The AMS-02 Transition Radiation Detector to Search for Dark Matter in Space

The Alpha Magnetic Spectrometer (AMS) is a high energy physics experiment to be installed on the International Space Station (ISS) to measure the primary cosmic ray spectrum in space. A Transition Radiation Detector (TRD) will provide a proton rejection factor of 10² - 10³ at 90% electron efficiency to search for SUSY dark matter neutralino annihilations in cosmic rays in the energy range from 10 GeV to 300 GeV. The TRD consists of 20 layers of straw proportional tubes interleaved with a fleece radiator; the tubes will be filled with a Xe:CO₂ (80:20) mixture at ~1.2 bar to detect the transition photons. To satisfy all the requirements for the expected detector performances, it is necessary to perform careful checks of the gas parameters and the gas gain. Several tests showed that the detector can fulfill all the stringent requirements for operation on the ISS, assuring the required rejection factor in the energy range of interest.