https://doi.org/10.1140/epja/i2018-12629-8
Regular Article - Theoretical Physics
Low-energy lepton-proton bremsstrahlung via effective field theory
1
Department of Physics, Indian Institute of Technology, Guwahati, 781039, Assam, India
2
Department of Physics and Astronomy, University of South Carolina, 29208, Columbia, SC, USA
* e-mail: udit.raha@iitg.ac.in
Received:
17
March
2018
Accepted:
4
October
2018
Published online:
22
November
2018
We present a systematic calculation of the cross section for the lepton-proton bremsstrahlung process 
in chiral perturbation theory at next-to-leading order. This process corresponds to an undetected background signal for the proposed MUSE experiment at PSI. MUSE is designed to measure elastic scattering of low-energy electrons and muons off a proton target in order to extract a precise value of the proton’s r.m.s. radius. We show that the commonly used peaking approximation, which is used to evaluate the radiative tail for the elastic cross section, is not applicable for muon-proton scattering at the low-energy MUSE kinematics. Furthermore, we point out a certain pathology with the standard chiral power counting scheme associated with electron scattering, whereby the next-to-next-to-leading order contribution from the pion loop diagrams is kinematically enhanced and numerically of the same magnitude as the next-to-leading order corrections. We correct a misprint in a commonly cited review article.
© SIF, Springer-Verlag GmbH Germany, part of Springer Nature, 2018
