Abstract
In project A.3, the reaction γ p → π 0 γ ’ p has been studied using the TAPS photon spectrometer in the energy range √s= 1221-1331 MeV. Energy tagged photon beams have been produced with the Glasgow tagging spectrometer from electron beams provided by the MAMI-B accelerator. Angle and energy differential cross sections have been measured and compared to theoretical calculations. This comparison allows the magnetic moment of the Δ + isobar to be extracted for the first time to μ Δ+ = [2.7 +1.3 −1.0 (stat)±1.5(syst)±3(theo)] μ N . In an extension of the A3 project to the meson sector, the time-like transition form factor of the η meson has been measured with the Crystal Ball/TAPS detector system at MAMI-C.
Highlights
The main goal of the Transregio TR16 is to explore the excitation energy spectrum of the nucleon in order to unravel its complex structure
In an extension of the A3 project to the meson sector, the time-like transition form factor of the η meson has been measured with the Crystal Ball/TAPS detector system at MAMI-C
Following pioneering experiments determining the magnetic moment of the Δ++ resonance [1, 2], a first attempt has been made within the A3 project to measure the magnetic moment of the Δ+ resonance
Summary
The main goal of the Transregio TR16 is to explore the excitation energy spectrum of the nucleon in order to unravel its complex structure. Apart from determining the mass, width and quantum number of excited states, information on the polarizability, magnetic moments and form factors provide further insight in the structure of the nucleon. For baryon ground states these properties have been measured with great precision. Because of its prominent position in the excitation energy spectrum, the properties of the Δ(1232) resonance are of particular importance. The broad Δ+ resonance (Γ = 120 MeV) is populated in the high mass regime via photon excitation, followed by a γ transition within the resonance and a subsequent π0 decay of the Δ+ resonance to the nucleon ground state. The measurement of the γp → π0γ’p reaction provides access to μΔ+. Our experimental data will be compared to these extended calculations by Drechsel and Vanderhaegen [7]
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