Measurement of the $\Lambda_b$ polarization and angular parameters in $\Lambda_b\to J/\psi\, \Lambda$ decays from pp collisions at $\sqrt{s}=$ 7 and 8 TeV

TL;DR

This paper reports measurements of the polarization and angular decay parameters of the $\\Lambda_b$ baryon in proton-proton collisions at 7 and 8 TeV, providing insights into baryon decay dynamics and testing QCD predictions.

Contribution

The study presents the first measurement of $\\Lambda_b$ polarization and angular parameters at LHC energies, comparing results with theoretical models.

Findings

$\\Lambda_b$ polarization measured as 0.00 ± 0.06 (stat) ± 0.06 (syst)

Parity-violating asymmetry parameter is 0.14 ± 0.14 (stat) ± 0.10 (syst)

Results are consistent with certain QCD predictions.

Abstract

An analysis of the decay $\Lambda_b \to J/\psi(\to\mu^+\mu^-)\Lambda(\to p \pi^-)$ decay 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 LHC. The $\Lambda_b$ polarization is measured to be 0.00 $\pm$ 0.06 (stat) $\pm$ 0.06 (syst) and the parity-violating asymmetry parameter is determined to be 0.14 $\pm$ 0.14 (stat) $\pm$ 0.10 (syst). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.