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+2-, K+K-+-, and 2K+2K-. For two quasireal incident photons, both the 2+2- and K+K-+- 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 00, 0+-, and +- are presented, together with upper limits for 0, , and K*0K *0. The 00 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 00 final states are consistent with the production of JP=2+ or 0+ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (m2=-Q2 0), the four-pion cross section is still dominated by 00 at low final-state masses W and by 2+2- at higher mass. Further, the dependence of the cross section on Q2 becomes increasingly flat as W increases.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)