A new measurement of the differential cross section and of the analysing power A 0 n of the charge-exchange reaction p − p → n − n at 875 MeV/ c is presented. The A 0 n data cover the entire angular range and constitute a considerable improvement over previously published data, both in the forward and in the backward hemisphere. The cross-section data cover only the backward region, but are unique at this energy. A careful study of the long-term drifts of the apparatus has allowed to fully exploit the good statistics of the data.
Forward hemisphere measurement. Additional systematic error of 4 pct due to target polarization uncertainty.
Backward hemisphere measurement. Additional systematic error of 15 pct.
Differential cross section in the backward hemisphere. Additional systematic error of 15 pct.
Reactions p p → p p and p p → n n were studied at the kinetic energy 230 MeV of incident p by using bubble chamber films. Total cross sections for both of the reactions were found to be 51.2 ± 1.6 mb and 9.1 ± 0.6 mb, respectively. Differential cross sections are well explained by the phenomenological theory given by Bryan and Phillips.
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The differential cross section of the charge-exchange reaction p p → n n has been measured at the CERN Low Energy Antiproton Ring (LEAR) at seven p momenta in the range 546–1287 MeV/ c . A pentanol polarized target has been used and the neutron and the antineutron have been detected in coincidence. The data cover most of the angular range.
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The depolarization parameter Donon of the p dash p → n dash n charge exchange reaction has been measured for the first time at the CERN Low Energy Antiproton Ring (LEAR) at two antiproton momenta, 546 and 875 MeV/ c . The transverse polarization of the recoil neutron was analyzed using a large-acceptance neutron polarimeter made up of two parallel plastic scintillator planes. D 0 n 0 n is usually less than 0.35 which suggests that the spin-spin amplitudes dominate in the scattering matrix. Results are compared with the predictions of various N dash N potential models. The agreement is in general satisfactory.
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The depolarization parameter D 0 n 0 n in the charge-exchange reaction p p ↑→ n n ↑ has been measured for the first time at the CERN Low Energy Antiproton Ring (LEAR) at 875 MeV/ c antiproton beam momentum, in the forward hemisphere. The measured values of D 0 n 0 n are always smaller than ±0.3, indicating that the two-spin amplitudes dominate the scattering matrix as suggested by the meson exchange potential models.
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The spin-transfer parameter K n 00 n of the p p↑ → n ↑n charge exchange reaction has been measured for the first time at the CERN Low Energy Antiproton Ring (LEAR), at 875 MeV/ c p momentum, in the centre-of-mass scattering-angle range from 45° to 78°. To measure the transverse polarisation of the n 's, a thick scintillator counter hodoscope was used as live target, and the elastic n p scattering on the hydrogen of the scintillator was used as analysing reaction of the n transverse polarisation. Its so far unmeasured analysing power is taken as linear in momentum transfer, A n p = α·q , and results are given for α · K n 00 n . The values one obtains for K n 00 n , estimating α from N N potential models, are less than 0.25, in agreement with the predictions.
Polarized beam. CONST is overall normalization unknown factor.
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The differential p p → n n charge-exchange cross section has been measured at the CERN Low Energy Antiproton Ring (LEAR), at two incident p momenta, 601 and 1202 MeV/c. features of the differential cross-section near the forward direction, i.e. a sharp peak at 0° scattering angle followed by an energy dependent dip-bump structure, are confirmed and measured with good precision and high statistical accuracy. The data show very clearly that the shape of the cross-section is a manifestation of the pion-exchange amplitude, and a simple extrapolation to the pion pole already indicates that the pion-nucleon coupling constant f c 2 can be determined with good precision.
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Corrected with data from PL B405,389.
The differential cross sections of the reaction p―p→n―n were measured at 390, 490, 590, 690, and 780 MeV/c. The existence of the theoretically predicted forward dip is confirmed. The results are compared with the predictions of various N―N potential models.
NUMERICAL VALUES SUPPLIED BY F. SAI.
NUMERICAL VALUES SUPPLIED BY F. SAI.
NUMERICAL VALUES SUPPLIED BY F. SAI.
First measurements of the differential cross section are presented for p ̄ p → n ̄ n at LEAR in the momentum range between 180 and 600 MeV/ c . The differential cross sections show a forward peaking followed by a smooth drop-off. No indication of the “bump-dip” structure reported at higher momenta has been observed. The angle-integrated charge-exchange cross sections are determined down to E n ̄ n cm = 6.6 MeV .
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As part of a programme to study the spin structure of the p p→ n n channel, we have measured the analysing power A 0 n and the differential cross section at an incident antiproton beam momentum of 704 MeV/ c . The analysing power exhibits a remarkable angular dependence, which is poorly reproduced by the existing potential models.
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