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Recent deviations from the standard model (SM) predictions of the experimental results on the R D ( * ) of the b → c l ν ̄ l semileptonic decay suggest the intervention of new physics (NP) mechanisms, which would affect the decay. Motivated by this, we investigate the possible NP effects on Ξ b → Ξ c τ ν ̄ τ and Ω b → Ω c τ ν ̄ τ processes in some NP models, such as the vector leptoquark (LQ) model, W′ model, aligned two-Higgs-doublet model and supersymmetry without R-parity model. Using the NP coupling parameter values obtained from different observables, we calculate various observables, such as the differential decay rate d B / d q 2 , the forward–backward asymmetry A FB l ( q 2 ) , the polarization fraction of final-state lepton and daughter baryon P L l ( q 2 ) as well as P L Ξ c ( Ω c ) ( q 2 ) , and the convexity parameter C F l ( q 2 ) in the SM and NP models. It is found that the SM predictions are consistent with those of previous works. In addition, the differential decay rate d B / d q 2 is quite sensitive to the contributions of some NP models. NP predictions generally show large deviations from the corresponding SM predictions. Nevertheless, the NP effects on some observables in the W′ model and LQ model are not sensitive, and these observables show the same variation tendency in the two NP models as in the SM.
Recent deviations from the standard model (SM) predictions of the experimental results on the R D ( * ) of the b → c l ν ̄ l semileptonic decay suggest the intervention of new physics (NP) mechanisms, which would affect the decay. Motivated by this, we investigate the possible NP effects on Ξ b → Ξ c τ ν ̄ τ and Ω b → Ω c τ ν ̄ τ processes in some NP models, such as the vector leptoquark (LQ) model, W′ model, aligned two-Higgs-doublet model and supersymmetry without R-parity model. Using the NP coupling parameter values obtained from different observables, we calculate various observables, such as the differential decay rate d B / d q 2 , the forward–backward asymmetry A FB l ( q 2 ) , the polarization fraction of final-state lepton and daughter baryon P L l ( q 2 ) as well as P L Ξ c ( Ω c ) ( q 2 ) , and the convexity parameter C F l ( q 2 ) in the SM and NP models. It is found that the SM predictions are consistent with those of previous works. In addition, the differential decay rate d B / d q 2 is quite sensitive to the contributions of some NP models. NP predictions generally show large deviations from the corresponding SM predictions. Nevertheless, the NP effects on some observables in the W′ model and LQ model are not sensitive, and these observables show the same variation tendency in the two NP models as in the SM.
In $$ {B}_c^{-} $$ B c − → J/ψ(→ μ+μ−)τ−$$ {\overline{\nu}}_{\tau } $$ ν ¯ τ decay, the three-momentum $$ {\boldsymbol{p}}_{\tau^{-}} $$ p τ − cannot be determined accurately due to the decay products of τ− inevitably include an undetected ντ. As a consequence, the angular distribution of this decay cannot be measured. In this work, we construct a measurable angular distribution by considering the subsequent decay τ− → π−ντ. The full cascade decay is $$ {B}_c^{-} $$ B c − → J/ψ(→ μ+μ−)τ−(→ π−ντ)$$ {\overline{\nu}}_{\tau } $$ ν ¯ τ , in which the three-momenta $$ {\boldsymbol{p}}_{\mu^{+}},{\boldsymbol{p}}_{\mu^{-}} $$ p μ + , p μ − , and $$ {\boldsymbol{p}}_{\pi^{-}} $$ p π − can be measured. The five-fold differential angular distribution containing all Lorentz structures of the new physics (NP) effective operators can be written in terms of twelve angular observables ℐi(q2, Eπ). Integrating over the energy of pion Eπ, we construct twelve normalized angular observables $$ {\hat{\mathrm{\mathcal{I}}}}_i $$ ℐ ̂ i (q2) and two lepton-flavor-universality ratios $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ (q2). Based on the Bc → J/ψ form factors calculated by the latest lattice QCD and sum rule, we predict the q2 distribution of all $$ {\hat{\mathrm{\mathcal{I}}}}_i $$ ℐ ̂ i and $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ both within the Standard Model and in eight NP benchmark points. We find that the benchmark BP2 (corresponding to the hypothesis of tensor operator) has the greatest effect on all ℐi and $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ , except $$ {\hat{\mathrm{\mathcal{I}}}}_5 $$ ℐ ̂ 5 . The ratios $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ are more sensitive to the NP with pseudo-scalar operators than the ℐi. Finally, we discuss the symmetries in the angular observables and present a model-independent method to determine the existence of tensor operators.
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