  The particle flow approach to calorimetry can provide unprecedented jet
energy resolution at a future high energy collider, such as the International
Linear Collider (ILC). However, the use of particle flow calorimetry at the
proposed multi-TeV Compact Linear Collider (CLIC) poses a number of significant
new challenges. At higher jet energies, detector occupancies increase, and it
becomes increasingly difficult to resolve energy deposits from individual
particles. The experimental conditions at CLIC are also significantly more
challenging than those at previous electron-positron colliders, with increased
levels of beam-induced backgrounds combined with a bunch spacing of only 0.5
ns. This paper describes the modifications made to the PandoraPFA particle flow
algorithm to improve the jet energy reconstruction for jet energies above 250
GeV. It then introduces a combination of timing and p_T cuts that can be
applied to reconstructed particles in order to significantly reduce the
background. A systematic study is performed to understand the dependence of the
jet energy resolution on the jet energy and angle, and the physics performance
is assessed via a study of the energy and mass resolution of W and Z particles
in the presence of background at CLIC. Finally, the missing transverse momentum
resolution is presented, and the fake missing momentum is quantified. The
results presented in this paper demonstrate that high granularity particle flow
calorimetry leads to a robust and high resolution reconstruction of jet
energies and di-jet masses at CLIC.
