Photoproduction is studied at 2.8 and 4.7 GeV using a linearly polarized monoenergetic photon beam in a hydrogen bubble chamber. We discuss the experimental procedure, the determination of channel cross sections, and the analysis of the channel γp→pπ+π−. A model-independent analysis of the ρ0-decay angular distribution allows us to measure nine independent density-matrix elements. From these we find that the reaction γp→pρ0 proceeds almost completely through natural parity exchange for squared momentum transfers |t|<1 GeV2 and that the ρ production mechanism is consistent with s-channel c.m. helicity conservation for |t|<0.4 GeV2. A cross section for the production of π+π− pairs in the s-channel c.m. helicity-conserving p-wave state is determined. The ρ mass shape is studied as a function of momentum transfer and is found to be inconsistent with a t-independent Ross-Stodolsky factor. Using a t-dependent parametrization of the ρ0 mass shape we derive a phenomenological ρ0 cross section. We compare our phenomenological ρ0 cross section with other experiments and find good agreement for 0.05<|t|<1 GeV2. We discuss the discrepancies in the various determinations of the forward differential cross section. We study models for ρ0 photoproduction and find that the Söding model best describes the data. Using the Söding model we determine a ρ0 cross section. We determine cross sections and nine density-matrix elements for γp→Δ++π−. The parity asymmetry for Δ++ production is incompatible with simple one-pion exchange. We compare Δ++ production with models.
FROM QUOTED TOPOLOGICAL CROSS SECTIONS. 1.44 GEV CROSS SECTION PUBLISHED PREVIOUSLY.
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NO TMIN CORRECTION HAS BEEN MADE.
The TPC/Two-Gamma Collaboration has measured the inclusive cross section for production of charmed D ∗± mesons in photon-photon collisions. The reaction utilized was e + e - →e + e - D ∗± X, with D ∗± →D O π +- , D O →K -+ π ± , and either zero or one outgoing e ± detected. The result, σ(e + e - → e + e - D ∗± X) = 74±26±19 pb , is in agreement with the quark parton mo del prediction for e + e - → e + e - c c , combined with a Lund model for the hadronization of the charmed quarks.
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In a 48 000-picture exposure of the Fermilab 30-inch hydrogen bubble chamber to a 205 GeV/ c π − beam, we have measured 169 events of the reaction, π − p → π − π + π − p, with a cross section of 635 ± 61 μ b. This reaction proceeds almost entirely via low mass π − → 3 π and p → p ππ dissociation. Factorization is satisfied for p → pππ dissociation in πp and pp interactions.
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The inclusive ϱ ° production cross section has been measured in the reaction π − p → π + π − X at 205 GeV/ c . We find σ ( ϱ ° ) = 13.5 ± 3.4 mb, with most of the production occuring in the central region. Assuming σ ( ϱ + ) ≈ σ ( ϱ − ) ≈ σ ( ϱ ° ), it is concluded that approximately one-third of the pions at this energy come from ϱ -decay.
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In 205 GeV / c π − p inelastic interactions, negative particles with transverse momentum greater than 1.0 GeV / c moving forward in the center of mass outnumber similar positive particles by a factor of 3.7 to 1, greatly in excess of the corresponding ratio for small transverse momentum. The asymmetry is reversed in the backward direction. The forward asymmetry is most prominent in 2-, 4-, and 6-prong interactions, but both forward and backward asymmetries are also substantial for higher multiplicity interactions.
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Diffractive dissociation of neutrons and N ∗ production are studied in the reaction π − n → π − π − p at 15 GeV/ c . The reaction is dominated by a broad, low-mass diffractive enhancement in the pπ − mass. Evidence is presented for the production of at least one N ∗ resonance in the mass region 1.4–1.8 GeV. Comparison with ISR data suggest that this N ∗ resonance is produced by pomeron exchange. The N ∗ production occurs predominantly at t ′ > 0.1 GeV 2 which suggests a different coupling from the usual diffractive reactions. The non-resonant diffractive background is compared with a double-Regge model and the statistical dissociation model.
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DEPENDENCE OF SLOPE OF D(SIG)/DT ON <P PI-> MASS. DATA FITTED OUT TO -TP=0.4 GEV**2, EXCEPT TO 0.2 GEV**2 FOR M < 1.2 GEV.
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Inclusive ϱ 0 production in γ p → ϱ 0 + anything is studied at 2.8, 4.7, and 9.3 GeV, using the SLAC linearly polarized backscattered laser photon beam and the 82 inch hydrogen bubble chamber. Over this energy range the inclusive inelastic ϱ 0 cross section rises from 6.0 μb to 20.5 μb. The multiplicity, i.e. the average number of μ 0 mesons per inelastic hadronic event, has an energy dependence consistent with 1n s .
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Charged-current neutrino and antineutrino interaction cross sections have been measured in the energy range 10 to 50 GeV using BEBC filled with a neon-hydrogen mixture. At these energies, σ/E was measured to be (0.73±0.08) 10−38 cm2/GeV per nucleon for neutrinos and (0.32±0.06) 10−38 cm2/GeV per nucleon for antineutrinos.
Axis error includes +- 9/9 contribution (NEUTRAL CURRENT EVENTS AND NEUTRAL HADRON INDUCED REACTIONS, LOSSES OF EVENTS WITH ONLY ONE VISIBLE CHARGED PARTICLE).
Axis error includes +- 9/9 contribution (NEUTRAL CURRENT EVENTS AND NEUTRAL HADRON INDUCED REACTIONS, LOSSES OF EVENTS WITH ONLY ONE VISIBLE CHARGED PARTICLE).
We have observed the π+π− decay of the ρ′(1600) in the production reaction γp→ρ′p at 20 GeV. Using a calculation which takes into account the interference of the ρ′ with the ρ(770) and a Drell background, we find good evidence that this resonance is a radial excitation of the ρ(770). The background interference strongly distorts the angular distributions predicted by a purely s-channel helicity-conserving production mechanism. We measure m0=(1.55±0.07) GeV/c2 and Γ0=(0.28−0.08+0.03) GeV/c2.
SLOPE VARIATION WITH M(PI+ PI-) IN THE RANGE 0.4 TO 2.5 GEV.
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Forty-seven charm events have been observed in an exposure of the SLAC Hybrid Facility bubble chamber to a 20-GeV backward-scattered laser beam. Thirty-seven events survive all the necessary cuts imposed. Based on this number the total charm cross section is calculated to be 63−28+33 nb.
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