/usr/include/fastjet/ is in libfastjetplugins-dev 3.0.6+dfsg-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/fastjet/CMSIterativeConePlugin.hh
/usr/include/fastjet/D0RunIBaseConePlugin.hh
/usr/include/fastjet/D0RunIConePlugin.hh
/usr/include/fastjet/D0RunIIConePlugin.hh
/usr/include/fastjet/D0RunIpre96ConePlugin.hh
/usr/include/fastjet/EECambridgePlugin.hh
/usr/include/fastjet/GridJetPlugin.hh
/usr/include/fastjet/JadePlugin.hh
/usr/include/fastjet/NestedDefsPlugin.hh
/usr/include/fastjet/PxConePlugin.hh
/usr/include/fastjet/SISConeBasePlugin.hh
/usr/include/fastjet/SISConePlugin.hh
/usr/include/fastjet/SISConeSphericalPlugin.hh
/usr/include/fastjet/TrackJetPlugin.hh