  The motivation for PF calorimetry is to experimentally measure the energy of
hadron jets with excellent resolution. In particle flow designs, sigma(E)/E <
5% should be possible for a range of jet energies from 50 GeV to 250 GeV,
important particularly for experiments at electron-positron colliders (ILC,
CLIC, FCCee, CEPC). The high granularity, which is essential for PF
calorimetry, can also be very beneficial for removal of background from pile-up
on an event-by-event basis making such calorimeters an attractive approach for
hadron collider experiments, for example the HGCAL under construction for CMS
at the CERN HL-LHC.
