Consideration of Photon Radiation in Kinematic Fits for Future e+ e- Colliders

TL;DR

This paper introduces a method to incorporate photon radiation effects into kinematic fits for future e+e- colliders, improving fit convergence and resolution despite energetic photon emissions.

Contribution

A novel parametrization of photon momentum in kinematic fits that accounts for photon radiation parallel to the beam at future colliders.

Findings

Method improves fit convergence with energetic photons

Maintains fit resolution in realistic simulations

Effective at sqrt(s) = 500 GeV for ILC conditions

Abstract

Kinematic fitting is an important tool to improve the resolution in high-energy physics experiments. At future e+e- colliders, photon radiation parallel to the beam carrying away large amounts of energy and momentum will become a challenge for kinematic fitting. A photon with longitudinal momentum pz({\eta}) is introduced, which is parametrized such that {\eta} follows a normal distribution. In the fit, {\eta} is treated as having a measured value of zero, which corresponds to pz = 0. As a result, fits with constraints on energy and momentum conservation converge well even in the presence of a highly energetic photon, while the resolution of fits without such a photon is retained. A fully simulated and reconstructed e+e- -> qqqq event sample at sqrt(s) = 500 GeV is used to investigate the performance of this method under realistic conditions, as expected at the International Linear Collider.