Upper limits are presented for the differential cross section in the reactions π−p→K+Σ− and π−p→K+Y*−(1385) with small momentum transfer from π− to K+.
EXTRAPOLATED TO T=0 ASSUMING SLOPE IS 5 GEV**-2.
ISOTROPIC ANGULAR DISTRIBUTION ASSUMED IN GIVEN T-RANGE.
We report on a measurement for the branching-ratio X 0 → 2γ X 0 ar all. Our result is X 0 → 2γ X 0 → all = (2.9 ± 0.9)% .
BY COMPARISON WITH THE KNOWN ETA PRODUCTION CROSS SECTION.
Using an 11-GeV bremsstrahlung beam and the SLAC 20-GeV spectrometer, we have measured K + missing mass spectra from hydrogen and deuterium at five angles with momentum transfer squared ranging from 0.025 to 0.46 GeV 2 . Steps in the spectra as a function of missing mass were found corresponding to production of Λ , Σ , Σ 1385 + Λ 1405 and Λ 1520 . The ratio Σ − and Σ 0 production is not consistent with pure isotopic spin 1 2 in the t -channel for the reaction γ N→K + Σ . The cross sections for γ N → K + Σ 1385 compared with γ N→ πΔ violate an SU(3) prediction.
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Differential cross section for π + photoproduction on hydrogen have been measured over a photon energy range from 220 to 425 MeV and for pion c.m. angles between 15° and 70°. The pions have been analysed in angle and momentum by a magnetic spectrometer.
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Differential cross sections for neutral-pion photoproduction on hydrogen in the region of the first resonance have been measured by two independent experiments detecting the recoil protons. The results of both measurements have been combined into one set of cross sections covering the photon energy range from 200 to 440 MeV at pion c.m. angles between 50 and 160 degrees.
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The reactions γA→π±A* have been studied at four-momentum transfers −t<~0.5 GeV2 for seven elements ranging from hydrogen to lead. Exclusion-principle suppression is clearly visible at small-momentum transfer. Neither the A dependence nor the energy dependence of the cross sections agrees with the predictions of the vector-dominance model. The ratio of π−π+ production requires equal spatial distributions for the protons and neutrons in nuclei. Some K+ data are also presented.
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Cross sections for the reactions γp→K+Λ and γp→K+Σ0 have been measured at squared four-momentum transfer (−t) from 0.005 to 2 GeV2, at photon energies 5, 8, 11, and 16 GeV. For −t>0.2 GeV2 each of the K+ cross sections is about ⅓ of the π+n photoproduction cross section, having nearly the same energy and momentum-transfer dependence. The K+ cross sections fall off at small |t|, however, in contrast to the sharp forward spike seen in π+n; this leads to a disagreement with an SU(3) prediction for −t<0.1 GeV2. The ratio of K+Σ0 to K+Λ cross sections is typically between 0.5 and 1.0.
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Over 100 unambiguous π − + p → Λ + Λ + n events have been observed in a magnet spark chamber. The data provide good evidence for peripheral production of Λ Λ and n Λ (via meson exchange) and against peripheral n Λ (double baryon exchange). No resonances in the Λ Λ system are observed. Angular distributions and Λ( Λ ) polarizations are analysed.
Axis error includes +- 0.0/0.0 contribution (?////Corrected for neutral decays, absorption).
The cross section for γp→π−Δ++(1236), measured at 5, 8, 11, and 16 GeV from nearzero momentum transfer to -1 GeV2 (-2 GeV2 at 16 GeV), rises from small t to a maximum near −t=mπ2, then falls as e12t out to −t≈0.2 GeV2, after which it becomes roughly equal in slope and magnitude to the single π+ photoproduction cross section (e3t). At fixed t, the cross section varies as k−2, where k is the laboratory photon energy. The results do not agree well with the simple vector-dominance model.
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