Measurement of the production fraction times branching fraction f(b --> \Lambda_b)B(\Lambda_b --> J/\psi \Lambda)

TL;DR

This paper reports a precise measurement of the combined production fraction and branching ratio for \\Lambda_b baryons decaying to J/\\psi \\Lambda, using proton-antiproton collision data, improving the accuracy over previous results.

Contribution

The study provides a more precise measurement of the \\Lambda_b production and decay rate, reducing uncertainty by a factor of three compared to previous world averages.

Findings

Measured f(b -> \\Lambda_b)B(\\Lambda_b -> J/\\psi \\Lambda) as (6.01 ± 0.60 (stat.) ± 0.58 (syst.) ± 0.28 (PDG)) x 10^{-5}

Determined the ratio of production and decay rates relative to B^0 decays as 0.345 ± 0.034 (stat.) ± 0.033 (syst.) ± 0.003 (PDG)

Achieved a threefold improvement in measurement precision over previous world averages.

Abstract

The \Lambda_b(udb) baryon is observed in the decay \Lambda_b --> J/\psi \Lambda using 6.1 fb^{-1} of p\bar{p} collisions collected with the D0 detector at \sqrt{s}=1.96 TeV. The production fraction multiplied by the branching fraction for this decay relative to that for the decay B^0 --> J/\psi K^0_s is measured to be 0.345 \pm 0.034 (stat.) \pm 0.033 (syst.) \pm 0.003 (PDG). Using the world average value of f(b --> B^0)B(B^0 --> J/\psi K^0_s) = (1.74 \pm 0.08) \times 10^{-5}, we obtain f(b --> \Lambda_b)B(\Lambda_{b} --> J/\psi \Lambda) = (6.01 \pm 0.60 (stat.) \pm 0.58 (syst.) \pm 0.28 (PDG)) \times 10^{-5}. This measurement represents an improvement in precision by about a factor of three with respect to the current world average.