Search

Inclusive measurements of pion double‐charge‐exchange in 3He[1] and 4He[2] in the Δ(1232) resonance region suggest the dominance of a two‐step sequential single‐charge‐exchange mechanism involving quasi‐free nucleons. To investigate this reaction mechanism, we have observed protons in coincidence with the outgoing pion in π++4He→π−+4p at Tπ+=240 MeV. Pions were detected in a magnetic spectrometer at θπ−=32°, while protons were detected in a close‐packed array of plastic scintillator telescopes covering θp=67.5°–157.5° on the same side of the beam as the spectrometer, and θp=22.5°–157.5° on the opposite side. We will present preliminary results for the distributions in energy and angle of the coincident protons.

A new experiment, designed to measure spin‐dependent lepton‐nucleon deep inelastic scattering, is being built on the HERA electron storage ring at DESY, Hamburg. The HERMES experiment will use a windowless internal gas cell of polarized H, D, or 3He nuclei as a target for the stored 27 GeV electron (or positron) beam. The pure target, coupled with a high luminosity, will enable greater statistical precision and much smaller systematic errors that has been possible thus far in previous measurements at CERN and SLAC. The construction of the experiment is underway. At the same time, a test experiment is being conducted on the HERA ring, using an unpolarized gas cell and prototypes of the detectors. This report briefly summarizes the results of the test run and the status of the construction of the full experiment.

Measurements of analyzing powers and spin correlation parameters for 3He(p↘,2p) and 3H↘e(p↘,pn) quasielastic scattering have been carried out using a polarized internal 3He target and a stored, polarized proton beam. They were made over a wide kinematic range with a proton energy of 197 MeV and a large acceptance detector system which allowed the simultaneous measurement of both reactions. At momentum transfers sufficiently high to minimize rescattering effects, the (p,pn) results are in agreement with PWIA calculations. The (p,2p) results were found to be less sensitive to kinematic conditions and are also in agreement with calculations.