We have studied the properties of hadron production in photon-photon scattering with tagged photons at the e + e − storage ring PETRA. A tail in the p T distribution of particles consistent with p T −4 has been observed. We show that this tail cannot be due to the hadronic part of the photon. Selected events with high p T particles are found to be consistent with a two-jet structure as expected from a point-like coupling of the photons to quarks. The lowest-order cross section predicted for γγ → q q , σ = 3 Σ e q 4 · σ γγ → μμ , is approached from above by the data at large transverse momenta.
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Production of pions, kaons, protons and antiprotons has been studied in e + e − annihilations at 12 and 30 GeV centre of mass energy using time of flight techniques. The fractional yield of charged kaons and baryons appears to rise with outgoing particle momentum. At our highest energy at least 40% of e + e − annihilations into hadrons are estimated to contain baryons.
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Inclusive K 0 -production has been measured in e + e - annihilation at a center of mass energy of about W = 30 GeV. The ratio of K 0 + K 0 production to μ + μ - production is R K 0 = 5.6 ± 1.1 (statist. error) ± 0.8 (system.error) This value is about a factor of three higher than R K 0 at W = 7 GeV. The cross sections ( s / β ) d σ /d x is consistent with a scaling behaviour.
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DIFFERENTIAL CROSS SECTION.
INVARIANT CROSS SECTION.
Hadron jets produced in e + e − annihilation between 13 GeV and 31.6 GeV in c.m. at PETRA are analyzed. The transverse momentum of the jets is found to increase strongly with c.m. energy. The broadening of the jets is not uniform in azimuthal angle around the quark direction but tends to yield planar events with large and growing transverse momenta in the plane and smaller transverse momenta normal to the plane. The simple q q collinear jet picture is ruled out. The observation of planar events shows that there are three basic particles in the final state. Indeed, several events with three well-separated jets of hadrons are observed at the highest energies. This occurs naturally when the outgoing quark radiates a hard noncollinear gluon, i.e., e + e − → q q g with the quarks and the gluons fragmenting into hadrons with limited transverse momenta.
NORMALIZED TRANSVERSE MOMENTUM DISTRIBUTION WITH RESPECT TO THE SPHERICITY AXIS AT 13, 17, AND 27.4 TO 31.6 GEV.
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