[Paper Review] Report of the Topical Group on Top quark physics and heavy flavor production for Snowmass 2021

R. Schwienhorst, Doreen Wackeroth+69 more|arXiv (Cornell University)|Sep 22, 2022

Distributed and Parallel Computing Systems6 citations

TL;DR

This Snowmass 2021 report outlines the physics potential of top quark and heavy flavor (bottom, charm) studies at the HL-LHC and future colliders, emphasizing precision measurements of the top quark mass, Yukawa coupling, and couplings to SM bosons. It identifies key theoretical challenges—such as N³LO QCD and NNLO EW calculations, PDF uncertainty reduction, and top quark mass scheme calibration—necessary to achieve sub-50 MeV mass precision at lepton colliders and percent-level coupling measurements at future hadron and lepton colliders.

ABSTRACT

This report summarizes the work of the Energy Frontier Topical Group on EW Physics: Heavy flavor and top quark physics (EF03) of the 2021 Community Summer Study (Snowmass). It aims to highlight the physics potential of top-quark studies and heavy-flavor production processes (bottom and charm) at the HL-LHC and possible future hadron and lepton colliders and running scenarios.

Motivation & Objective

• To assess the physics potential of top quark and heavy flavor (bottom, charm) production at the HL-LHC and future lepton and hadron colliders.
• To identify the theoretical and experimental challenges required to achieve sub-50 MeV top quark mass precision and percent-level coupling measurements.
• To evaluate the sensitivity of top quark final states to BSM physics, including flavor-changing neutral currents, SUSY, compositeness, and contact interactions.
• To establish the need for higher-order QCD and EW calculations, improved PDFs, and better parton shower modeling to match future experimental precision.
• To guide future collider and theory R&D by outlining a roadmap for precision top physics in the energy frontier.

Proposed method

• Proposes a comprehensive program of top quark and heavy flavor measurements at the HL-LHC, ILC, CLIC, FCC-ee, and FCC-hh, using inclusive and differential cross-sections.
• Relies on advanced theoretical calculations: N³LO QCD for top pair production, NNLO QCD for associated processes, and inclusion of EW corrections.
• Emphasizes calibration of the top quark MC mass to a well-defined perturbative scheme to match experimental precision.
• Integrates PDF uncertainty reduction through forward heavy flavor measurements and improved global PDF fits.
• Uses effective field theory (EFT) fits to constrain Wilson coefficients for top-quark couplings to W, Z, Higgs, and four-top interactions.
• Compares collider reach across future options using Table 10, projecting uncertainties in top mass, Yukawa coupling, and coupling strengths.

Experimental results

Research questions

• RQ1 What precision can be achieved in top quark mass measurements at future lepton colliders, and what theoretical advances are required to reach sub-50 MeV uncertainty?
• RQ2 How do higher-order QCD and EW corrections (N³LO, NNLO) impact the precision of top quark cross-section and coupling measurements at the HL-LHC and beyond?
• RQ3 To what extent can PDF uncertainties be reduced through differential measurements of top and heavy flavor production in the forward region?
• RQ4 What is the sensitivity of future colliders to BSM physics via top quark couplings, particularly flavor-changing neutral currents and contact interactions?
• RQ5 How do circular lepton colliders (FCC-ee) outperform linear colliders (ILC) in top quark mass and coupling determinations due to stronger constraints on the strong coupling constant?

Key findings

• A top quark mass precision of 50 MeV or better is achievable at circular lepton colliders (FCC-ee) running at the top threshold (340 GeV), significantly improving on the HL-LHC's ~500 MeV goal.
• The top quark Yukawa coupling can be measured with a precision of 1.0% at FCC-hh, down from 2–4% expected at the HL-LHC, requiring high-energy lepton or hadron colliders.
• Right-handed top-W and top-Z couplings can be probed with uncertainties below 0.01 TeV⁻² at FCC-ee and ILC 500, enabling sensitive tests of BSM models.
• Flavor-changing neutral current (FCNC) couplings such as $ tZu $ and $ tar{u} ilde{ u} $ can be probed at the $ 10^{-6} $ branching ratio level at lepton colliders, surpassing hadron collider reach.
• The four-top coupling $ c_{tt} $ can be constrained to 0.024 TeV⁻² at FCC-hh, improving on the HL-LHC's 0.6 TeV⁻², indicating enhanced sensitivity to new physics.
• Reducing PDF uncertainties through forward heavy flavor measurements is critical, as they currently dominate theory uncertainties in top pair production.