Completing the picture of the Roper resonance

TL;DR

This paper uses a continuum quantum field theory approach to predict properties of the Roper resonance, unifying it with other hadrons and highlighting the roles of quark core and meson cloud in its structure.

Contribution

It provides a unified continuum-based prediction of the Roper resonance's properties, emphasizing the quark core and meson cloud contributions, advancing understanding of nucleon excitations.

Findings

The Roper resonance is identified as the nucleon's first radial excitation.

The quark core's charge radius is 80% larger than the proton's.

The meson cloud reduces the Roper mass by approximately 20%.

Abstract

We employ a continuum approach to the three valence-quark bound-state problem in relativistic quantum field theory to predict a range of properties of the proton's radial excitation and thereby unify them with those of numerous other hadrons. Our analysis indicates that the nucleon's first radial excitation is the Roper resonance. It consists of a core of three dressed-quarks, which expresses its valence-quark content and whose charge radius is 80% larger than the proton analogue. That core is complemented by a meson cloud, which reduces the observed Roper mass by roughly 20%. The meson cloud materially affects long-wavelength characteristics of the Roper electroproduction amplitudes but the quark core is revealed to probes with $Q^2 \gtrsim 3 m_N^2$.