Two-photon decay of pseudoscalar quarkonia

TL;DR

This paper evaluates the two-photon decay widths of pseudoscalar quarkonia using Heavy-Quark Spin Symmetry, confirming experimental results for eta_c(1S) and suggesting anomalies for eta_c(2S), with implications for measuring the strong coupling constant.

Contribution

The study provides a parameter-free theoretical calculation of two-photon widths for eta_c and eta_b states, highlighting potential anomalies and proposing a method to extract alpha_s from decay ratios.

Findings

Agreement with experimental data for eta_c(1S) width

Possible anomaly in eta_c(2S) decay width

Proposed ratio to determine the strong coupling constant

Abstract

We report on our recent evaluation of the two-photon width of the pseudoscalar quarkonia, eta_c(nS) and eta_b(nS) in an approach based on Heavy-Quark Spin Symmetry (HQSS). To what concerns the 1S state eta_c, our parameter-free computation agrees with experiments, as well as most of other theoretical works. On the other hand, our computation for the 2S-state looks 2S like a confirmation that there may exist an anomaly related to the decay of eta_c(2S), especially in the light of the new preliminary result of the Belle collaboration. We also point out that the essentially model-independent ratio of eta_b two-photon width to the Upsilon leptonic width and the eta_b two-photon width could be used to extract the strong coupling constant alpha_s.