Charting the European Course to the High-Energy Frontier

TL;DR

This paper compares two proposed European particle physics projects, CLIC and FCC, highlighting their unique capabilities, potential physics discoveries, and strategic importance for Europe's leadership in high-energy physics.

Contribution

It provides a detailed assessment of the physics potential and strategic advantages of CLIC and FCC, emphasizing FCC's role in maintaining Europe's high-energy frontier leadership.

Findings

FCC-ee offers unparalleled precision in electroweak and Higgs physics.

FCC-hh provides the highest sensitivity for new physics and Higgs self-couplings.

CLIC enables energy upgrades up to 3 TeV for advanced exploration.

Abstract

We review the capabilities of two projects that have been proposed as the next major European facility, for consideration in the upcoming update of the European Strategy for Particle Physics: CLIC and FCC. We focus on their physics potentials and emphasise the key differences between the linear or circular approaches. We stress the uniqueness of the FCC-ee programme for precision electroweak physics at the $Z$ peak and the $WW$ threshold, as well as its unequalled statistics for Higgs physics and high accuracy for observing possible new phenomena in Higgs and $Z$ decays, whereas CLIC and FCC-ee offer similar capabilities near the $t \overline t$ threshold. Whilst CLIC offers the possibility of energy upgrades to 1500 and 3000 GeV, FCC-ee paves the way for FCC-hh. The latter offers unique capabilities for making direct or indirect discoveries in a new energy range, and has the highest sensitivity to the self-couplings of the Higgs boson and any anomalous couplings. We consider the FCC programme to be the best option to maintain Europe's place at the high-energy frontier during the coming decades.