Particle identification with the AMS-02 RICH detector: search for dark matter with antideuterons

The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be installed on the International Space Station (ISS) for at least 3 years, is a detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to a few hundred GeV, using state-of-the art particle identification techniques. It is equipped with several subsystems, one of which is a proximity focusing Ring Imaging Čerenkov (RICH) detector equipped with a dual radiator (aerogel+NaF), a lateral conical mirror and a detection plane made of 680 photomultipliers and light guides, enabling precise measurements of particle electric charge and velocity (∆β/β ∼ 10 and 10 for Z = 1 and Z = 10 − 20, respectively) at kinetic energies of a few GeV/nucleon. Combining velocity measurements with data on particle rigidity from the AMS-02 Tracker (∆R/R ∼ 2% for R = 1 − 10 GV) it is possible to obtain a reliable measurement for particle mass. One of the main topics of the AMS-02 physics program is the search for indirect signatures of dark matter. Experimental data indicate that dark, non-baryonic matter of unknown composition is much more abundant than baryonic matter, accounting for a large fraction of the energy content of the Universe. Apart from antideuterons produced in cosmicray propagation, the annihilation of dark matter will produce additional antideuteron fluxes. Detailed Monte Carlo simulations of AMS-02 have been used to evaluate the detector’s performance for mass separation, a key issue for D̄/p̄ separation. Results of these studies are presented. I. THE AMS-02 EXPERIMENT The Alpha Magnetic Spectrometer (AMS)[1], whose final version AMS-02 is to be installed on the International Space Station (ISS) for at least 3 years, is a detector designed to study the cosmic ray flux by direct detection of particles above the Earth’s atmosphere using state-of-the-art particle identification techniques. AMS-02 is equipped with a superconducting magnet cooled by superfluid helium. The spectrometer is composed of several subdetectors: a Transition Radiation Detector (TRD), a Time-of-Flight (TOF) detector, a Silicon Tracker, Anticoincidence Counters (ACC), a Ring Imaging Čerenkov (RICH) detector and an Electromagnetic Calorimeter (ECAL). Fig. 1 shows a schematic view of the full AMS-02 detector. A preliminary version of the detector, AMS-01, was successfully flown aboard the US space shuttle Discovery in June 1998. The main goals of the AMS-02 experiment are: • A precise measurement of charged cosmic ray spectra in the rigidity region between ∼ 0.5 GV and ∼ 2 TV, Fig. 1. Exploded view of the AMS-02 detector. and the detection of photons with energies up to a few hundred GeV; • A search for heavy antinuclei (Z ≥ 2), which if discovered would signal the existence of cosmological antimatter; • A search for dark matter constituents by examining possible signatures of their presence in the cosmic ray spectrum. The long exposure time and large acceptance (0.5 msr) of AMS-02 will enable it to collect an unprecedented statistics of more than 10 nuclei.