Analysis of the Lambda(b) -> Lambda l(+)l(-) transition in the SM4 using form factors from full QCD

Abstract

Using the responsible form factors calculated via full QCD, we analyze the Lambda(b) -> Lambda l(+)l(-) transition in the standard model containing fourth-generation quarks (SM4). We discuss the effects of the presence of the t' fourth-family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double-lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy-quark effective theory. The obtained results on the branching ratio indicate that the Lambda(b) -> Lambda l(+)l(-) transition is more probable in full QCD comparing to the heavy-quark effective theory. It is also shown that the results on all considered observables in the SM4 deviate considerably from the SM predictions when m(t') >= 400 GeV.