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Register a new userComparative analysis of the semileptonic $Lambda_b rightarrow Lambda ell^+ ell^-$ transition in SM and different SUSY scenarios using form factors from full QCD
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We work out the semileptonic $Lambda_brightarrow Lambda ell^+ ell^-$ transition in standard as well as different supersymmetric models. In particular, considering the parametrization of the matrix elements entered the low energy effective Hamiltonian in terms of form factors in full QCD, we calculate the amplitude and differential decay rate responsible for this decay channel in supersymmetric models. We then use the form factors calculated via light cone QCD sum rules in full theory to analyze the differential branching ratio and lepton forward-backward asymmetry of this decay channel in different supersymmetric models and compare the obtained results with those of the standard model. We also discuss how the results of different supersymmetric models deviate from the standard model predictions and which SUSY scenarios are favored.
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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 $m_{t}geq 400 GeV$.
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.
We comparatively analyze the rare $Lambda _brightarrow Lambda ell^+ ell^-$ channel in standard model, supersymmetry and Randall-Sundrum model with custodial protection (RS$_c$). Using the parametrization of the matrix elements entering the low energy effective Hamiltonian in terms of form factors, we calculate the corresponding differential decay width and lepton forward-backward asymmetry in these models. We compare the results obtained with the most recent data from LHCb as well as lattice QCD results on the considered quantities. It is obtained that the standard model, with the form factors calculated in light-cone QCD sum rules, can not reproduce some experimental data on the physical quantities under consideration but the supersymmetry can do it. The RS$_c$ model predictions are roughly the same as the standard model and there are no considerable differences between the predictions of these two models. In the case of differential decay rate, the data in the range $4 $ GeV$^2/$c$^4leq$ $q^2 leq 6$ GeV$^2/$c$^4$ can not be described by any of the considered models.
We present the first lattice QCD determination of the $Lambda_b to Lambda^*(1520)$ vector, axial vector, and tensor form factors that are relevant for the rare decays $Lambda_b to Lambda^*(1520)ell^+ell^-$. The lattice calculation is performed in the $Lambda^*(1520)$ rest frame with nonzero $Lambda_b$ momenta, and is limited to the high-$q^2$ region. An interpolating field with covariant derivatives is used to obtain good overlap with the $Lambda^*(1520)$. The analysis treats the $Lambda^*(1520)$ as a stable particle, which is expected to be a reasonable approximation for this narrow resonance. A domain-wall action is used for the light and strange quarks, while the $b$ quark is implemented with an anisotropic clover action with coefficients tuned to produce the correct $B_s$ kinetic mass, rest mass, and hyperfine splitting. We use three different ensembles of lattice gauge-field configurations generated by the RBC and UKQCD collaborations, and perform extrapolations of the form factors to the continuum limit and physical pion mass. We give Standard-Model predictions for the $Lambda_b to Lambda^*(1520)ell^+ell^-$ differential branching fraction and angular observables in the high-$q^2$ region.
We obtain a lower limit on the compactification scale of extra dimension via comparison of the branching ratio in the baryonic $Lambda_brightarrow Lambda mu^+ mu^-$ 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.
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