Determination of chi_c and chi_b polarizations from dilepton angular distributions in radiative decays

TL;DR

This paper presents a formalism to determine chi_c and chi_b polarizations from dilepton angular distributions in radiative decays, reducing dependence on photon reconstruction and multipole structure details.

Contribution

It introduces a frame-independent method to extract polarization information from decay distributions, clarifying previous calculation issues.

Findings

Provides a formalism for polarization extraction independent of production mechanisms.

Reduces reliance on photon reconstruction details in polarization measurements.

Clarifies and addresses issues in previous decay angular distribution calculations.

Abstract

The angular distributions of the decay products in the successive decays chi_c (chi_b) to J/psi (Upsilon) gamma and J/psi (Upsilon) to l+l- are calculated as a function of the angular momentum composition of the decaying chi meson and of the multipole structure of the photon radiation, using a formalism independent of production mechanisms and polarization frames. The polarizations of the chi states produced in high energy collisions can be derived from the dilepton decay distributions of the daughter J/psi or Upsilon mesons, with a reduced dependence on the details of the photon reconstruction or simulation. Moreover, this method eliminates the dependence of the polarization measurement on the actual details of the multipole structure of the radiative transition. Problematic points in previous calculations of the chi_c decay angular distributions are identified and clarified.