Abstract
The trace of the stress tensor characterizes the transformation of a theory under rescaling. In quantum chromodynamics (QCD), this trace contains contributions from the bare masses of the quarks and also from a purely quantum effect, called the QCD trace anomaly. It affects all masses in the theory. We present an estimation of the QCD trace anomaly from the near-threshold hbox {J}/{Psi } photo-production data of the GlueX experiment, at JLab. We apply a vector meson dominance model to describe the photo-production of hbox {J}/{Psi } and a running strong coupling which includes the nonperturbative effects in the low mu ^2 region. Despite the large uncertainty, we find that the experimental data favors a small value of the trace anomaly parameter b=0.07pm 0.17. We report the resulting proton mass decompositions at mu ^2=0.41hbox { GeV}^2 and mu ^2=4hbox { GeV}^2.
Highlights
Introduction and renormalizedIn Nobel Prize winning work this was done by ’t Hooft and Veltman [3] nearly 50 years ago, who found that an additional piece, known as the regulator, needs to be added to the theory in the process of removing the divergences
According to an analysis of quantum chromodynamics (QCD) theory, the mass of a nucleon MN is decomposed into four terms: the quark energy contribution Mq, the gluon energy contribution Mg, the quark mass contribution Mm, and the trace anomaly contribution Ma [4,5]
The dependences of these terms on the QCD trace anomaly parameter b and the momentum fraction a carried by all quarks are [5], Most of the mass of the observable Universe is contained in its protons and neutrons, collectively called nucleons
Summary
To avoid the Landau pole of the running strong coupling constant at low μ2, we fix αs using the analytic approach of Ref. [26], in which QCD nonperturbative effects are folded into the coupling. To avoid the Landau pole of the running strong coupling constant at low μ2, we fix αs using the analytic approach of Ref. [26], in which QCD nonperturbative effects are folded into the coupling. The resulting analytic expression for αs is αsana
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