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arXiv · 2504.00706

Lepton-proton two-photon exchange with improved soft-photon approximation including proton's structure effects in HB$\chi$PT

Rakshanda Goswami·Pulak Talukdar·Bhoomika Das·Udit Raha·Fred Myhrer
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Abstract

We present an improved evaluation of the two-photon exchange correction to the unpolarized lepton-proton elastic scattering process at very low-energies relevant to the MUSE experiment, where only the dominant intermediate elastic proton is considered. We employ the framework of heavy baryon chiral perturbation theory and invoke the soft-photon approximation in order to reduce the intricate 4-point loop-integrals into simpler 3-point loop-integrals. In the present work, we adopt a more robust methodology compared to an earlier work along the same lines for analytically evaluating the loop-integrations, and incorporate important corrections at next-to-next-to-leading order. These include the proton's structure effects which renormalize the proton-photon interaction vertices and the proton's propagator. Finally, our results allow a model-independent estimation of the charge asymmetry for the scattering of unpolarized massive leptons and anti-leptons.

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Rakshanda Goswami, Pulak Talukdar, Bhoomika Das, Udit Raha, Fred Myhrer. 2025-04-01. Lepton-proton two-photon exchange with improved soft-photon approximation including proton's structure effects in HB$\chi$PT. https://arxiv.org/abs/2504.00706

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