Angular distributions for $\Lambda_b\to \Lambda^*_J (pK^-)J/\psi$ Decays

TL;DR

This paper analyzes the angular distributions in the decay of Lambda_b baryons to excited Lambda* states and J/psi, deriving formulas, calculating decay widths, and exploring asymmetries to aid future studies of b to s transitions.

Contribution

It provides a new helicity amplitude framework for analyzing Lambda_b decays involving Lambda* resonances and J/psi, with calculations based on lattice QCD and quark models.

Findings

Branching fraction for Lambda_b to Lambda*_J J/psi is approximately 1.35e-5.

Derived angular distribution formulas for the decay chain.

Explored forward-backward asymmetry and polarization effects.

Abstract

We carry out an analysis of the multibody decay cascade $\Lambda_b\to \Lambda^*_J J/\psi \to pK^- J/\psi$ with the $ \Lambda^*_J$ resonance including $\Lambda^*_{1520},\Lambda^*_{1600}$, and $\Lambda^*_{1800}$, and $J/\psi$ reconstructed by the lepton pair final state. Using the helicity amplitude technique, we derive a compact form for the angular distributions for the decay chain, from which one can extract various one-dimensional distributions. Using the $\Lambda_b\to \Lambda_J^*$ form factors from lattice QCD and quark model, we calculate the differential and integrated partial widths. Decay branching fractions are found as $\mathcal{B}(\Lambda_b\to \Lambda^*_J( pK)J/\psi(\ell^+\ell^-))=(1.35\pm0.28)\times 10^{-5}$. In addition, we also explore forward-backward asymmetry, and various polarizations. Results in this work will serve a calibration for the study of $b\to s \ell^+\ell^-$ decays in $\Lambda_b$ decays in future and provide useful information towards the understanding of the properties of the $\Lambda_J^*$ baryons.