Measurement of the parity-violating asymmetry parameter αb and the helicity amplitudes for the decay Λ⁰b→J/ψΛ⁰ with the ATLAS detector

Abstract

A measurement of the parity-violating decay asymmetry parameter, alpha b, and the helicity amplitudes for the decay Lambda0b ->J/psi(mu+mu -)Lambda0(p pi -) is reported. The analysis is based on 1400 Lambda0b and Lambda -bar0b baryons selected in 4.6fb -1 of proton-proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the Lambda0b and Lambda -bar0b samples under the assumption of CP conservation, the value of alpha b is measured to be 0.30+/-0.16(stat)+/-0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.