R. Sanderson

In-medium modifications of the pi pi interaction in photon-induced reactions

Differential cross sections of the reactions (gamma,pi(0)pi(0)) and (gamma,pi(0)pi(+/-)) have been measured for several nuclei (1H,12C, and (nat)Pb) at an incident-photon energy of E(gamma)=400-460 MeV at the tagged-photon facility at MAMI-B using the TAPS spectrometer. A significant nuclear-mass dependence of the pipi invariant-mass distribution is found in the pi(0)pi(0) channel. This dependence is not observed in the pi(0)pi(+/-) channel and is consistent with an in-medium modification of the pipi interaction in the I=J=0 channel. The data are compared to pi-induced measurements and to calculations within a chiral-unitary approach.

Photoproduction of eta-mesic He-3

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma3He-->etaX has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonancelike structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasibound state. This is supported by studies of a competing decay channel of such a quasibound eta-mesic nucleus into pi(0)pX. A binding energy of (-4.4+/-4.2) MeV and a width of (25.6+/-6.1) MeV is deduced for the quasibound eta-mesic state in 3He.

The reaction gamma p ->pi(0)gamma ' p and the magnetic dipole moment of the Delta(+)(1232) resonance

The reaction

Photoproduction of πmesons from nuclei

\gamma p \to \pi^\circ \gamma^\prime p

Double pion photoproduction off 40Ca

has been measured with the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI for energies between

The reaction γp → π0γ'p and the magnetic dipole moment of the Δ+(1232) resonance

\sqrt{s}

Photoproduction ofη-MesicHe3

= 1221--1331 MeV. Cross sections differential in angle and energy have been determined for all particles in the final state in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the

Photoproduction of η-mesic ³He

\Delta^{+}(1232)

The Reactionγp→π0γ′pand the Magnetic Dipole Moment of theΔ+(1232)Resonance

resonance and, for the first time, a value of

Pfeiffer et al. Reply

\mu_{\Delta^+} = (2.7_{-1.3}^{+1.0}(stat.) \pm 1.5 (syst.) \pm 3(theo.)) \mu_N