Correction of beam-beam effects in luminosity measurement at ILC

TL;DR

This paper evaluates three methods to correct beam-beam effects in luminosity measurements at ILC, focusing on reducing biases and improving accuracy, especially above 80% of the nominal energy.

Contribution

It introduces and compares three approaches, including a novel collision-frame method, for more accurate luminosity measurement unaffected by beam parameter uncertainties.

Findings

Collision-frame method is independent of beam parameters.

The collision-frame method accurately reconstructs luminosity above 80% energy.

Optimized selection cuts improve background reduction compatibility.

Abstract

Three methods for handling beam-beam effects in luminosity measurement at ILC are tested and evaluated in this work. The first method represents an optimization of the LEP-type asymmetric selection cuts that reduce the counting biases. The second method uses the experimentally reconstructed shape of the $\sqrt{s'}$ spectrum to determine the Beamstrahlung component of the bias. The last, recently proposed, collision-frame method relies on the reconstruction of the collision-frame velocity to define the selection function in the collision frame both in experiment and in theory. Thus the luminosity expression is insensitive to the difference between the CM frame of the collision and the lab frame. The collision-frame method is independent of the knowledge of the beam parameters, and it allows an accurate reconstruction of the luminosity spectrum above 80 % of the nominal CM energy. However, it gives no precise infromation about luminosity below 80 % of the nominal CM energy. The compatibility of diverse selection cuts for background reduction with the collision-frame method is addressed.