  The design and performance of the LUX-ZEPLIN (LZ) detector is described as of
March 2015 in this Conceptual Design Report. LZ is a second-generation
dark-matter detector with the potential for unprecedented sensitivity to weakly
interacting massive particles (WIMPs) of masses from a few GeV/c2 to hundreds
of TeV/c2. With total liquid xenon mass of about 10 tonnes, LZ will be the most
sensitive experiment for WIMPs in this mass region by the end of the decade.
This report describes in detail the design of the LZ technical systems.
Expected backgrounds are quantified and the performance of the experiment is
presented. The LZ detector will be located at the Sanford Underground Research
Facility in South Dakota. The organization of the LZ Project and a summary of
the expected cost and current schedule are given.

Instrumentation and Detectors;Instrumentation and Methods for Astrophysics;High Energy Physics - Experiment