[Paper Review] The Physics potential of the CEPC. Prepared for the US Snowmass Community Planning Exercise (Snowmass 2021)

H. J. Cheng, Wen-Ta Chiu+21 more|arXiv (Cornell University)|May 17, 2022

Particle Detector Development and Performance20 citations

TL;DR

This paper updates the CEPC Higgs/EW/top physics potential under a new nominal run scenario, outlining projected precision, upgrade paths, and detector R&D for a Higgs/Z factory with future high-energy upgrade.

ABSTRACT

The Circular Electron Positron Collider (CEPC) is a large-scale collider facility that can serve as a factory of the Higgs, Z, and W bosons and is upgradable to run at the ttbar threshold. This document describes the latest CEPC nominal operation scenario and particle yields and updates the corresponding physics potential. A new detector concept is also briefly described. This submission is for consideration by the Snowmass process.

Motivation & Objective

• Quantify the Higgs, electroweak (EW), and top physics potential of CEPC under the updated nominal operation scenario.
• Assess the precision reach for Higgs couplings, Higgs width, and rare decays in different CEPC running modes (Z factory, Higgs factory, WW threshold, and t t̄ threshold).
• Evaluate the impact of SMEFT/Higgs EFT frameworks on interpreting CEPC measurements and their synergy with HL-LHC.
• Outline flavor, QCD, and beyond the Standard Model (BSM) opportunities, including exotic decays, dark matter, and long-lived particles, with detector requirements and R&D needs.

Proposed method

• Review updated CEPC running scenarios and yields (Z, WW threshold, Higgs, t t̄ upgrade).
• Perform projections of inclusive and exclusive Higgs cross sections, branching ratios, and total width using κ-framework and SMEFT frameworks.
• Compare CEPC projections against HL-LHC benchmarks to illustrate precision gains.
• Estimate EW precision impacts by projecting Z and W boson observables from Z-pole and WW-threshold runs.
• Incorporate detector performance assumptions and ML-based analyses to refine Higgs measurements and CP-violation sensitivity.
• Summarize detector R&D needs and MDI/vacuum/accelerator technologies underpinning the physics program.

Experimental results

Research questions

• RQ1 What precision on Higgs couplings and the Higgs width can CEPC achieve with the updated 240 GeV and 360 GeV running scenarios?
• RQ2 How do CEPC Higgs and EW measurements constrain SMEFT operators and anomalous triple gauge couplings in comparison to HL-LHC?
• RQ3 To what level can CEPC test CP violation in Higgs couplings and search for exotic decays and dark-sector signatures?
• RQ4 What are the projected electroweak precision improvements for W/Z properties and top-quark parameters at CEPC, especially from Z-pole and WW threshold runs?
• RQ5 What are the key detector requirements and R&D needs to realize the projected physics gains?

Key findings

• CEPC can deliver about 4 million Higgs bosons and nearly 4 trillion Z bosons, with over 400 million W-boson pairs and up to ~1 million top quarks after upgrades.
• The inclusive Higgs cross-section precision at CEPC improves to about 0.26% (240 GeV run with 20 ab−1) and Higgs width can be determined to roughly 1.1% when combining 240 GeV and 360 GeV runs.
• Higgs coupling precisions in SMEFT/kappa frameworks reach the 10−2 to 10−3 level for many couplings; hZZ and related operators are especially well constrained by the EW program, enabling strong indirect new-physics sensitivity.
• The 360 GeV run substantially enhances sensitivity to Higgs-WW coupling and SMEFT operators due to complementary production channels and improved separation of signal modes.
• CEPC provides an unprecedented EW precision program (Z pole and WW threshold) with projected uncertainties in mZ, ΓZ, mW, ΓW, sin^2 θWeff, and Alicoupled observables that surpass current measurements by about an order of magnitude; beam-energy calibration is a dominant systematic but can be improved.
• The document outlines extensive BSM exploration opportunities (exotic Higgs decays, SUSY-EW, dark matter/dark sector, long-lived particles) with near-detector and far-detector strategies, plus detector R&D needs.