Higher-order radiative corrections to low-angle Bhabha scattering: the YFS Monte Carlo approach

We calculate the QED-corrected integrated cross-section for small-angle Bhabha scattering with kinematical cuts identical to the real experimental cuts at the LEP/SLC experiments: no distinction between electrons and photons is made. We present a new second-order Monte Carlo calculation with the exponentiation of the Yennie-Frautschi-Suura type. It provides the integrated cross-section for the low-angle Bhabha scattering process (υ < 0.060), necessary for the luminosity measurement, with an overall precision of 0.16%. The corresponding computer program BHLUMI 4.01 is in the form of a stand-alone Monte Carlo event generator. The complete and explicit definition of the multiphoton matrix element is given. Examples of numerical results from Monte Carlo phase-space integration are demonstrated and discussed. The analytical integration of the cross section for simplified cuts, keeping terms up to third order, used for cross-checks of the Monte Carlo calculation, is also presented.