mardi 5 avril 2016 à 16:00
Despite the amazing progress in physics, some mysteries still remain. Nowadays, one of the most fundamental enigmas is the quest of dark matter. Dark matter is a mass observed in the universe, due to its gravitational effect, but not interacting with the light. XENON100 experiment aims to detect dark matter with liquid xenon. Its results put one of the most stringent limits on dark matter detection. XENON1T, the next generation operating this spring, will be 100 times more sensitive.
The XENON100 experiment is composed by xenon in two states, liquid and gaseous. When a particle interacts with the liquid xenon, it produces photons and electrons. The photons are detected by photomultipliers tubes, creating the signal called S1. Whereas the electrons will drift toward the gaseous xenon where they will interact to produce photons corresponding to the signal called S2. Photons from S1 or S2 may release electrons (one electron by photon) by interacting with the liquid xenon impurities or the detector components. These single electrons represent a great source to study the detector behavior at low energy.
In a first part, this work will present how single electron are used to measure the secondary scintillation gain (number of PE detected per electron) and how this gain permit to monitor the detector stability.
Dark matter search is mainly focus on mass from ~10GeV to ~10TeV, but light dark matter is not excluded. For dark matter mass below 10GeV, the S1 signal is too low to be identified correctly. A special analysis based only on S2 signal is needed. In such analysis, background rejection becomes more difficult. Moreover, the presence of residual (no production signals) single electrons has been observed in the detector. Single electrons signals have a maximal amplitude which can correspond to light dark matter signals. Thus, the measurement of the single electron residual rate can procure background estimation for light dark matter analysis. Therefore, the second study of this work aims to measure the single electron residual rate in the detector. The measurements are done for different cases and with different sources for comparison.