C. Ellegaard

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.

Coherent pions in charge-exchange reactions☆

Abstract Data are presented on the 12 C ( 3 He , t π + ) reaction at 2 GeV bombarding energy. In coincidence with forward scattered tritons, pions are momentum-analysed in a large acceptance detector. For events where the target is left in its g.s. or low-lying states, the angular correlation between the momentum transfer vector and the momentum of the pion is sharply peaked at small relative angles.

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.

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.

Excitation of the Δ resonance in relativistic heavy ion charge exchange reactions

Abstract Excitation of the Δ resonance has been observed for the first time in a heavy ion reaction. The strength of the Δ signal depends on the projectile nuclear structure. In the same incident energy range, about 900 MeV per nucleon, we observe — a strong Δ excitation in 27 Al( 20 Ne, 20 F) and 27 Al( 20 Ne, 20 Na), — a weak Δ in 12 C( 14 N, 14 C) and — nearly no Δ excitation in ( 12 C, 12 B) and ( 12 C, 12 N) whatever the target is among a sample of nuclei from 12 C to 89 Y.