Ph.D. degree thesis
accepted by University of Zaragoza, Spain

Javier Galan

Supervisor: Igor G. Irastorza

Probing eV-mass scale axions with a Micromegas detector in the CAST

 Keywords:

• Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid, etc) Noble-liquid detectors (scintillation, ionization two-phase)
• Particle identification methods
• Digital signal processing (DSP)
• X-ray detectors and telescopes

 Abstract:
The CAST (CERN Axion Solar Telescope) experiment is searching for axions, an hypothetical particle that emerges as a possible solution to the well known CP violation problem in strong interactions. CAST is using a decommissioned LHC dipole magnet able to track the Sun as a possible source of solar axions, and to convert them to X-rays photons detectable with low background X-ray detectors. CAST continues its data taking period scanning masses up to 1eV. This thesis presents the data obtained with a Micromegas detector for the scanned axion mass range up to 0.64eV. The working principle, characterization and analysis of the Micromegas detectors operating in CAST are detailed in this work. Moreover, the last detector data corresponding to the new data taking period, with 3He gas inside the bores, was used to obtain a preliminar and conservative upper limit on the axion-photon coupling for the new axion mass range explored, g_{a\gamma} < 2.44 10^{-10} GeV^{-1}.