A. Johansson

The pp → ppπ0 reaction near the kinematical threshold

The pp → ppη reaction has been measured at six energies close to threshold, from 1258 MeV to 1352 MeV, using an internal cluster gas jet target in the CELSIUS storage ring. The η is detected through its decay photons, in an array of CsI detectors, and the forward-going protons are detected in a plastic scintillator spectrometer. A complete event reconstruction is obtained at the higher energies in the measured interval. The new data, together with earlier data, give an accurate determination of the energy dependence close to threshold. The influence of the η-proton FSI is seen in the total cross section data as well as in a Dalitz plot of the η-p invariant mass distributions.

The WASA Detector Facility at CELSIUS

The WASA 4 pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A unique fea ...

Cross sections of the p p --> p p pi0 reaction between 310-MeV and 425-MeV

Abstract Extensive kinematically complete measurements of the pp → pp π 0 reaction have been made at six beam energies: 310, 320, 340, 360, 400, and 425xa0MeV. Angles and energies of both final-state protons are extracted from the forward detector system of the WASA-CELSIUS apparatus. Projected one-parameter distributions of the centre-of-momentum pion angle and the angle of the two-proton relative momentum show significant deviations from isotropy. The slope in the pion angular distribution changes from being negative at 310xa0MeV to positive at 425xa0MeV. These distributions, and that of the two-proton relative momentum, are described in terms of partial waves corresponding to the Ss,Ps,Pp,Sd and Ds final states. Commonly used amplitudes, derived from their simple threshold behaviour, fail to reproduce the data at the higher energies. However, in a DWBA treatment, assuming interaction ranges related either to π or ρ exchange, we find acceptable agreement, though the longer range of pion exchange provides significantly better description of the Ps and Pp waves.

Higher partial waves in p p ---> p p eta near threshold

Abstract Exclusive measurements of the production of η -mesons in the pp → ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η -meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the η -meson and also of the final proton-proton pair, probably to be associated with D -waves in this system interfering with the dominant S -wave term. The sign of the η angular anisotropy suggests that ρ -exchange is important for this reaction.

The asymmetry of 155 MeV protons elastically and inelastically scattered from carbon, oxygen, and calcium

Abstract The asymmetry of protons scattered elastically and inelastically from oxygen and calcium has been studied with the conventional double scattering technique using range telescopes. Results are given for the asymmetry in scattering from oxygen and calcium together with improved values of previously reported carbon data. The angular distributions of the elastic asymmetry are quite similar for the three elements. For the inelastic asymmetry of oxygen and calcium it has been possible to obtain only qualitative results.

Quasi-free proton-proton scattering in Li6 and Li7

Angular correlation distributions for quasi-free protonproton scattering in Li/sup 6/ and Li/sup 7/ were calculated and compared with experiment. The single particle model of the nucleus was used and the wave functions were adjusted to give electron form factors in agreement with Stanford scattering results. It is found that the best agreement with measured (p,2p) results is obtained when the p-state protons are moving in a potential of larger extension than that for the s-state protons. Configuration mixing or a different model such as the cluster model would have to be invoked in order to reproduce the small angular distance between the maxima of the Li/sup 6/ p-state distribution found experimentally. (auth)

The elastic scattering of 160 MeV protons from lithium, aluminum, indium and gold

Abstract The differential cross-sections and asymmetries of protons scattered elastically from lithium, aluminum, indium and gold have been measured in the angular range 3–30°. The results are compared with calculations using the optical model, and overall agreement is found.

Inelastic scattering of 185 MeV protons from Mg and Al

Abstract A magnetic spectrometer was used for the energy analysis of protons scattered from targets of magnesium (natural isotopic composition) and aluminium. The mean energy of the incident protons in the targets was 185 MeV. A total energy resolution of 350 keV (FWHM) was achieved, which made possible the observation of the excitation of a large number of discrete levels. Energy spectra were measured in the angular region of 4° to 40° (lab system). The results are presented partly in the form of tables giving measured excitation energies and maximum cross sections for resolved levels and partly in the form of graphs of angular distributions of the differential cross sections. A qualitative discussion of the results is given in terms of the multipolarities of the transitions involved and comparisons are made with similar results from other experiments in inelastic scattering and in a few cases with theoretical predictions.

The polarization of 155 MeV protons elastically and inelastically scattered from carbon

Abstract The polarization of 155 MeV protons elastically and inelastically (4.43 MeV level) scattered from carbon has been measured for angles up to 35° (lab. system). The energy spread of the protons was small enough to allow separation of energy levels by absorbers in a range telescope. The asymmetries were determined for two absorber settings, one corresponding to elastically scattered protons, and the other to elastically plus inelastically scattered protons. The elastic polarization rises from zero at 2° to a maximum of 99.5 % at 21°, then goes through a minimum of −18 % at 32°.5 and reaches 28.4 % at 35°. The inelastic polarization appears to increase from 59 % to 96 % in the angular region 16°.2 to 27°.4 and then to decrease to 2 % at 35°.

The Level Scheme of 107Cd Studied through the 107Ag (p,nγ) and 106Cd (d, pγ) Reactions and the 107In Decay

The excited levels of 107Cd have been investigated by studying the gamma-rays and internal conversion electrons from the 107Ag(p,n)107Cd and 106Cd(d,p)107Cd reactions and the 107In decay. Based on coincidence measurements, a completely revised 107Cd level scheme including 23 new levels has been constructed. Spins and parities for the levels were deduced from transition multipolarities, log ft-values and the relative excitation functions derived from the reaction measurements. A 1/2- isomeric state (T1/2 = 51.8±2.0 s) at 678.5 keV was identified in 107In.