Eur. Phys. J. C (2020) 80: 1044
https://doi.org/10.1140/epjc/s10052-020-8420-x

Regular Article - Experimental Physics

The LUX-ZEPLIN (LZ) radioactivity and cleanliness control programs

¹ SLAC National Accelerator Laboratory, 94025-7015, Menlo Park, CA, USA
² Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 94305-4085, Stanford, CA, USA
³ Randall Laboratory of Physics, University of Michigan, 48109-1040, Ann Arbor, MI, USA
⁴ National Research Nuclear University MEPhI (NRNU MEPhI), 115409, Moscow, Russia
⁵ Department of Physics, Brown University, 02912-9037, Providence, RI, USA
⁶ Department of Physics, University of Wisconsin-Madison, 53706-1390, Madison, WI, USA
⁷ Department of Physics and Astronomy, University College London (UCL), WC1E 6BT, London, UK
⁸ Blackett Laboratory, Physics Department, Imperial College London, SW7 2AZ, London, UK
⁹ Department of Physics, University of Maryland, 20742-4111, College Park, MD, USA
¹⁰ South Dakota School of Mines and Technology, 57701-3901, Rapid City, SD, USA
¹¹ Department of Physics, University of California, Davis, 95616-5270, Davis, CA, USA
¹² STFC Rutherford Appleton Laboratory (RAL), OX11 0QX, Didcot, UK
¹³ Lawrence Berkeley National Laboratory (LBNL), 94720-8099, Berkeley, CA, USA
¹⁴ South Dakota Science and Technology Authority (SDSTA), Sanford Underground Research Facility, 57754-1700, Lead, SD, USA
¹⁵ Department of Physics, University of Liverpool, L69 7ZE, Liverpool, UK
¹⁶ Fermi National Accelerator Laboratory (FNAL), 60510-5011, Batavia, IL, USA
¹⁷ School of Physics and Astronomy, University of Edinburgh, SUPA, EH9 3FD, Edinburgh, UK
¹⁸ Department of Physics, Brandeis University, 02453, Waltham, MA, USA
¹⁹ Department of Physics, University of California, Berkeley, 94720-7300, Berkeley, CA, USA
²⁰ Lawrence Livermore National Laboratory (LLNL), 94550-9698, Livermore, CA, USA
²¹ Department of Physics, University of Oxford, OX1 3RH, Oxford, UK
²² Department of Physics, Yale University, 06511-8499, New Haven, CT, USA
²³ Laboratório de Instrumentação e Física Experimental de Partículas (LIP), University of Coimbra, 3004 516, Coimbra, Portugal
²⁴ Department of Physics, Washington University in St. Louis, 63130-4862, St. Louis, MO, USA
²⁵ Department of Physics and Astronomy, University of Alabama, 34587-0324, Tuscaloosa, AL, USA
²⁶ Department of Physics, Pennsylvania State University, 16802-6300, University Park, PA, USA
²⁷ Department of Physics and Earth Sciences, University of South Dakota, 57069-2307, Vermillion, SD, UK
²⁸ Department of Physics and Astronomy, Northwestern University, 60208-3112, Evanston, IL, USA
²⁹ Department of Physics and Astronomy, University of Rochester, 14627-0171, Rochester, NY, USA
³⁰ H.H. Wills Physics Laboratory, University of Bristol, BS8 1TL, Bristol, UK
³¹ Brookhaven National Laboratory (BNL), 11973-5000, Upton, NY, USA
³² Department of Physics, University of California, Santa Barbara, 93106-9530, Santa Barbara, CA, USA
³³ Department of Physics, University of Massachusetts, 01003-9337, Amherst, MA, USA
³⁴ Department of Physics, University at Albany (SUNY), 12222-1000, Albany, NY, USA
³⁵ Royal Holloway, Department of Physics, University of London, TW20 0EX, Egham, UK
³⁶ IBS Center for Underground Physics (CUP), Yuseong-gu, Daejeon, Republic of Korea
³⁷ Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
³⁸ School of Natural Sciences, Black Hills State University, 57799-0002, Spearfish, SD, USA
³⁹ Department of Physics and Astronomy, Texas A&M University, 77843-4242, College Station, TX, USA
⁴⁰ Department of Physics, Case Western Reserve University, 44106, Cleveland, OH, USA

^fq akamaha@albany.edu

Received: 5 June 2020
Accepted: 29 August 2020
Published online: 10 November 2020

Abstract

LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above $1.4\times {10}^{-48}{\text{cm}}^2$ for a WIMP mass of $40\text{GeV}/{\text{c}}^2$ and a $1000\text{days}$ exposure. LZ achieves this sensitivity through a combination of a large $5.6\text{t}$ fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented.