Evidence of new nucleon resonances from electromagnetic meson production

The study of nucleon resonances in electromagnetic meson production with the CLAS detector is discussed. The electromagnetic interaction is complementary to pion scattering in the exploration of the nucleon excitation spectrum. Higher mass states often decouple from the $N\pi$ channel and are not seen in $\pi N \to \pi N$. Photoproduction of mesons, such as $K\Lambda$, $\omega p$ and $\eta^\prime p$ may be more sensitive to many of these states. The CLAS detector, combined with the use of energy-tagged polarized photons and polarized electrons, as well as polarized targets and the measurement of recoil polarization, are the tools needed for a comprehensive nucleon resonance program. Some of the recently published high statistics data sets had significant impact on further clarifying the nucleon excitation spectrum.Comment: 6 pages, 4 figures, presented at MESON 2012, Krako

Spin Physics in the Resonance Region

Recent results from Jefferson Lab on measurement of inclusive double polarization asymmetries in the nucleon resonance region are discussed. Preliminary results on the first moment of the structure function g_1(x,Q^2) for protons, and on the generalized Gerasimov-Drell-Hearn integral for neutrons are presented as well. The first moment for protons shows a strong Q^2 dependence below Q^2 = 1 GeV^2, and changes sign near Q^2 = 0.3 GeV^2. Strong double polarization asymmetries are observed in exclusive electroproduction of pions from polarized protons.Comment: 9 pages, 6 figures, Talk presented at the 3rd International Conference on Perspectives in Hadronic Physics, Trieste May 7-11, 200

Strangeness Physics with CLAS at JLab

A brief overview of strangeness physics with the CLAS detector at JLab is given, mainly covering the domain of nucleon resonances. Several excited states predicted by the symmetric constituent quark model may have significant couplings to the K-Lambda or K-Sigma channels. I will discuss data that are relevant in the search for such states in the strangeness channel, and give an outlook on the future prospects of the N* program at JLab with electromagnetic probes.Comment: 9 pages, 7 figures, Conference on Strangeness in Nuclei, SENDAI 200

The Nucleon Structure in the Resonance Region

Recent results on inclusive and exclusive electroproduction experiments at Jefferson Lab are discussed. They include measurements of the spin responses for protons and neutrons in and above the resonance region, exclusive single and double pion production to measure resonance transition multipoles, and searches for predicted yet unobserved quark model states. A brief outlook into the new domain of generalized parton distribution is given as well.Comment: 13 pages, 11 figures, Talk at the International Conference on Mesons and Light Nuclei, Prague July 2 - 6, 200

Excitation of Nucleon Resonances

I discuss developments in the area of nucleon resonance excitations that are necessary to bring our understanding of nucleon structure in the regime of strong QCD to a qualitatively new level. They involve the collection of high quality data in various channels, a more rigorous approach in the search for "missing" quark model states, an effort to compute some critical quantities in nucleon resonance excitations from first principles, i.e. QCD, and a proposal aimed at obtaining an understanding of a fundamental quantity in nucleon structure.Comment: 9 pages, 2 figure

Study of excited nucleons and their structure

Recent advances in the study of excited nucleons are discussed. Much of the progress has been achieved due to the availability of high precision meson production data in the photoproduction and electroproduction sectors, the development of multi-channel partial wave analysis techniques, and advances in Lattice QCD with predictions of the full excitation spectrum.Comment: 6 pages, 4 figures, Invited talk at NSTAR 201