Contribution Poster (A0 portrait)
A Dark Matter Detector Based on the Simultaneous Measurement of Phonons at low temperature.
S. TALBAOUI, H. GRIMECH, E. BAQLOUL, M.HABBAD Laboratory of Materials Physics, Faculty of Sciences and Technologies, Sultan Moulay Slimane University, Beni Mellal, Morocco
One of the most important issues in astrophysics and cosmology is understanding the nature of dark matter. One possibility is that it is made of weakly interacting subatomic particles created in the big bang, such as the lightest particle in supersymmetry models. These particles should scatter elastically of nuclei in a detector on earth at a rate of ~events/kg/week, and will deposit energies of a few keV. Current attempts to detect these interactions are limited by a radioactive background of photons and beta particles which scatter on electrons.Currently a novel particle detector have developed to look for dark matter based on the simultaneous measurement of ionization and phonons in some grammes of crystal of high purity germanium or silicon or diamond at a low temperature. Background events can be distinguished by this detector because they produce more ionization per unit phonon energy than dark matter interactions. The phonon energy is measured as a temperature change in the detector by means of neutron transmutation doped germanium thermistors attached to the crystal.For this reason we studied behavours of these dielectrics and comparing their dispersion relation. In this paper we present a theoretical study based on the vibrational properties of crystal lattices; such as diamond, silicon and germanium. A detailed calculation has been made to determine the dynamic matrices of these lattices. The phonon dispersion curves presented in this work concern the acoustic and optical modes propagating in the ΓX, ΓK and ΓL directions of the Brillouin zone (3D). In order to determine these dispersion curves we used the Born-von Karman model with the approximation of the central forces between the first and second neighbors. The radial and angular force constants were determined by fitting on experimental data using the generalised least squares method. This approach allows to determine the interaction parameters and the vibrational properties for each of the materials studied.
Keywords : phonons, force constants, dispersion curves, vibrational properties