Space qualification of the transition radiation detector of the AMS-02 experiment and indirect search for dark matter

We know that the universe consists of 22\% dark matter. The dark matter particle has to be stable, non-relativistic and only weakly interacting. But we don't know what the dark matter is made of and how it is distributed within our Galaxy. Supersymmetric models predict the existence of the lightest supersymmetric particle (LSP), which is stable if R-parity is conserved. In supersymmetric models inspired by supergravity, the commonly accepted LSP candidate is the lightest neutralino which is a neutral and weakly interacting massive particle. It is a viable candidate for dark matter since the derived relic abundance is naturally within the observed range. In general, the cosmic antiparticles are expected as secondary products of interactions of the primary cosmic-rays (CRs) with the interstellar medium during propagation. While the measurements of cosmic positrons, antiprotons and diffuse gamma rays have become more precise, the results still do not match with the pure secondary origins. The comparison of the expected background of positron, antiproton and gamma-ray fluxes with experimental data have been performed using CR propagation models. A phenomenological study based on the mSUGRA frameworks was carried out and showed a better interpretation of CR fluxes including neutralino annihilations in the galactic halo or center. The combined data of positrons, antiprotons and gamma rays give a strong constraint on the mSUGRA parameter space. The light neutralino has a mass between 80 and 120 GeV annihilating dominantly to W+W-. The most preferred mSUGRA parameter space belongs to the focus point region. This region also produced the correct dark matter abundance consistent with the WMAP3 and the 2dFGRS data. This result might be considered as first evidence of a neutralino dark matter scenario. However, future experiments have to provide measurements of CRs with higher precision. AMS-02 will be the major particle physics experiment on the ISS and will make a profound impact on our knowledge of high energy CRs with unprecedented accuracy. It will extend our knowledge on CR origins, acceleration and propagation mechanisms. Especially, the measurement of the positron flux may be the most promising for the detection of the neutralino dark matter, since the predicted positron flux is less sensitive to the astrophysical parameters responsible for the propagation and the dark matter halo profile. The AMS-02 Transition Radiation Detector (TRD) is designed to provide a positron separation from the proton background with high efficiency in the momentum range of 1 GeV/c upto $leq$ 300 GeV/c. It consists of 20 layers of straw module, proportional counters using Xe/CO2 gas mixtures, interleaved with fleece radiators supported in a conical octagon structure. Major design constraints arise from operating it in a space environment with limited power resources.The TRD readout system is divided into 82 front-end electronic circuits and two pairs of crate electronics and power distribution boxes. A front-end board employs a 64 channel charge sensitive amplifier, shaper and multiplexer based on low noise and low power with a high dynamic range. In addition, it contains an analog-digital-converter, calibration, hybrid control and logic circuits. The front-end electronics has been developed and constructed to meet the requirements of space qualification issued by NASA. Results of functional tests during a series of space qualification tests have been presented and the TRD performance has been investigated using a testbeam at CERN. All of the flight frond-end boards are produced and passed the EMI, vibration and thermal vacuum tests without any failure. Each AMS sub-detector will be delivered to CERN in 2007 for the detector integration. The fully assembled AMS-02 detector will be tested with high energy beams at CERN. Afterwards a space qualification test will be performed using a large space simulator at ESA-ESTEC. Then it will be delivered to NASA-KSC to prepare for the launch with a space shuttle. The launch and installation of the AMS-02 detector on ISS is scheduled for 2009. Now, we are on the threshold of a new and exciting era of unexpected discoveries at the frontiers of astroparticle physics