The hadron fractions in photon-photon collisions

The author has studied the reaction e+e- → e+e-γγ → e+e- + hadrons using the Time Projection Chamber (TPC) at the PEP storage ring at Stanford Linear Accelerator Center (SLAC). The final state particles are identified by measuring their ionization energy loss rate (dE/dx) and momentum. The data sample corresponds to an integrated luminosity of 67 pb-1 at √s = 29 GeV where only events containing a single tag with Q2 ≥ 0.03 GeV2 are considered. The Quark Parton Model (QPM) and Vector-meson Dominant Model (VDM) are used to explain the hadron productions in twophoton process. We use the Lund 5.3 for the quark fragmentation. The fractions of π±, K± and p bar p are studied in both data and Monte Carlo events. The data shows the γγ characteristic in favor of the VDM. No significant evidence has been found for the charm threshold in two-photon process at √s = 29 GeV