Search

Motivated by the persistent anomalies reported in the b → c τ ν ¯ data, we investigate the semileptonic decays B ¯ ∗ → V τ - ν ¯ τ (V = D u , d , s ∗ , J / ψ) , within the Standard Model and beyond. The relevant transition form factors, being calculated in the covariant light-front quark model, is the main source of theoretical uncertainties. Using various best-fit solutions for the new operator Wilson coefficients, we report numerical results on various observables related to the processes B ¯ ∗ → V τ - ν ¯ τ , such as the branching ratios, the ratio of branching fractions, the hadron and lepton polarization asymmetries, the forward–backward asymmetries and the convexity parameter. We also predict the q 2 distribution of these observables both within the Standard Model and in various new physics scenarios. The accessible observables are studied in order to assess their sensitivity to the different new physics scenarios. We can find that some of the new physics scenarios can be differentiated from each other by using these observables and their correlations. We also find that some observables of these decay modes are sizeable and deviate significantly (for new physics coupling parameter S R especially) from their corresponding standard model values, which are expected to be within the reach of Run III of Large Hadron Collider experiment. And experimental information on these distributions which will be testified in the future can help to disentangle the dynamical origin of the current anomalies. [ABSTRACT FROM AUTHOR]

In B c − → J/ψ(→ μ+μ−)τ− ν ¯ τ decay, the three-momentum 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 − → J/ψ(→ μ+μ−)τ−(→ π−ντ) ν ¯ τ , in which the three-momenta p μ + , p μ − , and 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 ℐ ̂ i (q2) and two lepton-flavor-universality ratios 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 ℐ ̂ i and 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 P L , T J / ψ , except ℐ ̂ 5 . The ratios 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. [ABSTRACT FROM AUTHOR]

In Λ b 0 → Λ c + → Λ 0 π + τ − v ¯ τ decay, the solid angle of the final-state particle τ− cannot be determined precisely since the decay products of the τ− include an undetected ντ. Therefore, 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 Λ b 0 → Λ c + → Λ 0 π + τ − → π − v τ v ¯ τ . The three-momenta of the final-state particles Λ0, π+, and π− can be measured. Considering all Lorentz structures of the new physics (NP) effective operators and an unpolarized initial Λb state, the five-fold differential angular distribution can be expressed in terms of ten angular observables K i q 2 E π . By integrating over some of the five kinematic parameters, we define a number of observables, such as the Λc spin polarization P Λ c q 2 and the forward-backward asymmetry of π− meson AFB(q2), both of which can be represented by the angular observables K ̂ i q 2 . We provide numerical results for the entire set of the angular observables K ̂ i q 2 and K ̂ i both within the Standard Model and in some NP scenarios, which are a variety of best-fit solutions in seven different NP hypotheses. We find that the NP which can resolve the anomalies in B ¯ → D ∗ τ − v ¯ τ decays has obvious effects on the angular observables K ̂ i q 2 , except K ̂ 1 ss q 2 and K ̂ 1 cc q 2 . [ABSTRACT FROM AUTHOR]

In recent years, several deviations from the Standard Model predictions in semileptonic decays of B-meson might suggest the existence of new physics which would break the lepton-flavour universality. In this work, we have explored the possibility of using muon sneutrinos and right-handed sbottoms to solve these B-physics anomalies simultaneously in R-parity violating minimal supersymmetric standard model. We find that the photonic penguin induced by exchanging sneutrino can provide sizable lepton flavour universal contribution due to the existence of logarithmic enhancement for the first time. This prompts us to use the two-parameter scenario (C 9 V , C 9 U) to explain b → s ℓ + ℓ - anomaly. Finally, the numerical analyses show that the muon sneutrinos and right-handed sbottoms can explain b → s ℓ + ℓ - and R (D (∗)) anomalies simultaneously, and satisfy the constraints of other related processes, such as B → K (∗) ν ν ¯ decays, B s - B ¯ s mixing, Z decays, as well as D 0 → μ + μ - , τ → μ ρ 0 , B → τ ν , D s → τ ν , τ → K ν , τ → μ γ , and τ → μ μ μ decays. [ABSTRACT FROM AUTHOR]

The R (D (∗)) anomalies observed in B → D (∗) τ ν decays have attracted much attention in recent years. In this paper, we study the B → D (∗) τ ν , Λ b → Λ c τ ν , B c → (J / ψ , η c) τ ν , B → X c τ ν , and B c → τ ν decays, all being mediated by the same quark-level b → c τ ν transition, in the Standard Model Effective Field Theory. The most relevant dimension-six operators for these processes are Q lq (3) , Q ledq , Q lequ (1) , and Q lequ (3) in the Warsaw basis. Evolution of the corresponding Wilson coefficients from the new physics scale Λ = 1 TeV down to the characteristic scale μ b ≃ m b is performed at three-loop in QCD and one-loop in EW/QED. It is found that, after taking into account the constraint B (B c → τ ν) ≲ 10 % , a single C lq (3) 3323 (Λ) or C lequ (3) 3332 (Λ) can still be used to resolve the R (D (∗)) anomalies at 1 σ , while a single C lequ (1) 3332 (Λ) is already ruled out by the measured R (D (∗)) at more than 3 σ . By minimizing the χ 2 (C i) function constructed based on the current data on R(D), R (D ∗) , P τ (D ∗) , R (J / ψ) , and R (X c) , we obtain eleven most trustworthy scenarios, each of which can provide a good explanation of the R (D (∗)) anomalies at 1 σ . To further discriminate these different scenarios, we predict thirty-one observables associated with the processes considered under each NP scenario. It is found that most of the scenarios can be differentiated from each other by using these observables and their correlations. [ABSTRACT FROM AUTHOR]

In recent years, the experimental results about the ratio of the branching ratios R D (∗) and R K (∗) , which are in the semileptonic b → c l ν ¯ l and b → s l + l - decays, have been observed to deviate from the Standard Model prediction by 1.4 σ , 2.5 σ , 2.4 σ and 2.2 σ respectively. Motivated by these anomalies and by the abundant B ∗ data samples, we investigate possible New Physics effects of the vector leptoquark in the semileptonic decay B ¯ u , d , s , c ∗ → V τ - ν ¯ τ ( V = D u , d , s ∗ , J / ψ ). which is induced by b → c τ - ν ¯ τ at the quark level. Using the best fit solutions for the new operator Wilson coefficients and the relevant form factors which are obtained in the light-front quark model, we find that (i) the contributions of the vector leptoquark to d Γ (L) / d q 2 ( B ¯ u , d , s , c ∗ → V τ - ν ¯ τ) and R V ∗ (L) (q 2) to be significant; (ii) the two best fit solutions in the vector leptoquark are indistinguishable from each other and give similar amounts of enhancements to these two observables; (iii) both two cases of the vector leptoquark give nearly same results as those of the Standard Model for A FB τ (q 2) , P τ (q 2) and F L ∗ V (q 2) . We hope that the numerical results in this work will be tested in the future high energy experiments. [ABSTRACT FROM AUTHOR]