  The X-IFU is the cryogenic spectrometer onboard the future ATHENA X-ray
observatory. It is based on a large array of TES microcalorimeters, which works
in combination with a Cryogenic AntiCoincidence detector (CryoAC). This is
necessary to reduce the particle background level thus enabling part of the
mission science goals. Here we present the first joint test of X-IFU TES array
and CryoAC Demonstration Models, performed in a FDM setup. We show that it is
possible to operate properly both detectors, and we provide a preliminary
demonstration of the anti-coincidence capability of the system achieved by the
simultaneous detection of cosmic muons.
