Rare decays of Λ b →Λ+γ and Λ b →Λ+l + l − in the light-cone sum rules

Abstract

The weak decays of Λ b → Λ + γ and Λ b → Λ + l + l − are investigated in the Standard Model using light-cone sum rules approach. The higher twist distribution amplitudes of Λ baryon to the leading conformal spin are included in the sum rules for transition form factors. Our results indicate that the higher twist distribution amplitudes almost have no influences on the transition form factors retaining the heavy quark spin symmetry, while such corrections can result in significant impacts on the form factors breaking the heavy quark spin symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of Λ baryon are also employed in the sum rules for a comparison, which can give rise to the form factors approximately five times larger than that in terms of conformal expansion. Utilizing the form factors calculated in LCSR, the physical observables like decay rate, polarization asymmetry and forward-backward asymmetry are analyzed for the decays of Λ b → Λγ, Λl + l − . I. INTRODUCTION Generally, new physics can be accessible through rare decays, where the contributions from the Standard Model (SM) are suppressed enough. Hence, such decays can provide an ideal platform to test the SM precisely as well as to bound new physics parameters stringently. Rare decays involving b → s flavor changing neutral current (FCNC), which are forbidden at the tree level in the standard model, can only be induced by Glashow-Iliopoulos-Maiani mechanism [1] via loop diagrams. The Cabibbo-Kobayashi-Maskawa (CKM) matrix [2, 3] elements can be determined quantitatively from b → s rare decays, B 0 s −B 0 s mixing [4] etc., which will test its unitarity under the requirement of the SM.It is well known that the inclusive decays are relatively robust theoretically, since the decay rate can be systematically and reasonably approximated by the decay of a free b quark into light quarks, gluons and photons; but the counterpart of experimental measurements are quite difficult. On the

Analysis of the radiativeΛb→Λγtransition in the standard model and scenarios with one or two universal extra dimensions

“…From this table we see that, within the errors, our result is consistent with those of QCD sum rules [56,57] and a special current [59] and exactly the same with pole model's prediction [60]. However, our prediction differs considerably from these of light-cone QCD sum rules [55], covariant oscillator quark model (COQM) [58] and Ioffe current [59]. The difference between our SM prediction on the branching ratio with that of Ref.…”

“…For comparison, we also give the results of other related works [55][56][57][58][59][60] in the same table as well as the upper limit from the Particle Data Group (PDG) [54]. From this table we see that, within the errors, our result is consistent with those of QCD sum rules [56,57] and a special current [59] and exactly the same with pole model's prediction [60].…”

“…[55] with the same method can be attributed to the point that in Ref. [55] the authors consider the distribution amplitudes (DAs) of an à baryon as the main inputs of the light-cone QCD sum rule method up to twist 6; however, in our case, the form factors have been calculated considering the DAs up to twist 8. Besides, in Ref.…”

“…Finally, in Ref. [55] the form factors are calculated in the heavy quark effective limit while we use form factors calculated in full QCD without any approximation. The order of the branching ratio shows that this channel can be accessible at the LHCb.…”

Perturbative corrections to Λ b → Λ form factors from QCD light-cone sum rules

“…A closely related approach was applied to construct the LCSR for Λ b → Λ form factors at tree level from the vacuum-to-Λ-baryon correlation function [23] where the Λ-baryon DA entering the sum rules were only considered at the leading conformal spin accuracy (the non-asymptotic corrections were worked out in [24] now) and the Chernyak-Zhitnitsky [25] type of the Λ-baryon interpolating current was used (see [26,27] for alternative choices and [28] for interesting comments on the choices of the baryonic interpolating currents). Another approach to compute the Λ b → Λ form factors based upon the transverse-momentum-dependent (TMD) factorization was carried out in [29] where the soft overlap contribution was assumed to be suppressed by the Sudakov factor and only the hard spectator interactions induced by twohard-collinear-gluon exchanges are taken into account.…”