The properties of the Roper resonance \ (N (1440) 12^+\) are reviewed. Quark models have long struggled to reproduce its mass relative to its negative-parity partner \ (N (1535) 12^-\). This discrepancy motivated interpretations of the Roper as a dynamically generated meson–baryon state. Including its isospin partners \ ( (1600) 32^+\) and \ ( (1700) 32^-\) further accentuates the tension between quark-model predictions and experiment. Recent developments based on AdS/QCD and functional methods achieve much improved agreement, identifying the Roper as an ordinary three-quark excitation. Electroproduction experiments at Jefferson Lab have now resolved this long-standing question, revealing the Roper as a \ (qqq\) core dressed by a substantial meson cloud. The Roper resonance belongs to a family of four \ (N^ \) states with \ (JP= 12^+\) ; the highest-mass member, \ (N (2100) 12^+\), likely represents a Roper-like excitation in the fourth shell. Abstract Published by the Jagiellonian University 2026 authors
Burkert et al. (Tue,) studied this question.