[Paper Review] Complementarity between ILC250 and ILC-GigaZ

A. Irles Quiles, R. Pöschl+2 more|arXiv (Cornell University)|May 1, 2019

Particle accelerators and beam dynamics7 references44 citations

TL;DR

The paper analyzes how running ILC250 and ILC-GigaZ complement each other for precision fermion coupling measurements, arguing that LEP1/SLC precision is insufficient and that Z-pole running with polarized electrons could enhance sensitivity to new resonances.

ABSTRACT

In view of the very precise measurements on fermion couplings which will be performed at ILC250 with polarized beams, there is emerging evidence that the LEP1/SLC measurements on these couplings are an order of magnitude too imprecise to match the accuracies reachable at ILC250. This will therefore severely limit the indirect sensitivity to new resonances and require revisiting the possibility to run ILC at the Z pole with polarized electrons. This work was done as a contribution to the ESU 2018-2020.

Motivation & Objective

• Motivate the need for extremely precise fermion coupling measurements at ILC250 with polarized beams.
• Evaluate whether LEP1/SLC precision is sufficient for indirect new-resonance sensitivity compared to ILC250.
• Revisit the feasibility and physics case for running at the Z pole (GigaZ) with polarized electrons.
• Assess how combining ILC250 data with GigaZ data improves constraints on beyond-Standard Model scenarios.

Proposed method

• Compare projected precision of ILC250 fermion coupling measurements with LEP1/SLC benchmarks.
• Argue for a Z-pole run with polarized electrons to enhance indirect sensitivity to new resonances.
• Outline the experimental and phenomenological implications of combining ILC250 results with GigaZ measurements.

Experimental results

Research questions

• RQ1 Does ILC250 achieve accuracies on fermion couplings that surpass LEP1/SLC precision?
• RQ2 What is the impact of adding GigaZ Z-pole data with polarized electrons on indirect constraints for new resonances?
• RQ3 How does the combination of ILC250 and ILC-GigaZ improve sensitivity to physics beyond the Standard Model?

Key findings

• LEP1/SLC measurements on fermion couplings are argued to be an order of magnitude too imprecise to match the accuracies reachable at ILC250.
• Running at the Z pole with polarized electrons is revisited as a way to recover or enhance indirect sensitivity to new resonances.
• The study emphasizes the complementarity between high-precision measurements at ILC250 and Z-pole data from GigaZ.
• The work situates the ILC program as capable of constraining new physics more effectively when both energy and Z-pole running are considered.