Measurements of Pion-Nucleon charge exchange at Low Energy
Abstract
Differential cross sections for π^-+p→π^0+n from 119 to 186 MeV/c were measured in 2002 at Brookhaven National Laboratory. The Crystal Ball multi-photon spectrometer, 672 NaI crystals that cover 94% of 4π sr, was used to detect the π^0's. Particular attention has been devoted to beam normalizations and momentum calibrations. The utilization of solid targets (CH2 with C subtraction) allowed the incorporation of a beam counter 30 cm from the target. This counter minimized corrections due to decay and multiple scattering that affected our data taken in 1998. We use TOF spectra to determine the pion fraction of the beam incident on this counter. A correction based on Monte Carlo simulation is applied for decay muons that cannot be separated in the TOF spectra. The Monte Carlo program also corrects for multiple scattering through air and beam counters. Absolute momentum calibration of the beam is accomplished by calibrating the Crystal Ball so that the invariant mass of the two γ events is the same as the π^0 mass and requiring the missing mass to be that of the neutron. These momenta are also compared with the channel calibration after correcting for energy loss in the beam elements Preliminary results show significant differences from the GW PWA at the back angles, especially at 126 MeV/c.
- Publication:
-
APS Division of Nuclear Physics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..DNP.GG007B