NGAMMA: A Monte Carlo generator for multiphoton production in $e^+e^-$ annihilation

Abstract

We present the NGAMMA Monte Carlo event generator for QED processes of $e^+e^-$ annihilation into a multiphoton final state, $e^+e^-\to N\gamma (N \ge 2)$. These processes are an important source of background in the study of $e^+e^-\to hadrons$ processes with a multiphoton final state, especially for experiments at low energy $e^+e^-$ colliders like SND, CMD-3, KLOE and for the BESIII experiment. For generation, NGAMMA exploits the exact tree-level amplitude.