An analysis of the angular distribution of the decay Λ b 0  → Λμ+μ− is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately 5 fb−1. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range 15 < q2 < 20 GeV2/c4. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be
ℓFB=−0.39±0.04(stat)±0.01(syst),AhFB=−0.30±0.05(stat)±0.02(syst),AℓhFB=+0.25±0.04(stat)±0.01(syst).
The measurements are consistent with Standard Model predictions.