The cross section for the reaction ep ! e′p_+_− was measured in the resonance region for 1.4
The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on N∗ and _ states shows an evident
discrepancy. A better description of the data is obtained either by a sizeable change of the properties of the P13(1720) resonance or by introducing a new baryon state, not reported in published analyses.
Physical Review Letters
Ripani, M.; Biselli, Angela; and CLAS Collaboration, "Measurement of ep→e′pπ+π− and Baryon Resonance Analysis" (2003). Physics Faculty Publications. 4.
M. Ripani et al. [CLAS Collaboration], "Measurement of ep→e′pπ+π− and Baryon Resonance Analysis", Physical Review Letters 91.2 (2003) DOI: 10.1103/PhysRevLett.91.022002