Collaborative Research: Continuation of the Dark Matter Search with XENON1T at LNGS

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Multiple astronomical observations have established that about 85% of the matter in the universe is not made of normal atoms, but must be otherwise undetected elementary "dark matter" particles that do not emit or absorb light. Deciphering the nature of this so-called Dark Matter is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. A leading hypothesis is that it is comprised of Weakly Interacting Massive Particles, or WIMPs, that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our galaxy may be detectable via scattering from atomic nuclei in detectors located deep underground to help reject backgrounds due to cosmic rays. Direct detection of WIMP dark matter would solve a fundamental mystery in particle physics and cosmology, providing a unique window to learning about the primary matter constituent of the Universe and of physics beyond the Standard Model of particle physics. This award supports the US groups involved in the XENON1T dark matter search program at the INFN Gran Sasso National Laboratory (LNGS) underground laboratory.The XENON project continues to captivate the imagination of the public. This is evidenced, for example, by several TV shows such as "The Big Bang Theory", which on several occasions featured XENON plots and results. Public interest in science is encouraged through talks and outreach activities. XENON1T will play a significant role in solving the dark matter puzzle, by either detecting WIMPs, or putting them under immense pressure as viable dark matter candidates. In addressing this fundamental physics problem, these awards will engage many undergraduate and graduate students as well as post-doctoral researchers, exposing them to a variety of subjects in physics and cosmology, and training them in state-of-the-art technologies, thus preparing to become future leaders in the field. Finally, the instrumentation and techniques used in XENON are relevant to a wide range of applications, from areas in homeland security and medical imaging, to the analysis and statistical treatment of large data sets.The program for the next four years will focus on the continued operation of the XENON1T experiment and its science data analysis. The international XENON Collaboration of 130 scientists continues to be led by the PI at Columbia University with key roles served by US members both in the management of the experiment and its scientific program. XENON1T uses the largest liquid xenon time projection chamber (TPC) built to-date, with 2 tonnes active Xe target, and the highest sensitivity to dark matter Weakly Interacting Massive Particles (WIMPs), at the level of 2 × 10^-47 cm^2 for 40 GeV WIMPs. With funding of this proposal, the US will remain in the lead of the direct search for dark matter well beyond the end of the decade.