From an experiment done with the CERN Omega spectrometer, triggered by a fast forward proton device, we present results on the differential cross section d σ d u for π − p backward elastic scattering. The d σ d u distribution agrees with an A e Bu law. The compilation of existing results shows a discrepancy between results but the ( d σ d u ) u=0 data fit perfectly an s 2 α 0 −2 dependence, as predicted by a single Δδ Regge trajectory exchange. A search for the reaction π − p → d p , with a fast forward deuteron, which can be produced by a double-baryon exchange mechanism, gives cross-section upper limits of ∼1% of the backward elastic cross section.
UMIN IS 0.0446 GEV**2.
UMIN IS 0.0333 GEV**2.
D(SIG)/DU FITTED FOR 0 < -U < 0.75 GEV**2 TO GIVE SLOPE/INTERCEPT.
In π − p interactions at 9 GeV/ c and 12 GeV/ c , the forward production of N ∗ 1680 and N ∗ 1520 has been observed with features of nucleon exchange. The production of Δ1232 is strongly suppressed.
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SLOPE ABOUT 6 GEV**-2 FOR SMALL U AND EVIDENCE FOR CHANGE OF SLOPE NEAR -U = 0.15 GEV**2.
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We have carried out high-statistics measurements of inclusive π0 and γ-ray spectra from p¯p annihilation at rest. From the monochromatic peaks in the π0 spectra, we derive the yield (or its upper limit) of the reaction p¯p→π0M for M=φ, η’, ω, ρ0, η, and π0. The same quantity was independently obtained from the γ-ray spectra, which included some π0’s that were mistaken as single γ rays due to the limited granularity of the γ detector. Taking the monochromatic peaks in the γ-ray spectra as being due to prompt γ rays, we also derive the upper limit for p¯p→γM.
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Using modularized NaI(Tl) detectors, we carried out a high statistics measurement of inclusive γ-ray, π0, and η spectra, and determined the branching ratios or upper limits of Pontecorvo reactions p¯d→π0n, π0Δ0, ηn, and ηΔ0 from the corresponding monochromatic peaks in them. The obtained branching ratios are B(p¯d→π0n)=(1.03±0.41)×10−5, B(p¯d→π0Δ0)=(4.67±1.66)×10−5, B(p¯d→ηn)<8.94×10−6 (95% C.L.), and B(p¯d→ηΔ0)<6.49×10−5 (95% C.L.).
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SIG(C=BACKWARD) = SIG(-UP<1 GEV**2)/(1-EXP(-SLOPE)). UP DISTRIBUTION OF EVENTS HAS A PERFECT EXPONENTIAL SHAPE.
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The differential asymmetry ratio for the process γ+n→p+π− was measured at 90° in the center-of-mass system and for incident photon energies from 352 to 550 MeV. The observed asymmetries are larger than the values predicted from the theory by Berends, Donnachie, and Weaver. A smaller M1- amplitude gives better agreement between the experiment and the theory.
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The angular dependence of the asymmetry for negative-pion photoproduction on neutrons by linearly polarized photons has been measured for photon energies 260, 300, 350, 400, 450, and 500 MeV at center-of-mass angles 60°, 75°, 90°, 150°, and 120°. The results are compared with theoretical models of low-energy single-pion photoproduction. The observed asymmetry below 400 MeV shows good agreement with predictions of dispersion-theoretical models by Berends, Donnachie, and Weaver and by Schwela. The asymmetry values in the 400-500 MeV energy region suggest that smaller M1− amplitude is more favorable.
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We have analyzed backward meson production in the reaction π − p → p f π + π − π − at 9 GeV/ c and 12 GeV/ c incident π − momenta, from an experiment performed at the CERN Ω Spectrometer using a fast proton (p f ) trigger device. We find strong production of quasi-two-body processes N ∗ ϱ and N ∗ f with a production mechanism consistent with u -channel nucleon exchange. At a lower level, we observe N ∗ π processes with a 3-body baryon decay through Δ(1232)π. In the (3π) − system, we find evidence for A 1 − and clear A 2 − backward production with similar cross sections (≈0.5 μb).
No description provided.
U-HELICITY JACKSON FRAME.
U-HELICITY JACKSON FRAME.