We have measured the cross section at 180° for K + p and K + n elastic scattering in the momentum range 1.0 to 1.5 GeV/ c . The K + n cross section was measured on deuterium and the K + p on hydrogen and deuterium. We were thus able to measure directly the difference between free nucleon (proton) scattering and bound nucleon (proton) scattering at large angles. This difference was found to be small and within our experimental accuracy the K + p(n) cross section should be equal to the K + p (free) cross section at 180°. We found no evidence for an s -channel resonance Z ∗ in either the K + p or K + n system. A comparison of our data and those of other groups with theoretical predictions is given.
DEUTERIUM TARGET. U IS ABOUT 0.1 GEV**2.
HYDROGEN AND DEUTERIUM TARGET DATA ARE IN GOOD AGREEMENT. THESE CROSS SECTIONS ARE A WEIGHTED AVERAGE.
The process e+ e- -> e+ e- Z/gamma* is studied with the OPAL detector at LEP at a centre of mass energy of sqrt(s) = 189 GeV. The cross-section times the branching ratio of the Z/gamma* decaying into hadrons is measured within Lorentz invariant kinematic limits to be (1.2 +/- 0.3 +/- 0.1) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and (0.7 +/- 0.2 +/- 0.1) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables s-hat, t-hat, and u-hat are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess e gamma -> e Z/gamma* are derived.
Measured values of the cross section times the branching ratio for the (Z0/GAMMA*) decay into hadrons within the restricted kinematic limits.
Differential cross-section dsig_ee/dm_qq.
Differential cross-section dsigma_ee/dsqrt(shat).
Differential cross sections and density-matrix elements in ρ− decay have been measured at 6 GeV/c for p¯p→π+ρ− and its line-reversed partner π−p→pρ− in the range tmin>t>−1.5 (GeV/c)2. The reactions satisfy line-reversal symmetry and the ρ− decay is consistent with isotropy for −t≲0.5 (GeV/c)2. For −t≳0.5 (GeV/c)2, the differential cross sections show a weaker t dependence, and the decays become anisotropic.
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FROM ROUGHLY EQUAL NUMBERS OF RHO- EVENTS AND BACKGROUND (CONSISTENT WITH ISOTROPY FOR BOTH REACTIONS).
Differential cross sections have been measured for p¯p→π−π+ (1) and its line-reversed partner π+p→pπ+ (2) in the range tmin>t>−1.5 (GeV/c)2 at 6 GeV/c. Clear structure is seen in the differential cross section for Reaction (1) at t∼−0.4 (GeV/c)2. However, this feature is quite different from the striking dip seen in (2) at t∼−0.15 (GeV/c)2, indicating a failure of line reversal and disagreement with simple Regge models.
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We have measured the differential cross sections and Λ polarizations in the reactions π−p→ΛK0 and π−p→ΛK*0 (890) near the backward direction, at 3, 4, 5, and 6 GeV/c. Data equal to several times the world's total sample above 2 GeV/c were recorded. Both reactions are characterized by cross sections falling rapidly with beam momentum, and by large positive Λ polarizations for u′ between 0.0 and 0.6 GeV2. Analysis of π−p→ΛK0 yields an effective Regge trajectory consistent with antishrinkage of the backward peak. Separation into amplitudes of definite-parity-naturality exchange shows the reaction to be dominated by unnatural-parity exchange. The energy behavior of this exchange is, however, not consistent with a single linear baryon Regge trajectory or exchange-degenerate pair of trajectories. An apparent normalization discrepancy between data on π−p→ΛK0 of a CERN-ETH group and other high-statistics data including that of this experiment is discussed.
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