W. Brodowski

Thepp→ppπ+π−reaction studied in the low-energy tail of the Roper resonance

Exclusive measurements of the p p ->p p pi+ pi- reaction have been carried out at Tp = 775 MeV at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes N* ->N sigma and N* ->Delta pi ->N sigma their energy-dependent relative branching ratio is determined.

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.

Spectator tagging in quasi-free proton–neutron interactions in deuterium using an internal cluster-jet target at a storage ring

Abstract Low-energy spectator protons (p s ) from quasi-free proton–neutron interactions on deuterium have been measured for the pd→dπ 0 p s and pd→pnπ 0 p s reactions at the CELSIUS storage ring of the The Svedberg Laboratory. The experiment used 320 MeV protons incident on a deuterium cluster-jet target. The spectator protons were detected inside the scattering chamber using a silicon detector system which is compatible with a high vacuum. The low target density allows the spectator proton emerge without undergoing significant secondary scattering. Its measurement is therefore a useful tag upon such reactions, allowing cross-sections for quasi-free reactions to be deduced at well-defined centre-of-mass energies. The comparison with the simulation for the pd→dπ 0 p s reaction shows that the energy dependence of the pn→dπ 0 cross-section can be extracted near the threshold. The method greatly improves the experimental resolution achievable in quasi-free p–n reaction studies.

Pionic D-wave effects in pp→ppπ0 near threshold

The angular distribution of neutral pions produced in the pp --> pp pi(0) reaction has been measured at a beam energy of 310 MeV. Significant deviations from isotropy are found, which increase f ...

Observation of strong final-state effects in pi(+) production in pp collisions at 400 MeV

Abstract Differential cross sections of the reactions pp→dπ+ and pp→pnπ+ have been measured at Tp=400 MeV by detecting the charged ejectiles in the angular range 4°≤ΘLab≤21°. The deduced total cross sections agree well with those published previously for neighbouring energies. The invariant mass spectra are observed to be strongly affected by Δ production and NN final-state interaction. The data are well described by Monte Carlo simulations including both these effects. The ratio of pp→pnπ+ and pp→dπ+ cross sections also compares favourably to a recent theoretical prediction which suggests a dominance of np-production in the relative 3 S 1 -state.

Upper limits for a narrow dibaryon in pp collisions at 200 and 310 MeV

Abstract Dibaryons, forbidden by mass to decay into NN π channel and by quantum numbers into NN channel, may still have escaped detection. In fact, recently an observation of a narrow dibaryon (D) with the mass close to 1920 MeV was reported in the process pp → γγ + X . This dibaryon should also appear in the proton-proton bremsstrahlung data from measurements at 200 and 310 MeV, which have been carried out at the CELSIUS storage ring in Uppsala. From these data upper limits of 10 and 3 nb are obtained for the dibaryon production cross section (at 95% confidence level) for the two energies, respectively.

Study of baryon and search for dibaryon resonances by the pp → ppπ+π− reaction

Exclusive measurements of the two-pion production channel pp → ppπ+π− have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal \(pp \to pp*\left( {1440} \right) \to pp\sigma \to pp\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0\) as the dominant process at these energies, however, the data exhibit also significant contributions from \({p^*}\left( {1440} \right) \to \Delta \pi \to p\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0\) \({p^*}\left( {1440} \right) \to \Delta \pi \to p\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0\) From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for N N-decoupled N N π-resonances is reviewed with regard to recent experimental searches in the pionic double charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.

Search for a narrow πNN-resonance in pp → ppπ+π−☆

Abstract We report on the current status of the search for the πNN-resonance d′ with I(J P ) = 0(0 − ) and M = 2.06 GeV in the 2π production in pp collisions.

2π production in pp collisions close to threshold

The reaction pp --> NN pi pi has been measured close to threshold in the energy range from 650 to 775 MeV using the PROMICE/WASA setup at CELSIUS. These data constitute the first exclusive high-statistics measurements of this reaction on a pure hydrogen t

Spectator tagging in quasi-free pn-reactions on deuterium at PROMICE/WASA, CELSIUS

A set of silicon detectors has been added to the PROMICE/WASA (P/W) experiment at CELSIUS. These detectors have been used for spectator-proton tagging in proton deuteron collisions to investigate proton-neutron reactions at intermediate energies. The performance of the setup has been tested by measuring the pd --> d pi(o)p(spectator) reaction.