Erratum to: Differential branching fraction and angular analysis of Λb0 → Λμ+μ− decays (Journal of High Energy Physics, (2015), 2015, 6, (115), 10.1007/JHEP06(2015)115)

Abstract

The angular distribution of the dimuon system of the decays Λ 0 b → Λµ+µ − and Λ 0 b → Λµ+µ − can be described by dΓ d cos θ` = 3 8 (1 + cos2 θ`)(1 − fL) + A ` FB cos θ` + 3 4 fL sin2 θ` , (1) where A` FB is the forward-backward asymmetry of the dimuon system and fL is its longitudinal polarisation fraction. For the Λ 0 b decay, the angle θ` is calculated as the angle between the direction of the µ + lepton, in the rest frame of the dimuon pair, and the direction of the dimuon pair, in the rest frame of the Λ 0 b decay. The forward-backward asymmetry of the lepton pair, A` FB, is "odd" under CP conjugation and changes in sign between the Λ 0 b and Λ 0 b decays. To compensate for this sign, the angle θ` is usually calculated from the µ − lepton rather than the µ + lepton such that A` FB can be calculated from the combined sample. This was the intended approach of this paper. Unfortunately, A` FB was determined using the µ + lepton when determining θ` for both the Λ 0 b and the Λ 0 b decays. Consequently, the value of A` FB in this paper corresponds to a difference A(A` FB) in asymmetries between the Λ 0 b and Λ 0 b decays rather than a proper average and is expected to be zero if CP is conserved. The result quoted as A` FB in this paper should therefore be interpreted as A(A ` FB) = −0.05 ± 0.09 (stat) ± 0.03 (syst), (2) and is indeed consistent with the Standard Model expectation that CP violating effects should be small in the decay Λ 0 b → Λµ+µ −. This is in itself a useful result. A measurement of A` FB has since been presented in ref. [1]. The results in ref. [1] supersede the corresponding results in this paper. Note, the mistake in the angular definition only affects the value of A` FB presented in the paper. The values of fL, Ah FB and the differential branching fraction are unchanged, due to the symmetry of the efficiency model in cos θ` .