We present the angular distribution of the four-fold $B\toρ(\toππ)μ^{+}μ^{-}$ and $B\to a_{1}(\toρ_{\parallel, \perp}π)μ^{+}μ^{-}$ decays both in the Standard Model and the family non-universal $Z^{\prime}$ model. At the quark level, these decays are governed by the $b\to dμ^{+}μ^{-}$ transition. Along with different angular observables, we also give predictions of differential branching ratios, forward-backward asymmetry, longitudinal polarization fraction of $ρ$, and $a_{1}$ mesons. Our analysis shows that the signatures of family non-universal $Z^{\prime}$ model are more distinct in the observables associated with the $B\toρ(\toππ)μ^{+}μ^{-}$ decay, compared to that of the $B\to a_{1}(\toρ_{\parallel, \perp}π)μ^{+}μ^{-}$ decay. Future measurements of the predicted angular observables, both at current and future high energy colliders, will add to the useful complementary data required to clarify the structure of the family non-universal $Z^{\prime}$ model in $|Δb|$=$|Δd|=1$ processes.
Angular and invariant-mass observables in the four-body Higgs decay $h\to\ell\barν_\ell\bar{\ell}^\primeν_{\ell^\prime}$
Zhengzhou University(郑州大学);Chongqing University of Posts & Telecommunications(重庆邮电大学);Chongqing University(重庆大学);Chongqing University of Science and Technology(重庆科技大学)
We enumerate various effective couplings that contribute to the mixings between an exotic vector boson $Z^{\prime}$ and the neutral electroweak vector bosons. The miscellaneous mixing patterns can be evaluated perturbatively. The effective oblique parameters $S^{\prime}$, $T^{\prime}$, and $U^{\prime}$ are calculated to compare with the electroweak precision test results. With the contributions to the non-negligible $U^{\prime}$ parameter from the $ε_{B,W}$ parameters and the aid of some other parameters to cancel the negative $T^{\prime}$, the recent CDF $W$-mass anomaly can therefore be expl…
The flavor anomalies reported in $R_K$, $R_{K^*}$, $P_{5}^{\prime}$ and $\mathcal{B}(B_s\, \to\, ϕ\, μ^+\, μ^-)$ indicate lepton flavor universality violation in $b \to s\,l^+\,l^-$ quark level transition decays. The deviation from the SM prediction reported in the underlying flavor observables currently stand at the level of $2.5σ$, $2.4σ$, $3.3σ$ and $3.7σ$, respectively. In this context, we perform an angular analysis of the four-body differential decay of $B_s\, \to\, f_{2}^{\prime}\,(1525)\,(\to K^+\,K^-)\,μ^+ \,μ^-$ in a model independent effective field theory framework. The decay mode …
We analyse the results recently presented on the $B^{+} \to K^{*+} μ^+ μ^-$ angular observables by the LHCb Collaboration which show indications for New Physics beyond the Standard Model. Within a model-independent analysis, we compare the fit results with the corresponding results for the angular observables in $B^{0} \to K^{*0} μ^+ μ^-$.
In 2015, the LHCb collaboration has measured $\frac{d{\mathcal{B}}}{dq^2}$, the lepton- and hadron-side forward-backward asymmetries, denoted by $A^\ell_{FB}$ and $A^Λ_{FB}$, respectively in the range $15 < q^2(=s) < 20$ GeV$^2$ with 3 fb$^{-1}$ of data. Motivated by these measurements, we perform an analysis of $q^2$ dependent $Λ_b \to Λ(\to p π) μ^+μ^-$ angular observables at large- and low-recoil in the SM and in a family non-universal $Z^{\prime}$ model. In the present study we use the recently performed high-precision lattice QCD calculations of the form factors that have well controlled …
Over the last few years LHCb with present energies found some discrepancies in $b\to s\ell^+\ell^-$ FCNC transitions including anomalies in the angular observables of $B\to K^*μ^+μ^-$, particularly in $P_5^\prime$, in low dimuon mass region. Recently, these anomalies are confirmed by Belle, CMS and ATLAS. As the direct evidence of physics beyond-the-SM is absent so far, therefore, these anomalies are being interpreted as indirect hint of new physics. In this context, we study the implication of non universal family of $Z^\prime$ model to the angular observables $P_{1,2,3}$, $P^{\prime}_{4,5,6}…
The rare $τ^- \to η^{(\prime)} π^- ν_τ$ decays, which are suppressed by $G$-parity in the Standard Model (SM), can be sensitive to the effects of new interactions. We study the sensitivity of different observables of these decays in the framework of an effective field theory that includes the most general interactions between SM fields up to dimension six, assuming massless neutrinos. Owing to the strong suppression of the SM isospin breaking amplitudes, we find that the different observables would allow to set constraints on scalar interactions that are stronger than those coming from other l…
We perform an analysis of angular distributions in semileptonic decays of charmed baryons $B_1^{(\prime)}\to B_2^{(\prime)}(\to B_3^{(\prime)}B_4^{(\prime)})\ell^+ν_{\ell}$, where the $B_1=(Λ_c^+,Ξ_c^{(0,+)})$ are the SU(3)-antitriplet baryons and $B_1'=Ω_c^-$ is an SU(3) sextet. We will firstly derive analytic expressions for angular distributions using helicity amplitude technique. Based on the lattice QCD results for $Λ_c^+\toΛ$ and $Ξ_c^0\toΞ^-$ form factors and model calculation of the $Ω_c^0\toΩ^-$ transition, we predict branching fractions: $\mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} e^{…
We apply the formalism of amplitude symmetries to the angular distribution of the decays $B \to D^* \ell ν$ for $\ell=e,μ,τ$. We show that the angular observables used to describe the distribution of this class of decays are not independent in absence of New Physics contributing to tensor operators. We derive sets of relations among the angular coefficients of the decay distribution for the massless and massive lepton cases which can be used to probe in a very general way the consistency among the angular observables and the underlying New Physics at work. We use these relations to access the …
Rare $b \to s\ell^+\ell^-$ flavour-changing-neutral-current processes provide important tests of the Standard Model of particle physics. Angular observables in exclusive $b \to s\ell^+\ell^-$ processes can be particularly powerful as they allow hadronic uncertainties to be controlled. Amongst the exclusive processes that have been studied by experiments, the decay $Λ_b\to Λ\ell^+\ell^-$ is unique in that the $Λ_b$ baryon can be produced polarised. In this paper, we derive an expression for the angular distribution of the $Λ_b\to Λ\ell^+\ell^-$ decay for the case where the $Λ_b$ baryon is produ…
The flavor changing rare decay $B\to K^{*}(\to Kπ)\ell^+\ell^-$ is one of the most studied modes due to its sensitivity to physics beyond the standard model and several discrepancies have come to light among the plethora of observables that are measured. In this paper we revisit the analogous baryonic decay mode $Λ_{b}\rightarrow Λ(\to pπ) \ell^{+}\ell^{-}$ and we present a complete set of ten angular observables that can be measured using this decay mode. Our calculations are done retaining the finite lepton mass so that the signal of lepton non-universality observed in $B\to K^{*} \ell^+\ell…
The $ρ(1450)$ vector meson ($ρ^\prime$) is becoming increasingly important to properly describe precision observables. We analyse a set of decay modes and cross sections, in the low-energy regime, to determine the role played by this meson. This is done through the extraction of the parameters for its description, in the context of the vector meson dominance model and its effective hadronic interactions, involving the low mass lying hadrons ($ρ$, $ω$ and $π$). In a first step, we determine the parameters of the model from ten decay modes which are insensitive to the $ρ^\prime$. Then, we consid…
We consider effects of spin-2 particle in the $b\rightarrow s μ^+ μ^-$ transition assuming that the spin-2 particle couples in a flavour non-universal way to $b$ and $s$ quarks and in the leptonic sector couples only to the muons, thereby only contributing to the process $b\rightarrow s μ^+ μ^-$. The $B_s - \bar B_s$ transition gives the strong constraint on the coupling of the spin-2 mediator and $b$ and $s$ quarks while the observed discrepancy from the SM prediction for the muon anomalous magnetic moment $ (g-2)_μ$ serves us to constrain the $μ$-coupling to spin-2 particle. We find that the…
A Phenomenological Study of Semileptonic $B^+$ and $B_s^0$ Decays into Axial-Vector Mesons $\big(D_1(2420),\, D_1^\prime(2430),\, D_{s1}(2460),\, \text{and } D_{s1}^\prime(2536)\big)$ within the Standard Model
National Centre for Physics, Quaid-i-Azam University(巴基斯坦国立物理中心,奎德-阿扎姆大学);Lahore University of Management Sciences (LUMS)(拉合尔管理科学大学);National University of Sciences and Technology(国立科学与技术大学)
We probe the effective field theory extending the Standard Model with a sterile neutrino in B meson decays at B factories and lepton colliders, using angular and polarization observables. We put bounds on different effective operators characterized by their distinct Dirac-Lorentz structure, and probe the $N$-mediated B decays sensitivity to these interactions. We define a Forward-Backward asymmetry $A_{FB}^{\ell γ}$ between the muon and photon directions for the $B \to μνγ$ decay, which allows us to separate the SM contribution from the effective lepton number conserving and violating processe…
Within QCD factorization approach, we employ the new results of form factors of $B_s \to ϕ$ and calculate the branching fractions, CP asymmetries (CPAs) and polarization fractions of the decay modes $B_s \to ϕ(ρ^0, ω)$ in both the standard model (SM) and the family non-universal $Z^\prime$ model. We find that in SM the above observables are relate to two parameters $ρ_H$ and $ϕ_H$, which characterize the end-point divergence in the hard spectator-scattering amplitudes. When setting $ρ_H=0.5$ and $ϕ_H\in [-180,180]^\circ$, the theoretical uncertainties are large. By combining the experimental d…
In recent years, several observables associated to semileptonic $b \to s$ processes have been found to depart from their predicted values in the Standard Model, including a few tantalizing hints of lepton flavor universality violation. In this work we consider an existing model with a massive $Z^\prime$ boson that addresses the anomalies in $b \to s$ transitions and extend it with a non-trivial embedding of neutrino masses. We analyze lepton flavor violating effects, induced by the non-universal interaction associated to the $b \to s$ anomalies and by the new physics associated to the neutrino…
Lepton polarization dependent angular observables and the polarization asymmetries in the four-fold $Λ_b \rightarrow Λ(\rightarrow N π) \ell^+\ell^-$ decay
National University of Sciences and Technology (NUST)(国立科学技术大学);National Centre for Physics(国家物理中心);Quaid-i-Azam University(奎德-e-阿扎姆大学)
We perform a study of the new physics effects in semileptonic FCNC processes within a low-energy approximation of the anomaly-free supersymmetic extension of the SM with additional $Z'$ vector field. The key feature of the model is the non-diagonal structure of $Z'$ couplings to fermions, which is parameterized by few new-physics parameters in addition to well-known mixing matrices for quarks and leptons in the SM. We not only consider CP-conserving scenarios with real parameters, but also account for possible CP violation due to new physical weak phases. We analyse the dependence of the $b\to…
We present predictions for the $e^{+}e^{-}$ event shape angularities at NNLL$^{\prime}$ resummed and $\mathcal{O}(α_s^{2})$ matched accuracy and compare them to LEP data at center-of-mass energies $Q=91.2$ GeV and $Q=197$ GeV. We perform the resummation within the framework of Soft-Collinear Effective Theory, and make use of recent results for the two-loop angularity soft function. We determine the remaining NNLL$^{\prime}$ and $\mathcal{O}(α_s^2)$ ingredients from a fit to the EVENT2 generator, and implement a shape function with a renormalon-free gap parameter to model non-perturbative effec…
We consider the time-dependent analysis of $B_d\to K_S\ell\ell$ taking into account the time-evolution of the $B_d$ meson and its mixing into $\bar{B}_d$. We discuss the angular conventions required to define the angular observables in a transparent way with respect to CP conjugation. The inclusion of time evolution allows us to identify six new observables, out of which three could be accessed from a time-dependent tagged analysis. We also show that these observables could be obtained by time-integrated measurements in a hadronic environment if flavour tagging is available. We provide simple …
We probe the rare semileptonic decays $B_{(s)} \to K_2^*(1430)(f_2'(1525)) \ell^+\ell^-$ proceeding via $b\to s \ell \ell$ transition in the presence of a light $Z^{\prime}$ boson. We employ the presence of an additional vector type interaction and constrain the new physics coupling parameter using the existing experimental measurements on $R_K$ and $R_{K^*}$ observables. To understand the sensitivity of the new physics coupling, we investigate the impact of this coupling on various physical observables such as differential branching ratio, the forward-backward asymmetry, the lepton polarizati…
Proton decay and new contribution to neutrino-less double beta decay in SO(10) with low-mass Z-prime boson, observable n-nbar oscillation, lepton flavor violation, and rare kaon decay
It is shown that general dilepton angular distribution (with parity violating terms taking into account) in vector particle decays can be described through a set of five SO(3) rotational-invariant observables. These observables are derived as invariants of the spacial part of the hadronic tensor (density matrix) expressed in terms of angular coefficients. The restrictions on the invariants following from the positivity of the hadronic tensor are obtained. Special cases of SO(2) rotations are considered. Calculation of invariants for available data on Z and J/ψ decays is performed.
In $Λ_b^0 \to Λ_c^+ (\to Λ^0 π^+) τ^- \barν_τ$ decay, the solid angle of the final-state particle $τ^-$ cannot be determined precisely since the decay products of the $τ^-$ include an undetected $ν_τ$. Therefore, the angular distribution of this decay cannot be measured. In this work, we construct a {\it measurable} angular distribution by considering the subsequent decay $τ^- \to π^- ν_τ$. The full cascade decay is $Λ_b^0 \to Λ_c^+ (\to Λ^0 π^+)τ^- (\to π^- ν_τ)\barν_τ$. The three-momenta of the final-state particles $Λ^0$, $π^+$, and $π^-$ can be measured. Considering all Lorentz structures …
Angular observables and branching ratio for $B_s\to ϕ\ell^+ \ell^-$ decay
The Institute of Nuclear Physics, Agency of the Republic of Kazakhstan for Atomic Energy(哈萨克斯坦原子能机构核物理研究所);Joint Institute for Nuclear Research(俄罗斯杜布纳联合核研究所)
Exclusive semileptonic decays based on $b\to s$ transitions have been attracting a lot of attention as some angular observables deviate significantly from the Standard Model (SM) predictions in specific $q^2$ bins. B meson decays induced by other Flavor Changing Neutral Current (FCNC), $b\to d$, can also offer a probe to new physics with an additional sensitivity to the weak phase in Cabibbo-Kobayashi-Masakawa (CKM) matrix. We provide predictions for angular observables for $b\to d$ semileptonic transitions, namely $\bar{B}_s\to K^{\ast}\ell^+\ell^-$, $\bar{B}^0\toρ^0 \ell^+\ell^-$, and their …
This paper describes the angular distribution of $Λ_b^0\to Λ(\to pK^-)\ell^+\ell^-$ decays. A full expression is given for the case of multiple interfering spin-states with spin $\leq \tfrac{5}{2}$. This distribution is relevant for future measurements of $Λ_b^0\to pK^-\ell^+\ell^-$ decays, where different states cannot easily be separated based on their mass alone. New observables arise when considering spin-$\tfrac{5}{2}$ states as well as interference between states. An exploration of their behaviour for a variety of beyond the Standard Model scenarios shows that some of these observables e…