Polarized J/psi production at CLEO

TL;DR

The study analyzes polarization of prompt $J/\psi$ production in $e^+e^-$ annihilation at CLEO energy ($\sqrt{s}=10.58$ GeV) within NRQCD factorization, showing strong sensitivity of polarization to the production mechanism. It derives and presents analytic differential cross sections for the dominant color-singlet and color-octet channels and uses them to evaluate the polarization observable $\eta(z)$ and the angular parameter $\alpha(z)$. The key finding is that color-singlet $e^+e^- \rightarrow J/\psi+gg$ dominates most of the phase space and yields largely longitudinal polarization, while near the endpoint the color-octet $e^+e^- \rightarrow (c\bar c)^{(8)}+g$ dominates and produces nearly unpolarized $J/\psi$; endpoint polarization measurements can thus test color-octet NRQCD matrix elements. The work argues that potential NRQCD breakdown near phase-space boundaries does not undermine the main predictions and highlights the value of polarization data in constraining NRQCD parameters.

Abstract

Polarizations of the prompt $J/ψ$'s produced in the $e^+e^-$ annihilation at CLEO energy ($\sqrt{s} = 10.58$ GeV) are considered in the framework of NRQCD factorization formalism. We find that the $J/ψ$ polarization has strong dependence on the production mechanism. At CLEO energy, the most dominant $J/ψ$ production mechanism in the most phase space is the color-singlet mechanism, $e^+e^- \to J/ψ+gg$, for which $J/ψ$'s are highly longitudinally polarized. On the other hand, the dominant $J/ψ$ production mechanism at the upper end point of $J/ψ$ energy distribution is the color-octet process, $e^+e^- \to (c\bar{c})^{(8)} +g$, for which $J/ψ$'s are almost unpolarized. Thus, the measurement of the polarization of the end point $J/ψ$'s can give another test of color-octet mechanism, and constraint on the NRQCD matrix elements.

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