Exploring new physics in the angular distribution of B̅→ D*(→ Dπ)τ-(→ V-ντ)ν̅τ
Abstract
The decays B̅→ D*τ−ν̅τ provide sensitive probes of new physics in the b→ cτν transition. We discuss the effects of new physics in the decay chain B̅→ D*(→ Dπ)τ−(→ V-ντ)ν̅τ where V is a vector meson. We first present a comprehensive analysis of the five-dimensional angular distribution for the full decay chain B̅→ D*(→ Dπ)τ−(→ ρ-ντ)ν̅τ, exploiting the hadronic τ decay to ρ-ντ to circumvent the experimental challenge of direct τ reconstruction. The differential decay rate is expressed in terms of measurable kinematic variables θ*, Eρ, θρ, χρ, and q2 -- with complete coefficient functions provided for scalar, pseudoscalar, vector, axialvector, and tensor new-physics interactions. From this distribution we construct a set of integrated observables, including the D* polarization fractions and lepton-side forward-backward and azimuthal asymmetries, which isolate distinct combinations of helicity amplitudes. We also show that by decomposing the vector-meson energy spectrum into its longitudinal (L) and transverse (T) helicity sectors, two additional analyzing powers (αL and αT) related to the measurement of τ polarization PτD*(q2) are obtained. Without information on the polarization of meson V, the spin analyzing power of ρ is much larger than that of a1 with αρ=0.45 and αa1=0.02. We further perform a numerical analysis using current experimental data on RD* and the D* longitudinal polarization fraction ⟨ FLD*⟩ to constrain the complex new-physics couplings gL, gR, gP, and gT, revealing the correlations among them.
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BibTeX
@misc{liu2026exploring,
title = {{Exploring new physics in the angular distribution of $\bar B\rightarrow D^*(\rightarrow Dπ)τ^-(\rightarrow V^-ν_τ)\barν_τ$}},
author = {Si-Yuan Liu and Alakabha Datta and Xian-Wei Kang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.15166},
eprint = {2606.15166},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.15166},
}
RIS
TY - UNPB
TI - Exploring new physics in the angular distribution of B̅→ D^*(→ Dπ)τ^-(→ V^-ν_τ)ν̅_τ
AU - Si-Yuan Liu
AU - Alakabha Datta
AU - Xian-Wei Kang
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2606.15166
UR - https://arxiv.org/abs/2606.15166
AB - The decays B̅→ D^*τ^−ν̅_τ provide sensitive probes of new physics in the b→ cτν transition. We discuss the effects of new physics in the decay chain B̅→ D^*(→ Dπ)τ^−(→ V^-ν_τ)ν̅_τ where V is a vector meson. We first present a comprehensive analysis of the five-dimensional angular distribution for the full decay chain B̅→ D^*(→ Dπ)τ^−(→ ρ^-ν_τ)ν̅_τ, exploiting the hadronic τ decay to ρ^-ν_τ to circumvent the experimental challenge of direct τ reconstruction. The differential decay rate is expressed in terms of measurable kinematic variables θ^*, E_ρ, θ_ρ, χ_ρ, and q^2 -- with complete coefficient functions provided for scalar, pseudoscalar, vector, axialvector, and tensor new-physics interactions. From this distribution we construct a set of integrated observables, including the D^* polarization fractions and lepton-side forward-backward and azimuthal asymmetries, which isolate distinct combinations of helicity amplitudes. We also show that by decomposing the vector-meson energy spectrum into its longitudinal (L) and transverse (T) helicity sectors, two additional analyzing powers (α_L and α_T) related to the measurement of τ polarization P_τ^D^*(q^2) are obtained. Without information on the polarization of meson V, the spin analyzing power of ρ is much larger than that of a_1 with α_ρ=0.45 and α_a_1=0.02. We further perform a numerical analysis using current experimental data on R_D^* and the D^* longitudinal polarization fraction ⟨ F_L^D^*⟩ to constrain the complex new-physics couplings g_L, g_R, g_P, and g_T, revealing the correlations among them.
ER -