A search for direct photons produced in proton-proton collisions has been performed at two s values at the CERN Intersecting Storage Rings (ISR). It is found that direct photons are produced preferentially with no accompanying particles on the same side. On the away side, the ratio of positive to negative high-xE particles is found to be higher for high transverse momentum direct-photon events, than for high transverse momentum neutral-meson events.
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separation between these two kinds of particles is achieved by measuring the fraction of particles that did not convert when passing through a 1.0 radiation length converter (the coil of a superconducting solenoid magnet), and contrasting it with the fraction expected if all the particles were neutral mesons, and the fraction expected if all were single photons. The integrated luminosities, energies, and trigger thresholds used are shown in table 1. The results (fig. 1) are 7 Present address: Physics Department, University of Manchester, Manchester, UK. s Present address: Brookhaven National Laboratory, Upton, NY, USA. 9 Permanent address: Physics Department, University of Washington, Seattle, WA, USA. lo Research supported in part by the National Science Foundation. 11 Research supported in part by the US Department of Energy.
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