Invariant-mass distribution of cc-bar in Upsilon(1S) -> cc-bar + X

TL;DR

This paper calculates the invariant-mass distribution of charm-anticharm pairs produced in Upsilon(1S) decay using nonrelativistic QCD, predicting a smaller decay rate ratio than previous estimates.

Contribution

It provides a leading-order calculation of the invariant-mass distribution in Upsilon(1S) decay within the color-singlet model, including new predictions for decay ratios.

Findings

Invariant-mass distribution peaks near threshold and at the kinematic end point.

Predicted decay ratio Gamma[Upsilon(1S)->cc-bar+X]/Gamma[Upsilon(1S)->light hadrons] = 0.065 alpha_s.

Result is about 20% smaller than previous estimates.

Abstract

We calculate the invariant-mass distribution for the cc-bar pair produced in the inclusive Upsilon(1S) decay based on the color-singlet mechanism of the nonrelativistic quantum chromodynamics factorization approach at leading order in the bottom-quark velocity v_b in the meson rest frame. As the short-distance processes, we consider bb-bar -> g^*gg followed by g^* -> cc-bar and bb-bar -> gamma^* -> cc-bar at leading order in the strong coupling. The invariant-mass distribution of the bb-bar -> cc-bar gg contribution has a sharp peak just above the threshold and that of the bb-bar -> gamma^* -> cc-bar channel is concentrated at the maximally allowed kinematic end point. We predict that Gamma[Upsilon(1S) -> cc-bar+X]/Gamma[Upsilon(1S)->light hadrons] = 0.065 alpha_s, which is smaller than a previous result by about 20%.