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SLAC Publication: SLAC-PUB-16368
SLAC Release Date: September 17, 2015
Predictions for the Top-Quark Forward-Backward Asymmetry at High Invariant Pair Mass Using the Principle of Maximum Conformality
Brodsky, Stanley F..
he D0 collaboration at FermiLab has recently measured the top-quark pair forward-backward asymmetry in \bar p p \to t \bar t X reactions as a function of the \bar t t invariant mass M_{t\bar{t}}. D0 observed that the asymmetry A_{\rm FB}(M_{t\bar{t}}) first increases and then decreases as M_{t\bar{t}} is increased. This behavior is not explained using conventional renormalization scale-setting, even by a next-to-next-to-leading order (N^2LO) QCD calculation -- one predicts a monotonically incre... Show Full Abstract
he D0 collaboration at FermiLab has recently measured the top-quark pair forward-backward asymmetry in \bar p p \to t \bar t X reactions as a function of the \bar t t invariant mass M_{t\bar{t}}. D0 observed that the asymmetry A_{\rm FB}(M_{t\bar{t}}) first increases and then decreases as M_{t\bar{t}} is increased. This behavior is not explained using conventional renormalization scale-setting, even by a next-to-next-to-leading order (N^2LO) QCD calculation -- one predicts a monotonically increasing behavior. In the conventional scale-setting method, one simply guesses a single renormalization scale \mu_r for the argument of the QCD running coupling and then varies it over an arbitrary range. However, the conventional method has inherent difficulties. ...... In contrast, if one fixes the scale using the Principle of Maximum Conformality (PMC), the resulting pQCD predictions are renormalization-scheme independent since all of the scheme-dependent \{\beta_i\}-terms in the QCD perturbative series are resummed into the QCD running couplings at each order. ...... In this paper we show that if one applies the PMC to determine the top versus anti-top quark forward-backward asymmetry in pQCD at the N^2LO level, one obtains accurate predictions without renormalization scheme or scale ambiguities. For example, the PMC predicts A^{\rm PMC}_{\rm FB}(M_{t\bar{t}}>450~\rm GeV)=29.9\% at the Tevatron, which is consistent with the CDF and D0 measurements. In addition, the PMC accounts for the "increasing-decreasing" behavior observed for A_{\rm FB} as the t \bar t invariant mass is increased. Thus by using the rigorous PMC scale-setting procedure, one obtains a comprehensive, self-consistent pQCD explanation for the Tevatron measurements of the top-quark pair forward-backward asymmetry. Show Partial Abstract
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  • Interest Categories: HEP Phenomenology