Ricerc@Sapienza

Dark Matter Weakly Interactive Massive Particles (WIMP) in the Galactic halo should have an apparent motion from the Cygnus constellation to the Earth. Most sensitive detectors for dark matter candidates currently in operation cannot measure the correlated direction of the WIMP scattered ion in the target bulk.
A new solution to the problem of dark matter directional detection might come from the use of new detectors constituted by large arrays of aligned carbon nanotubes (CNTs), as WIMP targets. A brush of aligned CNTs oriented in the direction parallel to the WIMP wind might represent an anisotropic medium for the carbon ion scattered off the CNT surface by the WIMP. This idea has been investigated with simulations in three papers (two published and one in preparation) authored by some of the participants. Carbon ions scattered by the WIMPs would induce defects into the CNT honeycomb mesh itself. We expect the density of defects being dependent on the relative orientation of the impinging WIMP and the CNT axes.
We propose to experimentally test this idea by emulating the scattered carbon ion with calibrated ion beams. The induced defect anisotropy can be directly measured by core-level X-ray photoemission (XPS) and Raman spectro-microscopies, both highly sensitive techniques to accurately control the chemical state, variation of bonding and density of defects and lattice strain in carbon-based materials. Preliminary XPS results carried out with low-energy (2-5 keV) Ar+ ions as a function of incidence angle with respect to the CNT axes reveal a slightly yet measurable modification of the C 1s lineshape, very promising for demonstrating directionality, whose angular and energy dependence will be fully determined in the context of this project.