The General Antiparticle Spectrometer (GAPS) is an Antarctic
balloon-borne detector designed to measure the low energy (< 0.25 GeV/n) antideuteron cosmic ray component as a distinctive
signal from dark matter annihilation or decay in the Galactic halo.

The detector consists of a tracker, made up by ten planes of lithium-drifted silicon Si(Li) detectors, surrounded by a plastic scintillator time-of-flight system.

GAPS uses a novel particle identification method based on exotic atom capture and decay with emission of pions, protons and atomic X-rays from a common annihilation vertex. The resulting "nuclear star" topology provide sufficient rejection power to suppress any non-antiparticle cosmic ray background.

Here we present results for a preliminary reconstruction algorithm that has been tested on simulated events.
The GAPS simulation software is based on GEANT4 and fully reproduce the detector geometry.
Various technique like Kalman filter, Hough-3D transform, Least Squares minimization were combined in order to precisely reconstruct the topology of the "nuclear star". The performance of the final algorithm in reconstructing the annihilation vertex position and the secondary pions will be discussed.