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Measurements of the $\Lambda_b^0 \to J/\psi \Lambda$ decay amplitudes and the $\Lambda_b^0$ polarisation in $pp$ collisions at $\sqrt{s} = 7$ TeV

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Abstract

An angular analysis of Lambda_b0 -> J/psi Lambda decays is performed using a data sample corresponding to 1.0 fb^{-1} collected in pp collisions at sqrt(s) = 7 TeV with the LHCb detector at the LHC. A parity violating asymmetry parameter characterising the Lambda_b0 -> J/psi Lambda decay of 0.05 +/- 0.17 +/- 0.07 and a Lambda_b0 transverse production polarisation of 0.06 +/- 0.07 +/- 0.02 are measured, where the first uncertainty is statistical and the second systematic.

Figures and captions

Definition of the five angles used to describe the $\Lambda ^0_ b \!\to { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\to \mu ^+ \mu ^- )\Lambda (\to p \pi ^- )$ decay.

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Mass distribution for the $\Lambda ^0_ b \!\to { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ mode for the (left) downstream and (right) long candidates. The fitted signal component is shown as a solid blue curve while the background component is shown as a dashed red line.

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Projections of the acceptance function together with the simulated signal data for (top) downstream and (bottom) long candidates.

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Projections of the angular distribution of the background subtracted and acceptance corrected $\Lambda ^0_ b \!\to { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ data for the (top) downstream and (bottom) long candidates. The fit is shown as solid lines.

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Animated gif made out of all figures.

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Tables and captions

Theoretical predictions for the $\Lambda ^0_ b \!\to { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ decay asymmetry parameter $\alpha_b$ .

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Functions used to describe the angular distributions in three dimensions.

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Absolute systematic uncertainties on the measured parameters.

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.