This research project addresses the question of the nature of galactic dark matter with a search for Weakly Interacting Massive Particles (WIMPs), using two-phase liquid xenon (LXe) Time Projection Chambers (LXeTPCs) as part of the XENON phased program. XENON100, building upon the success of the XENON10 prototype, represents the current state-of-the-art in WIMP search detectors. With a realistic discovery potential, XENON100 has already reached a world-leading sensitivity, and continues to accrue data at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy towards its ultimate sensitivity reach. To fully probe a particularly favorable region of electroweak physics for WIMP dark matter in search of a first robust and statistically significant discovery, the next phase of the XENON program will be a detector at the ton scale - XENON1T. The worldwide race towards direct dark matter detection has been dramatically accelerated by the remarkable progress and evolution of LXeTPCs. They have shifted the scale of target mass from a few to tens of kilograms whilst simultaneously reducing both electronic and nuclear recoil backgrounds to extremely low levels. The XENON collaboration has demonstrated the effective scaling of LXeTPCs with phased detectors of increasing sensitivity of at least an order of magnitude, and is ready to move to the ton scale.
This award will provide funding to the US groups for the construction of the XENON1T detector, cryogenics infrastructure and calibration systems. This experiment is based on a TPC with 2.2 ton of LXe viewed by low radioactivity photomultiplier tubes. By exploiting the excellent self-shielding and 3D position resolution of a LXeTPC, by selecting existing low radioactivity detector materials and by placing the detector in a large active water shield and Cherenkov muon veto, the overall event rate within the fiducial target of 1.1 ton is estimated to be over a factor of 100 lower than the background measured in XENON100. This rate translates to less than one event per ton per year in the WIMP search region - an unprecedented low background level for a dark matter experiment.
Broader Impact: The XENON scientific goal to detect the missing mass in the Universe has all the ingredients to captivate the interests and imagination of students and the general public alike. The technological advances of this project can impact society in a number of ways: liquid xenon imaging detectors and related technologies find applications in several fields outside particle astrophysics, including homeland security and medical imaging research.
