G. B. Pontecorvo

Low-energy Antiproton Neon Interaction

Abstract By means of a streamer chamber exposed to the LEAR antiproton beams, the total reaction cross sections, the charged-prong multiplicity distributions and lower limits for the production of negative pions and K s 0 in the p-Ne interaction were measured at 19.6, 48.7 and 179.6 MeV. Annihilation was found to be dominant over all other non-elastic p-Ne processes. An analysis of Ne and other nuclei data in the frame of the Glauber theory allowed us to determine the ratio between the p-n and the p-p cross sections. An analysis in the light of INC model predictions allowed us to show up events which can be interpreted as annihilations having occurred deeply inside the nuclei.

Inelastic interaction of antiprotons with 4He nuclei between 200 and 600 MeV/c

The antiproton-helium reaction cross section has been measured at 19.6 and 48.7 MeV with a streamer chamber in a magnetic field. Charged prongs and negative pion multiplicities and cross sections for the production of 3He are given. A comparison with p 2H is performed. he previously obtained 179.6 MeV results are also taken into account.

Determination of the ratio σ(p̄n)/σ(p̄p) from p̄4He reaction data

Abstract The ratio R a b between the cross sections for the annihilation of p on n and on p bound in the 4 He nucleus at four p momenta (at rest, 192.8, 306.2 and 607.7 MeV/ c ) has been obtained by the analysis of p 4 He annihilation events detected with a self-shunted streamer chamber exposed to the LEAR p beams. R a b increases from 0.42 ± 0.05 at rest up to 0.66 ± 0.09 at 607.7 MeV/ c . The results are discussed in the light of Glauber theory analyses of p 2 H and p -nucleus data.

Experimental apparatus for studying the interaction of antiprotons with light nuclei

Abstract A description is given of the detector system (self-shunted streamer chamber in a magnetic field) used in the PS-179 experiment at LEAR for studying antiproton interactions with light nuclei.

Neutral strange-particle production in p̄20Ne reactions at 607 MeV/c

Abstract The Λ 0 and K 0 s production cross sections have been measured at 607 MeV/ c for the reaction p + 20 Ne → V 0 + X ( V 0 =Λ, 0 , K 0 s ) . The Λ 0 /K 0 s production ratio is found to be (2.3±0.7). The data are consistent with an evaporative character of the emission mechanism from a multinucleon system for Λ 0 and from one nucleon for K 0 s . The rapidity distributions of negative tracks in K 0 x events are different from those in Λ 0 events without V 0 .

p4He reaction cross section at 610 MeV/c

Abstract Antiproton helium reaction cross section has been measured at 179.6 MeV with a self shunted streamer chamber in a magnetic field. Charged prong multiplicity, branching ratios and 3He production probability are given. Comparison with p 2 H data is performed.

Antiproton–neon annihilation at 57 MeV/c

Abstract The p Ne annihilation cross section is measured for the first time in the momentum interval (53÷63) MeV/c. About 9000 pictures collected by the Streamer Chamber Collaboration (PS179) at LEAR-CERN have been scanned. Four events are found, corresponding to σ ann =2210±1105 mb. The result is compared to the set of measurements presently available in the region of low p momentum.

Self-shunted streamer chamber

Abstract The self-shunted streamer chambers can be used as visualizers of particle tracks and as detectors of event vertices. We discuss the operating conditions of this type of chamber in the presence of a magnetic field, and the features of the hv-pulse generator connected to the chamber. The results in the precision which can be obtained in the reconstruction of the tracks are discussed.

Antiproton-helium annihilation around 45 MeV/c

Abstract The p ¯ 4 He annihilation cross section averaged over the interval 40–50 MeV/c has been measured using a streamer chamber in a magnetic field. The measured value is 1342±250 mb. It agrees with a behaviour like 1/p of the annihilation cross section. Our result has been obtained at the lowest momentum achieved till now in measurements of antiproton annihilation in flight.

Elastic scattering of π±-Mesons on3He in the energy interval (68÷208) MeV

SummaryDifferent cross-section measurements of elastic scattering of π± on3He are presented. The study was done both for positive and negative pions at 98, 120, 135, 145, 156 MeV, for negative pions also at 198 and 208 MeV and for positive pions also at 68MeV. The experiment was carried out with a high-pressure helium self-shunted streamer chamber surrounded by a hodoscope of scintillation counters. The results are compared with optical-model calculations using spin-and isospin-dependent potentials. The energy dependence of the total elastic (π±,3He) scattering cross-section is discussed. Estimates of the (π3He3H) coupling constant according to the theory of Chew and Low are presented.RiassuntoSono presenti i risultati della misura della sezione d’urto differenziale di diffusione elastica (π+,3He) a 68, 98, 120, 135, 145, 156 MeV e (π−,3He) as 98, 120, 135, 145, 156, 198, 208 MeV. I dati sperimentali sono confrontati con le previsioni del modello ottico ed inoltre viene fatta una stima della costante di accoppiamento (π3He3H).РеэюмеИэмерены дифференциальные сечения упругого рассеяния пионов на ядрах3He при знергиях 68, 98, 120,135, 145, 156, 198, 208 MзB. Эксперименты вы-полнены на гелиевой стримерной камере высокого давления. Данные сопоста-вляются с расчетами по оптииеской модели. Даются оценки констаяты свяэиf2(π3He3H).