The Roper Resonance and Kin

The properties of the Roper resonance \(N(1440) {1}{2}^+\) are reviewed. Quark models have long struggled to reproduce its mass relative to its negative-parity partner \(N(1535) {1}{2}^-\). This discrepancy motivated interpretations of the Roper as a dynamically generated meson–baryon state. Including its isospin partners \({ Δ }(1600) {3}{2}^+\) and \({ Δ }(1700) {3}{2}^-\) 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 \(J^P= {1}{2}^+\); the highest-mass member, \(N(2100) {1}{2}^+\), likely represents a Roper-like excitation in the fourth shell. Abstract Published by the Jagiellonian University 2026 authors