On Testing V - A in Λ b Decays ?

We comment on a recent suggestion by Amundson, Rosner, Worah and Wise to test the chirality of the b-quark decay coupling via polarized Λb baryons produced in e+e− → Z → Λb +X. We study the effect of contributions from an amplitude in which a right-handed b to c current couples to a V-A lepton current. Submitted to Physical Review D ? Work supported by the Department of Energy, contract DE–AC03–76SF00515. † On leave of absence from the Physics Department, Technion, Haifa, Israel. ‡ Permanent address: Department of Physics, School of Medical Sciences, University of Tokushima, Tokushima, Japan. b-quark decays are known to be governed by very weak couplings, which in the Standard Model are given by the two tiny mixing angles θ23, θ13 1 . These decays are therefore very sensitive to new kinds of interactions, and in particular to righthanded couplings 2 . Recently we described a viable SU(2)L×SU(2)R×U(1) model, in which b-quarks decay purely right-handedly 3 . We pointed out that measurement of the lepton asymmetry in B → D∗`ν 4 cannot distinguish our model from the Standard Model, since in this process the lepton current in our model is dominantly V+A 5 . A nice test, which may distinguish between the exchange of leftand righthanded gauge bosons in b decays was suggested by Amundson, Rosner, Worah and Wise 6 . These authors noted that the electron spectrum from highly polarized Λb’s produced in e+e− → Z → Λb + X is significantly harder for V-A than for V+A quark and lepton currents. Thus, ongoing experiments at LEP, in which leptons from Λb decay were already observed 7 , may offer an early test of the model. In this brief note we wish to study the effect of WL − WR mixing, which exists in our model in addition to WR exchange 3 , to see how much it can affect the electron spectrum calculated in 6 . Also, as a model-independent study and to demonstrate another version of right-handed b to c couplings, we will first calculate the electron spectrum for a V+A quark coupling, assuming that the lepton current is purely left-handed. Such a possibility is outside the parameter range of the model of 3 , since it corresponds to decays due to WL −WR mixing alone. This case, which seems to be one’s first guess of what right-handed b couplings might be, was recently excluded by the B → D∗`ν data . Our purpose of including a discussion of this case is to show that also in the case of Λb decays it can be most easily distinguished from other cases studied here. We use the physics of the heavy quark symmetry presented in 6 8 and the