I. Tezuka

Measurement of charm production in neutrino charged-current interactions

The nuclear emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy from 1994 to 1997. In total, about 100 000 charged-current (CC) neutrino interactions with at least one identified muon were located in the emulsion target and fully reconstructed, using newly developed automated scanning systems. Charmed particles were searched for by a program recognizing particle decays. The observation of the decay in nuclear emulsion makes it possible to select a sample with very low background and minimal kinematical bias. In all, 2013 CC interactions with a charmed hadron candidate in the final state were selected and confirmed through visual inspection. The charm production rate induced by neutrinos relative to the CC cross-section is measured to be σ(νμN→μ−CX)/σ(CC)=(5.75 ± 0.32(stat)±0.30(syst))%. The charm production cross-section as a function of neutrino energy is also obtained. The results are in good agreement with previous measurements. The charm-quark hadronization produces the following charmed hadrons with relative fractions (in %): fD0=43.7±4.5, fΛc+=19.2±4.2, fD+=25.3±4.2 and fDs+=11.8±4.7.

Production of a twin single hypernuclei and the Ξ−-nuclear interaction

Abstract An event accompanied by two single hyperfragments emitted from a Ξ− nuclear capture at rest was found in a nuclear emulsion. It is interpreted as a Ξ−-12C bound system decaying into either a) Λ4H + Λ9Be, b) Λ 4 H + Λ 9 Be ∗ or c) Λ 4 H ∗ + Λ 9 Be . The binding energy of the Ξ-12C system is obtained as a) 3.70−0.19+0.18 MeV, b) 0.62−0.19+0.18 MeV and c) 2.66−0.19+0.18 MeV, respectively. The system is considered as a Ξ− hypernucleus in the cases a) and c). In case b), this event and another event of the same type (Yokohama event) can both be interpreted as a decay from the Ξ-12C system in 2P state when a shallow Ξ−-nuclear potential is assumed.

THE DOUBLE ASSOCIATED PRODUCTION OF CHARMED PARTICLES BY THE INTERACTION OF 350 GEV/C PI-MESONS WITH EMULSION NUCLEI

Abstract Evidence is reported for the simultaneous production of four charmed particles in interactions induced by 350 GeV/ c π − mesons in stacks of nuclear emulsions. The events were found during a search for beauty particles among a sample of about 200 interactions with candidates for charmed particles. The events selected required the presence of at least one muon with a high component of momentum transverse to the beam direction.

A Hybrid Experiment to Search for Beauty Particles

We give here a detailed description of experiment WA75, which was performed at CERN to search for beauty particles. Events containing at least one muon with a high momentum transverse to the beam direction were selected; then the primary interactions and decay vertices, located in stacks of nuclear research emulsions, were examined and analysed. The various parts of the apparatus are described and the off-line analysis and search in emulsion are discussed. An estimate is made of the sensitivity of the experiment to beauty- and charmed-particle production.

Quasifree p(K-,K+)Xi- reaction in nuclear emulsion

Abstract A study of 1.66 GeV c K − beam induced ( K − ,K + ) reactions in the nuclear emulsion target is presented and 796 ( K − , K + ) reaction vertices ( p K + ⩾ 1 GeV /c ) containing 18 single hyperfragments are identified. There is no clear(spatially separated) double hyperfragment nor twin single hyperfragment in the identified 796 ( K − ,K + ) reactions. These events are classified and their characteristics are described in detail. In the region p K + ⩾ 1 GeV /c where the quasifree K − (p) → K + Ξ − is the dominant process, the probability of Ξ − emission from the reaction vertex is determined to be 73.9 −4.6 +4.5 %. From this value, the mean free path of Ξ − in a nucleus is estimated to be 4.7 −1.0 +1.5 fm for 〈p Ξ − 〉 ∼ 0.6 GeV /c by assuming a simple model of uniform nuclear matter.

Some properties of charmed particles produced in π−-nucleus interactions

Abstract The azimuthal correlation distribution of 102 charmed-particle pairs observed in the hybrid emulsion experiment WA75 is compared with theoretical predictions. The various pairs - (D − D 0 ), (D − D + ), (D 0 D 0 ) and (D + D 0 )-all s how, within statistical error, the same azimuthal correlation distribution, demonstrating its independence from the specific nature of the production channel. Among the decays of 150 charged charmed particles and 138 neutral ones seen, higher multiplicities are favoured for hadronic as opposed to semileptonic decays. The data are consistent with the muonic decays of charged D mesons proceeding through the channels (μ ± , v, K 0 ) and [μ ± , v, K ∗0 (892)] , the fraction through K 0 being 0.76±0.06.

Measurement of B(Ds+ → μ+νμ)B(Ds+ → φμ+νμ) and determination of the decay constant fDs

We have observed

New techniques for emulsion analysis in a hybrid experiment

23.2 \pm 6.0_{-0.9}^{+1.0}

Charged-particle multiplicities in charged-current neutrino– and anti-neutrino–nucleus interactions

purely-leptonic decays of

The production of charmed particles in high-energy 16O-emulsion central interactions

D_s^+ ->\mu^+ \nu_\mu