Color-Octet $\jpsi$ Production in $\Upsilon$ Decay near the Kinematic Limit

TL;DR

This paper combines NRQCD with soft collinear effective theory to better model the $0$ decay into $ ext{J/} extpsi$ near the kinematic limit, addressing discrepancies between previous predictions and experimental data.

Contribution

It introduces a novel approach by integrating soft collinear effective theory with NRQCD to improve predictions of $ ext{J/} extpsi$ production spectra near the kinematic endpoint.

Findings

The spectrum is significantly softened with the new method.

Better agreement with experimental data is achieved.

The approach addresses breakdowns of NRQCD near the endpoint.

Abstract

Recent experiments by the CLEO III detector at CESR indicate that the $\jpsi$ spectrum produced in $\Upsilon$ decay is in conflict with Non-Relativistic QCD (NRQCD) calculations. The measured $\jpsi$ momentum distribution is much softer than predicted by the color-octet mechanisms. The expected peak at the kinematic limit is not observed in the data. However it has recent been pointed out that NRQCD calculations break down near the kinematic endpoint due to large perturbative and non-perturbative corrections. In this paper we combine NRQCD with soft collinear effective theory to study the color-octet contribution to the $\Upsilon \to \jpsi + X$ decay in this region of phase space. We obtain a spectrum that is significantly softened when including the correct degrees of freedom in the endpoint region, giving better agreement with the data than previous predictions.