K. Yasuda

Subthreshold antiproton production in pA, dA and αA reactions

Abstract An enormous enhancement of antiproton production in deuteron- and α-induced reactions has been observed in the subthreshold energy region between 2 and 5 GeV/nucleon. Antiprotons produced at 5.1° with a momentum range of between 1.0 and 2.5 GeV/ c were measured by a beam-line spectrometer and identified by the time-of-flight method. The production cross sections in the deuteron- and α-induced reactions at an incident energy of 3.5 GeV/nucleon were 2 and 3 orders of magnitude larger than those in proton-induced reaction at the same energy. The enhancement in light-ion reactions could not be explained by the internal motion in the projectile and target nuclei. The target-mass dependence (C, Al, Cu and Pb) of the cross sections has also been studied. Further, the cross sections of π and K productions were measured.

Application of Bragg-curve counters to a target multifragmentation measurement

Abstract We have constructed Bragg-curve counters (BCCs) to detect the intermediate-mass fragments (IMFs) emitted during target multifragmentation induced by 12-GeV primary protons on Au, Ag targets. An energy resolution of ∼1.0% and an atomic-number resolution of 2.0% have been achieved. Long-term stability of the output pulse-heights, which was necessary for actual IMF measurements, was realized by employing a continuous gas-flow system with a constant pressure.

Energy spectra and angular distribution of intermediate mass fragments emitted in AuAg(p,X) reactions with Ep = 12 GeV (The first result of the KEK-12GeV-PS experiment; E288)

Abstract The latest results of the first nuclear multifragmentation experiment, E288 [1], at the KEK 12 GeV Proton Synchrotron (KEK-PS) are presented. The energy spectra of intermediate mass fragments (IMFs) were measured inclusively from 30° to 150° with 20° step in the lab. system. Coincidence measurements with one extra IMF emitted toward 90° direction in the opposite hemisphere were performed at the same time. Characteristic sideward flow of IMFs toward 70° direction was found with the usual isotropic component. This isotropic component was trongly suppressed in the coincidence measurement. These facts may indicate the formation of unusually shaped nuclear matter such as an expanding toroid.

Ionization chamber as a p, d and α beam intensity monitor

Abstract An ionization chamber was studied as a low-intensity beam monitor and worked well for p, d and α beams in the intensity range from 2.0 × 10 6 to 1.4 × 10 12 particles per 1.5 second spill. The stability of response to beams was within 2% during 3 weeks of measurements of subthreshold p production.

Subthreshold antiproton productions in pA, dA and αA reactions

Abstract In April 1994, 4 He ions were accelerated at the KEK proton synchrotron for the first time. Subthreshold antiproton productions with α beams in the incident energy range between 2.0 and 5.0 GeV/nucleon were measured for antiproton momenta between 1.0 and 2.5 GeV/c. The data are compared with the p production cross sections in pA and dA collisions measured previously by our group as well as those in heavy ion collisions.

Analyzing power of the reaction pp→ppπ0 at a beam energy of 390 MeV

Abstract The analyzing power of the reaction p p→ppπ 0 has been measured at a beam energy of 390 MeV. The dependences of the analyzing power on the pion emission-angle and the relative momentum of two outgoing protons have been obtained. The angular dependence could be decomposed by Legendre polynomial and the relative contribution of the P 21 to the P 11 function is less than 4%. The momentum dependence of the analyzing power has been studied to obtain information about the pion-production mechanism. It has been deduced that pion production due to the long-range interaction plays an important role in the momentum dependence of the P -state amplitude.