Differential cross sections for the reaction γ+p→n+π+ are presented for incident photon energies between 1.2 and 3 GeV and pion center-of-mass production angles of 15 to 50 deg.
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The reaction γ+p→π++n has been investigated for photon energies between 1.2 and 3 GeV and pion c.m. angles from 2.5 to 15°. The cross section is strongly peaked in the forward direction and shows resonance structure in the region of the N32*(1920) and N12*(2190).
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The reactions π−p→π−p and π−p→π−π0p for 1.7 GeV/c incident π− have been studied, in 3094 and 2244 interactions respectively, identified from 10 106 two-prong events measured in film exposed at the BNL 20 in. hydrogen bubble chamber. The differential elastic-scattering cross-section is found to show a first and second diffraction peak and a first diffraction minimum with indications of a second minimum and onset of a third maximum. The experimental curve has been fitted by a black-dise optical-model formula with radius (0.80±0.03) fm and by a differential cross-section computed from the Dirac equation depending on two ranges, 0.7 fm attractive imaginary and 0.4 fm repulsive. The dominant mode (∼40%) of the π−π0p production is through the two-body channel, π−p→ϱ−p. We find the following cross-sections: σ(π−p→π−p mb, σ(π−p→π−p mb. The differential rhomeson production cross-section shows a diffraction peak having a dependence (dσ/dt)(π−p→ϱ−p)=[(2.5±0.2) exp [(−5.3±0.5)t]] mb/(GeV/c)2, wheret is the squared four0momentum transfer between incoming and outgoing proton in (GeV/c)2, and a second diffraction maximum. It has been fitted by an optical-model formula for a bright ring of radius 0.80 fm and ring thickness 0.25 fm. The cross-section for σ(π−p→π−p was found to be (0.36±0.04) mb. From the inelastic data the Chew-Low dipion scattering cross-section has been computed, using various form factors. A form factor of unity is found to be acceptable.
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The cross sections for the two antiproton-proton annihilation-in-flight modes, ˉp + p → π+ + π- ˉp + p → k+ + k- were measured for fifteen laboratory antiproton beam momenta ranging from 0.72 to 2.62 GeV/c. No magnets were used to determine the charges in the final state. As a result, the angular distributions were obtained in the form [dσ/dΩ (ΘC.M.) + dσ/dΩ (π – ΘC.M.)] for 45 ≲ ΘC.M. ≲ 135°. A hodoscope-counter system was used to discriminate against events with final states having more than two particles and antiproton-proton elastic scattering events. One spark chamber was used to record the track of each of the two charged final particles. A total of about 40,000 pictures were taken. The events were analyzed by measuring the laboratory angle of the track in each chamber. The value of the square of the mass of the final particles was calculated for each event assuming the reaction ˉp + p → a pair of particles with equal masses. About 20,000 events were found to be either annihilation into π ±-pair or k ±-pair events. The two different charged meson pair modes were also distinctly separated. The average differential cross section of ˉp + p → π+ + π- varied from ~ 25 µb/sr at antiproton beam momentum 0.72 GeV/c (total energy in center-of-mass system, √s = 2.0 GeV) to ~ 2 µb/sr at beam momentum 2.62 GeV/c (√s = 2.64 GeV). The most striking feature in the angular distribution was a peak at ΘC.M. = 90° (cos ΘC.M. = 0) which increased with √s and reached a maximum at √s ~ 2.1 GeV (beam momentum ~ 1.1 GeV/c). Then it diminished and seemed to disappear completely at √s ~ 2.5 GeV (beam momentum ~ 2.13 GeV/c). A valley in the angular distribution occurred at cos ΘC.M. ≈ 0.4. The differential cross section then increased as cos ΘC.M. approached 1. The average differential cross section for ˉp + p → k+ + k- was about one third of that of the π±-pair mode throughout the energy range of this experiment. At the lower energies, the angular distribution, unlike that of the π±-pair mode, was quite isotropic. However, a peak at ΘC.M. = 90° seemed to develop at √s ~ 2.37 GeV (antiproton beam momentum ~ 1.82 GeV/c). No observable change was seen at that energy in the π±-pair cross section. The possible connection of these features with the observed meson resonances at 2.2 GeV and 2.38 GeV, and its implications, were discussed.
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The external beam of the 2.5 GeV-electron-synchrotron has been used to measre elastic electron proton scattering at four-momentum-transfers between 15 and 50 fm −2 . By combining these results with measurements at small angles at DESY, we have obtained the electric and magnetic form factors separately. Their ratio shows a deviation from the scaling law.
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The cross section for photoproduction of single π+ from hydrogen has been measured at laboratory angles of 110°, 127.5° and 152°, between 0.9- and 3.2-GeV incident photon energy. Measurements have been made with approximately 15% statistical accuracy at about 40 photon energies at each angle. The results agree well with the previous Caltech data of Thiessen. The cross section shows a rapid drop with increasing energy with superimposed bumps or shoulders corresponding to the N(1688), Δ(1920), and Δ(2420). A shallow minimum is observed at the N(2190) resonance.
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We present experimental results on K + d interactions from 865 to 1585 MeV/ c incident beam momentum. We report measurements of several K + d partial cross sections and calculate most of the others using relations derived from isospin conservation and data from other experiments. The most striking feature of the cross section data is the abrupt rise of the total single-pion-production cross section near 1000 MeV/ c . We extract isospin-0 KN partial cross sections and find a rapid quasi-two-body reaction KN → K ∗ N . As in the case of the isospin-1 K + N system, it appears that the structure around 1200 MeV/ c in the total cross section for the isospin-0 K ∗ N system is well reconstructed by the sum of three smoothly varying channel cross sections σ 0 (KN), σ 0 (KN π ) and σ 0 (KN ππ ). We study thereaction KN → K ∗ N near threshold and find that the production and decay angular distributions can be interpreted in terms of t -channel phenomena, specifically a superposition of ω, ϱ, and π exchange. As is true of the isospin-1 KΔ and K ∗ N final states, the isospin-0 K ∗ N state has a behavior near threshold which is not very different from its behavior at much higher energy.
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We present results on the differential cross sections for the process K + n → K 0 p extracted from the reaction K + d → K 0 pp measured at 13 momenta between 0.64 and 1.51 GeV/ c .
THESE TOTAL CROSS SECTIONS WERE PRESENTED WITH MORE EXPERIMENTAL DETAILS IN G. GIACOMELLI ET AL., NP B37, 577 (1972).
REACTION HAS A SPECTATOR PROTON. THESE ARE NOT FREE NEUTRON CROSS SECTIONS. A 250 MEV/C MOMENTUM CUT IS APPLIED TO THE SPECTATOR MOMENTUM AND D(SIG)/DOMEGA THEN NORMALIZED TO THE UNCUT TOTAL CROSS SECTION FOR K+ DEUT --> K0 P P.
We present experimental results on the K + n → K + n differential cross sections measured in deuterium at 13 momenta between 0.64 and 1.51 GeV/ c .
REACTION HAS A SPECTATOR PROTON. WHILE SOME DEUTERIUM CORRECTIONS HAVE BEEN APPLIED, THESE DATA ARE NOT DIVIDED BY THE DEUTERIUM FORM FACTOR APPEARING IN THE IMPULSE APPROXIMATION.
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