The nature of dark matter is one of the most intriguing open questions in fundamental physics. There is unambiguous evidence based on a broad range of astrophysical and cosmological observations indicating that about 84% of the mass of the universe is in a new form which does not emit or absorb light (i.e. dark matter), and whose nature is unknown. Many models of new physics suggest that dark matter is composed by one or more previously unobserved types of WIMPs. The route to solving this mystery must include the direct detection of the WIMPs composing our galactic dark matter. Indirect detection of WIMPs by observing products of their annihilation and searches for new particles in accelerators such as the LHC can complement but cannot replace the direct detection experiments. Amongst more than 20 experiments around the world, LUX (Large Underground Xenon) is the most sensitive WIMP search experiment. Deployed at the 1478 m deep level of the Sanford Underground Research Facility (SURF, SD, USA) in July 2012, it attained a world-leading result in just over one year. With only 85.3 live-days of data taking, it surpassed all existing dark matter limits for WIMP masses above 10 GeV, including the previous best result by XENON100, which had required 225 live-days of exposure. The LUX result allowed to probe WIMP theoretical models and excluded the low-mass WIMP regions where hints of signal have been published. This result from LUX has received enormous interest, from astrophysicists to particle physicists, its publication in Phys. Rev. Lett. having so far over 630 citations in Inspire-HEP. After a period for several tests, some upgrades and calibrations, LUX started a 300 live-day run in November 2014, expecting to boost its sensitivity by a factor of 3. Regardless of the outcome of the next run of LUX - either a discovery or a lowering of the cross-section limit - experiments able to reach sensitivities at least 10 times better than current detectors (the so-called second-generation dark matter experiments) are mandatory. In 2014, the LZ experiment was one of only three second-generation dark matter experiments selected by DOE for being funded. LZ aims to discover and to study dark matter in the form of WIMPs, and will improve the current LUX world-leading sensitivity by a factor of ~300. LZ will reach further and faster in sensitivity than any competing experiment being proposed on a similar timescale, including XENON1T (presently under construction). LZ is a dual-phase xenon time projection chamber (DPXe-TPC) using 7 ton of xenon. This is an extensively proven detection technology, and its leading role in dark matter search was demonstrated by several prominent experiments in the field (ZEPLIN-II, ZEPLIN-III, XENON10, XENON100 and finally LUX). LUX was explicitly designed to be the test-bed for the development of the technologies required to operate a multi-ton DPXe-TPC deployed inside a water tank, and its breakthrough result demonstrates the merits of this concept. LZ is largely based on LUX but with important enhancements such as a 4π scintillator veto and the instrumentation of the outer xenon layer for use as additional veto. Following an extensive R&D program dating back to 2009, LZ has already completed its concept design. After a period for procurement, the construction phase is expected to occur in 2016 and 2017. The underground deployment and commissioning is planned for 2018 and the science run is projected for 2019-2021. The LIP group has a long-standing experience in all aspects of the dark matter search with DPXe-TPCs. It participated in the ZEPLIN program (pioneer in the use of DPXe-TPCs for WIMP search) from 2002 to 2012 and joined LUX in 2010. In LUX, the group has made key contributions to data processing and analysis. Furthermore the group has had full responsibility for two systems (the slow control and the liquid nitrogen distribution and control systems) since LUX was deployed underground. Several members of the team served for periods of 6 or 3 months in key coordination positions, such as Analysis Group Coordinator, Deputy Science Coordination Manager, Data Processing Manager and Detector Working Group Coordinator. This demonstrates the expertise, involvement and leadership of the LIP group in the experiment. In LZ, we have had the leadership in the design and R&D of the overall instrument control system, and full responsibility for the R&D towards the selection of the light reflectors.

Photos

Contacts

Group Leader:  

Isabel Lopes

isabel@coimbra.lip.pt