In a 48 000-picture exposure of the Fermilab 30-inch hydrogen bubble chamber to a 205 GeV/ c π − beam, we have measured 169 events of the reaction, π − p → π − π + π − p, with a cross section of 635 ± 61 μ b. This reaction proceeds almost entirely via low mass π − → 3 π and p → p ππ dissociation. Factorization is satisfied for p → pππ dissociation in πp and pp interactions.
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The process pn → pp π − is studied in pd collisions at 11.6 GeV/ c . A broad low-mass enhancement of p π − is found in the diffractive reaction pn → p(p π − ) with a cross section slightly smaller than that of a similar analysis at 7.0 GeV/ c . The non-diffractive reaction pn → (p π − )p shows some evidence for resonance production and its cross-section dependence on energy is characteristic of meson exchange. Samples of mass, momentum transfer, and decay angular distributions are compared with the predictions of a double Regge model and a reggeized one-pion exchange model. Using in addition information from the reactions pp → pp π 0 , pp → pn π + at 12.0 GeV/ c , an isospin analysis of the single pion production reaction from nucleon-nucleon scattering, N 1 N 2 → N 3 (N 4 π ) is presented.
NON-DIFFRACTIVE CHARGE-EXCHANGE CROSS SECTIONS.
We report on the measurement of asymmetries in the single-pion photoproduction reactions γp→nπ+, γp→pπ0, and γn→pπ−, induced by linearly polarized photons of energies from 610 to 940 MeV. The experiment was carried out using the back-scattered laser beam and the 82-in. dubble chamber at SLAC. We compare the new data with predictions from a partial-wave analysis.
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A partial-wave analysis of the (K ππ ) 0 system produced in the charge exchange reaction K − p →( K 0 π + π − ) n has been made in the mass range 1.04 ⩽ M (K ππ ) < 1.56 GeV c data at 8, 10 and 16 GeV/ c . It was found that in about 2 3 of the cases, the (K ππ ) 0 system is produced in states of unnatural spin-parity, namely J P = 0 − and 1 + ; the rest is in the natural spin-parity state J P = 2 + state is consistent with being all K ∗ (1420). The unnatural spin-parity states are produced mostly (∼ 80% of the events) by natural parity exchange. The facts that unnatural spin-parity states are produced in this non-diffractive channel, with J P = 1 + dominant, and that the exchange responsible for their production is mostly of natural parity, are similar to what was found for the charged (K ππ ) − system in the diffractive reaction K − p→(K ππ ) − p. However, the absolute value and the energy dependence of the cross sections are very different in the two cases.
CORRECTED FOR UNSEEN AK0 DECAY MODES.
ACTUALLY CROSS SECTIONS FOR PRODUCTION IN MASS REGION 1.04 < M(AK0 PI+ PI-) < 1.56 GEV IN THE STATES JP = 1+, 2+ AND 0- RESPECTIVELY.
Cross sections, differential cross sections, and hyperon polarization results are presented for the reactions K¯0p→Λπ+ and K¯0p→Σ0π+ in the momentum interval 1 to 12 GeV/c. Emphasis is placed on the comparison of Λ and Σ channels, and on the momentum dependences of the data. In particular, the Λ polarization data are consistent with being independent of energy above 2 GeV/c; and the slopes of the forward cross sections are found to increase toward the slope values for the line-reversed reactions πp→K(Λ,Σ) as energy increases.
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RESONANCE REGION CROSS SECTIONS.
We have investigated the pp elastic scattering at the CERN Intersecting Storage Rings (ISR). We report results for centre-of-mass scattering angles between 30 and 100 mrad and for centre-of-mass energies of 23.5,30.7, 44.9 and 53 GeV. The elastic differential cross-section shows a diffraction-like shape with a sharp minimum at about t = −1.4 GeV 2 .
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We have measured the cross section, the distribution of scattering angles, and the distribution of noncoplanarity angles for electron-positron elastic scattering at 5 GeV c. m. energy. An analysis based on 230 events with scattering angles between 50 and 130° yields a ratio of the experimental to theoretical quantum-electrodynamic cross section of 1.03 ± 0.09. The scattering-angle and noncoplanarity-angle distributions are also found to be in excellent agreement with the quantum-electrodynamic predictions.
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A spin and parity decomposition is presented of the (π+π+π−) final state formed opposite a proton by incident 13-GeV/c π+ mesons. The A3 enhancement is identified as the 2− amplitude decaying to f0π+ via an S wave. A change in relative phase is noted between the 2−S amplitude and the other principal contributions; this is not incompatible with analyses of the (3π)− system. The method employs the University of Illinois three-body partialwave analysis program.
A3+ DEFINED AS JP=2- S-WAVE.
Differential cross sections for the elastic scattering of K + mesons on protons have been measured at 12 lab momenta between 130 and 755 MeV/ c using a hydrogen filled bubble chamber. The results are consistent with a repulsive S-wave nuclear force. A phase-shift analysis yielded the following values of the low-energy parameters: a S 1 2 =(0.309±0.002) fm , r S 1 2 =(0.032±0.02) fm a P 1 2 =(0.021±0.002) fm , a P 3 2 =(0.013±0.001) fm 3
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The missing mass spectrum opposite the proton in a 750 000 picture exposure, 13 GeV/ c π + p bubble chamber experiment, is investigated in two and four pion channels for structures observed or denied by boson spectrometers at the same energy in the reaction π − p→X − p.
BREIT-WIGNER FITS.
FOR 1.6 < M(4PI) < 1.8 GEV.
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