Production properties ofD 0,D +,D *+ andD s + in 230 GeV/cπ − andK −-Cu interactions

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D _s ⁺ →K ⁺ K ^?π⁺, 543D°→K ^?π⁺ andK ^?π⁺π^?π⁺ as well as 249D ⁺→K ^?π⁺π⁺ (or charge conjugate). 147 mesons out of our \({{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-0em} {\bar D^0 }}\) sample were produced via chargedD ^* state. For all charmed mesons we determine the total production cross-section and study thex _F andp _t ² distributions.     

Measurement ofD meson production in 200 GeV π−-Be interactions

We have measured the differential and total cross sections ofD meson production in 200 GeV π^?-beryllium interactions, using a sample of 48 fully reconstructed and nearly background-freeD mesons in the decay channelsK ^?π^±,K ^?π^±π^± andK ^?π^?π^±π^±. A single electron trigger has been used to select events containing a pair of charmed particles. A vertex telescope of 6 silison microstrip detectors allowed the reconstruction of tracks of charged secondaries and the reconstruction of primary and decay vertices with high precision. The ratio of branching fractions for \(\mathop {D^0 }\limits^{( - )} \to K^ \mp \pi ^ \pm \) to \(\mathop {D^0 }\limits^{( - )} \to K^ \mp \pi ^ \mp \pi ^ \pm \pi ^ \pm \) , and an upper limit for \(D^0 - \bar D^0 \) mixing are presented.     

Six-prong events produced in 16 GeV/c π−p interactions

About 12 000 events with six prongs have been measured in 16 GeV/c π⁻p interactions. Cross sections for the various reaction channels and for the production of mesonic baryonic resonances are given. In the reaction π⁻p → pπ⁺π⁺π⁻π⁻π⁻, the (π⁻π⁻π⁺) effective mass spectrum shows indications of enhancements near the A₁, A_1.5 and A₂-meson masses. The longitudinal momentum distributions and the average transverse momenta are presented. The distribution of the angles between pairs of pions is studied and it is shown that in π⁻p interactions the average opening angle for pairs of positive pions is smaller than that for pairs of negative pions.     

Neutral and charged D1 production in 360 GeV/c π−p interactions

The first data on the production of D¹(2010) are presented as observed in π⁻ -proton interactions at √s = 27 GeV. It is found that D¹(2010) dominates the total charm D-meson production, without a significant non-central component.     

Decay asymmetry of the K− π+ system in K− nucleon interactions at 3 GeV/c

The decay asymmetry of the K⁻π⁺ system was measured in two reactions and found to be equal to that observed for K⁺π⁻ systems, in agreement with its intepretation as an S waves effect in Kπ scattering.     

Search for π−ϱ− resonances produced in 7 GeV/c π−d interactions

A search has been carried out for resonances in the π⁻ϱ⁻ system produced in the reaction π^–d → ppπ⁻ϱ⁻; we observe no significant structure in the π⁻ϱ⁻ mass spectrum, and place an upper limit of 6ωb for resonance production in this channel.     

Inclusive production of vector mesons in π+ p interactions at 250 GeV/c

We report on a study of ρ⁰, ρ⁺, ω, \(\bar K^{*0} (892)\) andK ^*0 (892) inclusive production in π⁺ p interactions at 250 GeV/c, for ρ⁺, \(\bar K^{*0} (892)\) for the first time in a π⁺ p experiment. The data are compared withK ⁺ p data in the same experiment, with results of other experiments and with quark-parton models. Interesting differences are found between ρ^+,0 and ω production.     

Spallation hypernuclei produced by 6 GeV/c K−mesons

The production of short-range (⩽ 10 > m) hypernuclei from heavy emulsion nuclei by 6 GeV/c K⁻mesons is studied on the basis of the spallation model. Monte Carlo calculations are made to simulate the process and the calculated results compared with experimental data. It is concluded that for this incident K⁻ beam the main contributor to the momentum of the spallation product is the randomly directed component of the momentum from the cascade process, P incasc^r. The residual momentum due to the evaporation P_evap plays only a secondary role. However, the evaporation determines the mass of the spallation product and in this way can significantly affect the range of the product. Owing to the major role played by the cascade stage it is necessary that, if the spallation model is to be effective, the cascade stage of the calculations must be followed through in much greater detail than has been attempted to date. The wide range of masses of spallation hypernuclei from high-energy interactions is relevant to the attempts to use decays of these hypernuclei to measure the well depth of the Λ-hyperon in nuclear matter.     

A ϱ−π− enhancement at 1.32 GeV observed in 5 GeV/c π−d interactions

In the reaction π⁻d → p p π⁻π⁻π^o at 5.04 GeV′c, a ϱ⁻π⁻ enhancement at 1.32 GeV is observed. Its statistical significance is about 4 standard deviations. The production cross-section (15 μ b) excludes its identification with the (ϱ^oπ^±) A₂ resonance.     

Some aspects of π− −N interactions at 17.2 GeV/c

Results from the analysis of π⁻−N interactions at 17.2 GeV/c in photographic emulsions are presented. From the frequency of odd and even shower multiplicities, evidence is presented to support the conclusion of Davis et al. that the surface of heavy nuclei is rich in neutrons. Inelasticities for small and large shower multiplicities are deduced. Discrepancies in inelasticities obtained in emulsions and bubble chambers are attributed to the differences in the momentum selection criteria. It is concluded that the symmetry in angular distributions of pions in gp-π system in small multiplicity events, is accidental.The frequency of K mesons is indirectly estimated from the energy balance, and is found to be consistent with direct observations, in the hydrogen bubble chamber, at similar energy. The frequency of neutral pions is deduced for various groups of shower multiplicities. In very large multiplivity events (n_{s ⩾ 8}), negligible numbers of π^o are found to be produced.The transverse momentum (P_t) distribution for pions is found to be in agreement with Hagedorn's theory as well as with the formula of Cocconi et al. The P_t distribution for protons, on the other hand, is inconsistent with Hagedorn's theory.     

On the interactions of 17.2 GeV π− mesons with emulsion nuclei

260 m of track length was followed and 631 interactions were picked up. On the basis of the effective target mass M_T, these events were divided into pure pion-nucleon and pion-multinucleon interactions. The behaviour of various parameters like mean multiplicity, median angle, transverse momentum, energy in lab and c.m. system and coefficient of inelasticity has been studied for these two types of events. The study of heavy tracks is useful in understanding the mechanism of nuclear disintegration. The original picture of the internuclear cascade model requires some further modifications in the light of an effect called ‘trailing’.     

Pion and kaon production in 70 GeV/c K − p interactions

Results are presented on the total and differential cross sections for the production of π⁺, π^?, γ, \(\bar K^0 \) ,K ⁰,K ⁺, andK ^? in theK ^? p interactions at 70 GeV/c. The energy dependence of the various production processes shows in paticular a strong rise of the γ cross section and an increase of the average transverse momentum of the charged pion in the fragmentation regions.     

Observation of ω1− production in K−p interactions at 11 GeV/c

Clear evidence is presented for the production of an Ω¹⁻ resonance of mass 2253±13 MeV/c² and width 81±38 MeV/c² in K⁻p interactions at 11 GeV/c. The state is observed in the Ξ (1530)K̄ decay mode, and the corresponding inclusive cross section is estimated to be 630±180 nb. Comparisons are made with theoretical predictions and with similar states observed inhyperon beam induced data.     

Resonance production in K−-neutron interactions at K− momenta of 1.45 and 1.65 GeV/c

Results are reported on K⁻-neutron interactions at c.m. energies near 2 GeV. The interactions are dominated by strong production of hyperon resonances, particularly Σ(1385), Λ(1405) and Λ(1520). Production cross sections and angular distributions are given for the Σ(1385), Λ(1405) and Λ(1520) and branching fractions to decay modes observed in the experiment are given for Σ(1385) and Λ(1520). The strong energy dependence of some features of the data suggests that s-channel effects are dominant.     

Observation of the Ληo resonance in π−p interactions at 1.0 GeV/c

The radiative decays of resonances with Λ^o hyperons involved have been studied in the 24-liter propane bubble chamber exposed to 4.0 GeV/c negative pions. The M_Λγ effective mass distribution exhibits a peak which can be explained by the existence of the Λη^o-resonance with mass of about 1680 MeV. The kinematic influence of the known hyperon resonances on the distributions is discussed. An attempt is being made to determine the Λη^o-spin.     

General characteristics of π−-nucleon interactions at 60 GeV/c obtained in nuclear emulsion

Interactions of 60 GeV/c π⁻-mesons with nucleons of the nuclear emulsion have been studied. Average prong number in π⁻-proton collisions is 6.64 ± 0.16. The majority of secondary particles are emitted into the forward hemisphere in the π⁻-proton CM system especially in low-multiplicity events.