The origin of proton mass from J/Ψ photo-production data

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 J/Ψ J / Ψ photo-production data of the GlueX experiment, at JLab. We apply a vector meson dominance model to describe the photo-production of J/Ψ J / Ψ and a running strong coupling which includes the nonperturbative effects in the low μ ² μ 2 region. Despite the large uncertainty, we find that the experimental data favors a small value of the trace anomaly parameter b=0.07± 0.17 b = 0.07 ± 0.17 . We report the resulting proton mass decompositions at μ ²=0.41 GeV² μ 2 = 0.41 GeV 2 and μ ²=4 GeV² μ 2 = 4 GeV 2 .