An apparatus of the NBC type and the physics results obtained

Abstract

A nonbubble chamber (NBC) setup, especially designed to perform a series of experiments, is described. The setup consists of a neutron missing-mass spectrometer coupled with a system of large electromagnetic shower detectors. In spite of its large dimensions (the sensitive surface and volume are 2.16 × 10 4 cm 2 and 7.8 × 10 5 cm 3, respectively), the neutron spectrometer has a time resolution of ±0.70 nsec FWHM, with ∼25% detection efficiency in the range (70–390 MeV) neutron kinetic energy. The time equalization between the various components of the neutron spectrometer has been established to within ±0.1 nsec. At present this is the most powerful and the most accurate high-energy neutron detector. The electromagnetic shower detector is based on the principle of simultaneous measurements of the spatial development of the electromagnetic cascade and of its energy release. This is obtained with nine elements of lead foil — spark chamber — plastic scintillator, all sandwiched together. The sensitive surface and volume of the electromagnetic shower detector are 1.45 × 10 4 cm 2 and 7.2 × 10 5 cm 3, respectively. The setup has been used to perform a series of 14 experimental investigations. Ten of these have already produced conclusive results which are either published or submitted for publication: 1. 1. Evidence against the existence of the S 0 meson; 2. 2. an accurate measurement of the branching ratio η → neutrals η → total ; 3. 3. an accurate determination of the branching ratio ω → neutrals ω → total ; 4. 4. study of φ production in π − + p interactions at 2.1 GeV/ c; 5. 5. evidence for the new decay mode φ → e + e − and measurement of the cross section σ[ π − + p → ( φ → e + e −) + n]; 6. 6. evidence for the new decay mode ω → e + e − and measurement of the cross section σ[ π − + p → ( ω → e + e −) + n]; 7. 7. points (5) and (6) above allowed the first direct determination of the ( ω − φ) mixing angle; 8. 8. evidence for the new decay mode X 0 → γγ; 9. 9. cross section measurements for X 0 production and value of the branching ratio X 0 → neutrals X 0 → total ; 10. 10. evidence for a structure in the neutral A 2 mass region. The data of the following three experiments are being analysed: 11. 11. measurement of the branching ratio X 0 → γγ X 0 → total ; 12. 12. study of the ϱ − ω interference in the reaction π − + p → π + + π − + n at 1.67GeV/ c incident pion momentum; 13. 13. study of the ( π 0 π 0) system in the invariant mass region from 400–950 MeV. 14. 14. Finally, the last experiment is still under way: the apparatus is at present running for the detection of the decay mode φ → η + γ and for the measurement of the branching ratio φ → η + γ φ → total . The setup described and the experimental results obtained show that it is possible, in the field of NBC physics, to reduce the cost and the time needed for an experiment provided that multipurpose NBC setups are used.