We report the first observation of coherent pion production induced by a heavy ion charge exchange reaction The (C-12, N-12)reaction [1,2] at 1.1 GeV/nucleon has been used to shine negative (off-shell) pions on nuclei and observe (on-shell) pions, leaving the target nucleus in its ground state. The experiment was performed at the Laboratoire National Saturne with the SPES4-pi setup [3,4].

The paper describes the spectrometric system “SPES4–π” used at the National Laboratory Saturne (CE Saclay, France) for the exclusive study of the baryon resonance excitation in inelastic α and d scattering on the proton, as well as coherent pion production in charge exchange reactions. The system consists of the magnetic spectrometer SPES4 and two wide-aperture position-sensitive detector arrays, equipped with wire chambers and scintillator hodoscopes, installed around a large-gap C-shape dipole magnet.

The exclusive 2H( 3He, t)2p reaction has been studied at 2 GeV for energy transfers up to 500 MeV and triton angles up to 3.4°. The protons were measured in the large acceptance magnetic detector DIOGENE, in coincidence with the forward tritons detected in a dedicated magnetic arm. The energy transfer spectra extend well above the pion threshold. However, in the region of Δ excitation, the yield is less than 10% of the inclusive 2H( 3He, t) cross-section, which indicates the small contribution of the ΔN ↦ NN process. The angular distributions of the two protons in their center of mass have been analysed as a function of energy transfer and triton angle and a Legendre polynomial decomposition has been achieved. These data have been compared to a model based on a coupled-channel approach for describing the NN and NΔ systems.

A study of inelastic scattering of polarized 3.73-GeV/c deuterons on protons in the energy region,of the Roper N(1440) and the Delta (1232) resonances excitation has been performed in an exclusive experiment at LNS (Laboratoire National SATURNE, Saclay, France) using the SPES4-pi setup. Tensor and vector analyzing powers of pion production for the reactions: d + p --> d + n + pi (+), d + p --> d + p + pi (0), d + p --> d + N + pi pi have been measured as functions of the squared deuteron four-momentum transfer t, of the effective mass of the subsystems N pi, N pi pi, and of the pion emission angle. A strong dependence of these analyzing powers upon the pion emission angle is observed. It is found that A(yy) values for the considered reaction channels are systematically larger than the known inclusive p(d,d')X world data at the nearest beam energy.

The SATURNE charge-exchange program explored the spin-isospin response of nuclei in the Delta region [1]. New results on coherent pion production are presented. They give a precise measure of the spin longitudinal component of this response. This component is particularly interesting since theoretical models predict that attractive residual Delta -hole correlations in the longitudinal channel (pion exchange) softens the response.

The excitation mechanisms and properties of broad hadronic resonances in nuclei, which are intimately related with nuclear medium response on high energy excitations, have attracted much attention during last decade.

The inclusive 2(3He,t) reaction has been studied at 2 GeV for energy transfers up to 500 MeV and scattering angles from 0.250 up to 40. Data are well reproduced by a model based on a coupled-channel approach for describing the NN and NΔ systems. The effect of final state interaction is important in the low energy part of the spectra. In the delta region, the cross-section is very sensitive to the effects of Δ-N interaction and ΔN → NN process. The latter has also a large influence well below the pion threshold. The calculation underestimates the experimental cross-section between the quasi-elastic and the delta peaks; this is possibly due to projectile excitation or purely mesonic exchange currents.

Experimental evidence for coherent pi(+) production in C-12(He-3, t pi(+))C-12 charge exchange reactions at 2 GeV is presented. The excited states of carbon are found to be suppressed relative to the ground state. Angular distributions show that the momentum of the coherent pions is directed along the momentum transfer.

We present data on the decay of the Delta resonance excited in H-1, H-2, He-4, C-12 and Pb-208 by th, (He-3, t) reaction at 2 GeV incident energy. The quasi-free decay of the Delta resonance and the absorption process are investigated. We find indication for a coherent process where a pion is emitted and the target nucleus is left in its ground state. This process is now being studied with the dedicated set-up Spes4 pi. The first data with this new detection system have just been taken.

The (He-3, t) charge exchange reaction at 2. GeV incident energy with the new setup SPES IV-pi has been realized in December 1995 and March 1996, in order to study the coherent production process of pions. This setup allows to isolate the ground state of the target nucleus, and to sign this process without ambiguity. We give some preliminary results in target excitation energy and tranfered energy.

Three aspects of the response in the spin-isospin channel is discussed. Inclusive data with charge exchange reactions show significant cross sections in the spin-transverse channel beyond contributions from a 1p-1h model space. Similar effects are seen in electron scattering. One-proton emission spectra have been obtained to show missing momentum distributions in the quasielastic and dip region. Evidence for coherent pions in charge exchange are presented and discussed in terms of scattering of virtual pions.

The decay channels of the a resonance famed in nuclei, by the charge exchange reaction (He-3,t) at 2 GeV, have been studied, an H-2, He-4, C-12 and Pb targets, in exclusive experiments with the large acceptance detector Diogene. The quasi-free channel Delta(++) --> p + pi(+), the two proton decay channel and the single pion decay channel have been observed and investigated. The emission of coherent pions has been identified.

Experimental data on the nuclear spin-isospin response in the quasifree region, measured with the charge-exchange reaction (d\ensuremath{\rightarrow},2p${[}^{1}$${\mathit{S}}_{0}$]) at Laboratoire National Saturne, are presented. The use of a tensor-polarized beam enables us to separate the tensor analyzing powers ${\mathit{T}}_{20}$ and ${\mathit{T}}_{22}$. The present publication is intended to serve as a compilation of the complete set of quasifree data with the (d\ensuremath{\rightarrow}${,}^{2}$He) reaction at 1.6 GeV bombarding energy. Data for $^{12}\mathrm{C}$ are compared to calculated cross sections and tensor-analyzing powers. The cross section in the high-energy end of the quasielastic peak is underestimated, whereas the polarization observables are reasonably well reproduced. The distortion effects are, however, found to be large, suggesting that the (d\ensuremath{\rightarrow}${,}^{2}$He) reaction is not sensitive to spin correlations in the continuum.

New data on the decay of DELTA-hole states in nuclei are presented. The gross features of the decay pattern are reasonably well described in a cascade model with some remarkable exceptions indicating strong medium effects. Both mass and width of the DELTA-isobar are modified in the nucleus. The first evidence for the collective pionic mode, the pisobar, is presented.

Data are presented on the 12C(3He,tπ+) 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.

We present data on the decay of the DELTA resonance excited in H-1, H-2, He-4, C-12 and Pb-208 by the (He-3, t) reaction at 2 GeV bombarding energy. The quasi-free decay of the DELTA resonance and the absorption process on a (p, n) pair are clearly observed. We also find evidence for coherent pion production.

We present data on the decay of the DELTA resonance excited in H-1, H-2 and C-12 by the (He-3, t) reaction at 2 GeV incident energy. In the energy transfer spectra, the same position and width of the DELTA-resonance are observed on the three targets when one pi+ and one proton are detected in coincidence with the triton. On the C-12 target, the DELTA-peak associated with the detection of two protons is shifted by 100 MeV towards lower excitation energy.

We present data on the decay of the Δ resonance excited in 1H, 2H and 12C by the (3He, t) reaction at 2 GeV incident energy. In the energy transfer spectra, the same position and width of the Δ resonance are observed on the three targets when π+ and one proton are detected in coincidence with the triton. On the 12C target, the Δ peak associated with the detection of two protons is shifted by 100 MeV towards lower excitation energy.

Following a major shortage of 99Mo in the 2009–2010 period, concern grew that the aging reactor production facilities needed to be replaced. Most producers were using highly enriched 235U (HEU) as the target material. The Organisation for Economic Co-...Read More