u\tau \bar{\nu }$ mediated $B$ decays
• Model independent investigation of rare semileptonic b \to u l \barν_l decay processes

Cited by in corpus (1)

• Prospects for $B_c^{+}$ and $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ at FCC-ee