Double-lepton Polarization Asymmetries Research Articles

Imprints of New Physics in Baryonic Decay ΞΞb → ΞΞl+l− in Non-universal Z’ Model

In this paper, an extensive study of exclusive baryonic decay Ξb → Ξl+l− (l = μ, τ) in non-universal Z' model is carried out. We use the form factors calculated by light cone QCD sum rule and analyse the effect of neutral gauge boson Z' on this decay. We study different physical observables like differential branching ratio, FB asymmetry, single and double lepton polarization asymmetries in the SM as well as in Z' model for this decay and represent graphically. We also estimate the numerical values of these kinematic observables in Z' model and compare with the SM. Our results indicate that these observables are very sensitive for both μ and τ channels which would provide signal for NP beyond the SM.

Study of B̄s → ϕμ+μ− decays in the G(211) model and vector leptoquark model

We study [Formula: see text] decay in the [Formula: see text] model and vector leptoquark model, respectively. We consider the effects of these two new physics (NP) models on some measured physical observables of this decay process, such as the differential branching fraction and the angular distributions. We find that the large deviation of the differential branching fraction between the measurement and the Standard Model (SM) prediction can be explained in these two NP models. However, we found that not all observables of the double-lepton polarization asymmetries are sensitive to the contributions of these NP models.

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.

Two Higgs Doublet Model III and Double-Lepton Polarization Asymmetries in Λb → Λμ+μ− Decays**Supported by the National Natural Science Foundation of China under Grant Nos. 11345005 and Key Scientific Research projects of Henan Educational Committee (13A140814), and the National Science Foundation under Grant No. U1332103

Using the form factors calculated both in lattice QCD and HQET, we analyze the branching ratio, double-lepton polarization asymmetries and averaged double-lepton polarization asymmetries of Λb Λμ+μ− decay in the 2HDM III, respectively. Combining the experimental constrains on the 2HDM III parameters, we take two set of representative parameter spaces in our calculations. For the branching ratio of Λb → Λμ+μ− decay, considering the uncertainties of the form factors and input parameters, we find the results of both SM and 2HDM III can satisfy the current experimental data in the framework of lattice QCD, but not in HQET. Then we calculate the double-lepton polarization asymmetries Pij and their averaged values 〈Pij〉, we find the double-lepton polarization asymmetries PLT, PNN, and PTT are sensitive to the 2HDM III. However, PLN, PNL, PNT, and PTN show the opposite results. The contribution of the 2HDM III to their averaged values have similar results.

The effects of vector leptoquark on the ℬb(ℬ = Λ,Σ) →ℬμ+μ− decays

In this paper, we have studied the baryonic semileptonic [Formula: see text] decays in the vector leptoquark model with [Formula: see text] state. Using the parameters’ space constrained through some well-measured decay modes, such as [Formula: see text], [Formula: see text] mixing and [Formula: see text] decays, we show the effects of vector leptoquark state on the double lepton polarization asymmetries of [Formula: see text] decays, and find that the double lepton polarization asymmetries, except for [Formula: see text], [Formula: see text] and [Formula: see text], are sensitive to the contributions of vector leptoquark 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.

Lepton polarization asymmetries of H -> + - decay in the Standard Model

Recently, CMS and ATLAS collaborations at LHC announced a Higgs like particle with mass near $125$GeV. Regarding this, to explore its intrinsic properties, different observables are needed to be measured precisely at the LHC for various decay channels of the Higgs. In this context, we calculate the final state lepton polarization asymmetries, namely, single lepton polarization asymmetries ($P_i$) and double lepton polarization asymmetries ($P_{ij}$) in the SM for radiative semileptonic Higgs decay $H\to\gamma\tau^+\tau^-$. In the phenomenological analysis of these lepton polarization asymmetries both tree and loop level diagrams are considered and it is found that these diagrams give important contributions in the evaluation of said asymmetries. Interestingly, it is found that in $P_{ij}$ the tree level diagrams contribute separately, which however, are missing in the calculations of $P_i$ and the lepton forward-backward asymmetries ($A_{FB}$). Similar to the other observables such as the decay rate and the lepton forward-backward asymmetries, the $\tau$-lepton polarization asymmetries would be interesting observables. The experimental study of these observables will provide a fertile ground to explore the intrinsic properties of the SM Higgs boson and its dynamics as well as help us to extract the signatures of the possible new physics beyond the SM.

Implication of nonuniversalZ′boson to the lepton polarization asymmetries in theB→K*ℓ+ℓ−decay

In this work we study the implication of the nonuniversal ${Z}^{\ensuremath{'}}$ model to the double lepton polarization asymmetries in the $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$, $(l=\ensuremath{\mu},\ensuremath{\tau})$ decay. To see the variation in the values of lepton polarization asymmetries from the standard model values, we have taken bounds of the UTfit collaboration, namely, ${S}_{1}$ and ${S}_{2}$ on the values of different parameters of the universal ${Z}^{\ensuremath{'}}$ model such as left-right couplings of the extra gauge boson with leptons and the new weak phase ${\ensuremath{\phi}}_{sb}$. It is found that double lepton polarization asymmetries are sensitive to the coupling parameters of ${Z}^{\ensuremath{'}}$ boson with fermions. Therefore, the measurements of these lepton polarization asymmetries for the above-mentioned decay at current colliders can be helpful to clarify the status of the existence of the extra gauge boson, i.e., ${Z}^{\ensuremath{'}}$.

Lepton polarization asymmetries in B → K 1ℓ+ℓ− decay as a searching tool for new physics

We study the single and double lepton polarization asymmetries in B → K 1l+l− (l = μ, τ ) decay by using most general non-standard local four-fermi interactions, where K 1 is the mixture of axial vector states K 1A and K 1B , which are the 3 P 1 and 1 P 1 states respectively. This study shows that both single and double lepton polarization asymmetries are influenced by new physics couplings. We have also seen the dependence of these asymmetries on mixing angle θ K between K 1A and K 1B flavor states. In addition to these, correlations between the lepton polarization asymmetries and branching ratio are also calculated. We have found that the observation of the above mentioned asymmetries at present and future colliders such as LHC and Super B factories will assist to dig out the status of physics beyond the SM.

Polarized, unpolarized directCPviolation, and single lepton polarization asymmetries ofB→K*ℓ+ℓ−decay inZ′model

In this work we study the implication of the fourth generation standard model (SM4) to the single and double lepton polarization asymmetries in the $B\rightarrow K^{\ast}\ell^{+}\ell^{-}$, $(l=\mu,\tau)$ decay. To see the variation in the values of lepton polarization asymmetries from the standard model values, we have taken lower bound values of CMS and ATLAS for $m_{t^\prime}=404$GeV and 552GeV respectively whereas $\phi_{sb}$ is vary in two allowed regions $75^\circ-115^\circ$ and $240^\circ-290^\circ$ while for the numerical values of these asymmetries $|\lambda_{t^\prime}|$ is set to be $6\times10^{-3}$. It is found that both single and double lepton polarization asymmetries are sensitive to the SM4 parameters. Therefore, the measurements of the lepton polarization asymmetries for the above mentioned decay at current colliders can be helpful to clear the smog on the status of the existence of the fourth generation.

Analysis of the Λb → Λℓ+ℓ− transition in the SM4 using form factors from full QCD

Using the responsible form factors calculated via full QCD, we analyze the $\Lambda_{b}\rightarrow \Lambda \ell^{+}\ell^{-}$ transition in the standard model containing fourth generation quarks (SM4). We discuss effects of the presence of $t'$ fourth family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy quark effective theory. The obtained results on branching ratio indicate that the $\Lambda_{b}\rightarrow \Lambda \ell^{+}\ell^{-}$ transition is more probable in full QCD comparing to the heavy quark effective theory. It is also shown that the results on all considered observables in SM4 deviate considerably from the SM predictions when $m_{t'}\geq 400 GeV$.

Constraint on compactification scale via recently observed baryonic Λ b → Λℓ + ℓ − channel and analysis of the Σ b → Σℓ + ℓ − transition in SM and UED scenario

We obtain a lower limit on the compactification scale of extra dimension via comparison of the branching ratio in the baryonic $\Lambda_b\rightarrow \Lambda \mu^+ \mu^-$ decay channel recently measured by CDF collaboration and our previous theoretical study. We also use the newly available form factors calculated via light cone QCD sum rules in full theory to analyze the flavour changing neutral current process of the $\Sigma_b \rightarrow \Sigma \ell^+ \ell^-$ in universal extra dimension scenario in the presence of a single extra compact dimension. We calculate various physical quantities like branching ratio, forward-backward asymmetry, baryon polarizations and double lepton polarization asymmetries defining the decay channel under consideration. We also compare the obtained predictions with those of the standard model.

Two-Higgs-doublet model and double-lepton polarization asymmetries inB→K0*(1430)ℓ+ℓ−decay

In this paper, the dependency of ${P}_{ij}$'s on the dilepton invariant mass, ${q}^{2}$, and the model III two-Higgs-doublets model (2HDM) parameters for $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430){\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay were investigated, and the results were compared to those of the standard model (SM) and Appelquist, Cheng and Dobrescu model. Also, for this decay, the effects of model III 2HDM parameters on the averages of double-lepton polarization asymmetries, $⟨{P}_{ij}⟩$'s, were studied, and by taking into account the corresponding theoretical and experimental errors in the SM, the results of the SM and 2HDM were compared to each other. In addition, by comparing the averages of double-lepton polarization asymmetries in 2HDM to those of SM4 and obtaining the required number of events for detecting each asymmetry at the LHC or the Super Large Hadron Collider, we present a comprehensive discussion regarding the lepton polarizations of $B\ensuremath{\rightarrow}{K}_{0}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay. We discovered that the study of the double-lepton polarization asymmetries and the corresponding averages in the $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430){\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay can provide good signals for probing new physics beyond the SM in the future $B$-physics experiments.

DOUBLE-LEPTON POLARIZATION ASYMMETRIES IN B → K1l+l- DECAY IN UNIVERSAL EXTRA DIMENSION

The double-lepton polarization asymmetries for the exclusive B → K1l+l- transition is studied in the universal extra dimension. It is shown that most of the double-lepton polarization asymmetries are sensitive to the model parameters. Any experimental measurements on double-lepton polarizations and their comparison with theoretical results can give valuable information on the physics beyond the standard model.

Systematic analysis of the B s → f 0 ℓ + ℓ − in the universal extra dimension

Using form factors enrolled to the transition matrix elements and calculated via light-cone QCD sum rules including next-to-leading order corrections in the strong coupling constant, we provide a systematic analysis of the $ B_s\rightarrow f_0 (980)\ell^+\ell^- $ both in the standard and universal extra dimension models. In particular, we discuss sensitivity of the differential branching ratio and various double lepton polarization asymmetries on the compactification factor of extra dimension and show how the results of the extra dimension model deviate from the standard model predictions. The order of branching ratio makes this decay mode possible to be checked at LHCb in near future.

Double-lepton polarization asymmetries and branching ratio of the B → γl + l − transition in universal extradimension

We study the radiative dileptonic $B \rar \gamma l^+ l^- $ transition in the presence of a universal extra dimension in the Applequist-Cheng-Dobrescu model. In particular, using the corresponding form factors calculated via light cone QCD sum rules, we analyze the branching ratio and double lepton polarization asymmetries related to this channel and compare the results with the predictions of the standard model. We show how the results deviate from predictions of the standard model at lower values of the compactification factor ($1/R $) of extra dimension.

Double-lepton polarization asymmetries inB→K0*(1430)l+l−decay in the fourth-generation standard model

In this paper, by deriving the expressions for double-lepton polarization asymmetries for $B$ to a scalar meson transition in SM and SM4 and considering the corresponding uncertainties in SM we investigate the indirect effects of the fourth generation of quarks on such asymmetries in the $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430){\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay. We also compare these asymmetries with those of $B\ensuremath{\rightarrow}K{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay and find out that most of these asymmetries behave similarly to the corresponding asymmetries for $B\ensuremath{\rightarrow}K{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay. We finally show that in the $\ensuremath{\mu}$ channel all asymmetries, except $⟨{P}_{LL}⟩$, and in $\ensuremath{\tau}$ channel only $⟨{P}_{LN}⟩$ can manifest the influence of the fourth generation at the minimum value of ${m}_{{t}^{\ensuremath{'}}}$ around 200 GeV. In addition, it is shown that for the $\ensuremath{\tau}$ channel the asymmetries such as $⟨{P}_{LL}⟩$, $⟨{P}_{NN}⟩$, and $⟨{P}_{TT}⟩$ can indicate the effect of such new physics at ${m}_{{t}^{\ensuremath{'}}}\ensuremath{\ge}300\text{ }\text{ }\mathrm{GeV}$. Hence, the $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430){\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay is a valuable tool for probing new physics beyond SM, especially in the indirect searches of the fourth generation of quarks $({t}^{\ensuremath{'}},{b}^{\ensuremath{'}})$ via its manifestations in loop diagrams.

Investigation of the Λ b → Λℓ+ℓ− transition in universal extra dimension using form factors from full QCD

Using the related form factors from full QCD which recently are available, we provide a comprehensive analysis of the $\Lambda_b \rightarrow \Lambda \ell^+ \ell^-$ transition in universal extra dimension model in the presence of a single universal extra dimension called the Applequist-Cheng-Dobrescu model. In particular, we analyze some related observables like branching ratio, forward-backward asymmetry, double lepton polarization asymmetries and polarization of the $\Lambda$ baryon in terms of compactification radius and corresponding form factors. We present the sensitivity of these observables to the compactification parameter, 1/R up to 1/R=1000 GeV. We also compare the results with those obtained using the form factors from heavy quark effective theory as well as the SM predictions.

Double-lepton polarization asymmetries and branching ratio in B → K 0 * (1430)l + l − transition from universal extra dimension model

We investigate the $B \rar K_{0}^{*}(1430) l^+ l^- $ transition in the Applequist-Cheng-Dobrescu model in the presence of a universal extra dimension. In particular, we calculate double lepton polarization asymmetries and branching ratio related to this channel and compare the obtained results with the predictions of the standard model. Our analysis of the considered observables in terms of radius $R$ of the compactified extra-dimension as the new parameter of the model show a considerable discrepancy between the predictions of two models in low $\frac{1}{R}$ values.

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.