H. Loehner

Quasifree photoproduction of eta mesons off the neutron

Quasifree photoproduction of eta mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.

Modification of the {omega}-Meson Lifetime in Nuclear Matter

Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb.

Transparency ratio in gamma A -> eta ' A ' and the in-medium eta ' width

The photoproduction of eta`-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500-2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations describing the propagation of eta`-mesons in nuclei. The comparison indicates a width of the eta`-meson of the order of Gamma = 15-25 MeV at rho = rho(0) for an average momentum p(eta`) = 1050 MeV/c, at which the eta`-meson is produced in the nuclear rest frame. The inelastic eta`N cross section is estimated to be 3-10 mb. Parameterizing the photoproduction cross section of eta`-mesons by sigma(A) = sigma(0)A(alpha), a value of alpha = 0.84 +/- 0.03 has been deduced

Study of the reaction gamma p -> p pi(0)eta

The reaction

Observation of the Psi(1(3)D(2)) State in e(+)e(-) -> pi(+)pi(-)gamma chi(c1) at BESIII

\gamma p\to p\pi^0\eta

Photoproduction of η -mesons off nuclei for Eγ ⩽ 2.2 GeV

has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from

Confirmation of a charged charmoniumlike state Z(c)(3885)(-/+) in e(+)e(-) -> pi(+/-) (D(D)over-bar*)(-/+) with double D tag

\Delta^+(1232)\eta

Measurement of the beam asymmetry Sigma in the forward direction for (gamma)over-right-arrowp -> p pi(0)

,

Photoproduction of ω mesons off the proton

N(1535)^+\pi^0

K(0)pi(0)Sigma(+) and K*(0)Sigma(+) photoproduction off the proton

and