Lepton Polarization Research Articles

CPviolation, single lepton polarization asymmetry, and polarizedCPasymmetry inB→K*ℓ+ℓ−decay in the four-generation standard model

In this paper we present a study of $CP$ asymmetry, single lepton polarization asymmetry and polarized $CP$ asymmetry in $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay within the four-generation standard model. Taking $|{V}_{{t}^{\ensuremath{'}}s}^{*}{V}_{{t}^{\ensuremath{'}}b}|=0.01$, 0.02, 0.03 with phase ${60\ifmmode^\circ\else\textdegree\fi{}\char21{}120\ifmmode^\circ\else\textdegree\fi{}}$, which is consistent with the $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ rate and the Bs mixing parameter $\ensuremath{\Delta}{m}_{\mathrm{Bs}}$, we find that $CP$ asymmetry, single lepton polarization asymmetry and polarized $CP$ asymmetry are sensitive to the existence of the fourth generation. This can serve as an indirect method to search for new physics effects, in particular, to search for the fourth-generation $\mathrm{\text{quarks}}({t}^{\ensuremath{'}},{b}^{\ensuremath{'}})$ via their indirect manifestations in loop diagrams.

Lepton polarization inB→K1ℓ+ℓ−decays

We study the single and double lepton polarization asymmetries in the semileptonic B meson decays B → K1(1270)l+l− l≡e, μ, τ), where the strange P-wave meson, K1(1270), is the mixtures of the K1A and K1B, which are the 13P1 and 11P1 states, respectively. The lepton polarization asymmetries show relatively strong dependency in the various region of dileptonic invariant mass. The lepton polarization asymmetries can also be used for determining the K1(1270)–K1(1400) mixing angle, θK1 and new physics effects. Furthermore, it is shown that these asymmetries in B → K1(1270)l+l− decay compared with those of B → K*l+l− decay are more sensitive to the dileptonic invariant mass.

B→K0*(1430)l+l−decays in supersymmetric theories

The weak decays of $B \to K^{\ast}_0(1430) l^{+} l^{-}$ ($l=\mu, \tau$) are investigated in Minimal Supersymmetric Standard Model (MSSM) and also in Supersymmetric (SUSY) SO(10) Grand Unified Models. Neutral Higgs bosons are the point of main focus in MSSM because they make quite a large contribution in exclusive $B \to X_{s} l^{+} l^{-}$ decays at large $\tan{\beta}$ regions of parameter space of SUSY models, as part of SUSY contributions is proportional to $\tan^{3}{\beta}$. The analysis of decay rate, forward-backward asymmetries and lepton polarization asymmetries in $B \to K^{\ast}_0(1430) l^{+} l^{-}$ show that the values of these physical observables are greatly modified by the effects of neutral Higgs bosons. In SUSY SO(10) GUT model, the new physics contribution comes from the operators which are induced by the neutral Higgs boson penguins and also from the operators with chirality opposite to that of the corresponding Standard Model (SM) operators. SUSY SO(10) effects show up only in the decay $B \to K^{\ast}_0 \mu^{+} \mu^{-}$ where the transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, the longitudinal and normal lepton polarization asymmetries are very mild. The transverse lepton polarization asymmetry is almost zero in SM and in MSSM model, whereas it can reach to -0.3 in SUSY SO(10) GUT model which could be seen at the future colliders; hence this asymmetry observable can be used to discriminate between different SUSY models.

Role of polarization in probing anomalous gauge interactions of the Higgs boson

We explore the use of polarized e(+)/e(-) beams and/or the information on final state decay lepton polarizations in probing the interaction of the Higgs boson with a pair of vector bosons. A model independent analysis of the process e(+)e(-) -> f (f) over barH, where f is any light fermion, is carried out through the construction of observables having identical properties under the discrete symmetry transformations as different individual anomalous interactions. This allows us to probe an individual anomalous term independent of the others. We find that initial state beam polarization can significantly improve the sensitivity to CP-odd couplings of the Z boson with the Higgs boson (ZZH). Moreover, an ability to isolate events with a particular tau helicity, with even 40% efficiency, can improve sensitivities to certain ZZH couplings by as much as a factor of 3. In addition, the contamination from the ZZH vertex contributions present in the measurement of the trilinear Higgs-W (WWH) couplings can be reduced to a great extent by employing polarized beams. The effects of initial state radiation and beamstrahlung, which can be relevant for higher values of the beam energy are also included in the analysis.

Exclusive semileptonic decays ofΛb→Λl+l−in supersymmetric theories

The weak decays of ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}{l}^{+}{l}^{\ensuremath{-}}$ ($l=e$, $\ensuremath{\mu}$) are investigated in the minimal supersymmetric standard model (MSSM) and also in supersymmetric (SUSY) SO(10) grand unified models. In the MSSM special attention is paid to the neutral Higgs bosons (NHBs) as they make quite a large contribution in exclusive $B\ensuremath{\rightarrow}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$ decays at large $\mathrm{tan}\ensuremath{\beta}$ regions of parameter space of SUSY models, since part of SUSY contributions is proportional to ${tan}^{3}\ensuremath{\beta}$. The analysis of decay rate, forward-backward asymmetries, lepton polarization asymmetries, and the polarization asymmetries of the $\ensuremath{\Lambda}$ baryon in ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}{l}^{+}{l}^{\ensuremath{-}}$ show that the values of these physical observables are greatly modified by the effects of NHBs. In the SUSY SO(10) grand unified theory model, the new physics contribution comes from the operators which are induced by the NHBs' penguins and also from the operators having chirality opposite to that of the corresponding standard model (SM) operators. SUSY SO(10) effects show up only in the decay ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}+{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ where the longitudinal and transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, and polarization asymmetries of final state $\ensuremath{\Lambda}$ baryon are very mild. The transverse lepton polarization asymmetry in ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}+{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ is almost zero in the SM and in the MSSM model. However, it can reach to $\ensuremath{-}0.1$ in the SUSY SO(10) grand unified theory model and could be seen at the future colliders; hence this asymmetry observable will provide us useful information to probe new physics and discriminate between different models.

RareBc→Dsl+l−decay beyond the standard model

The rare ${B}_{c}\ensuremath{\rightarrow}{D}_{s}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay is investigated by using the most general model-independent effective Hamiltonian. The general expressions of longitudinal, normal, and transversal polarization asymmetries for ${\ensuremath{\ell}}^{\ensuremath{-}}$ and ${\ensuremath{\ell}}^{+}$ and the combined asymmetries of them are found. The dependencies of the branching ratios and polarizations on the new Wilson coefficients are presented. The analysis shows that the branching ratios and the lepton polarization asymmetries are very sensitive to the scalar- and tensor-type interactions. These results will be very useful in searching new physics beyond the standard model.

Exclusive Semileptonic Rare Decays B → K(*)l+l− in a Top Quark Two-Higgs-Doublet Model

Employing improved calculations of the decay form factors from light-cone sum rules, we evaluate the invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes B → K(*)l+l− in the SM and T2HDM. From the recent measurements of their branching ratios, we find that these processes do provide additional bounds on the new parameters in the model considered here. After the inclusion of the new physics contributions, the large enhancement of FBA, which is unobservably small within the SM and of the lepton polarization at large tanβ, may precisely test the SM or reveal new physics in forthcoming accurate experiments.

Scalar mesons in weak semileptonic decays ofB(s)

The transition form factors of ${B}_{(s)}\ensuremath{\rightarrow}S$, with $S$ denoting a scalar meson, are investigated in the light-cone sum rules approach. The numerical values are approximately twice the number estimated in the light-front quark model and QCD sum rules approach. Using these form factors, we present the analysis of the decay rates for $B\ensuremath{\rightarrow}{a}_{0}(1450)l{\overline{\ensuremath{\nu}}}_{l}$, $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430)l\overline{l}$, ${B}_{s}\ensuremath{\rightarrow}{K}_{0}^{*}(1430)l{\overline{\ensuremath{\nu}}}_{l}$, and ${B}_{s}\ensuremath{\rightarrow}{f}_{0}(1500)l\overline{l}$ with $l=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$. The results indicate that magnitudes of $BR({\overline{B}}_{0}\ensuremath{\rightarrow}{a}_{0}(1450)l{\overline{\ensuremath{\nu}}}_{l})$ and $BR({B}_{s}\ensuremath{\rightarrow}{K}_{0}^{*}(1430)l{\overline{\ensuremath{\nu}}}_{l})$ arrive at the order of ${10}^{\ensuremath{-}4}$, which can be measured in future experiments to clarify the inner structure of scalar mesons. It is also observed that $BR(B\ensuremath{\rightarrow}{K}_{0}^{*}(1430){\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}})$ and $BR({B}_{s}\ensuremath{\rightarrow}{f}_{0}(1500){\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}})$ are an order of magnitude smaller than the corresponding channels of ${e}^{+}{e}^{\ensuremath{-}}$ and ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ final states due to the heavily suppressed phase space. Moreover, the longitudinal lepton polarization asymmetry for $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430)l\overline{l}$ and ${B}_{s}\ensuremath{\rightarrow}{f}_{0}(1500)l\overline{l}$ are also investigated, whose values are close to $\ensuremath{-}1$ for the ${e}^{+}{e}^{\ensuremath{-}}$ and ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ pair except for the region close to the endpoints.

Lepton polarization asymmetry and forward–backward asymmetry in exclusive B→K1τ+τ- decay in universal extra dimension scenario

Decay rate, forward–backward asymmetry and polarization asymmetries of the final state leptons in B→K1τ+τ-, where K1 is the axial vector meson, are calculated in the standard model and in the universal extra dimension (UED) model. The sensitivity of the observables to the compactification radius R, the only unknown parameter in the UED model, is studied. Finally, the helicity fractions of the final state K1 are calculated and their dependence on the compactification radius is discussed. This analysis of the helicity fraction is briefly extended to B→K*ℓ+ℓ- (ℓ=e,μ) and compared with the other approaches existing in the literature.

Double lepton polarization in [formula omitted] decay in the Standard Model with fourth generations scenario

This study investigates the influence of the fourth generation quarks on the double lepton polarizations in Λ b → Λ ℓ + ℓ − decay by taking | V t ′ s * V t ′ b | = 0.005 , 0.01 , 0.02 , 0.03 with phase { 60 ° , 90 ° , 120 ° } . We will try to obtain a constrain on the mass of the 4th generation top like quark t ′ , which is consistent with the b → s ℓ + ℓ − rate. With the above mentioned parameters, we will try to show that the double lepton ( μ , τ ) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation quarks ( t ′ , b ′ ) via its indirect manifestations in loop diagrams.

Unpolarized and longitudinally polarized lepton forward-backward asymmetries inB→K*l+l−decay in the fourth-generation standard model

We investigate the influence of the fourth-generation quarks on the asymmetries for unpolarized and polarized leptons in $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay. We obtain that for both ($\ensuremath{\mu}$, $\ensuremath{\tau}$) channels the magnitudes of the differential forward-backward (FB) asymmetries and the average forward-backward asymmetries are quite sensitive to the fourth-generation quarks' mass and mixing parameters. We also achieve that, among the double lepton polarization FB asymmetries, just longitudinally polarized leptons' FB asymmetry shows considerable discrepancy with respect to the third-generation standard model. Moreover, we find that longitudinally polarized leptons' FB asymmetry and its variation with new fourth-generation standard model parameters coincide with unpolarized FB when the lepton mass vanishes. The study of FB asymmetries can serve as a good tool to search for new-physics effects, precisely, to search for the fourth-generation quarks (${t}^{\ensuremath{'}}$, ${b}^{\ensuremath{'}}$) via its indirect manifestations in the loop diagrams.

Analysis of theB→ πℓ+ℓ−decay in the standard model with fourth generation

We investigate the influence of the fourth generation quarks on the branching ratio and the CP-asymmetry in B → πl+l− decay. Taking the |Vt'dVt'b| ~ 0.001 with phase about 10°, which is consistent with the sin21 of the CKM and the Bd mixing parameter ΔmBd, we obtain that for both (μ, τ) channels the branching ratio, the magnitude of CP-asymmetry and lepton polarization depict strong dependency on the 4th generation quarks mass and mixing parameters. These results can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation quarks(t', b') via its indirect manifestations in loop diagrams.

Light mesons and muon radiative decays and photon polarization asymmetry

We systematically compute and discuss meson and muon polarized radiative decays. Doubly differential distributions in terms of momenta and helicities of the final lepton and photon are explicitly computed. The undergoing dynamics giving rise to lepton and photon polarizations is examined and analyzed in the soft and hard region of momenta. The particular configurations made by right-handed leptons with accompanying photons are investigated and interpreted as a manifestation of the axial anomaly. The photon polarization asymmetry is evaluated. Finiteness of polarized amplitudes against infrared and collinear singularities is shown to take place with mechanisms distinguishing between right- and left-handed final leptons. We propose a possible test using photon polarization to clarify a recently observed discrepancy in radiative meson decays.

The effects of fourth generation on the total branching ratio and the lepton polarization in Λb→ Λell+ell−decay

This study investigates the influence of the fourth generation quarks on the total branching ratio and the single lepton polarizations in \Lambda_b --> \Lambda \ell^+ \ell^- decay. Taking $|V_{t's}V_{t'b}| {0.01-0.03} with phase just below $90^\circ$, which is consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter \Delta m_{B_s}, we obtain that the total branching ratio and the single lepton(\mu, \tau) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to search for the fourth generation quarks(t', b').

General analysis of the rare Bc→Ds *ℓ+ℓ- decay beyond the standard model

The general analysis of the rare Bc→Ds*l+l- decay is presented by using the most general, model independent effective Hamiltonian. The dependencies of the branching ratios and of the longitudinal, normal and transversal polarization asymmetries for l- and the combined asymmetries for l- and l+ on the new Wilson coefficients are investigated. Our analysis shows that the lepton polarization asymmetries are very sensitive to the scalar and tensor type interactions, which will be very useful in looking for new physics beyond the standard model.

Study ofB→K0*(1430)ll¯decays

We examine the exclusive rare decays of B{yields}K{sub 0}*(1430)ll with K{sub 0}*(1430) being the p-wave scalar meson and l={nu}, e, {mu}, {tau} in the standard model. The form factors for the B{yields}K{sub 0}* transition matrix elements are evaluated in the light-front quark model. For the decays of B{yields}K{sub 0}*ll, the branching ratios are found to be (11.6,1.63,1.62,0.029)x10{sup -7} with l=({nu},e,{mu},{tau}) and the integrated longitudinal lepton polarization asymmetries (-0.97,-0.95,-0.03) with l=(e,{mu},{tau}), respectively.

Λb→Λℓ+ℓ- decay in universal extra dimensions

We study the exclusive Λb→Λl+l- decay in the Appelquist, Chang, Dobrescu model with a single universal extra dimension. We investigate the sensitivity of the branching ratio, lepton polarization and forward–backward asymmetry $\mathcal{A}_{\text{FB}}$ to the compactification parameter 1/R. We obtain the result that the branching ratio for the Λb→Λl+l- (l=μ,τ) decay changes about 25% compared to the SM value when 1/R=250 GeV, and the zero position of the forward–backward asymmetry is shifted to the left compared to the SM result. Therefore, measurement of the branching ratio of Λb→Λl+l- decay and determination of the zero position of $\mathcal{A}_{\text{FB}}$ are very useful in looking for new physics in the framework of the UED models.

Spin effects in rareB→Xsτ+τ−andB→K(*)τ+τ−decays in a single universal extra dimension scenario

We study the branching fractions and the lepton polarization asymmetries of rare $B\ensuremath{\rightarrow}{X}_{s}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ and $B\ensuremath{\rightarrow}{K}^{(*)}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ modes within the standard model and in the Appelquist-Cheng-Dobrescu model, which is a New Physics scenario with a single universal extra dimension. In particular, we investigate the sensitivity of the observables to the radius $R$ of the compactified extra dimension, which is the only new parameter in this New Physics model. For the exclusive transitions we study the uncertainties due to the hadronic matrix elements using two set of form factors, finding that in many cases such uncertainties are small. In particular, we show that the ${\ensuremath{\tau}}^{\ensuremath{-}}$ polarization asymmetries become free of hadronic uncertainties if Large Energy relations for the form factors, valid for low momentum transfer to the lepton pair, are used. We also consider ${K}^{*}$ helicity fractions and their sensitivity to the compactification parameter.

Nuclear effects on lepton polarization in charged-current quasielastic neutrino scattering

We use a correlated local Fermi gas (LFG) model, which accounts also for long distance corrections of the RPA type and final-state interactions, to compute the polarization of the final lepton in charged-current quasielastic neutrino scattering. The present model has been successfully used in recent studies of inclusive neutrino nucleus processes and muon capture. We investigate the relevance of nuclear effects in the particular case of τ polarization in tau-neutrino induced reactions for several kinematics of relevance for neutrino oscillation experiments.

B- c→η’ℓ-ν̄ decay and lepton polarization asymmetry

In this paper we study the lepton polarization asymmetry for the simileptonic OZI-forbidden annihilation B^-_c->\eta' \ell^- \bar{\nu} decay where \ell=\mu, \tau. Our results show that the branching ratio turn out to be of order 10^{-4}. Beside, we find that longitudinal, transversal and normal components of lepton polarizations can be measured for both \mu and \tau decay modes in the future experiments at the LHC.