The LZ experiment motivation, technical details, project organization, work breakdown structure (WBS), and preliminary cost and schedule may be found in the LZ Conceptual Design Report (CDR) (see Links). An even more detailed Technical Design Report is expected to be available in early 2016. We content ourselves here with a brief overview and refer the reader to these documents for further information.
The LZ cylindrical (1.5 m diameter x 1.5 m height) time-projection chamber contains ~7 active tonnes of purified liquid xenon in a ~1 kV/cm drift field below a thin gas-phase high field scintillation region. An electric field cage bounds the target region and is made of highly reflective PTFE (Teflon). Reflective coatings are applied to essentially all passive surfaces. Scintillation light (S1) from a nuclear recoil event is observed by 488 3-inch diameter UV-sensitive photomultiplier tubes (PMTs) distributed above and below the xenon. This prompt primary signal is confirmed and localized in space by light (S2) generated in the gas phase by electrons which drift to the top of the liquid where they are efficiently extracted by the electric field. The ratio of the S1 and S2 signal intensities distinguishes electron recoils (ER) from nuclear recoils (NR).
The xenon cryostat is surrounded by an outer detector comprising a gadolinium-loaded liquid scintillator (27 tonnes) and an outermost water shield (7.62 inner diameter, 5.92 m height) instrumented with 120 8-inch diameter PMTs. The outer detector vetos and measures cosmogenic and radiogenic background events, especially those producing neutrons.
The LZ experiment will be located in the Sanford Underground Research Facility (SURF) , replacing the LUX experiment. The mile-deep location, the significantly larger and self-shielding liquid xenon target, as well as the new instrumented liquid xenon skin region and the outer detector are key elements in achieving improved sensitivity. The LZ experiment is sensitive to keV-range nuclear recoil energies corresponding to WIMP masses of order 10 GeV/c2 with the expected galactic dark matter model velocity distribution. The projected reach in cross section sensitivity for spin-independent interactions is ~10-48 cm2/nucleon for 50 GeV/c2 WIMP mass. The isotope mix in naturally occurring xenon provides sensitivity to spin-dependent interactions at a reduced but also record level.
The LZ collaboration includes experienced US-based (LUX) and UK-based (ZEPLIN) experimenters and a strong management team. The collaboration passed a CD1 review in March 2015 with CD2 scheduled for early 2016, construction to commence in 2017, and physics commissioning planned for early 2019. The UW-Madison group has been active in the LZ project since 2014 and is committed to supporting it through commissioning and operation.