We have studied the ratio R=[dσ(γd→π−pp)dt][dσ(γd→π+nn)dt]−1 at 8 and 16 GeV for momentum transfers |t| from about 0.001 to 1.3 GeV2. R is close to unity for |t|<mπ2, but falls very rapidly with increasing |t|, passing through ½ near |t|=0.1 GeV2 and having a minium value of about 13 near |t|=0.4 GeV2; it slowly increases at larger momentum transfers. These results are similar to those obtained in other laboratories at 3.4 and 5 GeV. This implies considerable interference between the isoscalar and isovector photon amplitudes.
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A spark-chamber experiment on the peripheral production of 9245 pion pairs by 12- and 18-GeV/c incident pions is reported and analyzed in terms of a one-pion-exchange model in which the final state at the nucleon vertex contains generally one or more pions. The relevant dynamics and kinematics appropriate to this problem are reviewed, and the experimental and analysis techniques giving good resolution and detection-bias correction are discussed in some detail. From the results, fair agreement is found between the data and the one-pion-exchange calculation of the ρ0 production cross sections and of the associated missing-mass spectra. The ρ0 is found to be consistent with a single peak, and no evidence of peak splitting is observed. A search for a narrow s-wave dipion resonance is made with negative results. Normalizing to the ρ0 meson, the s-wave π+π− scattering cross section is computed from the abundant low-dipion-mass events, giving a cross section falling smoothly from 50 mb (300 MeV) to about 20 mb (600 MeV). No evidence of an s-wave resonance is found in this range of energies. Below 450 MeV, the pion-pion scattering asymmetry favors backward scattering (by 2½ standard deviations), which is consistent with a negative and falling J=T=0 phase shift. The extrapolated forward-backward asymmetry and the s-wave cross section are both consistent with a J=T=0 phase shift near|90°| at about 750 MeV.
Dipion production cross section under RHO resonance. Errors are statistical only.
Dipion production cross section under RHO resonance. Errors are statistical only.
RHO0 cross section. Errors are statistical only.
The differential cross sections for single-π+ photoproduction from hydrogen have been measured over a range of momentum transfers from -2×10−4 to -2 (GeV/c)2, and photon energies from 5 to 16 GeV. The differential cross section increases by roughly a factor of 2 as the magnitude of the square of the momentum transfer decreases from 0.02 (GeV/c)2. The cross section falls approximately as exp(−3|t|) at large momentum transfers, with a similar momentum-transfer dependence of the cross section at all photon energies studied.
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