The primary physics goal of the FPD is to measure hard diffractive
processes. Since the quadrupole spectrometers will have acceptance for elastic
events, it is possible that the FPD could also be
used to reduce the luminosity uncertainties for all DØ processes.
The dominant uncertainty in the 5.4% luminosity error of Run I [45]
was the discrepancy between the total cross
section values measured by the CDF and E710 collaborations [46, 47].
It should be possible for us to accurately
measure the total cross section, and also
to have a run-by-run determination of the luminosity using the FPD.