skip to main content

DOE PAGESDOE PAGES

Title: Importance of proper renormalization scale-setting for QCD testing at colliders

A primary problem affecting perturbative quantum chromodynamic (pQCD) analyses is the lack of a method for setting the QCD running-coupling renormalization scale such that maximally precise fixed-order predictions for physical observables are obtained. The Principle of Maximum Conformality (PMC) eliminates the ambiguities associated with the conventional renormalization scale-setting procedure, yielding predictions that are independent of the choice of renormalization scheme. The QCD coupling scales and the effective number of quark flavors are set order-by-order in the pQCD series. The PMC has a solid theoretical foundation, satisfying the standard renormalization group invariance condition and all of the self-consistency conditions derived from the renormalization group. The PMC scales at each order are obtained by shifting the arguments of the strong force coupling constant αs to eliminate all non-conformal {βi} terms in the pQCD series. The {βi} terms are determined from renormalization group equations without ambiguity. The correct behavior of the running coupling at each order and at each phase-space point can then be obtained. The PMC reduces in the NC → 0 Abelian limit to the Gell-Mann-Low method. In this brief report, we summarize the results of our recent application of the PMC to a number of collider processes, emphasizing the generalitymore » and applicability of this approach. A discussion of hadronic Z decays shows that, by applying the PMC, one can achieve accurate predictions for the total and separate decay widths at each order without scale ambiguities. We also show that, if one employs the PMC to determine the top-quark pair forward-backward asymmetry at the next-to-next-to-leading order level, one obtains a comprehensive, self-consistent pQCD explanation for the Tevatron measurements of the asymmetry. This accounts for the “increasing-decreasing” behavior observed by the D0 collaboration for increasing tt¯ invariant mass. At lower energies, the angular distributions of heavy quarks can be used to obtain a direct determination of the heavy quark potential. A discussion of the angular distributions of massive quarks and leptons is also presented, including the fermionic component of the two-loop corrections to the electromagnetic form factors. Furthermore, these results demonstrate that the application of the PMC systematically eliminates a major theoretical uncertainty for pQCD predictions, thus increasing collider sensitivity to possible new physics beyond the Standard Model.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Chongqing Univ., Chongqing (People's Republic of China)
  2. Chongqing Univ., Chongqing (People's Republic of China); Guizhou Minzu Univ., Guiyang (People's Republic of China)
  3. Stanford Univ., Stanford, CA (United States)
Publication Date:
OSTI Identifier:
1212291
Report Number(s):
SLAC-PUB--16357
Journal ID: ISSN 2095-0462; arXiv:1508.02332
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Frontiers of Physics
Additional Journal Information:
Journal Volume: 11; Journal Issue: 1; Journal ID: ISSN 2095-0462
Publisher:
Springer
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS Experiment-HEP; Phenomenology-HEP; HEPPH; HEPEX; QCD; proper renormalization scale-setting; PMC; high-energy colliders