MEASUREMENT OF THE TOTAL HADRONIC CROSS-SECTION IN TAGGED GAMMA-GAMMA REACTIONS

We present a measurement of the total cross section for {gamma}{gamma}{r arrow}hadrons, with one photon quasireal and the other a spacelike photon of mass squared {minus}{ital Q}{sup 2}. Results are presented as a function of {ital Q}{sup 2} and the {gamma}{gamma} center-of-mass energy {ital W}, with the {ital Q}{sup 2} range extending from 0.2 to 60 GeV{sup 2}, and {ital W} in the range from 2 to 10 GeV. The data were taken with the TPC/Two-Gamma facility at the SLAC {ital e}{sup +}{ital e}{sup {minus}} storage ring PEP, which was operated at a beam energy of 14.5 GeV. The cross section exhibits a gentle falloff with increasing {ital W}. Its {ital Q}{sup 2} dependence is shown to be well described by an incoherent sum of vector-meson and pointlike scattering over most of the observed {ital W} range. Agreement at high {ital Q}{sup 2} is improved if a minimum-{ital p}{sub {ital T}} cutoff (motivated by QCD) is imposed on the pointlike contribution.