mardi 2 juillet 2013 à 16:00
Amphi G. Besse
From the observation of the Universe, we know that the mass associated to visible matter represents only few percent of it, while the remaining part is composed by dark energy, responsible to the cosmological expansion, and by some hidden matter, the dark matter.
The likeliest particles family used to describe this dark matter is called WIMPs (Weakly Interacting Massive Particles). That kind of particle could be directly detected by measuring nuclear recoil during an elastic scattering inside a scintillating material.
For this, the XENON Collaboration has developed a detector consisting in a time projection chamber (TPC) using xenon dual phase (liquid and gas) detector, and placed underground. The different ionization density of nuclear recoils induced by WIMPs, and electronic recoils induced by � or γ background, induces different ratio between both signals (from the liquid and from the gas phase) and is used to discriminate WIMPs from background.
The latest dark matter results published by the XENON Collaboration with 224.6 live days of data have shown no excess above the expected background, corresponding to no evidence for dark matter. This result makes XENON100, the current phase of the XENON program, the most sensitive dark matter search experiment, with the best limit for WIMP-nucleon cross section1 lowered to 2.0∙10-45 cm2, and with the best limit for WIMP-neutron cross section2 lowered to 3.5∙10-40 cm2.
The detector is currently acquiring new data in order to improve these results for this exciting WIMP hunt.
In this context, I’ll present my study of the XENON100 response to single electron charge signals, that correspond to one or few more electrons extracted in the gas phase and that emit a signal seen by the detector. As an example, I'm interested in an innovative method to establish the extraction yield of electrons from the liquid phase to the gas phase needed to perform the response of the XENON program detectors.
In addition to this, I’ll also present some studies on specific expected background in the XENON1T future detector. I’ll more precisely focus my talk on the study of some rare multiple scatter background events that could be seen as WIMPlike signals while they aren't.
1. E. Aprile et al. (XENON100), Phys. Rev. Lett. 109, 181301 (2012), arXiv:1207.5988
2. E. Aprile et al. (XENON100), arXiv:1301.6620, Submitted to Phys. Rev. Lett