NNLO leptonic and hadronic corrections to Bhabha scattering and luminosity monitoring at meson factories

TL;DR

This paper presents precise NNLO leptonic and hadronic corrections to Bhabha scattering, combining virtual and real contributions, and compares them with approximate methods to ensure accurate luminosity measurements at meson factories.

Contribution

It provides the first comprehensive NNLO calculations for Bhabha scattering including both leptonic and hadronic effects, validated against experimental precision.

Findings

NNLO corrections agree within 0.07% with approximate methods

Virtual and real corrections are combined accurately at meson factory energies

The results confirm the reliability of current luminosity monitoring tools

Abstract

Virtual fermionic N_f = 1 and N_f = 2 contributions to Bhabha scattering are combined with realistic real corrections at next-to-next-to-leading order in QED. The virtual corrections are determined by the package bha_nnlo_hf, and real corrections with the Monte Carlo generators Bhagen-1Ph, Helac-Phegas and Ekhara. Numerical results are discussed at the energies of and with realistic cuts used at the Phi factory DAFNE, at the B factories PEP-II and KEK, and at the charm/tau factory BEPC II. We compare these complete calculations with the approximate ones realized in the generator BabaYaga@NLO used at meson factories to evaluate their luminosities. For realistic reference event selections we find agreement for the NNLO leptonic and hadronic corrections within 0.07% or better and conclude that they are well accounted for in the generator by comparison with the present experimental accuracy.