We have made a study of the coherent reaction K + d → K 0 π + d at 2 GeV/ c , using data obtained in the Lawrence Berkeley Laboratory 25 inch bubble chamber. The cross section for this reaction is 324 ± 25 μ b, after correction for invisible K 0 decays. This reaction is dominated primarily by vector exchange. We determine the parameters of the ω trajectory to be α ω = (0.33 ± 0.04) + t .
The reaction π−p→K0K−p has been measured from 50 to 175 GeV/c. The production characteristics of the A2 have been analyzed. We find spin and t dependence similar to lower energies, but the cross section falls rapidly with energy. In a Regge description of π−p→A2−p our data imply a rather small Pomeron-exchange component.
We present a summary of the physics results from an experimental study of the reaction π−p→π−π+n at 100 and 175 GeV/c incident-beam momentum. Our data show the continuing dominance of one-pion exchange in these reactions with the characteristic 1Plab2 momentum dependence. We extract the pion Regge trajectory from our data on π−p→ρ0n and study the zero structure of the ππ differential cross section up to sππ=12 GeV2.
The reaction π−p→X−p, X−→ηπ−, η→γγ has been studied in an optical spark-chamber experiment at the Argonne ZGS (Zero Gradient Synchrotron) at a beam momentum of 6.0 GeV/c and with 0.27≤|t|≤0.42 (GeV/c)2. The ηπ mass spectrum contains about 1400 events in the mass range 0.80<M(ηπ)<1.55 GeV/c2, and is dominated by approximately 1000 events of the type A2−→ηπ−. No structure is discernible within the A2 mass spectrum for an experimental resolution of 7.1 MeV/c2 [16.7 MeV/c2 FWHM (full width at half maximum)]. A single D-wave Breit-Wigner distribution fits the data with a high confidence level, yielding for the A2 the parameters M0=1.323±0.003 GeV/c2 and Γ0=0.108±0.009 GeV/c2. The angular distribution of the decay A2−→ηπ− is analyzed and the resultant density matrix elements have the values ρ11=0.45±0.02, ρ1−1=0.45±0.04, and ρ00=0.09±0.04. All other elements are consistent with zero. Finally, the missing-mass spectrum in the region of the A2 is presented. A signal of 230 events above background per 5-MeV/c2 interval is observed at the A2 peak, with a signal to background ratio of greater than 1:1. A single D-wave Breit-Wigner distribution together with a quadratic background fits the data well, with the parameters for the A2 being M0=1.324±0.003 GeV/c2 and Γ0=0.104±0.009 GeV/c2. Both A2 mass spectra are incompatible with the dipole shape.
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