a High Statistics Study of the Reaction Proton -PROTON--->PROTON - Positive Pion-Neutron from 1.2 to 2.0 Gev/c with a Polarized Beam.
The density matrix elements and their polarization correlations have been measured for the reaction pp(-- ->)p(pi)('+)n with a polarized proton beam (both transverse and longitudinal) of 1.18, 1.47, 1.70, and 1.98 GeV/c incident upon a liquid hydrogen target. The scattered particles were detected by the Argonne Effective Mass Spectrometer, which consisted of spark chambers, a trigger hodoscope, a SCM-105 dipole magnet, two cylindrical multiwire proportional chambers surrounding the target and used as a vertex detector, and veto counters. The forward particle ((pi)('+) or p) was required to traverse the spectrometer, which measured its angles and momentum. The recoil particle ((pi)('+) or p) was usually detected by the vertex detector which measured its angles, but some recoils were forward enough so that they could be momentum analyzed by the spectrometer. The neutron was undetected. The p(pi)('+)n final states were separated from the significant background reactions (pp(--->)pp, pp(- -->)d(pi)('+), and pp(--->)pp(pi)('0)). The two body final states were easily identified and eliminated by their distinctive kinematics. The three body final states were classified by a zero constraint fit (one constraint if both charged particles were momentum analyzed). All events which satisfied the pp(--->)pp(pi)('0) hypothesis were eliminated. The angular distributions of the pp(--->)p(pi)('+) events were fit by a maximum likelihood technique to the spherical harmonics (m (LESSTHEQ) 2, l (LESSTHEQ) 2), which are simply related to the density matrix elements. Since the reaction pp(--->)p(pi)('+)n proceeds predominantly via the intermediate reaction pp(--->)(DELTA)('++)n(--->)p(pi)('+)n, the density matrix formalism for (DELTA)('++) production (spin 3/2) was used. The data showed a remarkably smooth momentum dependence, with the exception of a striking change in the spin up/down (DELTA)('++) production asymmetry between 1.18 and 1.47 GeV/c. The asymmetry changes from a value of (TURN)0.4 in the central region (cos(THETA)(,(DELTA))(TURN)0) to a value near -0.1 between 1.18 and 1.47 GeV/c. At the present time, there are not any theoretical models for this data that are able to produce good fits. The data showed good agreement with other experiments that could be compared to ours. In addition, a preliminary analysis suggests that the value of the pp(--->)d(pi)('+) asymmetry is a manifestation of a final state interaction with pp(--->)p(pi)('+)n as the intermediate state.
- Pub Date:
- Physics: Elementary Particles and High Energy