The total photon-photon cross section for the production of hadrons, σ γγ ( W , Q 2 ), has been measured in the single-tag condition for 0.1 < Q 2 < 1.0 GeV 2 and 1.5 < W < GeV. The results are based on 2929 multihadron events obtained with the PLUTO detector at PETRA. The Q 2 dependence of σ γγ average over W can be described by GVDM. The dependence of σ γγ on the mass W of the hadronic final state has been extracted at Q 2 = 0.44 GeV 2 by unfolding the effects of experimental resolution and acceptance. The cross section is found to rise at small W . The result is compared with VDM and the parton model.
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DATA EXTRAPOLATED TO Q**2=0 USING THE GENERALIZED VECTOR MESON DOMINANCE MODEL (GVDM).
A measurement of the γγ total cross section, σγγ(Q2W), is presented for theQ2 range 0.1 to 100 GeV2, and for the massW of the hadronic final state between 1.5 and 10 GeV. The dependence of σγγ on bothQ2 andW is measured. The results are compared with theoretical predictions. It is found that the data are well described by a sum of quarkparton model and vector dominance contributions.
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We have measured the electron, muon, and charged-hadron pair production rates in two-phonon interactions for invariant masses above 2.0 GeV over a large of momentum transfer. The cross sections for electron and muon pairs show good agreement with the QED predictions at both small and large momentum transfer. The observed rate of hadron production is less than 6% of the rate that QED predicts for point-like hadrons, consistent with recent leading-order QCD calculations.
LOW Q**2 CROSS SECTIONS.
DIFFERENTIAL CROSS SECTIONS IN THE INVARIANT MASS FOR MUON AND ELECTRON PAIRS IN THE UNTAGGED, LOW Q**2 REGION.
HIGH Q**2 CROSS SECTIONS.
We present new high statistics data on hadron production in photon-photon reactions. The data are analyzed in terms of an electron-photon scattering formalism. The dependence of the total cross section of Q 2 , the four-momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector-Meson Dominance and the quark model.
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DEPENDENCE ON VISIBLE HADRONIC INVARIANT MASS.
Data read from graph.