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Summary: Working Group on QCD and Strong Interactions

E. L. Berger, Stephen Magill, I. Sarcevic, J. Jalilian-Marian, W. B. Kilgore, Anna Kulesza, W. Vogelsang, R. V. Harlander, E. Kinney, R. Ball, B. Flaugher, W. Giele, P. Mackenzie, Z. Sullivan, C. Balazs, L. Reina, W. -K. Tung, N. Kidonakis, P. Nadolsky, F. Olness, G. Sterman, S. D. Ellis

TL;DR

The Snowmass 2001 QCD Working Group provides a comprehensive blueprint for advancing QCD across perturbative and nonperturbative regimes, highlighting precision calculations (NLO/NNLO), resummation techniques, and lattice QCD as complementary approaches. It emphasizes robust determination of PDFs and their uncertainties, refined jet algorithms and energy-flow observables, and the critical role of QCD in searches for new physics at current and future colliders. The report connects small-x dynamics, diffraction, and nuclear effects to high-density QCD, while outlining polarization physics and the spin structure of the nucleon as a key frontier. Collectively, these efforts aim to deliver percent-level precision in standard-model processes, enable reliable extrapolations to TeV-scale phenomena, and bridge the perturbative and nonperturbative languages of QCD to illuminate fundamental interactions and new physics.

Abstract

In this summary of the considerations of the QCD working group at Snowmass 2001, the roles of quantum chromodynamics in the Standard Model and in the search for new physics are reviewed, with empahsis on frontier areas in the field. We discuss the importance of, and prospects for, precision QCD in perturbative and lattice calculations. We describe new ideas in the analysis of parton distribution functions and jet structure, and review progress in small-$x$ and in polarization.

Summary: Working Group on QCD and Strong Interactions

TL;DR

The Snowmass 2001 QCD Working Group provides a comprehensive blueprint for advancing QCD across perturbative and nonperturbative regimes, highlighting precision calculations (NLO/NNLO), resummation techniques, and lattice QCD as complementary approaches. It emphasizes robust determination of PDFs and their uncertainties, refined jet algorithms and energy-flow observables, and the critical role of QCD in searches for new physics at current and future colliders. The report connects small-x dynamics, diffraction, and nuclear effects to high-density QCD, while outlining polarization physics and the spin structure of the nucleon as a key frontier. Collectively, these efforts aim to deliver percent-level precision in standard-model processes, enable reliable extrapolations to TeV-scale phenomena, and bridge the perturbative and nonperturbative languages of QCD to illuminate fundamental interactions and new physics.

Abstract

In this summary of the considerations of the QCD working group at Snowmass 2001, the roles of quantum chromodynamics in the Standard Model and in the search for new physics are reviewed, with empahsis on frontier areas in the field. We discuss the importance of, and prospects for, precision QCD in perturbative and lattice calculations. We describe new ideas in the analysis of parton distribution functions and jet structure, and review progress in small- and in polarization.

Paper Structure

This paper contains 41 sections, 29 equations, 4 figures.

Table of Contents

  1. Introduction: The Languages of Quantum Chromodynamics
  2. Precision and a New Era of QCD
  3. Fixed Order Calculations and Top Quark Physics
  4. NLO
  5. NNLO
  6. Applications of Resummation to Fixed Order Calculations
  7. Top Quark Physics
  8. Parton Distribution Functions (PDFs)
  9. PDF Uncertainties: the Challenge
  10. Projects at Snowmass
  11. Summary
  12. Jet Physics
  13. Underlying Event
  14. $k_{T}$ Algorithm
  15. Cone Algorithm
  16. ...and 26 more sections

Figures (4)

  • Figure 1: QCD as a continent.
  • Figure 2: Scatter plot for PDFs in the space of vector boson cross sections. The D0 measurement is represented by the one-standard deviation error ellipse. The theory prediction is represented by a random sampling PDF set (using H1, ZEUS and E665). Changing the luminosity moves the error ellipse over the diagonal line, changing the luminosity probability.
  • Figure 3: Plot of energy flow in $\eta,\phi$ indicating the region averaged over to determine the JEF value at the center of the circle. In this figure, red (dark) pixels indicate high energy. The event was created with PYTHIA.
  • Figure 4: L3 data for first moments of various event shapes. The dashed line is perturbation theory, the solid line a fit based on Eq. ( \ref{['shift']})