F. Reide

Experimental study of coherent pion production in 4He(3He, π+)7Li and a test of the reaction mechanism

Abstract Pion production through the 4 He( 3 He, π + ) 7 Li reaction leading to the first three levels of the 7 Li nucleus has been measured at two incident energies close to threshold (280.5 and 266.5 MeV). A model previously used to analyse doubly coherent pion production on a 3 He target was found to give a good description of the present data.

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.

Positive pion production at threshold on A 10B target

Abstract The angular distribution of low-energy positive pions (Eπ ≈ 11 MeV) produced by 154 MeV protons on a 10B target has been measured between 16.2° and 54.8° c.m. angles. Only pions corresponding to the ground state of 11B were observed. The data have been compared with theoretical angular distributions calculated in the framework of the one-nucleon mechanism using the DWBA formalism.

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.

A study of the 3He(pπ+)4He reactions close to the threshold

The 3He(p, pi +)4He reaction has been measured at three different energies close to threshold. The laboratory angular range covered varies between 20 degrees and 110 degrees at 201 MeV, 20 degrees and 70 degrees at 190 MeV and 20 degrees and 40 degrees at 180 MeV. The forward cross sections are of the order of a few mu b sr-1.

Search for multibaryonic resonances in the p + d → π− + X reaction

Abstract The reaction p + d → π − + X has been studied at Saturne at 1.45, 2.10 and 2.70 GeV, using the spectrometer SPES III. The analysing power and the differential cross sections show no evidence for narrow structures which could be interpreted as a resonance in the three baryon system. At the lowest incident energy, the shapes of the experimental cross sections are well reproduced by phase-space distributions.

Experimental search for B=2, T=2 bound states around the πNN threshold

Abstract The differential cross section and analyzing power have been measured for the p( p , π − )X reaction at an incident energy of 1450 MeV and a pion angle of 13.8° in order to study eventual dibaryonic T =2 structures in the vicinity of the πNN threshold. No statistically significant evidence for such structures corresponding to πNN bound states or six-quark states could be established. Upper limits to the cross section are deduced. Analyzing power data are discussed.

Pion production near threshold on 40Ca: Energy dependence and angular distribution

Abstract The differential cross section for the 40 Ca(p, π + ) 41 Ca(g.s.) reaction has been measured as a function of energy for proton energies between 149 and 154 MeV and as a function of angle at 154 MeV. The simple formulations of both the one-nucleon and two-nucleon reaction mechanisms fail to account for the shape of the energy dependence of the cross section. DWBA calculations using the one-nucleon mechanism overestimate the cross sections by at least a factor of 30 and fail to reproduce the shape of the experimental angular distribution.

{pi}N and {eta}p deexcitation channels of the N* and {delta} baryonic resonances between 1470 and 1680 MeV

Two reactions, pp{yields}ppX and pp{yields}p{pi}{sup +}X, are used to study the 1.47{<=}M{<=}1.680 GeV baryonic mass range. Three different final states are considered in the invariant masses: N* or {delta}{sup +},n{pi}{sup +} or p{pi}{sup 0}, and p{eta}. The last two channels are defined by software cuts applied to the missing mass of the first reaction. Several narrow structures are extracted with widths {sigma}({gamma}) varying between 3 and 9 MeV. Some structures are observed in one channel but not in another. Such nonobservation may be due either to the spectrometer momenta limits or to the physics (e.g., no such disintegration channel is allowed from the narrow state considered).We tentatively conclude that the broad Particle Data Group (PDG) baryonic resonances--N(1520)D{sub 13},N(1535)S{sub 11},{delta}(1600)P{sub 33},N(1650)S{sub 11}, and N(1675)D{sub 15}--are collective states built from several narrow and weakly excited resonances, each having a (much) smaller width than the one reported by PDG.

Possible indication of narrow baryonic resonances produced in the 1720–1790 MeV mass region

Signals of two narrow structures at M = 1747 and 1772 MeV were observed in the invariant masses M p X and M π+ X of the pp \rightarrow ppX and pp \rightarrow p \pi ^{ + }X reactions, respectively. Many tests were made to see if experimental artefacts could have produced these structures. Their small widths and the stability of the extracted masses lead us to conclude that these structures are genuine and may correspond to new exotic baryons. Several attempts to identify them, including the possible “missing baryons” approach, are discussed.