Michael Tran

Differential cross sections for radiative capture of pions on hydrogen in the Δ (1232) region: A test of the isospin structure and t-symmetry of hadronic electromagnetic interactions

Abstract Radiation capture of π − on hydrogen has been measured in the momentum range from p π − = 210 MeV/ c to p π − = 385 MeV/ c and for c.m. angles between 30° and 120°, covering the Δ (1232) resonance. The unambiguous separation of the events from the charge exchange background is based on precise neutron time-of-flight measurements. Detector efficiencies were carefully determined in separate experiments. The experimental results are in good agreement with those of the inverse reaction and with most recent multipole analyses. An upper limit of ±2% can be set on the contribution of the isotensor term to the transition amplitude. A time reversal violating phase, when added to the resonant M 1+ 3 amplitude in the Donnachie-Shaw model, is found to be consistent with zero.

Measurement of the differential cross section for π−p → π0n around the Δ(1232) resonance and test of the charge independence principle

Abstract Differential cross sections for the charge-exchange reaction of π − on protons in the region of the Δ(1232) resonance (128 MeV ≦ T π − ≦ 246 MeV) are reported. Measurements were performed by detecting the neutron with a time-of-flight technique. The neutron counter efficiency was measured over the entire energy range. Particular care was devoted to eliminating possible sources of systematic error. Statistical errors are of the order of 4%, total errors of the order of 7%. The experimental results are in fair agreement with the most recent phase-shift analysis. Our data satisfy the triangle inequality. An analysis based on recent phase-shift values does not favour violation of charge independence.

Measurement of π−p → π0n differential cross-sections using a NaI(Tl) photon spectrometer

Abstract From the energy spectrum of photons produced in charge exchange of negative pions on protons one can deduce the differential cross-section of charge exchange scattering. The forward charge cross-sections have been measured in the Δ (1232 MeV) resonance region, using as photon spectrometer a large NaI(Tl) crystal with good energy and timing resolution. The method shows the promise of precision comparable to that achieved in reactions with charged particles in the final state and should be applicable throughout the resonance region.

Differential cross-sections for π−p → γn in the first resonance region

Abstract Differential cross-sections for negative pion radiative capture on protons at c.m. angles of 60°, 90°, and 120° have been measured at nine incident laboratory energies between 110 and 270 MeV. Comparison with measured cross-sections for pion photoproduction and with conventional multipole analyses shows neither evidence for a violation of time reversal invariance nor for an isotensor component of the electromagnetic current of hardrons.