Search

\(\bar pn\) annihilations into three and five charged mesons with or without neutrals have been studied in order to measure the contributions of the various final states to the 5.5 mb enhancement discovered in the totalI=1\(\bar {\mathcal{N}}\mathcal{N}\) cross-section at 2190 MeV total c.m. energy. Fits have been performed to the cross-sections as functions of the incident-\(\bar p\); momentum with background plus a resonant term. The fits show enhancements in several final states, the statistically most significant one being in the reaction\(\bar pn \to \pi ^ + 2\pi ^ - \) ((0.51 ± 0.13) mb over a background of 1.4 mb). Less significant effects are also found in all other pionic annihilation final states regardless of theirG-parity.

The annihilation\(\bar pn\) → π−π0 has been studied in a D2 bubble chamber at several beam momenta between 1.0 and 1.6 GeV/c. The cross-section has been measured to be (110±15) μb at an average beam momentum of 1.3 GeV/c. The study of the angular distribution shows the presence of anL = 3 wave.

Resonance production cross-sections in nonstrange annihilation channels have been studied in the c.m. energy interval from 2.13 to 2.29 GeV where the first bump in the\(\bar {\mathcal{N}} \mathcal{N}\) cross-section forI = 1 had been observed. None of the resonance intermediate states we have analysed shows a structure large enough to be mainly responsible for the enhancement.

In a stack of striped emulsions three cases of K-meson decays have been found. K2 and K3 have a mass of 915±130 m3e; the secondaries cannot be identified. The mass of K1-meson is 1020±270 me (scattering-range) and 1165±130 me (ionization-range); its secondary is a light meson withpβ= 104±24 MeV/c.

A considerable number of electromagnetic cascades have been analyzed to determine the increase of the multiplicity with the primary energy, the spectrum of the energies of the secondaries and the trident production. No appreciable discrepancy from the theory has been remarked.

This work concerns the study of 18 GeV/c π−-mesons interactions in which only one or two pions are produced. The results give support to the assumption that for these events the one-pion exchange is the dominant process. A tentative interpretation of the pion-pion vertex structure is also given.

A total of 2027 K+→π+π0π0 decays at rest were analysed in hydrogen and heavy liquid bubble chambers. The π+ energy spectrum is compared with 3 spectrum shapes:a) linear matrix element,b) linear spectrum, andc) σ resonance hypothesis. The comparison between τ′ and τ decays indicates that they are consistent withI=1 final state and that the agreement is better if one uses the linear matrix element fit in the τ′ decay. Our data fit also well the σ resonance hypothesis formσ∼350 MeV and Γσ∼80 MeV, but do not allow a definite conclusion on this point. The τ′ to τ branching ratio obtained is 0.303±0.009.

529 tracks of heavy primaries in the cosmic radiation have been studied. Charge measurements have been carried out on all tracks with a photometric method, and independent checks with gap counting have been performed on Boron and Carbon tracks. All tracks have been followed through and a total of 331 nuclear collisions observed. From the analysis of these interactions, the interaction mean free paths and fragmentation probabilities in emulsion and in air have been determined. The results are in good agreement with those of other workers and have been used to extrapolate the charge distribution at the top of the atmosphere: the ratios of light nuclei and of heavy nuclei to medium nuclei, at the top of the atmosphere, are 0.30 ±0.09 and 0.51 ±0.11 respectively. Results of energy determination on 275 tracks give a value 1.541-0.130.16 for the exponent of the integral energy spectrum. Some difficulties in the application of Peters’ relation between the energy of primary and the angles of emission of the fragmentation products are discussed.

The charge spectrum of heavy primaries (Z⩾3) of cosmic radiation has been measured in nuclear emulsion exposed in a high altitude ballon flight at a residual atmospheric thickness of about 6 g/cm2. The fluxes of light, medium and heavy nuclei at the top of the atmosphere, and also the relative abundances of charges betweenZ=3 andZ=14, are given.

This work follows a previous study of the interactions of long lived neutral K-mesons, already published. The increased statistics allows us to check the results previously obtained and to determine the cross section for charge exchange of the θ20 particles in the eigenstate of strangeness-1.

From a star observed in a stack of stripped emulsions, a K-meson and a neutral particle decaying in flight are emitted. The V-event can be interpreted either as a Λ0 decay (Q=36−16+67 MeV) or as a θ0-decay (Q=216−55+150 MeV).

The formula suggested byPeters for the energy determination of the heavy primaries, requires the knowledge of the mean energy of evaporation of the α-particles. The present work establishes that this energy depends slightly from the size of the evaporating nucleus.

Detailed experimental data on two events consisting of a narrow shower of pairs of charged particles are reported. An analysis of the common features of the events points out some difficulties in the explanation of the phenomenon as an ordinary cascade shower. Other possible interpretations are suggested.

We have analysed the reaction p - ;n→π−π+π− between 2.08 and 2.29 GeV c.m. energy. The population of the 3π Dalitz plot (a total of 2328 events at all energies) is strongly nonuniform and shows a structure that can be qualitatively interpreted with simple Veneziano-type formulae. The moments of the angular distributions of the three-pion plane are also examined.

We determined thepβ of the secondaries of a high energy jet from scattering measurements. We calculated the angular and momentum distribution in the centre of mass system and we found a good agreement with Heisenberg’s and Wataghin’s theories. We give also the value of the percentage of K-mesons emitted in the nuclear interaction and an estimate of the mean free path for nuclear interactions of the charged π-mesons.

Interactions of π− of 6.1, 11.6 and 18.1 GeV/c from the CERN PS on protons or quasi-free neutrons have been studied in the Ecole Polytechnique one-meter bubble chamber filled with a mixture 86% propane C3H8-14% freon CF3Br (by volume). Interactions have been selected in which two neutral strange particles are visible in order to study correlations among the strange particles and to study separately the behaviour of the K 1 0 ’s from the reactions: π−+N → K0 + -K0+nπ +N, π−+N → K0+Λ(Σ0)+nπ. It is found that πp c.m.s longitudinal and transverse momentum distributions are similar for the K 1 0 ’s from K0-K0 and from K0Y0 pairs. They tend to go forward in the c.m.s., small momenta being most probable. The baryon (A or nucleon) tends to go backward in the c.m.s. but with longitudinal momentum distributed roughly uniformly from slightly forward to the maximum kinematically possible backward. The K 1 0 ’s of K 1 0 K 1 0 pairs tend to have relative energy which is only a small fraction of that available with a distribution roughly independent of the π− beam momentum and of the πp c.m.s. momentum of the K 1 0 K 1 0 system. This effect does not seem to be due to phase-space limitations arising from backward peaking of the nucleon. We have too few events to decide whether this low-energy peaking of theQ-values is due to a resonance near 1.1 GeV or to a strong low-energy K0-K0 inter-action. Clear evidence of K* (0.89 GeV) and to a lesser degree of Y1* (1.39 GeV) are seen in K0A production. (47±15)% of all K 1 0 π+ systems are (K*)+, (30±20)% of all Λπ systems are Y1*. No evidence is seen of K* production in K 1 0 K 1 0 producing jets.

The reaction \(\bar pn \to p\bar p\pi ^ - \) has been studied in the c.m. energy interval from 2.08 to 2.29 GeV. Our data exclude that the bump observed in the Open image in new window cross-section forI=1 at a laboratory momentum of 1.32 GeV/c is due to the production of one pion. The cross-section for this reaction rises only slowly with energy after the threshold for isobar production is reached.

An unusual hyperon decay was observed during a study of the interactions of 1.15 Bev/c K--mesons in an emulsion slack. The interaction results in a star with four evaporation tracks, a pi /sup -/ of 21 Mev kinetic energy that comes to rest producing a sigma -star, and a hyperon decaying in flight. Measurements made on the primary and secondary tracks are tabulated. The discussion of the interpretation of the event includes the subjects of the two-bcdy decay of a particle of hyperonic mass, the interaction of a SIGMA /sup plus or minus /- hyperon, and the radiative decay of a SIGMA /sup +/. (B.O.G.)

The rate of K + →π + + π − + μ + + v decay mode has been determined in deuterium bubble chamber. Limits for the rates of the modes K + → μ + + μ − + π + and K + → e + + e − + π + are also given.

In a preliminary scanning of a large stuck of G-5 emulsions exposed to a 1.15 Bev/c K--meson beam a total of 400 interactions was studied. The mean number of prongs per star was determined to be 5.6 plus or minus 0.6 in the stars found by track following and 6.2 plus or minus 0.4 in the stars found by area scanning. The composition of the 400 stars is analyzed. (C.J.G.)

The relative abundance and energy spectrum of heavy primaries in the cosmic radiation were derived using 529 tracks found in two stacks flown at high altitude at a mean geomagnetic latitude of 46° North. The amount of atmosphere and of packing material above the scanned sections of both stacks was 17 g/cm2. A good resolution was obtained in the range 3 ≤ Z ≤ 10, while in the range Z > 10 the uncertainty was ▵Z = ± 1. In order to check the resolution between boron and carbon, gap-length measurements were made on 65 boron and carbon tracks. The results of the two methods are in good agreement. All tracks were traced through the stack and a total of 331 nuclear interactions found, in order to derive the interaction mean free path and the fragmentation probabilities. The results on the relative abundance of the three charge groups (light 3≤Z≤5 (L), medium 6≤Z≤9 (M), heavyZ ≥ 10 (H)) on a total of 242 tracks whose angle of incidence to the vertical was less than 30° are the following: Flight altitude Top of the atmosphere N1/NM 0.46 ± 0.07 0.30 ± 0.09 NHNM 0.40 ± 0.04 0.51 ± 0.11

The branching ratio and meson ( mu /sup +/) energy spectra were determined for the decay K/sup +/ yields mu /sup +/ + pi /sup 0/ + nu . The method used was the measurement of the meson ( mu /sup +/) stopping range in hydrogen and heavy liquid chambers. (C.E.S.)