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The QCD and Standard Model Working Group: Summary Report from Les Houches

P. Aurenche, C. Balazs, R. D. Ball, T. Binoth, E. Boos, S. Catani, J. Collins, V. del Duca, M. Dittmar, M. Fontannaz, S. Frixione, J. P. Guillet, G. Heinrich, J. Huston, V. Ilyin, Y. Kato, K. Odagiri, F. Paige, E. Pilon, A. Pukhov, I. Puljak, A. Semenov, A. Skatchkova, D. Soper, V. Tano, S. Tapprogge, W. K. Tung, W. Vogelsang, M. Werlen, D. Zeppenfeld

TL;DR

This report synthesizes the QCD/SM working group discussions at Les Houches 1999, detailing the status and challenges of QCD in Tevatron and LHC contexts. It surveys parton densities and their uncertainties, fixed-order versus resummed calculations, and the role of parton showers, soft-gluon resummation, and non-perturbative k_T effects. The volume highlights generalized factorization, NLO/NNLO progress, jet algorithms, and the underlying event, with particular attention to Higgs and photon-related processes as key LHC backgrounds and signals. The findings underscore the need for improved PDF uncertainty quantification, robust matching of resummation with fixed-order results, and refined Monte Carlo tools to support precision predictions at the LHC.

Abstract

The Les Houches Workshop on Physics at TeV Colliders took place from June 8-18, 1999. One of the three working groups at Les Houches concentrated on QCD issues, both at the Tevatron Collider and at the LHC. Besides the interest in QCD in its own right, QCD dynamics plays an important role in the production mechanisms for any new physics process that might be observed at either collider, as well as any processes that may form backgrounds to the new physics. This writeup serves both as a pedagogical overview of QCD as well as an update on the current status of the field.

The QCD and Standard Model Working Group: Summary Report from Les Houches

TL;DR

This report synthesizes the QCD/SM working group discussions at Les Houches 1999, detailing the status and challenges of QCD in Tevatron and LHC contexts. It surveys parton densities and their uncertainties, fixed-order versus resummed calculations, and the role of parton showers, soft-gluon resummation, and non-perturbative k_T effects. The volume highlights generalized factorization, NLO/NNLO progress, jet algorithms, and the underlying event, with particular attention to Higgs and photon-related processes as key LHC backgrounds and signals. The findings underscore the need for improved PDF uncertainty quantification, robust matching of resummation with fixed-order results, and refined Monte Carlo tools to support precision predictions at the LHC.

Abstract

The Les Houches Workshop on Physics at TeV Colliders took place from June 8-18, 1999. One of the three working groups at Les Houches concentrated on QCD issues, both at the Tevatron Collider and at the LHC. Besides the interest in QCD in its own right, QCD dynamics plays an important role in the production mechanisms for any new physics process that might be observed at either collider, as well as any processes that may form backgrounds to the new physics. This writeup serves both as a pedagogical overview of QCD as well as an update on the current status of the field.

Paper Structure

This paper contains 92 sections, 74 equations, 66 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Parton densities
  3. The gluon density issue
  4. Partonic cross sections: fixed-order expansions, resummed calculations, parton showers
  5. Soft-gluon resummation
  6. Other topics
  7. Introduction
  8. Processes Involved in Global Analysis Fits
  9. Evolution, Schemes and Parametrizations
  10. Evolution Codes
  11. Parametrization of Initial Distributions
  12. Evolution in time and $Q^2$
  13. Estimating Uncertainties
  14. Direct Photons and Jets in Global Fits
  15. Direct Photons
  16. ...and 77 more sections

Figures (66)

  • Figure 1: The $(x,Q^2)$ plane of the parton kinematics for the production of a heavy system of invariant mass $M$ and rapidity $y$ at LHC, HERA and fixed-target experiments.
  • Figure 1: The kinematic map in the $(x,Q)$ plane of data points used in the CTEQ5 analysis.
  • Figure 1: Transverse momentum distribution of electron-positron pairs from decays of (mostly) $Z^0$ bosons, produced at the Tevatron in $\sqrt{S}=1.8$ GeV center of mass proton--anti-proton collisions. The data are CDF preliminary CDFEWGWeb, and the curve is calculated by the ResBos Monte Carlo event generator BalazsYuanWZThesis.
  • Figure 1: The $Z^0$$p_T$ distribution (at low $p_T$) from CDF for Run 1 compared to predictions from ResBos and from PYTHIA. The two PYTHIA predictions use the default (rms) value for the non-perturbative $k_T$ (0.44 GeV) and the value that gives the best agreement with the shape of the data (2.15 GeV).
  • Figure 1: Squared matrix elements which contribute the NLO corrections to $e^+ e^- \rightarrow 3\, jets$. The dashed line represents a massive vector boson, $\gamma^*, W, Z$. $a)$ interference term between one-loop and tree amplitudes. The final-state partons are a $q{\bar{q}}$ pair and a gluon. $b)$ square of a tree amplitude. The final-state partons are a $q{\bar{q}}$ pair and two gluons, or two $q{\bar{q}}$ pairs. In figure $b)$ one of the partons is unresolved.
  • ...and 61 more figures