Xenon

Gridpix in WIMP search

WIMPs (Weakly Interacting Massive Particles) are dark matter candidates. WIMPs might be detected by their interactions with nuclei in low background environments such as underground experiments. Their  discovery would be a milestone in physics. However, signal rates are low and background events can easily spoil the measurements, therefore large massive detectors are needed. To avoid background domination, detectors should be placed underground in an ultra-low background radiation environment.

Current dual-phase noble liquid WIMP search experiments are done in a large tank filled with a noble liquid like xenon and a gas layer on top of it. The high Z-value of xenon results in self-shielding of background events. The top and bottom of the tank are covered with Photon Multiplier Tubes (PMTs) made of non-radioactive material. The purpose is to detect the rare interaction of a WIMP with a xenon atom. In this process photons and electrons might be emitted, due to the recoil that the Xe atom has to absorb it starts moving and can ionise other atoms. The liberated electrons will drift from the liquid through the gas, photons are detected by the PMTs.

Current experiments can upgrade their setup by replacing or augmenting the top PMT array with an array of GridPix detectors. Instead of a scintillation signal an accurate electron measurement will be obtained. GridPix detectors are proposed for upgrades in Noble Liquid WIMP search experiments in the DARWIN (Dark Matter WIMP search with Noble Liquids) internal proposal. Recently a test setup is designed, to study the performance of GridPix in gaseous xenon, the testing is expected to start at the first half of 2010