Dark Z at the International Linear Collider

TL;DR

This paper explores the potential for the International Linear Collider to detect and analyze a hypothetical dark Z boson, which could reveal new physics beyond the Standard Model through precision measurements.

Contribution

It demonstrates that the ILC can detect a dark Z within current constraints and measure its properties with high precision, surpassing LHC capabilities.

Findings

ILC can access dark Z with 250 or 500 GeV energy

ILC searches outperform high luminosity LHC in dark Z detection

One-month ILC run can measure dark Z couplings with percent accuracy

Abstract

A dark Z is a massive Abelian gauge boson which is coupled to the Standard Model through both kinetic and mass mixing with the electroweak sector. We study the phenomenology of the dark Z at an energy-frontier electron-positron collider, such as the proposed International Linear Collider (ILC). We show that precision electroweak constraints and the current bounds from the hadron colliders allow a dark Z that is kinematically accessible at the ILC with 250 GeV or 500 GeV center-of-mass energy. Further, the reach of the ILC searches for a dark Z significantly exceeds the expected reach of the high luminosity LHC. If a signal consistent with a dark Z is discovered, it would motivate a dedicated run of the ILC at the center-of-mass energy matching the dark Z mass. We demonstrate that a short one month run at design luminosity could measure the dark Z chiral couplings to fermions with percent precision. This measurement can be used to discriminate between competing theoretical models of the resonance: for example, the dark Z can be distinguished from a dark photon with purely kinetic mixing.