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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

The CMS collaboration
Phys.Rev. D97 (2018) 072010, 2018

Abstract (data abstract)
An analysis of the bottom baryon decay $\Lambda_{b}\to J/\psi \Lambda$ is performed to measure the $\Lambda_b$ polarization and three angular parameters in data from pp collisions at $\sqrt{s} = 7$ and $8\, {\rm TeV}$, collected by the CMS experiment at the Large Hadron Collider. The $\Lambda_b$ polarization is measured to be $0.00\pm0.06$ (stat) $\pm0.06$ (syst) and the parity-violating asymmetry parameter is determined to be $-0.14\pm0.14$ (stat) $\pm0.10$ (syst). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.

  • Table 1


    The measured values of the angular parameters and the $\Lambda_b$ polarization.

  • Table 2


    The values of the helicity amplitudes in the decay.

  • Table 3


    Correlation matrix for the fitted parameters.

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