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Calibration of the chaos spectrometer for small scattering angles Jamieson, Blair Alex


For measurements of pion-nucleon scattering in the Coulomb-Nuclear Interference (CNI) region, it is implicit that we are looking at small scattering angles. At small scattering angles the in-plane (x,y coordinate) scattering angle is not the true scattering angle. Since the Canadian High Acceptance Orbit Spectrometer (CHAOS) has a vertical extent of plus or minus seven degrees, an in-plane scattering angle of zero degrees could, i n three dimensions, be seven degrees. The CHAOS detector's out-of-plane (z coordinate) information comes from three wire chambers: wire chamber one ( W C l ) cathode strips and anode wires, wire chamber two (WC2) cathode strips and anode wires, and wire chamber four's (WC4) two resistive wires. The out-of-plane information from WC4 requires a fringe field correction, because it lies outside the uniform magnetic field of CHAOS. The fringe field of CHAOS acts like a lens, in that it has a slight focusing effect on charged particles. The fringe field correction moves the WC4 (x,y,z) data point so that it is on the linear object ray. In this paper I will present the model for the fringe field correction. I will explain how the three dimensional scattering angle resolution was determined, and as the final test of the scattering angle I will present the cross-section for fiC scattering, obtained using CHAOS data.

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