New CP observables in B0(t) -> hyperon + antihyperon from parity violation in the sequential decay

Abstract

We consider the decay B0(t) -> hyperon + antihyperon, followed by hyperon weak decay. We show that parity violation in the latter allows to reach new CP observables: not only Im(lambda_f) but also Re(lambda_f) can be measured. In the decay B0_d(t) -> Lambda LambdaBar (BR ~ 10-6), Lambda -> p pi- these observables reduce to sin(2alpha) and cos(2alpha) in the small Penguin limit, the latter solving the discrete ambiguity alpha -> pi/2 -alpha. For beta one could consider the Cabibbo suppressed mode B0_d(t) -> Lambda_c Lambda_cBar (BR \~ 10-4), Lambda_c -> Lambda pi+, p K0bar, ... (with BR ~ 10-2). The pure Penguin modes B0_s(t)->Sigma-Sigma-Bar, Xi-Xi-Bar, Omega-Omega-Bar (BR ~ 10-7) can be useful in the search of CP violation beyond the Standard Model. Because of the small total rates, the study of these modes could only be done in future high statistics experiments. Also, in the most interesting case Lambda LambdaBar the time dependence of the asymmetry can be difficult to reconstruct. On the other hand, we show that B_d mesons, being a coherent source of Lambda LambdaBar, is useful to look for CP violation in Lambda decay. We also discuss B0_d(t) -> J/Psi K*0 -> l+ l- K_S pi0 where the secondary decays conserve parity, and angular correlations allow to determine terms of the form cos(delta)cos(2beta), delta being a strong phase. This phase has been measured by CLEO, but we point out that a discrete ambiguity prevents to determine sign(cos(2beta)). However, if one assumes small strong phases, like in factorization and as supported by CLEO data, one could have information on sign(cos(2beta)). Similar remarks can be done for cos(2alpha) in the decay B_d0(t) -> rho rho -> 4pi.