P-wave spin-spin splitting and meson loops

TL;DR

This paper investigates how meson loops and quark pair creation affect P-wave meson hyperfine splitting, demonstrating that the splitting remains small despite mass shifts, consistent with experimental observations.

Contribution

It shows that hyperfine splitting remains negligible in models with spin-one light quark pair creation, even when meson loops cause significant mass shifts.

Findings

Hyperfine splitting remains small despite meson loop effects.

Mass shifts due to meson loops do not significantly alter hyperfine splitting.

The results are consistent with experimental data on charmonia and bottomonia.

Abstract

In quark potential models the hyperfine splitting of P-wave mesons is zero in the nonrelativistic limit, a prediction strikingly confirmed by experiment in both charmonia and bottomonia. The result, however, ignores the coupling of bare quarkonia to meson-meson pairs. This coupling causes mass shifts among the states and so could potentially spoil the quark model prediction. This turns out not to be the case: in a variety of models the hyperfine splitting remains small despite large mass shifts. This is shown to be a generic feature of models in which the coupling involves the creation of a light quark pair with spin-one and the quark spin wavefunctions are conserved. This talk reports on the results of Phys. Rev. D84, 034021 (2011).