The differential cross section for π+ photoproduction has been determined at 19 points, at center-of-mass angles from 30 to 150 deg, and at photon energies from 162 to 225 MeV. The data are concentrated near 180 MeV, where a full angular distribution has been determined. The relative values of the cross sections are accurate to 5% or better, and the absolute normalization is accurate to 4%. The experiment provides data of improved accuracy which are in general consistent with previous results. The extrapolation to threshold gives a value for (k*p*)(dσdΩ)* at threshold of 16.1±0.7 μb/sr, where k*, p*, and (dσdΩ)* are the photon energy, pion momentum, and differential cross section, all in the center-of-mass system.
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The cross section of the process e+ e- ---> eta gamma has been measured in the 600-1380 MeV c.m. energy range with the CMD-2 detector. The following branching ratios have been determined: B(rho ---> eta gamma) = (3.28 +- 0.37 +- 0.23) 10^{-4}, B(omega ---> eta gamma) = (5.10 +- 0.72 +- 0.34) 10^{-4}, B(phi --> eta gamma) = (1.287 +- 0.013 +- 0.063) 10^{-2}. Evidence for the rho'(1450) ---> eta gamma decay has been obtained for the first time.
The measured Born cross section for the ETA GAMMA final state.
Accurate measurements have been made of the π−π+ photoproduction ratio on deuterium, in the gammaray energy range 165-210 MeV, for several angles: 155°, 125°, 90° (center-of-mass system) and along Baldin's kinematical line. These last data are new contributions: π−π+=1.20±0.03 averaged between 165 and 180 MeV. The others are improvements of the accuracy of previous data. The comparison with Ball's theory, corrected for taking into account the I=12 phase shifts, gives for the coupling constant Λ for γ−π−p the value: 0.25<+Λe<0.75.
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This paper reports measurements of the total cross section from 150 to 240 Mev of incident photon energy and measurements of the 135° differential cross section from 180 to 215 Mev. A Monte Carlo evaluation of the γ-ray telescope efficiency by means of an electronic digital computer is outlined. The combined results indicate that a small but finite amount of S-state production occurs and that the angular distribution becomes flatter as the energy decreases. The latter effect is associated with production in unenhanced P-states and with a lack of electric quadrupole production. Good agreement with the Chew-Low theory is demonstrated by a comparison between the photoproduction and scattering of π0-mesons, where the scattering cross sections are derived from those for charged mesons by charge independence.
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Absolute differential cross sections for the photoproduction of pions of 33.8-MeV laboratory kinetic energy from protons were measured at eight angles between 29.5 and 146.1° in the center-of-mass system. The over-all absolute accuracy is 4%, while the relative accuracy within the angular distribution is 3%. Comparison is made to various theoretical calculations, with and without inclusion of the effect of a γ−π−ρ-meson coupling. Existing calculations based on dispersion theory give only fair agreement with the data.
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At the Bonn 500 MeV electron synchrotron the reaction γ+р=р+π0 has been studied for energies belowEγ=222 MeV using nuclear emulsions inside a low-pressure hydrogen gas target to detect the recoil protons. Angular distributions of the neutral pion were obtained for the energiesEγ=159, 180, 206 MeV (or, alternatively,Eγ=166, 195 MeV with a different grouping of tracks). In general they are in good agreement with other experimental data in the same energy region, and join also smoothly to recent measurements at higher energies. The agreement with recent theoretical approaches is fairly good in the coefficientsA andB of the expansion dσ/dΩ=A+B cos Ψ+C cos2 Ψ, but the theoretical values of the coefficientC are definitely too positive.
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The cross-sections σ(Eγ,ϑ ) for the reaction pγ→ n+ have been measured near threshold as a function of photon energy and at four angles. See Table I. These results combined with previously known data, have given a fairly complete and accurate description of σ(Eγ,θ) between the limits 30°≤θ≤180° and 170≤ Eγ 270 MeV. See Table II and Pig. 2. Writing σ(Eγ,θ) = W·a0 + a1 cos θ + a2 cos2 θ× withW= ηωl +(μ/Ei)ξ −1·l + (μ/E f )ω×−1 (see formula (5)) the experimental data indicate that (Table III) a0 is constant up to about Eγ ≃ 260 MeV; and that (Table V) the three ai coefficients analyzed in terms ofS andP waves give a very small spin flippingP-amplitudeK. The presumption that theS amplitudeE 1 ismainly due to the gauge invariance requirement is definitely not consistent with the data (see Table IV). A discussion based on the Kroll and Rudermann theorem leads to the conclusion that this inconsistency may be eliminated if allowance is made for the contribution of fairly large nucleon recoils. However, it turns out that only the changing sign part of these recoils is really large and apparently so up to terms of order higher than μM. The amount of the recoil at threshold is estimated and consequently a value for the pspv interaction constant is derived.
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perimental analysis of the process is presented. Theσ(−)/σ(+) ratio has been measured in the photon energy interval (170÷230) MeV and Lab. angles 45°, 75°, 105°, 150°. The results are interpreted on the base of the impulse approximation with the aim of getting information on the processhv+n →π −+p.
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Axis error includes +- 7/7 contribution (/LUMINOCITY, RADIATIVE CORRECTIONS, NUCLEAR ABSORPTION AND DECAY IN FLIGHT).
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