T. Hennino

Study of the Δ isobar excitation in nuclei with the (3He,t) reaction

Abstract Data for the Δ excitation by the (3He,t) reaction at 2.0 GeV on various nuclei are presented together with results on 12C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(3He,t) Δ++ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.

The p(3He,t)Δ++ reaction

Abstract Data are presented for the p(3He,t)Δ++ reaction at 2.0, 2.3 and 1.5 GeV. The reaction specifically excites the Δ++ with very little yield outside the resonance. The data are analysed as one pion exchange and the hadronic form factor for the 3He−1 system is extracted and compared with the magnetic form factor from electron scattering.

First observation of the Δ resonance in relativistic heavy-ion charge-exchange reactions☆

Abstract Excitation of the Δ resonance is observed for the first time with heavy ions. It is very strong in the two mirror charge-exchange reactions ( 20 Ne , 20 F ) and ( 20 Ne , 20 Na ) at 950 MeV per nucleon. With similar incident energies per nucleon, the Δ is weakly excited with a 14 N beam and nearly absent with a 12 C beam. The role of the ejectile bound states is discussed.

Study of decay and absorption of the Δ resonance in nuclei with a 4π detector

Charge exchange reactions have been investigated at Saturne with various projectiles (3He, (vec d), 12C,16O, 20Ne, 40Ar) and incident energies between.5 and 1.1 GeV/nucleon1. These experiments have given clear indication of the selectivity of charge exchange reactions for spin isospin excitations. In particular, a strong excitation of the Δ resonance shows up for energy transfers higher than the pion mass. The most striking common feature of all these charge exchange reactions is a shift of about 70 MeV between the positions of the Δ bump on nuclei and on hydrogen targets (fig.1). This result has been interpreted by theoreticians as a collective effect in the spin longitudinal channel2 and has been quantitatively reproduced by recent calculations3. An alternative qualitative explanation is the projectile excit ation4.

Spin structure of the Δ excitation

Spin structure and cross section data for Δ production in the (n, p-like reaction (d, 2p[1S0]) on p, d and 12C targets are presented. At laboratory kinetic energies 2 GeV and 1.6 GeV, and forward scattering angles, we find dominance of spin transverse over spin longitudinal cross section for free Δ production. On the nucleus 12C we find significant enhancement of the transverse dominance, and a large downwards shift in the peak position of the laboratory energy transfer associated with the production of the Δ.

The (3He, t) reaction at intermediate energies: Spin-isospin multipole transitions

Data for the (3He, t) reaction at 900 MeV and 2 GeV on the targets 26Mg, 40Ca, 48Ca, 54Fe, 90Zr and 208Pb are presented. A multipole decomposition for the data at 900 MeV has been made and the different distributions have been analysed. From the L = 0 cross section the Gamow-Teller strength distributions are extracted and compared with (p, n) data. The L = 1 and 2 distributions are analysed in a schematic model which describes the general systematics fairly well. The spectra at 2 GeV and Θ = 4° show for all targets a well-developed quasi-elastic peak. The A-dependence of the cross section is analysed in a simple model.

A detection system using drift chambers for the SPES4 spectrometer at Laboratoire National Saturne

Abstract We describe the “drift chamber” detection setup of SPES4, the 4 GeV/c spectrometer at Laboratoire National Saturne. The particle identification is performed by combining magnetic rigidity selection with energy loss and time of flight measurements. This allows to separate analysed isotopes from Z = 1 to at least Z = 10 up to a rigidity of 4 GeV/c. A charge resolution of ΔZrms = 0.1 and a time resolution of Δtrms = 120 ps for 18Ne at about 3 GeV/c per Z are easily obtained. Two sets of multiwire drift chambers are used to measure and reconstruct the particle trajectories at the output of the system. A position resolution better than Δxrms = 160 μm can be achieved in the focal plane. This corresponds to a momentum resolution of Δδrms = 0.22 × 10−4. The performances of SPES4 (Δδrms = 2.2 × 10−4) can then be wholly exploited.

Coherent pion production in 6Li(3He, π+) 9B and 10B(3He, π+)13C close to threshold

Abstract The energy dependence of the 6Li(3He, π+) 9Begs reaction at θlab = 20° has been studied for TeHe = 235, 260, 270 and 283 MeV and at 40° and 55° for 235 and 283 MeV. A semiphenomenological model reproduces the shape of the angular distribution and the order of magnitude of the cross section but predicts a too sharp energy variation. Experimental results on 10B (3He, π+) 13Cgs at 20°lab for 260 and 283 MeV are of a similar size.

Excitation of the Δ resonance in heavy ion charge exchange reactions

Abstract Results on the Δ excitation by heavy ion charge exchange are presented. 900 MeV per nucleon 12C, 16O, 20Ne and 1100 MeV per nucleon 12C have been used. The Δ excitation strength depends on the projectile — ejectile nature and on the incident energy. The role of the target mass is also discussed. The peak for the Δ in nuclei is energy shifted from the free Δ peak.

Energy dependence of the 3He(3He, π+)6 Li reaction

Abstract The 3 He( 3 He, π + ) 6 Li reaction has been studied as a function of energy using the 3 He beam at SATURNE. Cross sections for the 6 Li ground state (1 + ) and 2.18 MeV (3 + ) levels have been obtained at 350,420,500 and 600 MeV incident energies at angles θ π (lab) = 15° and 40°. These results are compared with two theoretical predictions.