NNLO massive corrections to Bhabha scattering and theoretical precision   of BabaYaga@NLO
  We provide an exact calculation of next-to-next-to-leading order (NNLO) massive corrections to Bhabha scattering in QED, relevant for precision luminosity monitoring at meson factories. Using realistic reference event selections, exact numerical results for leptonic and hadronic corrections are given and compared with the corresponding approximate predictions of the event generator BabaYaga@NLO. It is shown that the NNLO massive corrections are necessary for luminosity measurements with per mille precision. At the same time they are found to be well accounted for in the generator at an accuracy level below the one per mille. An update of the total theoretical precision of BabaYaga@NLO is presented and possible directions for a further error reduction are sketched. 
C. M. Carloni Calame, H. Czyz, J. Gluza, M. Gunia, G. Montagna, O.   Nicrosini, F. Piccinini, T. Riemann, M. Worek
hep-ph