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Report of the 2005 Snowmass Top/QCD Working Group

A. Juste, Y. Kiyo, F. Petriello, T. Teubner, K. Agashe, P. Batra, U. Baur, C. F. Berger, J. A. R. Cembranos, A. Gehrmann-De Ridder, T. Gehrmann, E. W. N. Glover, S. Godfrey, A. Hoang, M. Perelstein, Z. Sullivan, T. Tait, S. Zhu

TL;DR

This Snowmass report surveys precision top-quark and QCD physics for the ILC, highlighting threshold scans, electroweak top couplings, and the interplay of SM predictions with potential new physics. It details NNLO/NNLL QCD corrections, nonrelativistic EFT approaches (such as vNRQCD/pNRQCD) for threshold phenomena, and novel subtraction frameworks (antenna subtraction) for jet observables, all while addressing beam-energy spectra and luminosity considerations. The collection of studies also examines new-physics scenarios affecting the top sector—Randall–Sundrum bulk fields and Little Higgs models—and assesses CPT symmetry tests with top quarks. Collectively, the work demonstrates that percent-level theoretical and experimental control at the ILC can sharply test the SM and discriminate among competing new-physics explanations through precision top-quark measurements.

Abstract

This report discusses several topics in both top quark physics and QCD at an International Linear Collider (ILC). Issues such as measurements at the $t\bar{t}$ threshold, including both theoretical and machine requirements, and the determination of electroweak top quark couplings, are reviewed. New results concerning the potential of a 500 GeV $e^+e^-$ collider for measuring $Wtb$ couplings and the top quark Yukawa coupling are presented. The status of higher order QCD corrections to jet production cross sections, heavy quark form factors, and longitudinal gauge boson scattering, needed for percent-level studies at the ILC, are reviewed. A new study of the measurement of the hadronic structure of the photon at a $γγ$ collider is presented. The effects on top quark properties from several models of new physics, including composite models, Little Higgs theories, and CPT violation, are studied.

Report of the 2005 Snowmass Top/QCD Working Group

TL;DR

This Snowmass report surveys precision top-quark and QCD physics for the ILC, highlighting threshold scans, electroweak top couplings, and the interplay of SM predictions with potential new physics. It details NNLO/NNLL QCD corrections, nonrelativistic EFT approaches (such as vNRQCD/pNRQCD) for threshold phenomena, and novel subtraction frameworks (antenna subtraction) for jet observables, all while addressing beam-energy spectra and luminosity considerations. The collection of studies also examines new-physics scenarios affecting the top sector—Randall–Sundrum bulk fields and Little Higgs models—and assesses CPT symmetry tests with top quarks. Collectively, the work demonstrates that percent-level theoretical and experimental control at the ILC can sharply test the SM and discriminate among competing new-physics explanations through precision top-quark measurements.

Abstract

This report discusses several topics in both top quark physics and QCD at an International Linear Collider (ILC). Issues such as measurements at the threshold, including both theoretical and machine requirements, and the determination of electroweak top quark couplings, are reviewed. New results concerning the potential of a 500 GeV collider for measuring couplings and the top quark Yukawa coupling are presented. The status of higher order QCD corrections to jet production cross sections, heavy quark form factors, and longitudinal gauge boson scattering, needed for percent-level studies at the ILC, are reviewed. A new study of the measurement of the hadronic structure of the photon at a collider is presented. The effects on top quark properties from several models of new physics, including composite models, Little Higgs theories, and CPT violation, are studied.

Paper Structure

This paper contains 17 sections, 24 equations, 25 figures, 4 tables.

Table of Contents

  1. INTRODUCTION
  2. PRECISION STUDIES OF THE TOP QUARK AT THE ILC
  3. Measuring the $Wtb$ Coupling Below the $t\bar{t}$ Threshold P. Batra, T. Tait
  4. Probing Electroweak Top Quark Couplings at the ILC and the LHC U. Baur
  5. Two-loop Corrections to Heavy Quark Form Factors T. Gehrmann
  6. Electroweak Effects at the $t\bar{t}$ Threshold A. Hoang
  7. Towards a Precise Measurement of the Top Quark Yukawa Coupling at the ILC Juste:2005vs A. Juste
  8. The $t\bar{t}$ Threshold at an $e^+e^-$ Collider Y. Kiyo
  9. Differential Distributions and Experimental Aspects of the $t\bar{t}$ Threshold Scan T. Teubner
  10. QCD EFFECTS IN ILC PHYSICS
  11. Precision QCD at the ILC: $e^+e^- \rightarrow 3$ Jets A. Gehrmann-De Ridder, T. Gehrmann, E.W.N. Glover
  12. Study of $V_L V_L \rightarrow t\bar{t}$ at the ILC Including ${\cal O}(\alpha_s^2)$ Corrections Godfrey:2005gp S. Godfrey
  13. QCD at a Photon Collider Sullivan:2005pb Z. Sullivan
  14. NEW PHYSICS EFFECTS ON TOP QUARK PROPERTIES
  15. Top Compositeness at Colliders K. Agashe
  16. ...and 2 more sections

Figures (25)

  • Figure 1: Inclusive rates for $e^+ e^- \rightarrow W^+ b W^- \bar{b}$ as a function of the center-of-mass energy for $g_{Wtb} = g_{SM}$ (black solid), $g_{Wtb} = 2 g_{SM}$ (blue dashed), and $g_{Wtb} = g_{SM} /2$ (red dotted).
  • Figure 2: Curve corresponding to the SM rate and its 1$\sigma$ and 2$\sigma$ deviations in the plane of $g_{Wtb}$ and $\Gamma_t$. Also overlaid is an expected measurement of $\Gamma_t$ from the on-shell threshold scan with an uncertainty of $100$ MeV.
  • Figure 3: The differential cross sections as a function of the photon transverse momentum for $\gamma\ell\nu_\ell b\bar{b}jj$ production at the LHC. Part a) shows the SM signal and the various contributions to the background. Part b) shows the SM signal and background, and the signal for various anomalous $tt\gamma$ couplings.
  • Figure 4: a) The differential cross sections at the LHC as a function of $p_T(Z)$ for ${\ell'}^+{\ell'}^-\ell\nu b\bar{b}jj$ final states. Shown are the SM predictions for $t\bar{t}Z$ production, for several non-standard $ttZ$ couplings, and for various backgrounds. Only one coupling at a time is allowed to deviate from its SM value. b) The differential cross sections as a function of the missing transverse momentum for $p\hbox{/}_Tb\bar{b}+4$j production at the LHC. Shown are the SM predictions for $t\bar{t}Z$ production and for various backgrounds.
  • Figure 5: Feynman diagrams contributing to the two-loop QCD corrections to heavy quark form factors
  • ...and 20 more figures