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

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.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-15-002 (CMS Public Pages)

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