Detectors for antideuteron search in cosmic rays: Current status and new ideas

The observation of sub-GeV antideuteron in the cosmic ray flux could be a very strong signature of dark matter (DM) annihilation in our galaxy. The predicted antideuteron flux resulting from secondary interactions of primary cosmic rays with the Inter-Stellar medium is expected to be very low and in particular is kinematically suppressed at low energy (sub-GeV). Well motivated theories beyond the Standard Model contain viable dark matter candidates, which could lead to a significant enhancement of the antideuteron flux due to annihilation or decay of dark matter particles. This flux contribution is believed to be relatively large at low energies, where the secondary background is suppressed, which leads to an high interest in the development of new detection techniques for low energy antideuteron. Current search of antideuteron in cosmic rays are based on the well established technique of magnetic spectrometry (BESS-Polar II and AMS-02 experiments). With the aim to explore kinetic energy regions below 0.2 GeV/n, i.e. below the lower threshold of current and past magnetic spectrometers, some new detection techniques, involving stopping antideuterons captured to form exotic atoms, have been developed. The GAPS experiment, based on the detection of characteristics X-rays, and the ADHD concept, based on the metastable states in Helium target, will be described. In particular the performances of an high pressure (200 bar) Helium scintillator prototype, capable of fast timing and good spatial and energy resolution will be shown. As a result of the preliminary test phase of this prototype in the INFN-TIFPA laboratory, the perspectives of this detection technique for antiproton rejection and its sensitivity to the Dark Matter search in the antideuteron annihilation channel will be described.