Kinematic Fitting in the Presence of ISR at the ILC

TL;DR

This paper discusses an advanced kinematic fitting method at the ILC that accounts for ISR and Beamstrahlung effects, enabling improved jet energy and mass resolution despite undetected momentum losses.

Contribution

It introduces a novel approach to kinematic fitting that incorporates ISR and Beamstrahlung effects, overcoming limitations of traditional methods.

Findings

Enhanced mass resolution achieved with the new fitting technique

Effective handling of undetected collinear photon momentum

Significant improvement over naive energy constraints

Abstract

Kinematic fitting is a well-established tool to improve jet energy and invariant mass resolutions by fitting the measured values under constraints (e.g. energy conservation). However, in the presence of substantial ISR and Beamstrahlung, naive energy and (longitudinal) momentum constraints fail due to the a priori unknown amount of undetected momentum carried away by collinear photons. It is possible to take care of those two effects and thus obtain significantly higher mass resolutions.