Production of four-prong final states in photon-photon collisions

Results are presented on the exclusive production of four-prong final states in photon-photon collisions from the TPC/Two-Gamma detector at the SLAC e⁺{e}^{{{-}}}$ storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2${{π}}⁺$2${{π}}^{{{-}}}$, ${K}⁺K^-{{π}}⁺π^-, and 2K⁺2K^-. For two quasireal incident photons, both the 2π⁺2π^- and K⁺{K}^{{{-}}}π⁺{{π}}^{{{-}}}$ cross sections show a steep rise from threshold to a peak value, followed by a decrease at higher mass. Cross sections for the production of the final states ${{ρ}}⁰ρ⁰, ρ⁰{{π}}⁺π^-, and {φ}π⁺{{π}}^{{{-}}}are presented, together with upper limits for φ{{ρ}}⁰, φφ, and{K}*0K*0$. The ${{ρ}}⁰ρ⁰ contribution dominates the four-pion cross section at low masses, but falls to nearly zero above 2 GeV. Such behavior is inconsistent with expectations from vector dominance but can be accommodated by four-quark resonance models or by t-channel factorization. Angular distributions for the part of the data dominated by ρ⁰{{ρ}}⁰$ final states are consistent with the production of ${J}P=2⁺ or 0⁺ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (m_γ²=-Q²{≠}0), the four-pion cross section is still dominated by ρ⁰{{ρ}}⁰$ at low final-state masses ${W}_{{γ}{γ}}$ and by 2${{π}}⁺$2${{π}}^{{{-}}}$ at higher mass. Further, the dependence of the cross section on ${Q}²$ becomes increasingly flat as ${W}_{{γ}{γ}}$ increases.