Theory Seminar

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(Abstract)

The photon is one of the most familiar elementary particles for us; it is the fundamental gauge boson of QED. In high energy reactions, however, the photon exhibits complex hadronic structure, because for a short period of time it can fluctuate into quark-antiquark pairs as well as vector mesons. Such structure of the photon can be investigated, for example, in $e^+ e^-$ collision experiments via the two-photon process $e^+ e^- \to (e^+ e^- \gamma^* \gamma^*) \to e^+ e^- X,ドル which may be viewed as a deep-inelastic electron-photon scattering where the target is a (virtual) photon rather than a nucleon.
In this work, especially we focus on unpolarized (spin-averaged) photon structure functions in the kinematic region $\Lambda2 \ll P2 \ll Q2$. Here $-Q2$ is the square of four-momentum transfer, $-P2$ is the virtuality of the target photon and $\Lambda$ is the QCD scale parameter. Thanks to the asymptotic freedom in QCD, in this region, a definite prediction of the whole structure functions can be achieved in perturbation theory. We present the $O(\alpha \alpha_s)$ results for the unpolarized virtual photon structure functions $F_2^\gamma$ and $F_L^\gamma$.