Neutral Beams at Fermilab:
E687 and FOCUS (E831)
FOCUS (E831) is a collaboration between the University of Illinois and other groups from the
United States, Italy, Korea, Mexico, and Brazil. The FOCUS spectrometer was significantly upgraded
from E687 in the areas of lepton identification, vertexing capabilities, and data acquisition.
FOCUS obtained roughly twelve times the E687 data sample in many decay modes and a considerably
larger factor for semileptonic decays and Cabibbo suppressed decays.
With the excellent FOCUS data set, the Illinois group has produced interesting new results in the charm mixing sector. We have also studied the Dalitz structure of hadronic charm meson decays. Currently we are pursuing precision analyses of semileptonic charm meson decays and the production dynamics of charm particles from photon beams interacting with nuclear targets. We recently discovered a new s-wave interference phenomenon in D+ ® K p m n decays. Thanks to a much larger statistical sample than was available in previous analyses, we have improved the measurement of this decay channel's form factor.
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