Abstract
A measurement of the parity-violating decay asymmetry parameter, alpha_b, and the helicity amplitudes for the decay Lambda_b->J/psi(mu mu)+Lambda(p pi) is reported. The analysis is based on 1400 Lambda_b and anti-Lambda_b baryons selected in 4.6/fb 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 Lambda_b and anti-Lambda_b 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.
Highlights
Parity violation, a well-known feature of weak interactions [1,2,3,4], is exhibited in its maximal form in decays of muons and τ leptons
Several models have been employed to predict the value of the parity-violating decay asymmetry parameter αb for the weak decay Λ0b → J=ψΛ0
This paper provides a measurement of comparable precision using 4.6 fb−1 pp collision data recorded by the ATLAS detector with a center-of-mass energy of 7 TeV
Summary
A well-known feature of weak interactions [1,2,3,4], is exhibited in its maximal form in decays of muons and τ leptons. Several models have been employed to predict the value of the parity-violating decay asymmetry parameter αb for the weak decay Λ0b → J=ψΛ0. The decay asymmetry parameter αb is related to the helicity amplitudes as follows [15]: αb 1⁄4 jaþj2 − ja−j2 þ jbþj2 − jb−j2:. Only six out of the eight helicity amplitude parameters are independent, taking into account the normalization constraint [Eq (2)] and, due to the arbitrary value of the common phase, only differences between the four phases are relevant. Assuming CP conservation, the Λ0b and Λ 0b samples are combined to measure αb and the helicity amplitudes
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