Near threshold positive pion production by protons on nuclei

The IUCF QDDM magnetic spectrograph and a Danti D magnetic spectrometer designed specifically for low-energy pion detection have been used to study the near-threshold behavior of the proton-induced positive pion production reaction to discrete states from 10B, 16O, 40Ca, and 90Zr targets. Proton beam energies in the range 140 to 175 MeV were employed. Pions of laboratory energies from 2.1 to 32 MeV were observed. Angular distributions were measured at two proton energies for the 16O(p,π+)17O/sub g.s./ and 90Zr(p,π+)91Zr/sub g.s./ reactions, while the 10B(p,π+)11B/sub g.s./ and 40Ca(p,π+)41Ca/sub g.s./ reactions were studied more extensively. Angular distributions were obtained at five different proton energies for the 40Ca(p,π+) reaction from 4 to 24 MeV above threshold and at four different energies for the 10B(p,π+) reaction from 7 to 22 MeV above threshold. The energy dependence of the 10B(p,π+) reaction was further explored by measuring the differential cross section at a 25 degree laboratory angle at ten different proton energies covering the range 2 to 41 MeV above threshold. The angular distributions generally covered 25 to 155 degrees in the laboratory frame, but measurements were made at zero degrees in a few cases. The magnitude of measured laboratory differential cross sections rangedfrom below 1 nb/sr to over 1 μb/sr. The data are presented together with a discussion of the experimental techniques. Comparisons are made with selected pion production data from other laboratories, and the present status of understanding of the pion production process is discussed