Application of the principle of maximum conformality to top-pair production

被引：48

作者：

Brodsky, Stanley J. ^{[1
]}

Wu, Xing-Gang ^{[1
,2
]}

机构：

[1] SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA

[2] Chongqing Univ, Dept Phys, Chongqing 401331, Peoples R China

来源：

PHYSICAL REVIEW D | 2012年 / 86卷 / 01期

关键词：

PRODUCTION CROSS-SECTION; HEAVY-QUARK PRODUCTION; HADRONIC PRODUCTION; UPGRADED VERSION; QCD CORRECTIONS; BARYONS XI(CC); FIELD THEORY; GENERATOR; SCALE; DISTRIBUTIONS;

D O I：

10.1103/PhysRevD.86.014021

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

A major contribution to the uncertainty of finite-order perturbative QCD predictions is the perceived ambiguity in setting the renormalization scale mu(r). For example, by using the conventional way of setting mu(r) is an element of [m(t)/2; 2m(t)], one obtains the total t (t) over bar production cross section sigma(t (t) over bar) with the uncertainty Delta sigma(t (t) over bar)/sigma(t (t) over bar) similar to ((+3%)(-4%)) at the Tevatron and LHC even for the present next-to next-to-leading-order level. The principle of maximum conformality (PMC) eliminates the renormalization scale ambiguity in precision tests of Abelian QED and non-Abelian QCD theories. By using the PMC, all nonconformal {beta(i)} terms in the perturbative expansion series are summed into the running coupling constant, and the resulting scale-fixed predictions are independent of the renormalization scheme. The correct scale displacement between the arguments of different renormalization schemes is automatically set, and the number of active flavors n(f) in the {beta(i)} function is correctly determined. The PMC is consistent with the renormalization group property that a physical result is independent of the renormalization scheme and the choice of the initial renormalization scale mu(init)(r). The PMC scale mu(PMC)(r) is unambiguous at finite order. Any residual dependence on mu(init)(r) for a finite-order calculation will be highly suppressed since the unknown higher-order {beta(i)} terms will be absorbed into the PMC scales' higher-order perturbative terms. We find that such renormalization group invariance can be satisfied to high accuracy for sigma(t (t) over bar) at the next-to next-to-leading-order level. In this paper we apply PMC scale setting to predict the t (t) over bar cross section sigma(t (t) over bar) at the Tevatron and LHC colliders. It is found that sigma(t (t) over bar) remains almost unchanged by varying mu(init)(r) within the region of [m(t)/4, 4m(t)]. The convergence of the expansion series is greatly improved. For the (q (q) over bar) channel, which is dominant at the Tevatron, its next-to-leading-order (NLO) PMC scale is much smaller than the top-quark mass in the small x region, and thus its NLO cross section is increased by about a factor of 2. In the case of the (gg) channel, which is dominant at the LHC, its NLO PMC scale slightly increases with the subprocess collision energy root s, but it is still smaller than m(t) for root s less than or similar to 1 TeV, and the resulting NLO cross section is increased by similar to 20%. As a result, a larger sigma(t (t) over bar) is obtained in comparison to the conventional scale setting method, which agrees well with the present Tevatron and LHC data. More explicitly, by setting m(t) = 172.9 +/- 1.1 GeV, we predict sigma(Tevatron, 1.96 TeV) = 7.626(-0.257)(+0.265) pb, sigma(LHC, 7 TeV) = 171.8(-5.6)(+5.8) pb and sigma(LHC, 14 TeV) = 941.3(-26.5)(+28.4) pb.

引用

页数：13

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