Two-loop QED Corrections to Bhabha Scattering

Bhabha scattering, ee → ee, is a crucial process in the phenomenology of particle physics. Its relevance is mainly due to the fact that it is the process employed to determine the luminosity L at ee colliders: in fact, L = NBhabha/σth, where NBhabha is the rate of Bhabha events and σth is the Bhabha scattering cross section calculated from theory. Two kinematic regions are of special interest for the luminosity measurements, since in these regions the Bhabha scattering cross section is comparatively large and QED dominated. At colliders operating at c. m. energies of O(100GeV), the relevant kinematic region is the one in which the angle between the outgoing particles and the beam line is of few degrees. This, for instance, was the case at LEP, where the luminometers were located between 50 and 100 mrad, and it will be also the case at the future ILC (luminometers between 25 and 80 mrad [1]). At machines operating at c. m. energies of the order of 1 − 10GeV, the region of interest is instead the one in which the scattering angle is large; as an example, at KLOE, the luminosity measurement involves Bhabha scattering events that take place at angles between 55◦ and 125◦ [2]. Moreover, the large angle Bhabha scattering will be employed at the ILC in order to study the beam