Robert C. Bilger

Measurement of the eta production in proton proton collisions with the COSY time-of-flight spectrometer

Abstract:The reaction pp → ppη was measured at excess energies of 15 and 41 MeV at an external target of the Jülich Cooler Synchrotron COSY with the time-of-flight spectrometer. About 25000 events were measured for the excess energy of 15 MeV and about 8000 for 41 MeV. Both protons of the process ppη were detected with an acceptance of nearly 100% and the η was reconstructed by the missing-mass technique. For both excess energies the angular distributions are found to be nearly isotropic. In the invariant-mass distributions strong deviations from the pure phase space distributions are seen.

Two-pion production in proton-proton collisions with a polarized beam

The two-pion production reaction pp → ppπ+π− was measured with a polarized proton beam at Tp ≈ 750 and 800MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed-pulse technique for Quirl and central calorimeter provided positive π+ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1–4 overconstraints. Total and differential cross-sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing-power values up to Ay = 0.3. The data taken in the energy region of the excitation of the Roper resonance confirm that its dominant ππ decay channel is N* → Nσ.

Proton proton bremsstrahlung at 797 MeV/c

Abstract At COSY pp-bremsstrahlung was measured at a beam momentum of 797 MeV/c using an external proton beam. Data were taken with a wide angle spectrometer covering a solid angle of approximately 1 sr. The complete data set is presented in a series of c.m. angular distributions as well as a single Dalitz plot. The absence of final state interaction effects is understood as being due to a general insensitivity of the pp γ reaction to the spin-singlet component of the NN interaction. Coplanar angular distributions (in the laboratory system) are well reproduced by recent model calculations; also good agreement is found with the original TRIUMF data [K. Michaelian et al., Phys. Rev. D 41 (1990) 286] when omitting the rescaling factor of 2/3.

Single-pion production in pp collisions at 0.95 GeV/c (II)

The single-pion production reactions pp

Compton scattering from the free and bound proton above π-threshold

rightarrow

Low-energy differential cross sections of pion-proton ( pi +/-p) scattering. II. Phase shifts at T pi =32.7, 45.1, and 68.6 MeV.

d

Three-particle final states measured at the pion threshold with the COSY-TOF spectrometer.

pi^{+}_{}

Two-Pion Production in Proton--Proton Collisions Near Threshold at CELSIUS

, pp

A signal of a narrow NN resonance in pp ! pp +?

rightarrow

Study of the reaction pp -> pp pi 0 within 10 MeV above the threshold

np