Lepton-side Forward-backward Asymmetry Research Articles

Imprints of new physics in Λb → Λ∗l+l− decay in nonuniversal Z′ model

Inspired by various updated tantalizing results of LHCb on baryonic sector we study the [Formula: see text] decay in nonuniversal [Formula: see text] model. We present the fourfold angular distributions of the decay in terms of transversity amplitudes. We structure the observables: differential branching ratio, lepton side forward–backward asymmetries and polarization fractions in terms of the transversity amplitudes and incorporate the new physics (NP) terms in it. We reduce the number of the form factors using the improved Isgur–Wise relations. We study the observables in the Standard Model (SM) as well as in nonuniversal [Formula: see text] model. The predicted values are very interesting for the high energy physics community and results might provide prominent footprints of NP.

Lepton flavour violating {Lambda }_{{b}} decays in non-universal {Z}^{prime } model

Motivated by the recent LHCb results of lepton flavour violation on brightarrow s and brightarrow c transitions we study the lepton flavour violating (LFV) baryonic decays {Lambda }_{b}rightarrow {Lambda }l_{i}^{+}l_{j}^{-} in non-universal Z^{prime } model. We discuss the two-fold decay distribution of {Lambda }_{b}rightarrow {Lambda }l_{i}^{+}l_{j}^{-} decays in terms of transversity amplitudes. From this distribution we study the differential branching ratio and lepton side forward-backward asymmetry in new physics (NP). The predicted values of the observables are very interesting and that might emboss the footprints of NP more aesthetically.

Probing new physics in semileptonic Σb and Ωb decays

Recently, several hints of lepton non-universality have been observed in the semileptonic B meson decays in terms of both in the neutral current ($b\to s l \bar{l}$) and charged current ($b\to c l \bar{\nu_{l}}$) transitions. Motivated by these inspiring results, we perform the analysis of the baryon decays ${\Sigma_b}\to \Sigma_c l \bar{\nu_{l}}$ and $\Omega_b\to \Omega_c l \bar{\nu_{l}} (l=e,\mu,\tau)$ which are mediated by $ b \to c l \bar{\nu_{l}}$ transitions at the quark level, to scrutinize the nature of new physics (NP) in the model independent method. We first use the experimental measurements of $\mathcal{B}( B\to D^{(*)} l\bar{\nu_{l}})$, ${\rm R}_{D^{(*)}}$ and ${\rm R}_{J/\psi}$ to constrain the NP coupling parameters in a variety of scenarios. Using the constrained NP coupling parameters, we report numerical results on various observables related to the processes ${\Sigma_b}\to \Sigma_c l \bar{\nu_{l}}$ and $\Omega_b\to \Omega_c l \bar{\nu_{l}}$, such as the branching ratios, the ratio of branching fractions, the lepton side forward-backward asymmetries, the hadron and lepton longitudinal polarization asymmetries and the convexity parameter. We also provide the $q^2$ dependency of these observables and we hope that the corresponding numerical results in this work will be testified by future experiments.

Probing the effects of some new physics models in Bs→ [formula omitted] decay

Recent measurements on the semi-leptonic b→cℓν¯ℓ and b→sℓ+ℓ− decays imply possible hints of Lepton Flavor Universality (LFU) violation and therefore have attracted much attention. In this paper, motivated by these anomalies, we analyze the Bs→Dsτν¯ decay in some New Physics (NP) models, such as the Supersymmetry with R-parity violation (RPV SUSY) model, the W′ model, the vector leptoquark model and the aligned two-Higgs-doublet model (A2HDM). Using the parameter spaces obtained from various flavor constraints, we calculate the branching fraction B(Bs→Dsτν¯) and the ratio RDs of this decay process, and also show the effects of NP models on the differential branching fraction dBdq2, the differential ratio RDs(q2), the lepton-side forward-backward asymmetry AFB(q2), the convexity parameter CFτ(q2) and the τ polarization fraction PLτ(q2). We find that: (i) the effects of NP models are significant for B(Bs→Dsτν¯), but RDs is only sensitive to the effect of A2HDM; (ii) both dBdq2 and RDs(q2) in the four NP models show obvious deviations from the SM predictions; (iii) for AFB(q2), CFτ(q2) and PLτ(q2), only the A2HDM presents obvious effect because the scalar type interactions can be generated in such model.

Lepton flavor violating Lambda _brightarrow Lambda ell _1ell _2 decay

Inspired by the recent hints of lepton flavor universality violation in brightarrow sell ell and brightarrow cell nu transitions, we study lepton flavor violating exclusive Lambda _brightarrow Lambda ell _1^+ell _2^- (ell _1ne ell _2) decay, which is forbidden in the Standard Model. Starting from a general effective Hamiltonian for a brightarrow sell _1^+ell _2^- transition that includes vector and axial-vector operators, and scalar and pseudo-scalar operators, we derive a two-fold decay distribution of Lambda _brightarrow Lambda ell _1^+ell _2^-. The distribution helps us to construct the differential branching ratio and the lepton-side forward–backward asymmetry, which are studied in a vector leptoquark model. The parameter space of the vector leptoquark model is constrained by low energy observables.

Contributions of vector leptoquark to [formula omitted] decay

Motivated by the RD(⁎) anomalies in semileptonic B meson decay which can be explained by adding a single vector leptoquark U3(3,3,23) to the Standard Model, we further analyse the New Physics effects of vector leptoquark to the heavy baryon Ξb→Ξcτ−ν¯τ decay. Using the best-fit solutions for Wilson coefficients of operators resulted from experimental measurement RD(⁎) anomalies and the form factors resulted from relativistic quark model, we study the contributions of the leptoquark to several observables, such as differential branching ratio, ratio of differential branching ratio, lepton-side forward-backward asymmetry, longitudinal polarization fraction of Ξc baryon and τ lepton as well as the convexity parameter of this decay with the helicity amplitude formalism. We find that the contributions of vector leptoquark to differential branching ratio, ratio of differential branching ratio and convexity parameter are significant which show deviations at high level from the corresponding Standard Model predictions. Nevertheless, the observables lepton-side forward-backward asymmetry, longitudinal polarization fraction of Ξc baryon and τ lepton have the same behaviours in vector leptoquark as that in the Standard Model which displays the three observables are not sensitive to the New Physics effects of vector leptoquark.

Impact of vector new physics couplings on Bs→(K,K*)τν and B→πτν decays

Experimental measurements of $R_{D}$, $R_{D^*}$ and $R_{J/\Psi}$ in $B \to (D,\,D^{\ast})l\nu$ and $B_c \to J/\Psi l \nu$ decays mediated via $b \to c\,l\,\nu$ charged current interactions deviate from standard model prediction by $2.3\sigma$, $3.4\sigma$ and $2\sigma$, respectively. In addition, a deviation of $1.5\sigma$ from the standard model prediction has been witnessed in $\mathcal B(B \to \tau \nu)$ mediated via $b \to u\,l\,\nu$ charged current interactions as well. Motivated by the anomalies present in $B$ and $B_c$ meson decays, we analyze the corresponding $B_s \to (K,\,K^{\ast})\,\tau\,\nu$ and $B \to \pi\tau\nu$ semileptonic decays within the standard model and beyond. We use an effective field theory formalism in which $b \to c$ and $b \to u$ semileptonic decays are assumed to exhibit similar new physics patterns. We give the predictions of various observables such as the branching fractions, ratio of branching ratios, lepton side forward backward asymmetry, lepton polarization fraction and convexity parameter for $B_s \to (K,\,K^{\ast})\tau \nu$ and $B \to \pi\tau\nu$ decay channels within the standard model and within various NP scenarios.

Phenomenology of Ξb→Ξcτν decays

Deviations from the standard model prediction have been reported in various semileptonic $B$ decays mediated via $b \to c$ charged current interactions. In this context, we analyze semileptonic baryon decays $\Xi_b \to \Xi_c\,\tau\,\nu$ using the helicity formalism. We report numerical results on various observables such as the decay rate, ratio of branching ratio, lepton side forward backward asymmetries, longitudinal polarization fraction of the lepton, and the convexity parameter for this decay mode using results of relativistic quark model. We also provide an estimate of the new physics effect on these observables under various new physics scenarios.

Study of Λb → Λℓ+ℓ− (ℓ = e,μ,τ) decays in the G(221) model

We study respectively the baryonic semilepton decays [Formula: see text][Formula: see text] in the [Formula: see text] model, which includes the tree-level flavor-changing-neutral-currents (FCNCs) induced by [Formula: see text] and [Formula: see text] bosons and modifies the Wilson coefficients [Formula: see text] and [Formula: see text]. For the form factors, we use the results of QCD light-cone sum rules (LCSR) in the low [Formula: see text] region and lattice QCD in the high [Formula: see text] region, respectively. We consider the effects of this new physics (NP) model on some measured physical observables, like the differential branching ratio, the longitudinal polarization of the dilepton system, the lepton-side forward–backward asymmetry and the baryon-side forward–backward asymmetry, and find, obvious differences occur in some observables between the Standard Model (SM) and this NP model. Meanwhile, we also discuss the double lepton polarization asymmetries of these decay channels, and find, [Formula: see text], [Formula: see text] and [Formula: see text] of these decay channels are sensitive to the contribution of this NP model.

Analysis ofΛb→Λμ+μ-Decay in Scalar Leptoquark Model

We analyze the baryonic semilepton decayΛb→Λμ+μ-in the scalar leptoquark models withX(3,2,7/6)andX(3,2,1/6)states, respectively. We also discuss the effects of these two NP models on some physical observables. For some measured observables, like the differential decay width, the longitudinal polarization of the dilepton system, the lepton-side forward-backward asymmetry, and the baryon-side forward-backward asymmetry, we find that the prediction values of SM are consistent with the current data in mostq2ranges, where the prediction values of these two NP models can also keep consistent with the current data with1σ. However, in someq2ranges, the prediction values of SM are difficult to meet the current data, but the contributions of these two NP models can meet them or keep close to them. For the double-lepton polarization asymmetries,PLT,PTL,PNN, andPTTare sensitive to the scalar leptoquark modelX(3,2,7/6)but not toX(3,2,1/6). However,PLN,PNL,PTN, andPNTare not sensitive to these two NP models.

Semileptonic decayΛb→Λc+τ−+ν¯τin the covariant confined quark model

Recently there has been much interest in the tauonic semileptonic meson decays B -> D + tau + nu_tau and B -> D* + tau + nu_tau where one has found larger rates than what is predicted by the Standard Model. We analyze the corresponding semileptonic baryon decays Lambda_b(0) -> Lambda_c(+) + tau(-) + antinu_tau with particular emphasis on the lepton helicity flip and scalar contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization of the daughter baryon Lambda_c(+) and the tau-lepton, and the lepton-side forward-backward asymmetries. The nonvanishing polarization of the daughter baryon Lambda_c(+) leads to hadron-side asymmetries in e.g. the decay Lambda_c(+) -> Lambda(0) + pi(+) and azimuthal correlations between the two final state decay planes which we specify. We provide numerical results on these observables using results of the covariant confined quark model. We find large lepton mass effects in the q2-spectra and in the polarization observables.

Physical observables in the decay Λb → Λc(→ Λ + π) + τ− + ν̄τ

We analyze the tauonic semileptonic baryon decays [Formula: see text] with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the [Formula: see text] and the [Formula: see text], and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.