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/sup +/e/sup -/ storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2...
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Veröffentlicht in: | Phys. Rev. D; (United States) 1988-01, Vol.37 (1), p.28-40 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | 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/sup +/e/sup -/ storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2..pi../sup +/2..pi../sup -/, K/sup +/K/sup -/..pi../sup +/..pi../sup -/, and 2K/sup +/2K/sup -/. For two quasireal incident photons, both the 2..pi../sup +/2..pi../sup -/ and K/sup +/K/sup -/..pi../sup +/..pi../sup -/ 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 rho/sup 0/rho/sup 0/, rho/sup 0/..pi../sup +/..pi../sup -/, and phi..pi../sup +/..pi../sup -/ are presented, together with upper limits for phirho/sup 0/, phiphi, and K/sup *//sup 0/K-bar /sup *//sup 0/. The rho/sup 0/rho/sup 0/ 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 rho/sup 0/rho/sup 0/ final states are consistent with the production of J/sup P/ = 2/sup +/ or 0/sup +/ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (m/sub ..gamma..//sup 2/ = -Q/sup 2/not =0), the four-pion cross section is still dominated by rho/sup 0/rho/sup 0/ at low final-state masses W/sub ..gamma..//sub ..gamma../ and by 2..pi../sup +/2..pi../sup -/ at higher mass. Further, the dependence of the cross section on Q/sup 2/ becomes increasingly flat as W/sub ..gamma..//sub ..gamma../ increases. |
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ISSN: | 0556-2821 |
DOI: | 10.1103/PhysRevD.37.28 |