F. Bonutti

The CHAOS spectrometer for pion physics at TRIUMF

Abstract The Canadian high acceptance orbit spectrometer (CHAOS) is a unique magnetic spectrometer system recently commissioned for studies of pion induced reactions at TRIUMF. It is based on a cylindrical dipole magnet producing vertical magnetic fields up to 1.6 T. The scattering target is located in the center of the magnet. Charged particle tracks produced by pion interactions there are identified using four concentric cylindrical wire chambers surrounding the target. Particle identification and track multiplicity are determined by cylindrical layers of scintillation counters and lead-glass Cherenkov counters, which also provide a first level trigger. A sophisticated second level trigger system permits pion fluxes in excess of 5 MHz to be employed. The detector subtends 360° in the horizontal plane, and ±7° out of this plane for a solid angle coverage approximately 10% of 4π sr. The momentum resolution delivered by the detector system is 1% (σ).

The CHAOS Fast Trigger An array of telescopes for e, π and p mass identification in the intermediate energy region

Abstract The CHAOS Fast Trigger (CFT) is a system of 20 telescopes of plastic scintillator and lead-glass detectors, designed for the discrimination of charged e, π, p (and d) particles in the momentum range 40 to 400 MeV/c for e and π, and from 200 to 800 MeV/c for p. The results from a test measurement performed at TRIUMF show that the π-p and the π-e discrimination efficiency (i.e. the percentage of particles identified) is > 99% and > 90% in the whole momentum range, respectively. The π-e discrimination efficiency has been improved to > 93% through the application of neural networks.

A method for monitoring the stability of photomultipliers

Abstract A method for monitoring hundreds of photomultipliers has been developed in conjunction with the first level trigger of the pion spectrometer CHAOS being constructed at TRIUMF. The system for monitoring the photomultiplier gain stability simply consists of a xenon lamp which operates in the nanosecond time region, a light guide which diffuses the light, and bundles of optical fibers which transport the light to photocathodes. The photomultiplier gain stability can be probed up to few percent (FWHM).

The CHAOS program and detector for pion physics at TRIUMF

The Canadian High Acceptance Orbit Spectrometer (CHAOS) is a unique magnetic spectrometer system recently commissioned for studies of pion induced reactions at TRIUMF. It is based on a cylindrical dipole magnet producing vertical magnetic fields up to 1.6 T. The scattering target is located in the center of the magnet. Charged particle tracks produced by pion interactions there are identified using four concentric cylindrical wire chambers surrounding the target. Particle identification and track multiplicity are determined by cylindrical layers of scintillation counters and lead‐glass Cerenkov counters, which also provide a first level trigger. A sophisticated second level trigger system permits pion fluxes in excess of 5 MHz to be employed. The detector subtends 360° in the horizontal plane, and ±7° out of this plane for a solid angle coverage approximately 10% of 4π sr. The momentum resolution delivered by the detector system is 1% (σ). The experimental program includes extensive measurements of H(π,2π...

New experimental results on the ππ interaction in nuclear matter

Single pion production A(π +, π + π ±) was investigated in nuclei (2H 12C, 40Ca, 208Pb) at an incident pion energy of T π+=280 MeV. Data were obtained at TRIUMF using the CHAOS spectrometer which detected the two final pions in coincidence. The results presented focus here on two aspects of the ππ reaction in nuclei: the reaction mechanism and the invariant mass behaviour above the 2m π threshold.