Measurement of the Λ_b polarization and angular parameters in Λ_b → J/ΨΛ decays from pp collisions at √s = 7 and 8 TeV

Abstract

An analysis of the bottom baryon decay \({\Lambda }_{b}\to J/\psi \left(\to {\mu }^{+}{\mu }^{-}\right)\Lambda \left(\to p{\pi }^{-}\right)\) is performed to measure the \({\Lambda }_{b}\) polarization and three angular parameters in data from \(pp\) collisions at \(\sqrt{s}=7\) and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The \({\Lambda }_{b}\) polarization is measured to be \(0.00±0.06\left(\mathrm{stat}\right)±0.06\left(\mathrm{syst}\right)\) and the parity-violating asymmetry parameter is determined to be \(0.14±0.14\left(\mathrm{stat}\right)±0.10\left(\mathrm{syst}\right)\). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.