T. Miczaika

Photoproduction of neutral pions at backward angles in the resonance region and the η-cusp

At the Bonn 2.5 GeV electron synchrotron we have measured the differential cross section of the reaction γp→π0p at a pion CM angle of 170° and at photon energiesKγ between 0.6 and 1.8 GeV. In comparison to previous measurements the accuracy of the data was improved substantially. For the first time in neutral pion photoproduction a cusp structure at the η-threshold has been confirmed [1].

Observation of a narrow enhancement in the pp mass distribution from the reaction γd → ppπ−

Abstract Studying the reaction γ d → pp π − , a narrow resonance structure in the pp invariant mass distribution has been observed at 2014 ± 2 MeV/ c 2 with a statistical significance of 4.7 standard deviations. Using a bremsstrahlung photon beam ( k 0 = 520 MeV), the kinematics of the reaction were completely determined by detecting both outgoing protons in two large solid angle time-of-flight spectrometers. By accepting only proton momenta greater than ∼300 MeV/ c , the predominant contribution from quasi-free pion production was suppressed.

Angular distribution of the target asymmetry on polarized protons for the reaction γp↑ → π+n at a photon energy of 700 MeV

Abstract At the Bonn 2.5 GeV electron synchrotron the angular distribution of the target asymmetry T = (σ↑ − σ↓) (σ↑ + σ↓) for the reaction γp↑ → π+n was measured at a mean photon energy of 700 MeV and pion CM-angles from 50° to 155°. The combination of a 3He-cryostat, polarizing the free protons in the target up to 65%, with a large acceptance magnet for pion detection led to statistical errors of the target asymmetry comparable with those of cross section measurements.

Photoproduction of pions on polarized protons and neutrons in the second resonance region

Abstract Measurements of the target asymmetry T = ( σ ↑ − σ ↓)/( σ ↑ + σ ↓) for the reactions γ p → π + n and γ n → π − p at a fixed photon energy of 850 MeV and pion c.m. angles between 70° and 150° are reported. The data are compared to the previously measured angular distribution at 700 MeV.

Measurement of the target asymmetry for the reaction γp↑ → π+n at photon energies between 0.7 and 2.2 GeV and a pion CM-angle of 65°

Abstract At the Bonn 2.5.GeV electron synchrotron the target asymmetry for the photoproduction of positive pions has been measured. Data were taken at photon energies between 0.7 and 2.2 GeV and a pion CM-angle of 65°.

Photoproduction of negative pions on polarized neutrons in the region of the second resonance

Abstract A polarized neutron target was used at the Bonn 2.5 GeV Synchrotron to measure the target asymmetry for the reaction γ n↑→ π − p at a fixed photon energy of 700 MeV and pion c.m. angles between 50° and 140°. The pions were detected in a large aperture magnetic spectrometer. The data show a structure which is quite different from the distribution previously measured for the reaction γ p↑→ π + n.

Search for dibaryon resonances of masses between 2.16 and 2.32 GeV/c2 in the reaction γd → ppπ−

Abstract The reaction γ d → pp π − has been studied in order to investigate whether dibaryon resonances contribute to the cross section in the invariant mass region from 2.16 to 2.32 GeV/ c 2 . Using a bremsstrahlung photon beam we have determined the invariant mass M ppπ by detecting both outgoing protons in large solid angle TOF spectrometers, thus achieving a statistical accuracy of 1 to 2% per 2.5 MeV/ c 2 bin, a mean invariant mass resolution of 4.4 MeV/ c 2 (σ) and a smooth M ppπ acceptance. Despite the resulting high resonance sensitivity no evidence for a dibaryon resonance in the M ppπ distribution was found. Assuming an isotropic phase space decay we estimate the upper limit for the dibaryon resonance cross section to be 1μb for masses around 2.23 GeV/ c 2 and resonance widths between 5 and 40 GeV/ c 2 .

Photoproduction of K+Λ0 on polarized protons

The target asymmetry for the reaction γp → K+Λ0 was measured at the Bonn 2.5 GeV synchroton. Data were taken at a fixed kaon c.m. angle of 90° and at photon energies between 1.1 and 1.3 GeV. The kaons were detected in a large aperture magnetic spectrometer.

Measurement of the polarization of the Λ0 in the reaction γ + p → K+ + Λ0 in the resonance region

Abstract At the Bonn 2.5 GeV synchrotron the polarization of the Λ0 was measured at 40° and 90° for three energies. The kaon was detected with a strong focussing magnetic spectrometer and separated from other particles with the help of a differential liquid Cerenkov counter. The polarization was determined by means of the angular distribution of the decay proton which was measured with a combination of sonic spark chambers and a scintillation counter hodoscope. The typical statistical errors are about 13%. The systematic errors add up to 8%.

Photoproduction of neutral pions in the region of the fourth nucleon resonance

We report the measurement of the differential cross section of the reaction γ +p→π0 +p at a photon energy of 1.4 GeV and pion c.m. angles between 60 and 175 degrees. The angular distribution confirms the simple quark model prediction of a pure magnetic excitation of theF37 (1950) resonance.