AloHEP Software: A luminosity optimizer for High Energy Physics colliders

Abstract

The luminosity quoted for proposed particle colliders is usually derived from the analytic geometric formula, which assumes head-on collisions of identical, rigid Gaussian bunches. For the new generation of asymmetric machines---in particular lepton--hadron colliders such as the EIC, LHeC and FCC-eh---this assumption can misestimate the luminosity, because it ignores a few coupled effects that act in the interaction region such as hourglass effect, crossing angle, and mutual electromagnetic (beam--beam) deformation of the colliding bunches. We present \textbf{AloHEP} (A luminosity optimizer for High Energy Physics), an open-source, cross-platform Java application that simulates the interaction region of both symmetric and asymmetric colliders. AloHEP represents each bunch by an ensemble of macroparticles deposited on the grid with a cloud-in-cell scheme, and slices the crossing longitudinally. On each transverse slice it solves the two-dimensional electrostatic problem by a direct Green's-function convolution, then obtains the beam--beam forces by finite differencing and continuous bicubic interpolation. The hourglass effect, finite crossing angle and beam--beam pinch/disruption can be enabled independently, and the two colliding beams may consist of entirely different species (leptons, protons, heavy ions). A JSON-backed parameter database and an interactive graphical interface make AloHEP a flexible tool for the rapid prototyping of realistic luminosity estimates. We verify that the code reproduces the analytic geometric luminosity in the appropriate limit and present scaling, grid-convergence and asymmetric-collider benchmarks.