Electroexcitation of the Roper resonance from CLAS data
The helicity amplitudes of the electroexcitation of the Roper resonance on proton are extracted at $1.7<4.2~GeV^2$ from recent high precision JLab-CLAS cross sections data and longitudinally polarized beam asymmetry for $$\pi^+$$ electroproduction on protons. The analysis is made using two approaches, dispersion relations and unitary isobar model, which give consistent results. It is found that the transverse helicity amplitude for the $$\gamma^* p\rightarrow P_{11}(1440)$$ transition, which is large and negative at $Q^2=0$, becomes large and positive at $$Q^2\simeq 2~GeV^2$$, and then drops slowly with $Q^2$. Longitudinal helicity amplitude, that was previously found from CLAS data as large and positive at $Q^2=0.4,~0.65~GeV^2$, drops with $Q^2$. These results rule out the presentation of $$P_{11}(1440)$$ as a $q^3G$ hybrid state, and provide strong evidence in favor of this resonance as a first radial excitation of the $3q$ ground state.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC05-06OR23177
- OSTI ID:
- 918575
- Report Number(s):
- JLAB-PHY-07-743; DOE/OR/23177-0182; TRN: US0805422
- Resource Relation:
- Conference: NSTAR2007, 5-8 Sep 2007, Bonn, Germany
- Country of Publication:
- United States
- Language:
- English
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