Speaker
Description
Precision studies of low-energy e⁺e⁻ annihilation, most notably the extraction of the hadronic vacuum polarisation contribution to the muon anomalous magnetic moment, require theoretical control over the multi-photon radiation phase-space. This demands inclusion of soft photon emission to all orders, consistently matched to fixed-order cross-sections.
I present a Fortran implementation of Coherent Exclusive Exponentiation (CEEX), based on the Yennie–Frautschi–Suura (YFS) formalism, for lepton and hadron pair production at low centre-of-mass energies. CEEX organises the emission of an arbitrary number of photons into a coherent sum over photon multiplicities, exponentiating the infrared-singular part of the amplitude while retaining exact spin correlations and hard photon contributions order by order in perturbation theory. The residual hard-photon amplitudes entering the exponentiated cross section are obtained via a tensor decomposition of the underlying Feynman amplitudes, providing a systematic route to incorporate higher-order (NNLO) corrections consistently into the resummed prediction.
I will describe the structure and numerical implementation of the CEEX algorithm, discuss validation against fixed-order and alternative exponentiation schemes, and present first results for muon and pion pair production. This work is developed within the RadioMonteCarlow2 initiative, aiming to deliver next-generation precision Monte Carlo tools for radiative-return and energy-scan experiments at low-energy e⁺e⁻ colliders.