Lepton Polarization Asymmetries Research Articles

Analysis of B s →φ ℓ + ℓ − decay with new-physics effects

The rare B s →φ ℓ + ℓ −decay is investigated by using the most general model-independent effective Hamiltonian for ℓ=μ,τ. The calculated value of Br(B s →φ μ + μ −)=1.92×10−6 is consistent with the experimental upper bound. The dependencies of the branching ratios and polarization asymmetries of leptons and combined lepton–antilepton asymmetries on the new Wilson coefficients are presented. The analysis shows that the branching ratios and the lepton-polarization asymmetries are very sensitive to scalar- and tensor-type interactions. The results obtained in this work will be very useful in searching new physics beyond the standard model.

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.

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.

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.

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.

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.

Lepton Polarization Asymmetry in B→ℓ+ℓ− Decaybeyond the Standard Model

The lepton polarization asymmetry in the B→ℓ+ℓ− decay, when one of the leptons is polarized, is investigated by using the most general form of the effective Hamiltonian. We find allowedregions for the new scalar Wilson coefficients, assuming that theexperimental branching ratio is measured within 10% percentuncertainty. Then using these restrictions to the new coefficientsthe sensitivity of the lepton polarization asymmetry to them isstudied. Moreover, it is observed that there are regions of termsdescribing the scalar interactions, where lepton polarizationasymmetry differs from zero, which can serve as a good test forsearching new physics beyond the standard model.

Exclusive semileptonic rare decays $B \to K^{(*)} l^ + l^-$ in a SUSY SO(10) GUT

In the SUSY SO(10) GUT context, we study the exclusive processes $B \to K^{(*)} l^+l^-(l=\mu,\tau)$. Using the Wilson coefficients of relevant operators including the new operators $Q_{1,2}^{(\prime)}$ which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like, the invariant mass spectrum (IMS), lepton pair forward backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients $C_{Q_{1,2}}^\prime$, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA, $dL/d\hat{s}$, and $dT/d\hat{s}$ of $B \to K^{(*)} \tau^+ \tau^-$ decay, which are expected to be measured in B factories, and the average of the normal polarization $dN/d\hat{s}$ can reach several percent for $B \to K \mu^+ \mu^-$ and it is 0.05 or so for $B\to K \tau^+\tau^-$, which could be measured in the future super B factories and provide a useful information to probe new physics and discriminate different models.

THE EFFECTS OF NONSTANDARD Z COUPLINGS ON THE LEPTON POLARIZATIONS IN Bs→γℓ+ℓ-DECAYS

The fact that the measured B→ππ, πK branching ratios exhibit puzzling patterns has received a lot of attention in the literature and motivated the formulation of a series of new physics scenarios with enhanced Z-penguins. Here, we analyze the effect of such an enhancement on the lepton polarization asymmetries of Bs→γℓ+ℓ-decays by applying the results of a specific scenario for the solution of "B→πK puzzle".

Lepton polarization asymmetries forB→K*ell+ell−: A Model Independent approac

In this work we shall derive expressions for the single and double lepton polarization asymmetries for the exclusive decay $B \to K^* \ell^+ \ell^-$, using the most general model independent effective Hamiltonian. We have conducted this study with this particular channel as it has the highest branching ratio among the various purely leptonic and semi-leptonic decay modes, making this mode particularly useful for studying physics beyond the SM. We have also analyzed the effects on these polarization asymmetries, and hence the physics underlying it, when complex phases are included in some of the Wilson coefficients.

Effects of enhancedZpenguin diagrams on lepton polarizations inB→Xsℓ+ℓ−

The sensitivity of the $B\ensuremath{\rightarrow}\ensuremath{\pi}K$ mode to electroweak penguin diagrams and the recent experimental data for the $B\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi},\ensuremath{\pi}K$ modes has given rise to what is known as the ``$B\ensuremath{\rightarrow}\ensuremath{\pi}K$ puzzle.'' Recently it has been observed that this puzzle can be resolved by considering the new physics which can enter via ${Z}^{0}$ penguin diagrams. In this note we analyze the effect of these enhanced ${Z}^{0}$ penguin diagrams on the lepton polarization asymmetries of $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$.

Lepton polarization correlations inB→K*τ−τ+

In this work we will study the polarizations of both leptons $(\ensuremath{\tau})$ in the decay channel $\stackrel{\ensuremath{\rightarrow}}{B}{K}^{*}{\ensuremath{\tau}}^{\ensuremath{-}}{\ensuremath{\tau}}^{+}.$ In the case of the dileptonic inclusive decay $\stackrel{\ensuremath{\rightarrow}}{B}{K}^{*}{\mathcal{l}}^{\ensuremath{-}}{\mathcal{l}}^{+},$ where apart from the polarization asymmetries of a single lepton $\mathcal{l},$ one can also observe the polarization asymmetries of both leptons simultaneously. If this sort of measurement is possible then we can have, apart from decay rate, forward backward asymmetry and the six single lepton polarization asymmetries (three each for ${\mathcal{l}}^{\ensuremath{-}}$ and ${\mathcal{l}}^{+}),$ nine more double polarization asymmetries. This will give us a very useful tool in more strict testing of the standard model (SM) and the physics beyond. We discuss the double polarization asymmetries of the $\ensuremath{\tau}$ leptons in the decay mode $\stackrel{\ensuremath{\rightarrow}}{B}{K}^{*}{\ensuremath{\tau}}^{\ensuremath{-}}{\ensuremath{\tau}}^{+}$ within the SM and the minimal supersymmetric extension of it.

Study of decays

We study the rare decays of Bs → Msℓ (Ms = η, η′, ϕ and ℓ = ν, e, μ, τ) in the standard model. With the hadronic form factors evaluated in the light front and constituent quark models, we estimate the decay branching ratios, respectively. We also discuss the longitudinal lepton polarization and forward-backward asymmetries.

T-odd correlations inπ→eνeγandπ→μνμγdecays

The transverse lepton polarization asymmetry in ${\ensuremath{\pi}}_{l2\ensuremath{\gamma}}$ decays may probe T-violating interactions beyond the Standard Model. Dalitz plot distributions of the expected effects are presented and compared to the contribution from the Standard Model final-state interactions. We give an example of a phenomenologically viable model, where a considerable contribution to the transverse lepton polarization asymmetry arises.

New physics effects inΛb→Λl+l−decay with lepton polarizations

We study lepton polarization asymmetries in the (Lambda_b -> Lambda l^+ l^-) decay using the most general model independent effective Hamiltonian. The dependence of the lepton polarizations and their combinations on the new Wilson coefficients are studied in detail. It is observed that there is a region for the new Wilson coefficients for which the branching ratio coincides with the standard model prediction, while lepton polarizations show considerable departure from standard model.

Bs→τ+τ−γdecay in the general two Higgs doublet model including the neutral Higgs boson effects

We investigate the differential branching ratio, branching ratio, differential forward-backward asymmetry, the forward-backward asymmetry of the lepton pair and the lepton polarization asymmetry of the exclusive $B\to \tau^+ \tau^- \gamma$ decay in the general two Higgs doublet model including the neutral Higgs boson effects. We analyse the dependencies of these quantities on the model parameters and also on the neutral Higgs boson effects. We found that they get considerable enhancement from the two Higgs doublet model compared to the standard model and neutral Higgs boson effects are quite sizable.

Light-front quark model analysis of rareB→Kl+l−decays

Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare $B\to K\ell^+\ell^-(\ell=e,\mu,\tau$) decays within the standard model. Evaluating the timelike form factors, we use the analytic continuation method in $q^+=0$ frame to obtain the form factors $F_+$ and $F_T$, which are free from zero-mode. The form factor $F_-$ which is not free from zero-mode in $q^+ = 0$ frame and contaminated by the higher(or nonvalence) Fock states in $q^+ \neq 0$ frame is obtained from an effective treatment for handling the nonvalence contribution based on the Bethe-Salpeter formalism. The covariance(i.e. frame-independence) of our model calculation is discussed. We obtain the branching ratios for ${\rm BR}(B\to K\ell^+\ell^-)$ as $4.96\times10^{-7}|V_{ts}/V_{cb}|^2$ for $\ell=e,\mu$ and $1.27\times 10^{-7}|V_{ts}/V_{cb}|^2$ for $\ell=\tau$.

Precision Tau and Electron Neutral Current Asymmetry Measurements from the Tau Polarization at OPAL

A measurement of the τ lepton polarization and forward-backward asymmetry near the Z0 resonance using the OPAL detector is described. The measurement is based on analysis of [Formula: see text], [Formula: see text], τ → π (K) ντ, τ → ρ ντ and τ → a1 ντ decays from a sample of 144, 810 e + e - → τ+ τ- candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the τ lepton decays according to V - A theory, we measure the average τ polarization near [Formula: see text] to be <Pτ> = (-14.11 ± 0.73 ± 0.56)% and the τ polarization forward-backward asymmetry to be [Formula: see text], where the first error is statistical and the second systematic. These results are consistent with the hypothesis of lepton universality and, within the context of the Standard Model, combine to produce [Formula: see text].