Completing the Picture of the Roper Resonance

Area of Science:

• * Quantum Field Theory
• * Hadron Spectroscopy
• * Nuclear Physics

Background:

• * Understanding the structure of hadrons, like the proton, is crucial in nuclear physics.
• * The proton's radial excitation, the Roper resonance, has properties that require explanation.
• * Relativistic quantum field theory provides a framework for studying subatomic particles.

Purpose of the Study:

• * To predict properties of the proton's radial excitation using a continuum approach.
• * To unify the properties of the Roper resonance with other hadrons.
• * To investigate the internal structure of the Roper resonance.

Main Methods:

• * Employing a continuum approach within relativistic quantum field theory.
• * Analyzing the three valence-quark bound-state problem.
• * Calculating the charge radius and mass of the Roper resonance.

Main Results:

• * The nucleon's first radial excitation is identified as the Roper resonance.
• * The Roper resonance has a core of three dressed quarks with a charge radius 80% larger than the proton.
• * A meson cloud reduces the Roper mass by approximately 20% and affects its electroproduction amplitudes.

Conclusions:

• * The Roper resonance's properties are explained by a composite structure of a quark core and a meson cloud.
• * The quark core is observable at higher momentum transfers (Q^2 ≳ 3m(N)^2).
• * This model unifies the Roper resonance with other hadrons, providing a consistent picture.