We report on results of an experiment to study the reaction π−p → π− π+ in the incident pion momentum region between 295 and 450 MeV/c. A departure from phase space was observed in invariant-mass spectra and angular distributions which cannot be explained with Δ and ϱ resonance production. It indicates aI=0,J P = 0+ π− π+ final-state interaction.

Results of full‐kinematics measurements of π−p → π−π+n, π−p → π−π0p and π+p → π+π+n in the threshold region are compared with current‐algebra calculations. Discrepancies can be largely attributed to isobar production, but even the threshold behavior is not adequately described by existing calculations.

A full-kinematics measurement of the π − p→ π − p π 0 reaction in the incident π − momentum region from 295 to 450 MeV/ c is presented. The measurement was performed with the OMICRON spectrometer at the CERN synchrocyclotron. An incident-momentum dependent number of π − p→ π − p π 0 events, ranging from 6 to 430 has been extracted from collected data. Differential cross sections are found to be consistent with phase-space distributions. Integrated cross-sections are used to determine the value of the chiral symmetry breaking parameter ξ. The measured value of ξ =0.1 −0.7 +0.5 is obtained in a model-independent way, strongly favouring Weinberg's choice of ξ =0.

The production of wide-angle e+e- pairs by pi -p at 0.3 GeV/c has been studied using a magnetic spectrometer. The forward cross section obtained for pi -p to ne+e- agrees with theoretical calculations. The rare decay pi 0 to e+e- is shown to have a branching ratio B<5.3*10-7=11 times the unitarity lower bound and it is argued that there is as yet no convincing evidence for an anomalously large branching ratio.

Cross sections are presented for the reaction pi -p to pi -p gamma at square root s=1234 MeV.

A measurement of the cross sections of several πp → ππN reaction channels in the region of incident pion momenta of 300 to 460 MeV/c has been performed with Omicron, a multi-arm magnetic spectrometer of large solid angle. This paper describes the apparatus, the trigger, the readout and data-acquisition systems and the off-line analysis. Sample data illustrating the operation of the apparatus are also presented.

A long liquid Cherenkov counter has been used to measure the proportion of muons in positive and negative pion beams in the momentum range between 300 and 460 MeV/c. A nine-parameter function fits all the spectra well. The data show a smooth dependence on incident momenta and agree with calculations of pion and muon pulse heights.

A second level trigger system using conventional wire chamber readout and NIM modules is described. The events to be processed by the on-line computer are selected in a time interval of one microsecond on the basis of number of hits in the wire chambers. Some applications and performances of the system are described in detail.

Abstract Differential cross sections for backward elastic scattering of negative pions by 16 O have been measured in the angular range 140° ⩽ θ ⩽ 180° at energies of 115, 163 and 244 MeV in the laboratory system. The results are compared with some recent theoretical calculations.

A displacement method for measuring electron drift velocities in adjustable-field drift-chambers has been developed and its results have been compared to those of a track-reconstruction method, which uses a least-squares track-fitting procedure and computes drift velocities by iteration. The reconstruction method has been adapted for use with tracks of unknown momentum curved by a magnetic field.

A simple, large-solid-angle apparatus, specially suited for the measurement of backward elastic scattering of medium-energy pions on protons and deuterons, is described. The method of analysis which reduces background and determines elastic events from a data sample of 185 MeV negative pions incident on a D2O target is discussed. Results for 141 MeVπ+pand 185 MeVπ−p backward cross-sections are also presented and compared with cross-sections calculated from known phase shifts.