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arXiv · 1610.06575

Partonic structure of neutral pseudoscalars via two photon transition form factors

Khepani Raya·Minghui Ding·Adnan Bashir·Lei Chang·Craig D. Roberts
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Abstract

The $\gamma \gamma^\ast \to \eta_{c,b}$ transition form factors are computed using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory, and thereby unified with equivalent calculations of electromagnetic pion elastic and transition form factors. The resulting $\gamma \gamma^\ast \to \eta_c$ form factor, $G_{\eta_c}(Q^2)$, is consistent with available data: significantly, at accessible momentum transfers, $Q^2 G_{\eta_c}(Q^2)$ lies well below its conformal limit. These observations confirm that the leading-twist parton distribution amplitudes (PDAs) of heavy-heavy bound-states are compressed relative to the conformal limit. A clear understanding of the distribution of valence-quarks within mesons thus emerges; a picture which connects Goldstone modes, built from the lightest-quarks in Nature, with systems containing the heaviest valence-quarks that can now be studied experimentally, and highlights basic facts about manifestations of mass within the Standard Model.

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Khepani Raya, Minghui Ding, Adnan Bashir, Lei Chang, Craig D. Roberts. 2016-10-20. Partonic structure of neutral pseudoscalars via two photon transition form factors. https://doi.org/10.1103/physrevd.95.074014

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