An angular analysis of $\Lambda_b \to \Lambda \mu^+ \mu^-$ decays at the LHCb experiment.

This work presents an angular analysis of the suppressed $\Lambda_b^0 \rightarrow \Lambda\mu^+\mu^-$ decay, performed using proton-proton collision data collected by the LHCb experiment during 2011 and 2012. The distribution of moments describing the decay with a non-zero transverse $\Lambda_b^0$ baryon polarisation production are extracted for the first time, and used to determine the 5-dimensional angular distribution in the 15 to 20 GeV$^2/c^4$ dimuon invariant mass squared interval for the first time. The forward-backward asymmetry of the $\Lambda$ baryon and $\mu^+\mu^-$ produced from the $\Lambda_b^0$ baryon ($A_{FB}^{lh}$ ) is measured, along with the previously published $f_L$, $A^l_{FB}$ and $A^h_{FB}$. These values are found to be $f_L = 0.546 \pm 0.132$, $A^l_{FB} = -0.004 \pm 0.077$, $A^h_{FB} = -0.312 \pm 0.150$ and $A_{FB}^{lh} = -0.007 ± 0.071$, where uncertainties are statistical, and account for correlation between the moments used to determine them.