NEW RESULTS IN DIFFRACTIVE PHOTOPRODUCTION FROM E687 AT FNAL.

A narrow dip structure has been observed at 1.9 GeV/c 2 in a study of diffractive photoproduction of the 3� + 3� final state performed by the Fermilab experiment E687. Prelim- inary results on new structures in 2� + 2� final states are also given. trometer with excellent vertexing, particle identificatio n, and reconstruction capabilities for photons and � 0 's. The photon beam is derived from the Bremsstrahlung of sec- ondary electrons of � 300 GeV endpoint energy, which were produced by the 800 GeV/c Tevatron proton beam. The charged particles emerging from the target are tracked by a system of twelve planes of silicon microstrip detec- tors arranged in three views. These provide high-resolution separation of primary (production) and secondary (charm decay or interaction) vertices. The momentum of a charged particle is determined by measuring its deflections in two analysis magnets of opposite polarity with five stations of multiwire proportional chambers. Three multicell thresh- old ˇ Cerenkov counters are used to discriminate between pi- ons, kaons, and protons. Photons and neutral pions are re- constructed by electromagnetic (EM) calorimetry. Hadron calorimetry and muon detectors provide triggering and ad- ditional particle identification.