A Linear Collider Vision for the Future of Particle Physics

Abstract

In this paper we review the physics opportunities at linear $e^+e^-$ colliders with a special focus on high centre-of-mass energies and beam polarisation, take a fresh look at the various accelerator technologies available or under development and, for the first time, discuss how a facility first equipped with a technology mature today could be upgraded with technologies of tomorrow to reach much higher energies and/or luminosities. In addition, we will discuss detectors and alternative collider modes, as well as opportunities for beyond-collider experiments and R\&D facilities as part of a linear collider facility (LCF). The material of this paper will support all plans for $e^+e^-$ linear colliders and additional opportunities they offer, independently of technology choice or proposed site, as well as R\&D for advanced accelerator technologies. This joint perspective on the physics goals, early technologies and upgrade strategies has been developed by the LCVision team based on an initial discussion at LCWS2024 in Tokyo and a follow-up at the LCVision Community Event at CERN in January 2025. It heavily builds on decades of achievements of the global linear collider community, in particular in the context of CLIC and ILC.

Figures (80)

• Figure 1: Instantaneous luminosity (a), total site power (b), and their ratios (c), (d) as a function of the centre-of-mass energy for various $\HepParticle{\HepParticle{e}{}{}\xspace}{}{+}\xspace\HepParticle{\HepParticle{e}{}{}\xspace}{}{-}\xspace$ colliders. The LCF is drawn only up to 550GeV, since the luminosity and power consumption of higher energies will depend on the yet-to-be-chosen technology for these energies. However, they can be expected to be similar to the high-energy stages of CLIC and C$^3$, as indicated by the red arrow.
• Figure 2: (a) Determination of the Higgs mass at the ILC at a centre-of-mass energy of 250GeV Yan:2016xyx. The statistics of the data points correspond to an integrated luminosity of 250$\text{fb}^{-1}$ with a polarisation of (-0.8,+0.3). (b) Determination of the Higgs mass at CLIC at a centre-of-mass energy of 350GeV Abramowicz:2016zbo. The statistics of the data points correspond to an integrated luminosity of 500$\text{fb}^{-1}$ with unpolarised beams.
• Figure 3: The scale evolution of the bottom quark $\overline{MS}$ mass. The markers are projections for $m_{\HepParticle{b}{}{}\xspace}(m_{\HepParticle{Z}{}{}\xspace})$ from three-jet rates at the Z pole and for $m_{\HepParticle{b}{}{}\xspace}(m_{\HepParticle{H}{}{}\xspace})$ from Higgs boson branching fractions. The prediction of the evolution of the mass is calculated at five-loop precision with REvolver Hoang:2021fhn. The grey error band includes the effect of missing higher orders and the projected parametric uncertainties from $m_{\HepParticle{b}{}{}\xspace}(m_{\HepParticle{b}{}{}\xspace})$ and $\alpha_{\mathrm{s}}$. Figure from Snowmass:bprospects.
• Figure 4: $\HepParticle{Z}{}{}\xspace$ lineshape with polarised beams. The blue, red, and violet curves are the measurable averaged hadronic cross section after including ISR for various polarisation values of the electron and positron beams. The black curve is with unpolarised beams and no QED radiative corrections.
• Figure 5: (a) Illustration of the centre-of-mass energy dependence of the $\HepParticle{W}{}{}\xspace\HepParticle{W}{}{}\xspace$ cross section on $m_W$ and the level of polarisation. (b) The intrinsic sensitivity, $K$, of polarised cross section measurements to $m_W$ near threshold assuming an efficiency-purity product of unity.