Other
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........82z&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF MARYLAND COLLEGE PARK, 1990.Source: Dissertation Abstracts International, Volume: 52-02, Section:
Other
8
Pion, Delta Resonance
Scientific paper
A systematic study of the energy dependence of two-nucleon pion absorption on ^6Li was performed. The inclusive ^6Li( pi^+,p) and exclusive ^6Li(pi^+,pp) reactions were measured at five different pion kinetic energies of 115, 140, 165, 190, and 220 MeV at the PSI laboratory. The first proton was detected by one of three DeltaE-E NaI telescopes with a 19.2 msr solid angle for each telescope. The second proton was stopped at a large acceptance (600 msr) array of plastic scintillator with two additional wire chambers. During the course of the experiment, the three NaI telescopes were fixed at the angles 35^circ, 57.5^circ, and 80 ^circ, and the plastic scintillator was moved from -30^circ to -150^circ . The angular correlations {d ^2sigmaover dOmega_1dOmega _2} and the energy sharing distributions {d^2sigmaover dOmega_1dE_1} are presented for the four different missing mass cuts: (-20,10) MeV, (10,35) MeV, (35,80) MeV, and (80,140) MeV. Agreements with the renormalized DWIA calculations are good for the low missing mass regions, (-20,10) MeV and (10,35) MeV. Our simple three-nucleon absorption model (four-body phase space simulation) seems to describe the data reasonably well for the high missing mass regions, (35,80) MeV and (80,140) MeV. For (-20,10) and (10,35) MeV excitation energies, the single differential cross section {dsigmaover dOmega_1}, which are obtained by integrating the data, have the same angular dependence as the free reaction d(pi^+,pp) at the five pion incident energies. Comparing the inclusive and exclusive measurements, the FSI corrections are found to be important. Our DWIA model employing a deuteron optical potential for the outgoing proton distortions seems to predict reasonable FSI corrections. Including other published ^6Li( pi^+,pp) data, the two-nucleon absorption cross sections on the two p-shell nucleons ( (-20,10) MeV) have the same energy dependence as the free reaction d(pi^+,pp). The scaling factor (effective quasideuteron number) is 0.92 +/- 0.03 for the direct quasideuteron absorption, and 1.11 +/- 0.04 after the FSI corrections. Similarly, after inclusion of the FSI corrections the quasideuteron absorption cross sections, involving at least one s-shell nucleon ( (10,80) MeV), follow the same energy dependence as the free reaction d(pi^+,pp). The average effective quasideuteron number is 1.95 +/- 0.07 without the FSI corrections, and 3.63 +/- 0.14 with the FSI corrections. The importance of the total two-nucleon absorption cross section in ^6Li decreases with the pion incident energy, a feature which is described reasonably well by the calculations of Oset et al.
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