Model-independent determination of the two-photon exchange contribution to hyperfine splitting in muonic hydrogen

TL;DR

This paper provides a model-independent calculation of the two-photon exchange contribution to hyperfine splitting in muonic hydrogen, using effective field theory and experimental data, leading to precise theoretical predictions.

Contribution

It introduces a novel, model-independent method to determine the two-photon exchange contribution in muonic hydrogen using Wilson coefficients and chiral perturbation theory.

Findings

Two-photon exchange contribution: -1.161(20) meV for 1S state.

Predicted hyperfine splitting: 182.623(27) meV (1S), 22.8123(33) meV (2S).

Error dominated by two-photon exchange uncertainty.

Abstract

We obtain a model-independent prediction for the two-photon exchange contribution to the hyperfine splitting in muonic hydrogen. We use the relation of the Wilson coefficients of the spin-dependent dimension-six four-fermion operator of NRQED applied to the electron-proton and to the muon-proton sectors. Their difference can be reliably computed using chiral perturbation theory, whereas the Wilson coefficient of the electron-proton sector can be determined from the hyperfine splitting in hydrogen. This allows us to give a precise model-independent determination of the Wilson coefficient for the muon-proton sector, and consequently of the two-photon exchange contribution to the hyperfine splitting in muonic hydrogen, which reads $\delta \bar E_{p\mu,\rm HF}^{\rm TPE}(nS)=-\frac{1}{n^3}1.161(20)$ meV. Together with the associated QED analysis, we obtain a prediction for the hyperfine splitting in muonic hydrogen that reads $E^{\rm th}_{p\mu,\rm HF}(1S)=182.623(27)$ meV and $E^{\rm th}_{p\mu,\rm HF}(2S)=22.8123(33)$ meV. The error is dominated by the two-photon exchange contribution.