B. Van de Vyver

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.

Prompt ντ background in wide band νμ beams

Abstract To estimate the prompt background for ν μ → ν τ oscillation search in the Chorus and Nomad experiments, two possible sources of tau-neutrinos were considered. The first is the production and (semi-)leptonic decay of heavy flavour mesons. Secondly, the Drell-Yan mechanism can lead to tau-pairs. It is shown that this last contribution is negligible. However, the decay of D s ± mesons to τ ± ν τ gives rise to 3.3 × 10 −6 ν τ charged-current interactions per ν μ charged-current interaction. Over the course of the Chorus experiment, this corresponds to 0.1 detected ν τ charged-current events. This value is an upper limit and the actual background might be smaller by a factor of 2. However, it should carefully be taken into account, especially in view of future experiments, wishing to explore smaller values of mixing.

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

The CHORUS experiment, designed to search for νμ→ντ oscillations, consists of a nuclear emulsion target and electronic detectors. In this paper, results on the production of charged particles in a small sample of charged-current neutrino– and anti-neutrino–nucleus interactions at high energy are presented. For each event, the emission angle and the ionization features of the charged particles produced in the interaction are recorded, while the standard kinematic variables are reconstructed using the electronic detectors. The average multiplicities for charged tracks, the pseudo-rapidity distributions, the dispersion in the multiplicity of charged particles and the KNO scaling are studied in different kinematical regions. A study of quasi-elastic topologies performed for the first time in nuclear emulsions is also reported. The results are presented in a form suitable for use in the validation of Monte Carlo generators of neutrino–nucleus interactions.

THE COMPACT EMULSION SPECTROMETER

Abstract An emulsion spectrometer has been built and tested with pion beams in a 0.7 T magnetic field. A momentum resolution, ΔP/P=13%±1%, has been obtained for 5 and 10 GeV /c particles.