Measurement of the total hadronic cross section in virtual photon-photon interactions

The total hadronic cross section for virtual photon-photon interactions is reported for center-of-mass energy, W, between 2 and 20 GeV. The data were obtained via the process $e^{+}$ $e^{\mathrm{-}}$→$e^{+}$ $e^{\mathrm{-}}$ ${\gamma }^{\mathrm{*}}$ ${\gamma }^{\mathrm{*}}$→e ${}_{}{}^{+}{}_{}{}^{}e_{}^{\mathrm{-}}{}_{}{}^{}$+hadrons with both scattered $e^{+}$ and $e^{\mathrm{-}}$ detected. Each photon’s four-momentum squared, $q^2$, ranges from -0.1 to -1.6 ${\mathrm{GeV}}^2$. Dependence upon $q^2$ agrees with a generalized vector-meson-dominance model. The total cross section shows little W dependence, averaging 125 nb at $q_1^2$=$q_2^2$=-0.3. Photon helicity interference terms are determined.