  The KOALA experiment measures the differential cross section of
(anti)proton-proton elastic scattering over a wide range of four-momentum
transfer squared 0.0008 < |t| < 0.1 (GeV/c)$^2$ . The forward scattering
parameters and the absolute luminosity can be deduced by analyzing the
characteristic shape of the differential cross-section spectrum. The experiment
is based on fixed target kinematics and uses an internal hydrogen cluster jet
target. The wide range of |t| is achieved by measuring the total kinetic energy
of the recoil protons near 90{\deg} with a recoil detector, which consists of
silicon and germanium single-sided strip sensors. The energy resolution of the
recoil detector is better than 30 keV (FWHM). A forward detector consisting of
two layers of plastic scintillators measures the elastically scattered beam
particles in the forward direction close to the beam axis. It helps suppress
the large background at small recoil angles and improves the identification of
elastic scattering events in the low |t| range. The KOALA setup has been
installed and commissioned at COSY in order to validate the detector by
measuring the proton-proton elastic scattering. The results from this
commissioning are presented here.
