The NUSES fiber tracker.

We have built a tracker prototype for the ZIRÈ detector to be installed onboard the NUSES satellite. The tracker consists of multiple planes of scintillating fibers readout with Silicon Photomultipliers (SIPMs). The fibers in each plane are oriented perpendicularly to those in the adjacent plane, in order to allow 3D track reconstruction. Scintillating fibers allow a reduced material budget while providing a good spatial resolution and a fast response. This design is therefore suitable to track low-energy cosmic rays down to a few MeV. The prototype has been tested with particle beams, cosmic rays and radioactive sources. The tracker design will be presented and some preliminary results obtained with the prototype will be discussed.