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Predictions for the Top-Quark Forward-Backward Asymmetry at High Invariant Pair Mass Using the Principle of Maximum Conformality | | Sheng-Quan Wang
; Xing-Gang Wu
; Zong-Guo Si
; Stanley J. Brodsky
; | | Date: |
15 Aug 2015 | | Abstract: | The D0 collaboration at FermiLab has recently measured the top-quark pair
forward-backward asymmetry in $ar p p o t ar t X$ reactions as a function
of the $ar t t $ invariant mass $M_{tar{t}}$. D0 observed that the
asymmetry $A_{
m FB}(M_{tar{t}})$ first increases and then decreases as
$M_{tar{t}}$ is increased. This behavior is not explained using conventional
renormalization scale-setting, even by a next-to-next-to-leading order
(N$^2$LO) 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
${eta_i}$-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$^2$LO level, one obtains accurate predictions
without renormalization scheme or scale ambiguities. For example, the PMC
predicts $A^{
m PMC}_{
m FB}(M_{tar{t}}>450~
m GeV)=29.9\%$ at the
Tevatron, which is consistent with the CDF and D0 measurements. In addition,
the PMC accounts for the "increasing-decreasing" behavior observed for $A_{
m
FB}$ as the $t ar t$ 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. | | Source: | arXiv, 1508.3739 | | Services: | Forum | Review | PDF | Favorites | |
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