Speaker
Description
To resolve the tension between lattice QCD and data-driven evaluations of the hadronic
vacuum polarization contribution to the muon anomaly $a_\mu$, precise cross-section measurements
of the dominant $\pi^+\pi^-$ channel are highly relevant. The radiative return process
$e^+e^- \to \pi^+\pi^-\gamma$ at flavor factories is essential for extracting this
cross section below $2\,\mathrm{GeV}$, requiring tight control over theoretical systematic uncertainties.
To this end, we present the first calculation of QED
next-to-leading order (NLO) corrections to radiative pion and muon pair production in
$e^+e^-$ annihilation, matched to a QED Parton Shower (PS) algorithm for fully exclusive
simulations, achieving NLOPS accuracy. For the dipion channel, we go beyond the
factorized approach (FxsQED) to evaluate structure-dependent corrections by
including the pion form factor in the one-loop
amplitudes according to different formulations. These developments are implemented in a new version of the
BabaYaga@NLO event generator, and we present the corresponding
phenomenological results for $e^+e^- \to X^+X^-\gamma$ ($X=\mu,\pi$) in different experimental scenarios from 1 GeV to 10 GeV.