The dimensions of the target stream are defined by a system of skimmers downstream of the
nozzle. The jet, which is in the shape of a cone, intersects the Fermilab
Antiproton Accumulator: in this region, the jet target is 7 mm in diameter.
A system of detectors is installed downstream with respect to the antiproton current.
E835 detects the events coming from the proton-antiproton
annihilation in this intersection region, while E862
detects the antihydrogen atoms formed.
The rate of annihilation is equal to the cross section of the annihilation process (/e835/people/70 mBarn at 3-4 GeV) times the value
of the instantaneous luminosity. This luminosity is proportional to the product of the antiproton current times the density
of the jet target. Therefore, as the density increases, the number of events it is possible to get in one second also increases.