Higgs Boson Studies at Future Particle Colliders

Abstract: This document aims to provide an assessment of the potential of future colliding beam facilities to perform Higgs boson studies. The analysis builds on the submissions made by the proponents of future colliders to the European Strategy Update process, and takes as its point of departure the results expected at the completion of the HL-LHC program. This report presents quantitative results on many aspects of Higgs physics for future collider projects of sufficient maturity using uniform methodologies.

• The paper demonstrates that future colliders can significantly enhance precision in Higgs coupling measurements using EFT and κ-framework analyses.
• The study integrates HL-LHC constraints with projected data from various collider designs to benchmark capabilities in measuring rare decays and self-couplings.
• The findings provide concrete prospects for probing Beyond Standard Model physics and deepening our understanding of electroweak symmetry breaking.

Higgs Boson Studies at Future Particle Colliders

The paper "Higgs Boson studies at future particle colliders" presents a comprehensive evaluation of the potential for conducting Higgs boson research at a range of proposed future particle collider projects. The assessment considers and compares different colliders, investigating their capability to unravel various aspects of Higgs physics. This includes precision measurements of Higgs couplings, exploration of rare decays, determination of self-couplings, and examination of BSM (Beyond Standard Model) scenarios that might manifest through deformations in the Higgs sector.

Methodology

The study benchmarks the potential capabilities of several state-of-the-art colliders, namely, the High-Energy LHC (HE-LHC), Future Circular Colliders (FCC-{\it ee, eh, hh}), the Circular Electron-Positron Collider (CEPC), the International Linear Collider (ILC), the Compact Linear Collider (CLIC), and the Large Hadron electron Collider (LHeC). Evaluations are made in the context of constraints obtained from these colliders, integrated with inputs from the High Luminosity LHC (HL-LHC).

The work pivots on the methodology of analyzing projected collider data using a set of theoretical frameworks, including the $\kappa$-framework and Effective Field Theory (EFT), which model possible deviations in Higgs couplings from Standard Model predictions in the presence of new physics. A significant goal is to distinguish between various EFT parameters by using projected measurements of Higgs boson processes combined with electroweak precision history.

Key Numerical Results

The paper underscores the sensitivity of future colliders by detailing prospective limits on the precision of measurements for Higgs couplings to fundamental particles, such as $W$ and $Z$ bosons, tops, bottoms, and taus. Notably, the FCC's integrated program combining $ee$, $eh$, and $hh$ endpoints is projected to afford the most precise constraints, with uncertainties on several couplings potentially reduced to a few per mille.

The research considers several benchmark scenarios, particularly focusing on scenarios where collider data can be interpreted in frameworks that do not imply new physics in Higgs boson decays alone. Limits on branching ratios for Higgs to invisible or untagged modes are discussed, where FCC facilities show potential sensitivities well below the percent level.

Implications and Future Prospects

The implications of these prospective analyses are profound both in confirming the SM predictions and in probing paths for potential BSM physics. The reduction in uncertainties associated with Higgs measurements strengthens the framework to evaluate scenarios like composite Higgs models and the consequences of deeper electroweak symmetry breaking mechanisms.

Furthermore, paper speculates on further precision that could be achieved in SMEFT analyses, should experimental systematics and SM intrinsic theoretical uncertainties be adequately reduced—a feasible goal with advancements in theoretical calculations.

The document posits that the ongoing effort to rigorously assess the viability of future collider projects regarding Higgs physics is vital. Future developments, including the potential of muon colliders and high-gradient plasma-wakefield accelerators, could thrust the exploration of the Higgs landscape into unprecedented domains, offering clarity into symmetry breaking processes and the nature of the fundamental constituents of matter.

Conclusion

The paper effectively provides a critical projection of the role future colliders will play in enhancing our understanding of the Higgs boson. It marshals robust theoretical tools and exhaustive analyses of potential experimental datasets to highlight the frontier of particle physics that lies ahead. While the study refrains from making speculative claims, it lays a meticulous groundwork, resonating the importance of strategic foresight in pushing the boundaries of contemporary particle physics.