/usr/src/linux-headers-3.13.0-48-lowlatency/scripts/rt-tester is in linux-headers-3.13.0-48-lowlatency 3.13.0-48.80.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-3.13.0-48-lowlatency/scripts/../../linux-headers-3.13.0-48/scripts/rt-tester