[en] The π+A→π+π±A reactions were studied on 2H, 12C, 40Ca and 208Pb nuclei at Tπ+ =283 MeV. Pions were detected in coincidence using the CHAOS spectrometer. The composite ratio CππA between the π+π± invariant masses on nuclei and on the nucleon is presented. Near the 2mπ threshold pion pairs couple to (ππ)I=J=0 when produced in the π+→π+π- reaction channel. There is a marked near-threshold enhancement of Cπ+π-A which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. On the other hand, nuclear matter only weakly influences Cπ+π+A, which displays a flat behaviour throughout the energy range regardless of A. (author)

[en] The pion production reaction π⁺ → π⁺π^± on ⁴⁵Sc was studied at incident pion energies of T_π+ = 240, 260, 280, 300 and 320 MeV. The experiment was performed using the M11 pion-channel at TRIUMF, and multiparticle events, (π⁺, π⁺π^±) and (π⁺, π⁺π^±p), were detected with the CHAOS spectrometer. Results are reported in the form of both differential and total cross sections, and are compared to theoretical predictions and the reaction phase space. The present investigation of the T-dependence of the π⁺ A → π⁺π^±A' reaction complements earlier examinations of the A-dependence of the reaction, which was measured using ²H, ⁴He, ¹²C, ¹⁶O, ⁴⁰Ca and ²⁰⁸Pb targets at ∼280 MeV. Some general properties of the pion-induced pion production reaction in nuclear matter will be presented, based on the combined results of the two studies. (author)

[en] The A(ΚΛρ) A' absorption reaction on light nuclei was studied to learn about the Κ-stop pp→ [K-.pp]bound →∇ρ process. The process is examined only on p-shell nuclei, i.e., 6Li, 7Li, 9Be, 13C, 16O. In fact, light nuclei limit the effects of ∇ (ρ) distortions while providing pp targets. In addition, the measurement involves several nuclei since it is mandatory to investigate the influence of the nuclear structure on a [K-pp]bound system. The interest in studying bound nuclear clusters involving one or more kaons and two or more nucleons is surely grown in the last decade. In this realm, several models were developed able to predict the existence of a [K-pp]bound nuclear system. Such a system is commonly characterized by a binding energy (BK) and a width (TK). Nevertheless, the values of BK and TK reported in the literature vary widely, so that [K-pp]bound can be seen either as a weakly-bound or as a strongly-bound system. The model-dependent values of BK and TK motivated the starting of some measurements; however, the scarcity of results available nowadays is unable to indicate the right theoretical approach to the nature of [K-pp]bound. The experimental results that will be presented in this talk can help explaining the physics of the [K-pp] formation and decay. They can also provide valuable information on in-medium modification of the PKN interaction. The reaction final channel (Λρ→)πρρ was measured by means of the FINUDA spectrometer. The spectrometer allowed the π and ρ masses to be selectively identified from other particle masses. As well, πand ρ vector momenta were precisely analyzed over a ∼ 2π solid angle. A ∇ event was finally selected only when a π-ρ vertex was reconstructed with a mass of M∇± 3 MeV/c2. Several observables were then built, i.e., Ρρ, ρ∇ cos θ∇ρ and M∇ρ. Such observables were globally fit via a Monte Carlo model, which incorporates any single channel (up to 10) contributing to the kaon absorption reaction being measured, A(K- stop.Λρ )A'. The results will explicitly be discussed for the 9Be target; however, a table will summarize the results obtained for all the studied nuclei. Overall, they indicate the existence of a [K-pp]bound system with Bk ≅70 MeV/c2 and TK ≤50 MeV/c2

[en] Published in summary form only

[en] The performances of large area plastic scintillator counters for time measurements are investigated. The results show that it is possible to obtain time resolutions of the order of 0.5 ns for electrons releasing in the counter energies of the order of 1 MeV. (Auth.)

[en] The time resolution measurements of a plastic scintillator neutron detector of large area (200x15 cm²) are reported. For neutrons of 16 MeV, obtained with the T(d,n)⁴He reaction and a solid Ti-T target, the corrected time resolution turns out to be equal to 670 ps, for a proton threshold energy of 10 MeV. (Auth.)

[en] An experimental method for performing the time-of-flight analysis, and the discrimination of the particles (π^-,μ^-,e^-) present in a negative pion beam extracted from a cyclotron is described. The possibility is illustrated and discussed of (a) determining the absolute number of pions absorbed in the target in experiments regarding the π^--absorption at rest in nuclei, and (b) performing tests and calibrations by means of the fast electrons present in the beam and discriminated with respect to the pions and the muons. Some relevant effects due to a degrader of the pion-beam energy are discussed. (Auth.)

No abstract available

[en] Results from a coincidence measurement of the /sup 16/O(π⁺,π⁺π^-) reaction at T/sub π//sub =/ = 280 MeV are reported, the first of this class. The energy- and angular-integrated cross section was found to be 2950 +- 450 μb and is compared with theoretical predictions. Low-energy positive-pion intensities are found to be much higher than those yielded by a four-body phase-space calculation

[en] Some preliminary results are given on an experiment in progress on the π^- absorption at rest in helium 4. The neutron energy spectrum is reported and discussed. It is concluded that there is in helium 4 definite evidence of the importance of the two-nucleon absorption process. It is believed there is some balance between the two-nucleon absorption mechanism and the quasi-alpha absorption mechanism clearly depending on the structure of the nucleus. 7 references