Nuovo Cim.A

The production rate of3H in$\bar p^4$He annhilation between 0 and 600 MeV/c is deduced in an approximate way from that of3He, and the lower and upper limits for the production rate of p and2H are measured. The momentum distributions for the different particles are given.

Nucl. Phys. A

At LEAR of CERN the annihilation of antiprotons, stopping in 3 He and 4 He filling a self-shunted streamer chamber in a magnetic field, has been studied. The charged-particle multiplicities have been measured and the relative probabilities of π − production in p 3 He and p 4 He annihilation events have been obtained. The ratio between the p annihilation probability on the neutron and the proton for 3 He and 4 He has been deduced to be about half the value obtained for 2 H in bubble chamber experiments. The analysis of the results shows that this difference cannot be due only to the pion final-state interaction or to the shadow effect of the nucleons of the nuclei. The probability of p annihilation at rest on a proton bound in the nucleus results to be twice as high as that on a bound neutron, showing the dominance of annihilation in the I = 0 isospin states.

Nucl. Phys. B

The experimental results are presented for ratios of ν-meson inclusive differential cross sections in 10.5 GeV/ c π + p, π + D and π + A collisions, R D/p =(d σ /d x F )( π + D → η X)/ (d σ /d x F ) π + p→ η X), R A =(d σ /d x F )( π + D→ η X) in the beam fragmentation region. The results are based on the statistics of ≈ 5 × 10 4 detected η → 2 γ decays. It is shown that the power α in the parametrisation R A ≈ A α ( xf ) does not change significantly with x F and its mean value is 0.50±0.02. The lower limit is obtained for the effective coefficient with string tension in the colour string model, κ ⩾ 3 GeV/fm. The observed growth of R A with x F can be explained by an assumption of a neutron halo with the factor H ≈ 4 in the nuclei.

Nucl. Instrum. Meth. A

Several types of wide-gap electrodeless drift chambers, including those with dimensions 1×1 m 2 , have been tested at accelerator beams. The chambers work with high efficiency (>99\), good spatial resolution ( σ = 0.2−0.4 mm) and good linearity at flux rates up to 2×10 5 particles −1 per wire in spill, which corresponds to 3×10 6 particles/s m 2 on colliders.

Phys. Lett. B

Evidence is presented for an anomalously shorter mean free path (mfp) of 3 He uniquely identified secondary nuclei originating from 3 He-p interactions at 13.5 GeV/ c incident momenta in a hydrogen bubble chamber. A sample of 7211 primary collisions leading to 1069 secondary 3 He-p interactions has been analysed. The mfp of secondary nuclei was found to be significantly shorter for the first 10 cm. An admixture of 1.6% of anomalons was found with a mfp of 6 cm as compared to 280 cm for the 3 He beam nuclei.

EPL

In the reaction of π- dissociation into a μ+μ-π- system on a Cu nucleus, a clear enhancement in the ρ0π- effective-mass distribution has been observed in the π2(1680) region. Partial-wave analysis shows that this enhancement is due to the P-wave and has a resonant nature. Coherent and incoherent cross-sections for this enhancement have been measured.

Nucl.Phys.A

The nuclear vertex function of 3 He → ppn disintegration has been determined from analysis of the reaction 3 He p → pppn . The experimental data have been obtained in the 4π geometry by means of the 80 cm ITEP liquid-hydrogen bubble chamber, exposed to 3 He separated beams at momenta of 2.5 and 5 GeV/ c . The method used for extraction of the nuclear vertex function is well founded. For the first time, the 3 He → ppn vertex function has been investigated simultaneously as a function of two Jacobi momenta. The singlet part of the vertex function has been extracted separately. The momentum distributions of protons, neutrons, pp and pn pairs in 3 He have been obtained also. These results are compared with the available data and with theoretical calculations performed with the wave functions for the Reid and Yamaguchi potentials.

Z.Phys.C

Measurements ofKs0, Λ and$\bar \Lambda$ production in π− nucleus (C, Cu, Pb) interactions are presented. The experiment was carried out with the streamer chamber spectrometer RISK using a π− beam of ∼40 GeV/c and a trigger requiring a secondary charged particle with transverse momentum above 1.1 GeV/c. Production cross sections, relative production rates and distributions of Feynmanx and transverse momentum squared as well as correlations between theV0 and the trigger particle are presented. The results are compared and found to be in agreement withKs0, Λ and$\bar \Lambda$ data from untriggered π−p and π−C interactions, except for the relative production rate of antilambdas which is about to times larger in high-pt collisions. Our results can be well interpreted within the dual topological unitarization model.

Nucl.Instrum.Meth.A

The characteristics of a drift chamber with 3 mm drift gap were investigated at a particle beam momentum of 10 GeV/ c . The chamber has good linearity of the drift characteristics. It was tested and could reliably work in a particle flux of ∼ 3 × 10 5 s −1 cm −2 . A spatial resolution of ∼ 45 μm in the centre of the drift gap has been achieved.

Phys.Lett.B

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 .

Phys.Lett.B

We have measured a value of 15.5±2.9 mb for the p - 4 He break-up cross section at 179.6 MeV. This low value is in agreement with the prediction of the Glauber model and is due to the large probability for the antiproton to annihilate into the nuclei, which makes only a surface layer of the nuclear volume effective for the break-up process.

Nucl. Phys. A

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.