We have analyzed 2560 events in the final-state K O 1 K O 1 n produced in π − p interactions at 5, 7 and 12 GeV/ c . We observe the S ∗ (1070), f O and A 2 decaying into K O 1 K O 1 . Resonance parameters, cross sections, and branching ratios are given.
Cross section times branching ratio.
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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We measured the π0 photoproduction differential cross section at 180° for a range of incident photon energies between 650 and 1750 MeV. The cross sections are dominated by the D13(1525), D15(1688), and F37(1920) resonances.
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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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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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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).
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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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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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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