We report the results of the investigation of 18 500 frames of π+p interactions in the Brookhaven 20-in. bubble chamber at an incident energy of 900 MeV. It is found that single-pion production proceeds almost entirely through formation of the N33* isobar. The production mechanism of the N33* is analyzed in terms of its spin density matrix. Comparison is made with Stodolsky and Sakurai's ρ-exchange model and with the absorptive peripheral model.
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A systematic study has been made of the reactions pp→pp and pp→pN* in the angular range from θlab=10∘ to θc.m.=90∘ at 3, 4, 5, 6, and 7 GeVc. An orthogonal dispersion magnetic spectrometer detected protons from interactions in hydrogen with momentum transfer (−t) in excess of 0.5 (GeV)2. Well-defined peaks in the missing-mass spectra occurred at average N* masses of 1240±6, 1508±2, and 1683±3 MeV with average full widths of 102±4, 92±3, and 110±4 MeV, respectively. Below 2400 MeV no other significant enhancements were found. The N* production cross sections dσdt near θc.m.=90∘ are in qualitative agreement with the predictions of the statistical model. For each isobar the differential cross section at fixed energy varies as exp(−vv0), where v≡[−tu(t+u)]; v0 varies systematically with energy and tends toward the same value (≈0.4 GeV2) for each isobar at the upper limit of our energy range.
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The p¯−p elastic scattering at 6.9 GeV/c was studied by the analysis of antiproton film taken by the Brookhaven National Laboratory 80-in. hydrogen bubble chamber. The cross section of the elastic scattering was 14.7 ± 1.5 mb. The angular distribution showed a dip in the region of −t≈0.6 (GeV/c)2 and a secondary maximum at −t≈0.8 (GeV/c)2.
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The differential asymmetry ratio for the process γ+n→p+π− was measured at 90° in the center-of-mass system and for incident photon energies from 352 to 550 MeV. The observed asymmetries are larger than the values predicted from the theory by Berends, Donnachie, and Weaver. A smaller M1- amplitude gives better agreement between the experiment and the theory.
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For the reaction γ+p→γ′+p′ (proton Compton effect), we have measured the ratio dσIIdσ⊥ between the cross sections for linearly polarized photons, using the coherent bremsstrahlung beam of the Frascati electron synchrotron. At 90° in the c.m. system and in the photon energy region 300≤K≤335 MeV, we find dσIIdσ⊥=2.1−0.4+0.5. In the absence of theoretical predictions based on the dispersive theory in this energy region, this result is compared with the values obtained using an isobaric model, taking into account various possible intermediate states.
Axis error includes +- 0.0/0.0 contribution (?////).
We have studied nonstrange p¯−p interactions observed in 7000 pictures of the 80-in. Brookhaven National Laboratory hydrogen bubble chamber exposed to an antiproton beam with a momentum of 6.94 BeVc. The total cross section was measured to be 58.7±2.8 mb, and the elastic interaction cross section 14.2±1.2 mb. The elastic differential cross section for four-momentum transfers (−t)≤0.3 (BeVc)2 is well described by the exponential form dσeldt=(dσdt)t=0ebt, where b=13.1±1.1 (BeVc)−2. The single-pion production cross section is 4.0±0.9 mb. This channel proceeds 70% through resonance formation. N*(1238) isobar and anti-isobar formation dominates pion production in four- and six-pronged events; the double-isobar formation cross section in the final state pπ+p¯π− is 1.35±0.2 mb. Isobar production was observed to be consistent with the predictions of a dominant one-particle-exchange process. The pion-annihilation process, which has a cross section of 25±5 mb, shows substantial pion resonance formation.
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The reactions pp → NN π are studied at 19 GeV/ c and analysed in terms of the amplitudes with the low mass N π system in isospin states 1 2 and 3 2 respectively. The I − 1 2 cross section is compared with the corresponding one in π p→ ππ N at 8 GeV/ c .
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The inelastic scattering of muons has been measured using positive muons of momentum 10 GeV/c incident upon a liquid-hydrogen target. We present values of the differential cross section and of the virtual photon-photon absorption cross section for |q| in the range 0.05 to 1.2 (GeV/c)2 and for equivalent photon laboratory energies of 0.6 to 6.5 GeV.
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