Flavor-Dependent Supersymmetric Phases andCPAsymmetry inB→XsγDecays

Abstract

We study the direct CP asymmetry in B → Xsγ decay in SUSY models with non-universal Aterms. We show that the flavour-dependent phases of the A-terms, unlike the flavour-independent ones, can give rise too large contribution to the CP asymmetry while respecting the experimental bounds on the branching ratio of B → Xsγ decay and the electric dipole moments of the electron and neutron. The CP asymmetry of this decay is predicted to be much larger than the standard model prediction in a wide region of the parameter space. In particular, it can be of order 10 − 15% which can be accessible at B factories.PACS numbers:12.60. Jv, 11.30.Er, Direct CP asymmetry in the inclusive radiative decay B → X s γ is measured by the quantityThe Standard Model (SM) prediction for this asymmetry is very small, less than 1%. Thus, the observation of sizeable asymmetry in the decay B → X s γ would be a clean signal of new physics.The most recent result reported by CLEO collaboration for the CP asummetry in these decays is [1]and it is expected that the measurements of A b→sγ CP will be improved in the next few years at the B-factories.Supersymmetric predictions for A b→sγ CP are strongly dependent on the flavour structure of the soft breaking terms. It was shown that in the universal case, as in the minimal supergravity models, the prediction of the asymmetry is less than 2%, since in this case the electric dipole moments (EDM) of the electron and neutron constrain the SUSY CP-violating phases to be very small [2,3]. Furthermore, it is also known that in this case, one can not get any sizeable SUSY contribution to the CP-violating observables, ε and ε ′ /ε [4][5][6][7]. The impact of flavour structure in the non-degenerate A-terms, which is expected in string inspired models, has been studied [6][7][8]. In these works, it was emphasized that the flavour-dependent SUSY CP-violating phases are not essentially constrained by the EDMs and can lead to large contributions to the observed CP-violating phenomena in the kaon system and, in particular, to the direct CP violation measured by ε ′ /ε.In this letter, we explore the effect of these large flavour-dependent phases on inducing a direct CP violation in B → X s γ decay. We will show that the values of the asymmetry A b→sγ CP in this class of models are much larger than the SM prediction in a wide region of the parameter space allowed by experiments, namely the EDM experimental limits and the bounds on the branching ratio of B → X s γ . The enhancement of A b→sγ CP is due to the important contributions from gluino-mediated diagrams, in this scenario, in addition to the usual chargino and charged Higgs contributions.The effective Hamiltonian for b → sγ decay is given bywhere Q i (µ b ) and C i (µ b ) represent an operator for the ∆B = 1 transition and its Wilson coefficient, respectively, evaluated at the renormalization scale µ b ≃ O(m b ). The relevant operators for b → sγ decay are given byThe expression for the asymmetry A b→sγ CP , corrected to next-to-leading order is given by [9]where...

Present status of inclusive rareBdecays

“…34). Nonminimal models with squark mixing or models with R-parity violation allow for asymmetries, of the order of 10% or even larger (Kagan and Neubert, 1998; Aoki et al, 1999;Baek and Ko, 1999;Chua et al, 1999;Giusti et al, 1999;Kim et al, 1999;Chun et al, 2000;Bailin and Khalil, 2001;Demir and Olive, 2002) argue that the asymmetry in nonminimal models could be even larger than Ϯ15% if the gluino mass is significantly lighter than the squark masses. Recent studies of the B→X d ␥ rate asymmetry in specific models led to asymmetries between Ϫ40% and ϩ40% (Akeroyd et al, 2001) and Ϫ45% and ϩ21% (Asatryan and Asatrian, 1999;.…”

Comparative study of CP asymmetries in supersymmetric models

“…Recently it has been shown that the SUSY contribution to the CP asymmetry in the b → sγ decay, even with the inclusion of experimental constraints on electric dipole moments and branching ratio of B → X s γ, could be much larger than the SM expectation [36] . Therefore, in the light of present experimental results, it would be challenging to analyze the SUSY predictions for the correlation between A CP (b → sγ) and S φ,(η ′ )K S , since in SUSY models these asymmetries are strongly correlated.…”

“…This can be possible, for instance, in SUSY models where the CP violating phases entering in b → s transitions are independent from the corresponding ones affecting EDMs. An interesting example is provided by SUSY models with flavor dependent CP violating phases [35][36][37].…”

On the B→Xll decays in general supersymmetric models

“…Therefore, to be consistent, one has to include the contributions of these operators. Indeed, the effects of the operatorsQ 7,8 have been found to be very significant for the branching ratio of the B → X s γ decay [5] and for the CP asymmetry of this decay as well [6]. The Wilson coefficients C i (µ) can be decomposed as…”