14 research outputs found
Rare Decays of Heavy Baryons using Soft Collinear Effective Theory
No full textIn the era of high-luminosity hadronic colliders, the rare heavy-to-light decay Lambda_b to Lambda l+ l- receives increasing research attention in both experimental and theoretical particle phenomenology. This flavour-changing neutral-current decay is a potential window for the discovery of new Physics beyond the Standard Model through its helicity-sensitive nature, complementing past and ongoing searches and calculations related to the B meson.
In this work the universal soft form factor in the heavy-quark and large-recoil limits is calculated using light-cone sum rules in the framework of soft-collinear effective theory, as is the O(alpha_s) correction from hard-collinear gluon exchange.
Numerical estimates on form-factor ratios and experimental observables are presented. Related issues, including baryonic transition form factors and in particular light-cone distribution amplitudes for the heavy baryon Lambda_b, are also discussed
Radiative Sigma(b)->Sigma gamma decay in SM and BSM
No full textUsing transition form factors calculated via light cone QCD sum rules in full theory, we comparatively analyze the rare radiative Sigma(b) -> Sigma gamma decay in the standard model (SM) and models with one or two universal extra dimensions, such as beyond the SM scenarios. We estimate the total decay width and branching ratio associated with this decay channel in the SM and compare the obtained results with those of scenarios with one or two universal extra dimensions. We discuss how the results of universal extra dimensional models approach the SM predictions when the compactification factor of extra dimension is increased
Effects of vector leptoquarks on Lambda(b) -> Lambda(c)l(v)over-bar(l) decay
No full textExperimental data on, R(D-(*()), R(K-(*()), and R(J/psi),, provided by different collaborations, show sizable deviations from the standard model predictions. To describe these anomalies, many new physics scenarios have been proposed. One of them is the leptoquark model, which introduces the simultaneous coupling of vector and scalar leptoquarks to quarks and leptons. To look for similar possible anomalies in the baryonic sector, we investigate the effects of a vector leptoquark U-3(3, 3, 2/3) on various physical quantities related to the tree-level Lambda b -> Lambda(c)l (v) over bar (l) decays (l = mu, tau), which proceed via b -> cl (v) over bar (l) transitions at the quark level. We calculate the differential branching ratio, forward-backward asymmetry, and longitudinal polarizations of leptons and Lambda(c) baryons at the mu and tau lepton channels in the leptoquark model and compare their behavior to the predictions of the SM in terms of q(2). In the calculations, we use the form factors calculated in full QCD as the main input and account for all errors coming from the form factors and model parameters. We observe that at the tau channel, the R-A fit solution to data related to the leptoquark model sweeps some regions out of the SM band; nevertheless, the fit has a considerable intersection with the SM predictions. The R-B type solution gives roughly the same results as the SM on DBR(q(2)) - q(2). At the mu channel, the leptoquark model gives results that are consistent with the SM predictions and existing experimental data on the behavior of DBR(q(2)) with respect to q(2). Concerning the q(2) behavior of the AFB(q(2)), the two types of fits for and the predictions at the mu channel in the leptoquark model give exactly the same results as the SM. We also investigate the behavior of the parameter R(q(2)) with respect to q(2) and the value of R(Lambda(c)) in both the vector leptoquark and SM models. Both fit solutions lead to results that deviate considerably from the SM predictions for R(q(2)) - q(2) and R(Lambda(c)). Future experimental data on R(q(2)) - q(2) and R(Lambda(c)), made available by measurements of the Lambda(b) -> Lambda(c)tau(nu) over bar tau channel, will be particularly helpful. Any experimental deviations from the SM predictions in this channel would emphasize the importance of tree-level hadronic weak transitions as good probes of new physics effects beyond the SM
Comparative analysis of the Λb → Λℓ+ℓ- decay in the SM, SUSY, and RS model with custodial protection
No full textAzizi, Kazem (Dogus Author)We comparatively analyze the rare Λb→Λℓ+ℓ- channel in the standard model, supersymmetry, and Randall-Sundrum model with custodial protection (RSc). 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, cannot reproduce some experimental data on the physical quantities under consideration, but the supersymmetry model can do it. The RSc 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 GeV2/c4≤q2≤6 GeV2/c4 cannot be described by any of the considered models
Analysis of the radiative Lambda(b) -> Lambda(gamma) transition in the standard model and scenarios with one or two universal extra dimensions
No full textWe investigate the radiative process of Lambda(b) -> Lambda(gamma) in the standard model as well as models with one or two compact universal extra dimensions. Using the form factors entered to the low-energy matrix elements, calculated via light-cone QCD in full theory, we calculate the total decay width and branching ratio of this decay channel. We compare the results of the extra-dimensional models with those of the standard model on the considered physical quantities and look for the deviations of the results from the standard model predictions at different values of the compactification scale (1/R)
Comparative analysis of the semileptonic Lambda(b) -> Lambda l(+)l(-) transition in SM and different SUSY scenarios using form factors from full QCD
No full textWe work out the semileptonic Lambda(b) -> Lambda l(+)l(-) 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
Analysis of the semileptonic Lambda(b) -> Lambda l(+)l(-) transition in the topcolor-assisted technicolor model
No full textWe comparatively analyze the flavor-changing neutral current process of Lambda(b) -> Lambda l(+)l(-) in the standard model as well as the topcolor-assisted technicolor model using the form factors calculated via light cone QCD sum rules in full theory. In particular, we calculate the decay width, branching ratio and lepton forward-backward asymmetry related to this decay channel. We compare the results of the topcolor-assisted technicolor model with those of the standard model and debate how the results of the topcolor-assisted technicolor model depart from the standard model predictions. We also compare our results on the branching ratio and differential branching ratio with recent experimental data provided by CDF and LHCb Collaborations
Impact of Scalar Leptoquarks on Heavy Baryonic Decays
No full textWe present a study on the impact of scalar leptoquarks on the semileptonic decays of Λb, Σb, and Ξb. To this end, we calculate the differential branching ratio and lepton forward-backward asymmetry defining the processes Λb→Λl+l-, Σb→Σl+l-, and Ξb→Ξl+l-, with l being μ or τ, using the form factors calculated via light cone QCD in full theory. In calculations, the errors of form factors are taken into account. We compare the results obtained in leptoquark model with those of the standard model as well as the existing lattice QCD predictions and experimental data
Constraint on compactification scale via recently observed baryonic nu(b) -> nu l(+)l(-) channel and analysis of the Sigma(b) -> Sigma l(+)l(-) transition in SM and UED scenario
No full textWe obtain a lower limit on the compactification scale of extra dimension via comparison of the branching ratio in the baryonic A(b) -> A 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) -> Sigma l(+)l(-) 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
Feasibility studies for the measurement of time-like proton electromagnetic form factors from p ̄ p→ μ+μ- at P ̄ ANDA at FAIR
No full textThis paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, | GE| and | GM| , using the p ̄ p→ μ+μ- reaction at P ̄ ANDA (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at P ̄ ANDA , using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is p ̄ p→ π+π-, due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented
