K. Fransson

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.

Two-pion production in proton-proton collisions ― experimental total cross sections and their isospin decomposition

The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to T-P = 1.36 GeV. Total and differential Cross sections have been obtained for ...

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.

Delta Delta excitation in proton-proton induced pi(0)pi(0) production

Exclusive measurements of the pp -> pp pi(0)pi(0) reaction have been performed at CELSIUS/WASA at energies from threshold up to T-p = 1.3 GeV. Total and differential cross sections have been obt ...

Exclusive measurements of pd→He3ππ: The ABC effect revisited

Abstract Exclusive measurements of the reactions p d → He 3 π + π − and p d → He 3 π 0 π 0 have been carried out at T p = 0.893 GeV at the CELSIUS storage ring using the WASA detector. The π + π − channel evidences a pronounced enhancement at low invariant ππ masses—as anticipated from previous inclusive measurements of the ABC effect. This enhancement is seen to be even much larger in the isoscalar π 0 π 0 channel. The differential distributions prove this enhancement to be of scalar–isoscalar nature. ΔΔ calculations give a good description of the data, if a boundstate condition is imposed for the intermediate ΔΔ system.

Measurement of the slope parameter for the eta ---> 3pi0 decay in the pp->pp eta reaction

The CELSIUS-WASA setup is used to measure the 3π0 decay of η mesons produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV. The efficiency-corrected Dalitz plot and density distributions for this decay are shown, together with a fit of the quadratic slope parameter α yielding α = −0.026 ± 0.010(stat) ± 0.010(syst). This value is compared to recent experimental results and theoretical predictions.

Rotational bands in 195, 197Tl

Abstract High-spin states in 195, 197 Tl have been populated with ( α , x n) reactions and studied by means of in-beam γ-ray and e − spectroscopic methods. Complementary studies of the decay of 195, 197 Pb to 195, 197 Tl have been carried out. Several new features have been observed in these nuclei. The 9 2 − bands of 195, 197 T1. extended to 27 2 (−) and 29 2 (−) , respectively, show a quenching of energy spacings between the 23 2 − , 25 2 − , 27 2 (− and 29 2 (− states. This has been interpreted as resulting from the coupling of a h 9 2 proton to the ( π h −2 11 2 ) 8+, 10+ configurations in the core nuclei 194, 196 Hg. Furthermore, positive-parity bands based on 15 2 + states were established up to the 35 2 (+) and 29 2 (+) states in 195, 197 Tl respectively. Probably these bands originate from the coupling of a h 9 2 proton to a broken neutron pair. This pair consists of a rotation-aligned i 13 2 neutron and a low- j neutron in the P 1 2 , P 3 2 or f 5 2 shell. It is known to constitute the 5 − bands in 194, 196 Hg.

Band crossing in184Pt

The levels in the ground band of184Pt are identified up to the member with spin 20 in an in-beam spectroscopy experiment on theγ-rays following the177Hf(12C, 5n)184Pt reaction. In contrast to the situation in the heavier Pt isotopes, where the 10+ to 12+ level spacing is very small, the transition energies in184Pt show a monotonie increase with spin. However, between spin 10+ and 14+ the moment of inertia grows quite rapidly and this appears to be reminiscent of the much more pronounced irregularity encountered in the isotopes of larger mass. This property of the moment of inertia is discussed within a model where twoi13/2 neutron quasiparticles or twoh9/2 orh11/2 proton quasiparticles may be excited and coupled to the rotation of the core.

Isospin resolved double pion production in the reaction p+d→3He+2π

Abstract Neutral and charged two-pion production in p+d→ 3 He+2 π reactions has been studied at CELSIUS at a proton beam energy of 477 MeV. The total cross section for double pion production is 0.22±0.03 μ b. The ratio of the cross sections for the production of charged pion pairs with isospin T =1 and T =0 was determined to be σ ( π + π − ; T =1)/ σ ( π + π − ; T =0)=1.4±0.4.

The inclusive reaction d + d → 4He + X 29 MeV above the 2π0 threshold☆

Abstract The momentum spectrum of 4 He particles from d + d reactions at E lab = 569 MeV has been measured at zero degrees in the laboratory. The missing-mass spectrum is consistent with a pure phase space behaviour for the isospin zero channel of two pions, corresponding to a total cross section of 43 ± 5 nb.