Nucleon Resonance Electroexcitation Amplitudes and Emergent Hadron Mass

Abstract

Understanding the strong interaction dynamics that govern the emergence of hadron mass (EHM) represents a challenging open problem in the Standard Model. In this paper we describe new opportunities for gaining insight into EHM from results on nucleon resonance ($N^\ast$) electroexcitation amplitudes (i.e. $\gamma_vpN^\ast$ electrocouplings) in the mass range up to 1.8\,GeV for virtual photon four-momentum squared (i.e. photon virtualities $Q^2$) up to 7.5\,GeV$^2$ available from exclusive meson electroproduction data acquired during the 6-GeV era of experiments at Jefferson Laboratory (JLab). These results, combined with achievements in the use of continuum Schwinger function methods (CSMs), offer new opportunities for charting the momentum dependence of the dressed quark mass from results on the $Q^2$-evolution of the $\gamma_vpN^\ast$ electrocouplings. A successful description of the $\Delta(1232)3/2^+$ and $N(1440)1/2^+$ electrocouplings has been achieved using CSMs with, in both cases, common momentum-dependent mass functions for the dressed quarks, for the gluons, and the same momentum-dependent strong coupling. Parameter-free CSM predictions for the electrocouplings of the $\Delta(1600)3/2^+$ became available in 2019. The experimental results obtained in the first half of 2022 have confirmed the CSM predictions. We also discuss prospects for these studies during the 12-GeV era at JLab using the CLAS12 detector, with experiments that are currently in progress, and canvass the physics motivation for continued studies in this area with a possible increase of the JLab electron beam energy up to 22\,GeV.