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We report the result of a brief experiment to measure the cross section for photoproduction of Jψ(3100). At a mean energy of 55 GeV we find this cross section per nucleon to be 37.5 ± 8.2 (statistical) ± 4 (systematic) nb. The result establishes the previously indicated rise in Jψ photoproduction on protons above 20 GeV and suggests that the rise has occurred by 55 GeV.
CROSS SECTION PER NUCLEON DERIVED FROM DEUTERIUM DATA ASSUMING INCOHERENT PART OF T DISTRIBUTION HAS EXPERIMENTAL SLOPE OF 1.8 +- 0.4 GEV**-2, 6 PCT COHERENT PART CALCULATED WITH KNOWN DEUTERIUM WAVE FUNCTION AND NEGLECTING SHADOWING. The mean P quoted in the table assumes the J/PSI energy equals the photon energy.
The total cross section of hadron photoproduction on C, Cu and Pb nuclei is measured for six energy values in the range 12–30 GeV. The obtained cross-section values for C and Cu nuclei have a weak energy dependence at high energies (above 20 GeV). The cross section for the Pb nucleus is somewhat higher in comparison with that expected, and energy dependence is not observed. The A -dependence of the effective number of hadrons agrees with VDM predictions.
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A-EFFECTIVE/A = SIG(GAMMA A)/(Z*SIG(GAMMA P) + (A-Z)*SIG(GAMMA N)) WHERE SIG(GAMMA P) = (98.7 +- 3.6) + (65 +- 10)/SQRT(P) MUB, SIG(GAMMA N) = SIG(GAMMA P) - (18.3 +- 6.1)/SQRT(P) MUB AND A IS 12, 64 AND 207 FOR THESE NUCLEI.
The photon total cross section on protons has been measured with high precision in the Fermilab tagged-photon beam for photon energies from 18 to 185 GeV. The cross section decreases to a broad minimum near 40 GeV, and then rises by about 4 μb over the remainder of the range. A ρ+ω+ϕ vector-dominance model (normalized to low-energy data) falls below the high-energy results by 2 to 6 μb, suggesting a contribution from charm-anticharm states.
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We have measured total hadronic photoproduction cross sections on carbon, copper, and lead. Tagged-photon energies ranged from 20 to 185 GeV for copper and from 45 to 82 GeV for carbon and lead. The energy and A dependence of shadowing were computed by comparing these results to the hydrogen cross section as measured nearly simultaneously with the same apparatus. We observed somewhat more shadowing than did most experiments at lower photon energies.
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Measurements of the photoproduction processes γρ→ρ+n and γρ→ρ-Δ++ (1236) are reported in the energy range 2.8 to 4.8 GeV. The data show shrinkage of the differential cross section in this energy region for the process γρ→ρ-Δ++ (1236); no shrinkage is observed for the ρ+n process. The energy dependences of the ρ+n and ρ-Δ++ (1236) total cross sections are much steeper than current model prediction. The ρ spin density matrices for each process are also presented.
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SLOPE AND INTERCEPT OF D(SIG)/DT.
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The elastic photoproduction cross sections for ρ and ϕ mesons from protons have been measured from 30 to 180 GeV. The energy dependences agree well with predictions made by using vector-meson dominance and an additive quark model. The ρ cross section is approximately constant with energy while the ϕ cross section rises from 0.5 to 0.7 μb with increasing energy.
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The elastic photoproduction of four pions has been studied at incident photon energies between 2.8 and 4.8 GeV. Production cross-sections are presented and an analysis of the angular decay correlations is also described, indicating a large 1− contribution in both final states, π+ π− π+ π− and π+ π− π0 π0. A quantitative understanding of these and other available 4π photoproduction data in terms of the ρ′(∼1.2GeV) and the ρ′(∼1.6) is presented.
WITH OMEGA/RHO DECAY PARAMETRIZATION.
WITH OMEGA/A1 DECAY PARAMETRIZATION.
Elastic ω-meson photoproduction on protons has been measured from 46 to 180 GeV. The cross section is approximately constant with photon energy and averages 1.10 ± 0.08 μb. The t dependence of the differential cross section is consistent with A exp(bt), where b=8.4±0.7 GeV−2. The photon-omega coupling constant, obtained from a normalization of hadron elastic-scattering cross sections to the photoproduction data of this experiment (with use of vector-meson dominance and an additive quark model), is γω24π=5.4±0.4.
THE QUOTED STATISTICAL ERRORS INCLUDE THE UNCERTAINTY IN THE CORRECTION FOR INELASTIC EVENTS. AVERAGE CROSS SECTION IS 1.10 +- 0.08 MUB.
EXPONENTIAL FIT TO DIFFERENTIAL CROSS SECTION.
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