Chirality structure of vector like new physics operators in charged current transitions

TL;DR

This work addresses potential new physics in charged-current semileptonic B-meson decays by studying the cascade $B^{*0}_{s} \to D_s^-(\to \tau^-\,\bar{\nu}_{\tau})\,\ell^{+}\,\nu_\ell$ within a weak effective theory framework. It combines helicity amplitude formalism with covariant light-front quark model form factors, extrapolated to the timelike region via a double-pole ansatz, to compute branching ratios, forward-backward asymmetry $A_{FB}$, and a set of angular observables. A key finding is the chirality-dependent impact of vector-like NP: left-handed couplings ($C_{V_L}$) modify $Br$ but do not affect $A_{FB}$ or angular observables at tree level, whereas right-handed couplings ($C_{V_R}$) alter all these quantities; this pattern also holds in $c\to s$ transitions, as shown by related decays. The paper provides semi-analytic expressions and NP sensitivity studies across $q^2$ bins, highlighting how angular distributions can discriminate NP scenarios and helping guide future experimental tests of charged-current NP signals.

Abstract

We investigate the cascade decay $B^{*0}_{s} \rightarrow D_s^-(\rightarrow τ^-\,\barν_τ)\,\ell^{+}\,ν_\ell$ induced by flavor changing charged currents in the context of the Standard Model and in vector-like couplings beyond the Standard Model. We employ the helicity amplitude formalism for analysis and highlight the role of new vector-like couplings in charged current interactions. We find, in particular, that while new left handed chiral-vector like interactions contribute to the branching ratio, they do not affect the forward-backward asymmetry, or the angular observables. On the other hand, the right handed chiral vector-like coupling in the case of this decay contributes to the branching ratio, forward-backward asymmetry and the angular observables. We confirm that this difference in behavior between the left and right handed NP couplings is a general feature of charged current processes with a vector meson going to a pseudoscalar at the tree level in effective weak theory by cross checking with the cascade decays $B^{*+}_c \rightarrow P(\rightarrow P'\,μ^+\,ν_μ)\,\ell^{+}\,ν_\ell$ where $P$ is $B_s^0$ ($D^0$) and $P'$ is $D_s^{*-}$ ($K^-$).

Figures (9)

• Figure 1: Feynman diagram for semi leptonic $B^{*0}_{s} \rightarrow D_s^-(\rightarrow \tau^-\,\bar{\nu}_{\tau})\ell^{+}\,{\nu}_\ell$ and $B^{*+}_{c} \rightarrow P^0(\rightarrow P'\,\mu^+\,\nu_{\mu}) \ell^{+}\,{\nu}_\ell$ transitions.
• Figure 2: $\text{Br}\times 10^8$ (first two plots) and $A_{FB}$ (last two plots) of $B^{*0}_{s} \rightarrow \left[ D_s^-(\rightarrow \tau^-\,\bar{\nu}_{\tau}) \right]\, \ell^{+}\,{\nu}_\ell$ for decay to the muon and the tauon.
• Figure 3: Angular Observables $A_{I_{c1}}$, $A_3$, $A_4$, $A_5$, and $A_{6s}$ for muon and tauon for $B^{*0}_{s} \rightarrow \bigl[ D_s^-(\rightarrow \tau^-\,\bar{\nu}_{\tau}) \bigr]\, \ell^{+}\,{\nu}_\ell$ decay.
• Figure 4: The variation in the magnitudes of Br, $A_{FB}$, and angular observables $A_i$ due to the presence of NP. The first two plots correspond to low $q^2\in[s_{\text{min}},6]$GeV$^2$ and the last two plots correspond to high $q^2\in[6,s_{\text{max}}]$GeV$^2$ for $B^{*0}_{s} \rightarrow \bigl[ D_s^-(\rightarrow \tau^-\,\bar{\nu}_{\tau}) \bigr]\, \mu^{+}\,{\nu}_\mu$ decay.
• Figure 5: The variation in the magnitudes of Br, $A_{FB}$, and angular observables $A_i$ due to the presence of NP. The first two plots correspond to low $q^2\in[s_{\text{min}},6]$GeV$^2$ and the last two plots correspond to high $q^2\in[6,s_{\text{max}}]$GeV$^2$ for $B^{*0}_{s} \rightarrow \bigl[ D_s^-(\rightarrow \tau^-\,\bar{\nu}_{\tau}) \bigr]\, \tau^{+}\,{\nu}_\tau$ decay.