LBNL-1007256

The LUX-ZEPLIN (LZ)Technical Design Report

In this Technical Design Report (TDR) we describe the LZ detector to bebuilt at the Sanford Underground Research Facility (SURF). The LZ darkmatter experiment is designed to achieve sensitivity to a WIMP-nucleonspin-independent cross section of 3 × 10−48 cm2.

The LUX-ZEPLIN (LZ) CollaborationB.J. Mount

Black Hills State University, School of Natural Sciences, 1200 University Street, Spearfish, SD 57799-0002, USA

S. Hans, R. Rosero, M. YehBrookhaven National Laboratory (BNL) P.O. Box 5000, Upton, NY 11973-5000, USA

C. Chan, R.J. Gaitskell, D.Q. Huang, J. Makkinje, D.C. Malling,1 M. Pangilinan,2 C.A. Rhyne,W.C. Taylor, J.R. Verbus 3

Brown University, Department of Physics, 182 Hope Street, Providence, RI 02912-9037, USA

Y.D. Kim, H.S. Lee, J. Lee, D.S. Leonard, J. LiIBS Center for Underground Physics (CUP), 70, Yuseong-daero 1689-gil, Yuseong-gu, Daejeon, Korea

J. Belle,4 A. Cottle, W.H. Lippincott, D.J. Markley, T.J. Martin, M. Sarychev, T.E. Tope, M. Utes, R. Wang,I. Young

Fermi National Accelerator Laboratory (FNAL), Batavia, IL 60510-0500, USA

H.M. Araújo, A.J. Bailey,5 D. Bauer, D. Colling, A. Currie,6 S. Fayer, F. Froborg, S. Greenwood,W.G. Jones, V. Kasey, M. Khaleeq, I. Olcina, B. López Paredes, A. Richards, T.J. Sumner, A. Tomás,

A. VacheretImperial College London, Physics Department, Blackett Laboratory, Prince Consort Road, London, SW7 2BW, UK

P. Brás, A. Lindote, M.I. Lopes, F. Neves, J.P. Rodrigues, C. Silva, V.N. SolovovLaboratório de Instrumentação e Física Experimental de Partículas (LIP), Department of Physics, University of

Coimbra, Rua Larga, 3004-516, Coimbra, Portugal

M.J. Barry, A. Cole, A. Dobi,7 W.R. Edwards, C.H. Faham,3 S. Fiorucci, N.J. Gantos, V.M. Gehman,8

M.G.D. Gilchriese, K. Hanzel, M.D. Hoff, K. Kamdin,9 K.T. Lesko, C.T. McConnell, K. O’Sullivan,10

K.C. Oliver-Mallory,9 S.J. Patton, J.S. Saba, P. Sorensen, K.J. Thomas,11,12 C.E. Tull, W.L. Waldron,M.S. Witherell9

Lawrence Berkeley National Laboratory (LBNL), 1 Cyclotron Road, Berkeley, CA 94720-8156, USA

A. Bernstein, K. Kazkaz, J. XuLawrence Livermore National Laboratory (LLNL), 7000 East Avenue, Livermore, CA 94550-9698, USA

1Now at: Lincoln Laboratory, 244 Wood Street, Massachusetts Institute of Technology, Lexington, MA 02421-6426, USA2Now at: Samba TV, 301 Brannan Street, Floor 6, San Francisco, CA 94107-3816, USA3Now at: LinkedIn Corporation, 1000 West Maude Avenue, Sunnyvale, CA 94085, USA4Also at: Belle Aerospace Corporation, 2237 Warrenville Ave., Wheaton, IL 60189, USA5Now at: University of Valencia, Instituto de Física Corpuscular, Parc Científic de la Universitat de València, C/ Catedrático José

Beltrán, 2, E-46980 Paterna, Spain6Now at: HM Revenue and Customs, 100 Parliament Street, London, SW1A 2BQ, UK7Now at: Zenysis Technology, 535 Mission Street Floor 14, San Franciso, CA 94105-3253, USA8Now at: Cainthus, Otherlab, 701 Alabama Street, San Francisco, CA 94110-2022, USA9Also at: University of California (UC), Berkeley, Department of Physics, 366 LeConte Hall MC 7300, Berkeley, CA 94720-7300,

USA10Now at: Insight Data Science, 260 Sheridan Avenue Suite 310, Palo Alto, CA 94306-2010, USA11Also at: University of California (UC), Berkeley, Department of Nuclear Engineering, 4155 Etcheverry Hall MC 1730, CA

94720-1730, USA12Now at: Lawrence Livermore National Laboratory (LLNL), 7000 East Avenue, Livermore, CA 94550-9698, USA

D. Yu. Akimov, A.I. Bolozdynya, A.V. Khromov, A.M. Konovalov, A.V. Kumpan, V.V. SosnovtsevNational Research Nuclear University MEPhI (NRNU MEPhI), 31 Kashirskoe shosse, Moscow, 115409, RUS

C.E. Dahl,13 D. TemplesNorthwestern University, Department of Physics & Astronomy, 2145 Sheridan Road, Evanston, IL 60208-3112, USA

M.C. Carmona-Benitez, L. de ViveirosPennsylvania State University, Department of Physics, 104 Davey Lab, University Park, PA 16802-6300, USA

D.S. Akerib,ba H. Auyeung,b T.P. Biesiadzinski,ba M. Breidenbach,b R. Bramante,ba R. Conley,b

W.W. Craddock,b A. Fan,ba A. Hau,b C.M. Ignarra,ba W. Ji,ba H.J. Krebs,b R. Linehan,ba C. Lee,ba,14

S. Luitz,b E. Mizrachi,b M.E. Monzani,ba F.G. O’Neill,b S. Pierson,b M. Racine,b B.N. Ratcliff,b

G.W. Shutt,b T.A. Shutt,ba K. Skarpaas,b K. Stifter,ba W.H. To,ba,15 J. Va’vra,b T.J. Whitis,ba

W.J. WisniewskibaKavli Institute for Particle Astrophysics and Cosmology (KIPAC), 452 Lomita Mall, Stanford University, Stanford,CA 94305, USA; bSLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94205-7015, USA

X. Bai, R. Bunker,16 R. Coughlen, C. Hjemfelt, R. Leonard, E.H. Miller, E. Morrison, J. Reichenbacher,R.W. Schnee, M.R. Stark,17 K. Sundarnath, D.R. Tiedt, M. Timalsina

South Dakota School of Mines and Technology, 501 East Saint Joseph Street, Rapid City, SD 57701-3901, USA

P. Bauer, B. Carlson, M. Horn, M. Johnson, J. Keefner, C. Maupin, D.J. TaylorSouth Dakota Science and Technology Authority (SDSTA), Sanford Underground Research Facility, 630 East Summit

Street, Lead, SD 57754-1700, USA

S. Balashov, P. Ford, V. Francis, E. Holtom, A. Khazov, A. Kaboth,18 P. Majewski, J.A. Nikkel, J. O’Dell,R.M. Preece, M.G.D. van der Grinten, S.D. Worm19

STFC Rutherford Appleton Laboratory (RAL), Didcot, OX11 0QX, UK

R.L. Mannino, T.M. Stiegler, P.A. Terman, R.C. WebbTexas A&M University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843-4242, USA

C. Levy, J. Mock,20,21 M. SzydagisUniversity at Albany (SUNY), Department of Physics, 1400 Washington Avenue, Albany, NY 12222-1000, USA

J.K. Busenitz, M. Elnimr,22 J.Y-K. Hor, Y. Meng, A. Piepke, I. StancuUniversity of Alabama, Department of Physics & Astronomy, 206 Gallalee Hall, 514 University Boulevard,

Tuscaloosa, AL 34587-0324, USA13Also at: Fermi National Accelerator Laboratory (FNAL), Batavia, IL 60510-0500, USA14Now at: IBS Center for Underground Physics (CUP), 70, Yuseong-daero 1689-gil, Yuseong-gu, Daejeon, Korea15Now at: California State University, Stanislaus, Department of Physics, 1 University Circle, Turlock, CA 95382-3200, USA16Now at: Pacific Northwest National Laboratory (PNNL), 902 Battelle Blvd., Richland WA 99354-1793, USA17Now at: Northeastern University, 360 Huntington Ave. 111 Dana Research Center, Boston, MA 02115, USA18Also at: Royal Holloway, University of London, Department of Physics, Egham Hill, Egham, Surry, TW20 0EX, UK19Now at: University of Birmingham, Particle Physics Group, School of Physics and Astronomy, Edgbaston, Birmingham, B15

2TT, UK20Also at: Lawrence Berkeley National Laboratory (LBNL), 1 Cyclotron Road, Berkeley, CA 94720-8156 USA21Now at: Cosylab USA, Inc., 1530 Page Mill Road, Suite 200, Palo Alto, CA 94304-1140, USA22Now at: University of California (UC), Irvine, Department of Physics & Astronomy, 4129 Frederick Reines Hall, Irvine, CA

92697-4575, USA

L. Kreczko, B. Krikler, B. PenningUniversity of Bristol, School of Physics, Bristol, BS8 1TL, UK

E.P. Bernard, 20 R.G. Jacobsen, D.N. McKinsey,20 R. Watson20

University of California (UC), Berkeley, Department of Physics, 366 LeConte Hall MC 7300, Berkeley, CA94720-7300, USA

J.E. Cutter, S. El-Jurf, R.M. Gerhard, D. Hemer, S. Hillbrand, B. Holbrook, B.G. Lenardo,23

A.G. Manalaysay, J.A. Morad, S. Stephenson,24 J.A. Thomson, M. Tripathi, S. UvarovUniversity of California (UC), Davis, Department of Physics, One Shields Avenue, Davis, CA 95616-5270, USA

S.J. Haselschwardt, S. Kyre, C. Nehrkorn, H.N. Nelson, M. Solmaz, D.T. WhiteUniversity of California (UC), Santa Barbara, Department of Physics, Broida Hall, Santa Barbara, CA 93106-9530,

USA

M. Cascella, J.E.Y. Dobson, C. Ghag, X. Liu, L. Manenti, L. Reichhart,25 S. Shaw,26 U. UtkuUniversity College London (UCL), Department of Physics and Astronomy, Gower Street, London, WC1E 6BT, UK

P. Beltrame, T.J.R. Davison, M.F. Marzioni, A.St.J. Murphy, A. NilimaUniversity of Edinburgh, SUPA, School of Physics and Astronomy, Edinburgh, EH9 3FD, UK

B. Boxer,27 S. Burdin, A. Greenall, S. Powell, H.J. Rose, P. SutcliffeUniversity of Liverpool, Department of Physics, Liverpool, L69 7ZE, UK

J. Balajthy, T.K. Edberg, C.R. Hall, J.S. SilkUniversity of Maryland, Department of Physics, College Park, MD 20742-4111, USA

S. HertelUniversity of Massachusetts, Department of Physics, 1126 Lederle Graduate Research Tower (LGRT), Amherst, MA

01003-9337, USA

C.W. Akerlof, M. Arthurs, W. Lorenzon, K. Pushkin, M. SchubnellUniversity of Michigan, Randall Laboratory of Physics, 450 Church Street, Ann Arbor, MI 48109-1040, USA

K.E. Boast, C. Carels, T. Fruth, H. Kraus, F.-T. Liao, J. Lin,28 P.R. ScovellUniversity of Oxford, Department of Physics, Oxford, OX1 3RH, UK

E. Druszkiewicz, D. Khaitan, M. Koyuncu, W. Skulski, F.L.H. Wolfs, J. YinUniversity of Rochester, Department of Physics and Astronomy, Rochester, NY 14627-0171, USA

E.V. Korolkova, V.A. Kudryavtsev, P. Rossiter, D. WoodwardUniversity of Sheffield, Department of Physics and Astronomy, Sheffield, S3 7RH, UK

23Also at: Lawrence Livermore National Laboratory (LLNL), 7000 East Avenue, Livermore, CA 94550-9698, USA24Now at: Deepgram, 148 Townsend Street, San Francisco, CA, 94107-1919, USA25Now at: IMS Nanofabrication AG, Wolfholzgasse 20-22, 2345 Brunn am Gebirge, AUT26Now at: University of California (UC), Santa Barbara, Department of Physics, Broida Hall, Santa Barbara, CA 93106-9530, USA27Also at: STFC Rutherford Appleton Laboratory (RAL), Didcot, OX11 0QX, UK28Now at: University of California (UC), Berkeley, Department of Physics, 366 LeConte Hall MC 7300, Berkeley, CA 94720-7300,

USA

A.A. Chiller, C. Chiller, D.-M. Mei, L. Wang, W.-Z. Wei, M. While, C. ZhangUniversity of South Dakota, Department of Physics, 414 East Clark Street, Vermillion, SD 57069-2307, USA

S.K. Alsum, T. Benson, D.L. Carlsmith, J.J. Cherwinka, S. Dasu, G. Gregerson, B. Gomber, A. Pagac,K.J. Palladino, C.O. Vuosalo, Q. Xiao

University of Wisconsin-Madison, Department of Physics, 1150 University Avenue Room 2320, Chamberlin Hall,Madison, WI 53706-1390, USA

J.H. Buckley, V.V. Bugaev, M.A. OlevitchWashington University in St. Louis, Department of Physics, One Brookings Drive, St. Louis, MO 63130-4862, USA

E.M. Boulton,9,20 W.T. Emmet, T.W. Hurteau, N.A. Larsen,29 E.K. Pease,9,20 B.P. Tennyson,L. Tvrznikova9,20

Yale University, Department of Physics, 217 Prospect Street, New Haven, CT 06511-8499, USA

29Now at: The University of Chicago, The Kavli Institute for Cosmological Physics, William Eckhardt Research Center (ERC) -Suite 499, 5640 South Ellis Avenue, Chicago, IL 60637-1433, USA

Acknowledgements

This work was partially supported by the U.S. Department of Energy (DOE) under award numbersDESC0012704, DE-SC0010010, DE-AC02-05CH11231, DE-SC0012161, DE-SC0014223, DE-FG02-13ER42020, DE-FG02-91ER40674, DE-NA0000979, DE-SC0011702, DESC0012034, DESC0010072,DESC0006572, DE-SC0006605, DE-FG02-10ER46709, DE-AC02-07CH11359, DE-AC02-76SF00515,DE-AC52-07NA27344, DE-FG02-01ER41166, DE-FG02-91ER40628, DE-SC0015535, DE-SC0015708,and DE-SC0220187; by the U.S. National Science Foundation (NSF) under award numbers NSFPHY-110447, NSF PHY-1506068, NSF PHY-1312561, NSF PHY-1406943, NSF PHY-1642619, and NSFPHY-1429544, by the U.K. Science & Technology Facilities Council under award numbers ST/K006428/1,ST/M003655/1, ST/M003981/1, ST/M003744/1, ST/M003639/1, ST/M003604/1, ST/M003469/1,ST/M003779/1, and ST/N000250/1; by the Portuguese Foundation for Science and Technology (FCT)under award numbers CERN/FP/123610/2011 and PTDC/FIS-NUC/1525/2014; by the National ResearchNuclear University MEPhI (Moscow Engineering Physics Institute) in the framework of the MEPhIAcademic Excellence Project (contract 02.a03.21.0005, 27.08.2013); and by the Institute for Basic Science,Korea (budget numbers IBS-R016-D1, and IBS-R016-S1).

University College London and Lawrence Berkeley National Laboratory thank the U.K. Royal Societyfor travel funds under the International Exchange Scheme (IE141517). We acknowledge additional supportfrom the Boulby Underground Laboratory in the U.K., the University of Wisconsin for grant UW PRJ82AJ,the GridPP Collaboration, in particular at Imperial College London, and from the South Dakota Science andTechnology Authority, and the State of South Dakota. The University of Edinburgh is a charitable body,registered in Scotland, with the registration number SC005336.

Disclaimers

This document was prepared as an account of work sponsored by the United States Government. While thisdocument is believed to contain correct information, neither the United States Government nor any agencythereof, nor the Regents of the University of California, nor any of their employees, makes any warranty,express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, or represents that its use would not infringe privatelyowned rights. Reference herein to any specific commercial product, process, or service by its trade name,trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommen-dation, or favoring by the United States Government or any agency thereof, or the Regents of the Universityof California. The views and opinions of authors expressed herein do not necessarily state or reflect those ofthe United States Government or any agency thereof or the Regents of the University of California.

Copyright Notice

This manuscript has been authored by an author at Lawrence Berkeley National Laboratory under Con-tract No. DE-AC02-05CH11231 with the U.S. Department of Energy. The U.S. Government retains, andthe publisher, by accepting the article for publication, acknowledges, that the U.S. Government retains anon-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of thismanuscript, or allow others to do so, for U.S. Government purposes.

Contents

1 Overview 11.1 Direct Detection of Dark Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Cosmology and Complementarity . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Direct Detection Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Instrument Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3 Design Drivers for WIMP Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.3.1 Overview of the Experimental Strategy . . . . . . . . . . . . . . . . . . . . . . . . 101.3.2 Self-shielding in Liquid Xenon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.3.3 Low-energy Particle Detection in Liquid Xenon . . . . . . . . . . . . . . . . . . . . 16

1.3.3.1 Low Energy and Low Mass Sensitivity . . . . . . . . . . . . . . . . . . . 181.3.4 Electron/Nuclear Recoil Discrimination . . . . . . . . . . . . . . . . . . . . . . . . 191.3.5 Outer Detector Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1.3.5.1 Xenon Skin Veto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.3.5.2 Scintillator Outer Detector . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.4 Internal Calibration with Dispersed Sources . . . . . . . . . . . . . . . . . . . . . . . . . . 251.5 Xenon Purity for Detector Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251.6 Dominant Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

1.6.1 Backgrounds from Material Radioactivity . . . . . . . . . . . . . . . . . . . . . . . 271.6.2 Surface Plating of Radon Progeny . . . . . . . . . . . . . . . . . . . . . . . . . . . 291.6.3 Intrinsic Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291.6.4 Cosmogenic Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.6.5 Fiducialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.7 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2 Scientific Performance 372.1 WIMP Sensitivity and Discovery Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.1.1 S1+S2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382.2 Neutrino Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.2.1 Solar and Atmospheric Neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . 402.2.1.1 Elastic Scattering of Solar Neutrinos . . . . . . . . . . . . . . . . . . . . 402.2.1.2 Coherent Nuclear Scattering of Solar Neutrinos . . . . . . . . . . . . . . 412.2.1.3 Atmospheric Neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . 422.2.1.4 Neutrino Magnetic Moment . . . . . . . . . . . . . . . . . . . . . . . . . 432.2.1.5 Other Neutrino Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . 43

2.2.2 Double Beta Decay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442.2.2.1 Neutrinoless Double Beta Decay . . . . . . . . . . . . . . . . . . . . . . 442.2.2.2 Two Neutrino Double Beta Decay . . . . . . . . . . . . . . . . . . . . . . 45

2.2.3 Supernova Neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452.2.4 Sterile Neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.3 New Physics Beyond Nuclear Recoils from WIMPs . . . . . . . . . . . . . . . . . . . . . . 472.3.1 Electrophilic WIMPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

2.3.2 Axions and Axion-like Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472.4 Physics with the Outer Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

2.4.1 Muons and muon-induced neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . 492.4.2 Neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502.4.3 Exotic particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

2.5 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

3 Xenon Detector System 553.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553.2 The Liquid Xenon Time Projection Chamber . . . . . . . . . . . . . . . . . . . . . . . . . 58

3.2.1 Drift Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583.2.2 Reverse-Field Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593.2.3 Electroluminescence Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.2.4 VUV Reflectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.2.5 Thermal Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

3.3 Cathode HV Delivery System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633.3.1 Cathode HV Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633.3.2 HV System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.3.3 Cathode Supply and Cable Connection . . . . . . . . . . . . . . . . . . . . . . . . 653.3.4 Cathode Feedthrough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653.3.5 Cathode HV Umbilical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653.3.6 Spark and Discharge Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663.3.7 HV Connection to Cathode Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673.3.8 HV Safety Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

3.4 Photomultiplier Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693.4.1 PMT Test Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703.4.2 PMT Radioactivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703.4.3 PMT Bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713.4.4 Cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733.4.5 Assembly and Integration with TPC . . . . . . . . . . . . . . . . . . . . . . . . . . 743.4.6 PMT Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

3.5 S1 Light Collection Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773.5.1 Overview of Design and Optical Performance of the TPC . . . . . . . . . . . . . . . 773.5.2 TPC Optical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793.5.3 PMT Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

3.6 S2 Production and Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823.6.1 S2 Photon Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833.6.2 S2 Photon Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843.6.3 S2 Resolution and Electrode Configuration . . . . . . . . . . . . . . . . . . . . . . 853.6.4 Design and Fabrication of the Grids . . . . . . . . . . . . . . . . . . . . . . . . . . 873.6.5 Reconstruction of Peripheral Interactions . . . . . . . . . . . . . . . . . . . . . . . 89

3.7 The Xe Skin Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.7.1 Skin performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

3.8 Internal Fluid System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943.9 Xenon System Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

3.9.1 Thermometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973.9.2 Liquid Level Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

3.9.3 Acoustic Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993.9.4 Loop Antennae for Discharge Detection . . . . . . . . . . . . . . . . . . . . . . . . 1003.9.5 Position Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

3.10 Integrated System Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003.10.1 Reflectivity Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003.10.2 HV Studies in Small Two-Phase Chambers . . . . . . . . . . . . . . . . . . . . . . 1023.10.3 TPC Design Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053.10.4 Full Scale Grid Testing at SLAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

3.11 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

4 Outer Detector 1154.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154.2 Function and Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154.3 Outer Detector Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174.4 Mechanical Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

4.4.1 Acrylic Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1194.4.2 PMT Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1214.4.3 Scintillator Distribution System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

4.5 Liquid Scintillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224.6 Light Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

4.6.1 Photomultipliers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1254.7 Optical Calibration System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264.8 Threshold, singles rate, deadtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264.9 Environment, Safety, and Health Considerations . . . . . . . . . . . . . . . . . . . . . . . . 1274.10 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

5 Cryostat 1295.1 Material Search Campaign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

5.1.1 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1295.1.2 Stainless Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

5.2 Monte Carlo simulations of background from the cryostat . . . . . . . . . . . . . . . . . . . 1335.3 Cryostat technical specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1335.4 Inner Cryostat Vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355.5 Outer Cryostat Vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375.6 Cryostat Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1385.7 Cryostat Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1385.8 Thermal Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1385.9 Fabrication, Cleanliness, Tests and Certifications . . . . . . . . . . . . . . . . . . . . . . . 1405.10 Transportation and Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425.11 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

6 Xenon and Cryogenics Systems 1476.1 Introduction and overview of requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 1476.2 Xenon purification and storage specifications . . . . . . . . . . . . . . . . . . . . . . . . . 148

6.2.1 Air leaks during storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1486.2.2 One-time air contamination during operations. . . . . . . . . . . . . . . . . . . . . 1486.2.3 Continuous air leak during operations. . . . . . . . . . . . . . . . . . . . . . . . . . 1486.2.4 Cosmogenic activation of the Xe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

6.3 Krypton Removal via Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1496.4 Online Xenon Purification System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

6.4.1 Gas recirculation system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1576.4.2 Liquid xenon tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1616.4.3 LXe transfer lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1646.4.4 SLAC System Test prototype of the circulation architecture . . . . . . . . . . . . . . 1656.4.5 Radon removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1666.4.6 Slow controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

6.5 Xenon Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1706.6 Long-term xenon storage and transportation . . . . . . . . . . . . . . . . . . . . . . . . . . 1756.7 Xenon Sampling and Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1786.8 Cryogenics, vacuum services, and breakout boxes . . . . . . . . . . . . . . . . . . . . . . . 1816.9 Xenon Procurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1866.10 Solubility and diffusion constants of common impurity gas species . . . . . . . . . . . . . . 1866.11 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

7 Calibration Systems 1897.1 Internal Radioisotope Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

7.1.1 Metastable Krypton 83 (83mKr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1907.1.2 Metastable Xenon 131 (131mXe) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1907.1.3 Tritium-Labeled Methane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1917.1.4 Radon 220 (220Rn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1927.1.5 Internal Radioisotope Source Delivery . . . . . . . . . . . . . . . . . . . . . . . . . 192

7.2 External Radioisotope Source Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1937.2.1 Neutron sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1947.2.2 Gamma Sources for Calibration of the Active Xe TPC . . . . . . . . . . . . . . . . 1957.2.3 Gamma Sources for Calibration of Xenon Skin and the Scintillator Veto . . . . . . . 1957.2.4 Calibration Source Deployment (CSD) . . . . . . . . . . . . . . . . . . . . . . . . 1957.2.5 Radioisotope Capsule Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

7.3 Photoneutron Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1977.3.1 Physics of Photoneutron Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1977.3.2 Photoneutron Source Deployment . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

7.4 Deuterium-Deuterium Neutron Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1997.4.1 Physics motivation of Deuterium-Deuterium Neutron Sources . . . . . . . . . . . . 200

7.4.1.1 NR Qy / Ly calibration of the LZ detector . . . . . . . . . . . . . . . . . 2007.4.1.2 Calibrating LZ detector using Reflected Neutrons from D2(O) Target . . . 2007.4.1.3 Calibrating LZ Detector with Neutron Events with no S1 Light . . . . . . 2007.4.1.4 Direct Ly Measurement Using Double (Multiple) Scatter Events . . . . . 200

7.4.2 DD Source Deployment and Neutron Rates . . . . . . . . . . . . . . . . . . . . . . 2027.5 Calibration Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

7.5.1 Effect of Gd doping in liquid scintillator . . . . . . . . . . . . . . . . . . . . . . . . 2037.5.2 Effect of gamma captures on useful neutron event rates . . . . . . . . . . . . . . . . 2037.5.3 Maximum useful calibration rates . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

7.6 Environment, Health and Safety Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . 2057.7 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

8 Electronics, DAQ, Controls, and Online Computing 2078.1 Signal Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2078.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2088.3 Analog Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

8.3.1 Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2108.3.2 LZ Amplifier Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

8.4 Digital Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2168.5 DAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

8.5.1 Data Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2188.5.2 Data Sparsification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

8.6 PMT HV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2248.7 Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2248.8 Slow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

8.8.1 Functions of the slow control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2258.8.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2268.8.3 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2268.8.4 PLC System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2278.8.5 Ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2288.8.6 Tags and device interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2288.8.7 Historian, alarms and automation . . . . . . . . . . . . . . . . . . . . . . . . . . . 2298.8.8 Graphical User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2298.8.9 Integration into experiment online IT . . . . . . . . . . . . . . . . . . . . . . . . . 230

8.9 Online System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2308.10 Electronics Chain Test Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

8.10.1 Description and goals of the Electronics chain test facility . . . . . . . . . . . . . . 2348.10.2 Single photoelectron pulse propagation . . . . . . . . . . . . . . . . . . . . . . . . 2348.10.3 PMT Base Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2378.10.4 DAQ Code and Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2378.10.5 Real Signals from LUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

8.11 Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2408.12 Network Infrastructure, Security, Remote Access . . . . . . . . . . . . . . . . . . . . . . . 241

8.12.1 Local Area Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2418.12.2 Reliability and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2428.12.3 Information Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2428.12.4 Remote Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

8.13 Installation and Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2438.14 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

9 Material Screening 2479.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2479.2 Goals, Requirements and Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

9.2.1 Materials Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2519.2.2 Backgrounds Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

9.3 Techniques and Sensitivities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2619.4 Intrinsic Contamination Techniques and Devices . . . . . . . . . . . . . . . . . . . . . . . 264

9.4.1 HPGe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2649.4.1.1 BHUC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

9.4.1.2 BUGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2659.4.1.3 Surface HPGe Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

9.4.2 ICP-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2679.4.3 NAA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

9.5 Radon Emanation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2709.6 Surface Cleanliness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

9.6.1 Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2749.6.2 Radon Plate–out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276

9.7 Liquid Xenon Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2799.7.1 Krypton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2809.7.2 Argon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

9.8 Laboratory and Cosmogenic Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . 2819.8.1 Laboratory Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2819.8.2 Cosmogenic Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282

9.9 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

10 SURF Infrastructure, Assembly, and Integration 28710.1 Surface Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

10.1.1 Surface Assembly Laboratory (SAL) . . . . . . . . . . . . . . . . . . . . . . . . . 28810.1.2 Radon-reduced Air System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28810.1.3 Surface Storage Facility (SSF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

10.2 Yates Shaft Infrastructure and Custom Transport . . . . . . . . . . . . . . . . . . . . . . . 29010.3 Underground Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29210.4 Integration and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

10.4.1 Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29510.4.2 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

10.4.2.1 TPC Assembly (Steps SA2 – SA6) . . . . . . . . . . . . . . . . . . . . . 29810.4.2.2 TPC Insertion into Cryostat with Fluid and Electrical Final Routing . . . . 30010.4.2.3 Underground Outer Detector Tank Preparation / Staging (Steps U1 – U2) . 30010.4.2.4 Cryostat Transportation and Underground Assembly (Steps U3 – U6) . . . 30210.4.2.5 Utility Connection (Step U7) . . . . . . . . . . . . . . . . . . . . . . . . 30310.4.2.6 Outer Detector Assembly (Steps U8 – U9) . . . . . . . . . . . . . . . . . 304

10.5 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

11 Offline Computing and Software 30711.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30711.2 Data Volume, Data Processing, and Data Centers . . . . . . . . . . . . . . . . . . . . . . . 308

11.2.1 The U.S. Data Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30911.2.2 The U.K. Data Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310

11.3 Analysis Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31111.4 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31311.5 Software Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31411.6 Schedule and Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31611.7 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

12 Simulations, Requirements, and Detector Performance 31912.1 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

12.1.1 Geometry construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

12.1.2 Event Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32112.1.2.1 Neutron production in detector materials . . . . . . . . . . . . . . . . . . 32212.1.2.2 Muon-induced neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . 32212.1.2.3 Gamma activity in large detector components . . . . . . . . . . . . . . . 32212.1.2.4 Gammas from the cavern rock . . . . . . . . . . . . . . . . . . . . . . . . 32312.1.2.5 Benchmark points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

12.1.3 From energy deposition to signals . . . . . . . . . . . . . . . . . . . . . . . . . . . 32312.1.4 Analysis cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32412.1.5 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

12.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32612.2.1 WBS 1.1 Xenon Procurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32912.2.2 WBS 1.2 Xenon Vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33012.2.3 WBS 1.3 Cryogenic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33112.2.4 WBS 1.4 Xenon Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33212.2.5 WBS 1.5 Xenon Detector System . . . . . . . . . . . . . . . . . . . . . . . . . . . 33312.2.6 WBS 1.6 Outer Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33412.2.7 WBS 1.7 Calibration System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33412.2.8 WBS 1.8 Electronics, DAQ, Controls, and Computing . . . . . . . . . . . . . . . . 33612.2.9 WBS 1.9 Integration and Installation . . . . . . . . . . . . . . . . . . . . . . . . . 33712.2.10 WBS 1.10 Cleanliness and Screening . . . . . . . . . . . . . . . . . . . . . . . . . 33812.2.11 WBS 1.11 Offline Computing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

12.3 Sensitivity and Detector Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34012.3.1 Profile Likelihood Ratio Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34012.3.2 LZ Sensitivity Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34312.3.3 Parameter Scans of LZ Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

12.4 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

13 Management, Cost, and Schedule Summary 35513.1 LZ Project Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355

13.1.1 Project Advisory Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35613.1.2 Project Management Office . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35613.1.3 Project Work Breakdown Structure . . . . . . . . . . . . . . . . . . . . . . . . . . 35713.1.4 Project Subsystem Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358

13.2 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36213.3 Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36213.4 Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36313.5 Cost and Schedule Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

13.5.1 Project Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36413.6 Project Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36513.7 Cost Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

List of Figures

1.1.1 Scan of pMSSM parameter space and complementarity . . . . . . . . . . . . . . . . . . . . . . 21.1.2 Compilation of current WIMP-nucleon SI cross-section upper limits (90 % CL) . . . . . . . . . 31.1.3 Evolution of cross-section limits for 50-GeV WIMPs as function of time . . . . . . . . . . . . . 41.1.4 A compilation of WIMP-nucleon SI cross-section sensitivity . . . . . . . . . . . . . . . . . . . 51.2.1 The LZ detector concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3.1 Integrated rates above threshold for various targets . . . . . . . . . . . . . . . . . . . . . . . . 111.3.2 Operating principle of the double-phase Xe TPC . . . . . . . . . . . . . . . . . . . . . . . . . 111.3.3 A double-scatter neutron event recorded in ZEPLIN-III . . . . . . . . . . . . . . . . . . . . . . 121.3.4 Mean interaction lengths for neutrons and gamma rays . . . . . . . . . . . . . . . . . . . . . . 141.3.5 Self-shielding of external neutrons and gamma rays in LXe . . . . . . . . . . . . . . . . . . . . 151.3.6 Absolute ER scintillation yield in LXe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.3.7 ER ionization yield in LXe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.3.8 Absolute NR scintillation yield in LXe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.3.9 Absolute NR ionization yield in LXe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181.3.10 Low-energy performance of double-phase Xe detectors . . . . . . . . . . . . . . . . . . . . . 201.3.11 Discrimination in LUX with calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.3.12 ER leakage into the NR band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231.5.1 Evolution of electron lifetime in LUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261.6.1 Fiducialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.1.1 The LUX WIMP search data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382.1.2 LZ sensitivity projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402.2.1 Calculated PDFs for NR from neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422.2.2 Neutrino magnetic moment signal in LZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432.2.3 Sensitivity to oscillations to sterile neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . 462.3.1 Dark-matter axion-like particle sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482.3.2 Solar axion-like particle sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.1.1 Schematic views of the Xenon Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563.2.1 TPC electric field regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583.2.2 TPC field non-uniformity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603.2.3 TPC reverse-field region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.2.4 Electroluminescence region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.3.1 Cathode HV delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653.3.2 Cathode feedthrough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663.3.3 Cathode field-grading and connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673.3.4 Cathode connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683.3.5 Cathode connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683.4.1 Xenon-space photomultipliers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693.4.2 Photomultiplier test setups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713.4.3 Photomultiplier base voltage-divider circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

3.4.4 R11410 voltage-divider base prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723.4.5 PMT assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753.4.6 TPC photomultiplier arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763.5.1 S1 photon detection efficiency scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793.5.2 S1 PDE as a function of photon absorption length and PTFE reflectivity . . . . . . . . . . . . . 803.5.3 Layout of bottom and top PMT arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813.6.1 S2 photon yield and pulse width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833.6.2 S2 photon detection efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853.6.3 Energy-resolution for high energy electron recoils . . . . . . . . . . . . . . . . . . . . . . . . . 863.6.4 Simulation of S2 electroluminescence response . . . . . . . . . . . . . . . . . . . . . . . . . . 883.6.5 Reconstruction of wall events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.7.1 Mounting of dome and lower side Skin PMTs . . . . . . . . . . . . . . . . . . . . . . . . . . . 913.7.2 Xe Skin inefficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923.7.3 Light collection efficiency of Xe Skin detector . . . . . . . . . . . . . . . . . . . . . . . . . . 933.7.4 Skin performance as a function of PTFE reflectivity . . . . . . . . . . . . . . . . . . . . . . . 933.8.1 Overview of internal circulation flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.8.2 Details of fluid distribution pipes at the bottom of the vessel . . . . . . . . . . . . . . . . . . . 963.9.1 Internal monitoring sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973.9.2 Xenon level sensors data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993.10.1 PTFE reflectivity measurements at LIP-Coimbra . . . . . . . . . . . . . . . . . . . . . . . . . 1023.10.2 U. Michigan chamber and results for PTFE reflectivity measurements . . . . . . . . . . . . . . 1033.10.3 Imperial chamber to study high-field emission processes in thin wires . . . . . . . . . . . . . 1043.10.4 LBNL test chamber for small wire grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053.10.5 SLAC System Test Phase-I TPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1063.10.6 LAr System Test at Yale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073.10.7 Glow detected from Reverse Field Region tested in LAr . . . . . . . . . . . . . . . . . . . . . 1083.10.8 LArTest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093.10.9 SLAC System Test platform at SLAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103.10.10 SLAC Phase-I and Phase-II vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

4.2.1 NR Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164.3.1 Layout of the LZ outer detector system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174.3.2 Neutron Capture Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184.4.1 Stress on vessels during filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1204.4.2 Two steps in the assembly sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1214.4.3 Plan view of the PMT support system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224.8.1 Inefficiency for vetoing neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

5.1.1 Stages in commercial production of Ti metal . . . . . . . . . . . . . . . . . . . . . . . . . . . 1305.3.1 LZ cryostat overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1345.4.1 LZ cryostat assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1365.5.1 OCV tie rod port assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375.8.1 Inner cryostat vessel thermal insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1405.10.1 Cryostat assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

6.3.1 Kr removal R&D system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1496.3.2 Kr removal time profiles of Kr and Xe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1506.3.3 Kr removal simplified schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

6.3.4 Kr removal condenser and LN system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536.3.5 Kr removal physical layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1546.3.6 Kr removal P&ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1556.4.1 Schematic diagram of LZ online purification system . . . . . . . . . . . . . . . . . . . . . . . 1566.4.2 Xe Gas Recirculation system P&ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1586.4.3 Fluitron all-metal diaphragm compressor at SLAC . . . . . . . . . . . . . . . . . . . . . . . . 1596.4.4 P&ID of Detector and Xenon Handling Tie-Ins . . . . . . . . . . . . . . . . . . . . . . . . . . 1606.4.5 Xe Tower with Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1616.4.6 P&ID of the LXe Tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1626.4.7 LXe Tower and LXe transfer lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1646.4.8 System Test LXe Tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1666.4.9 Breakthrough time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1686.4.10 LZ radon removal system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1686.4.11 PLC Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1696.5.1 Simplified flow schematic of LZ Xe Recovery System . . . . . . . . . . . . . . . . . . . . . . 1716.5.2 Xe system pressure threshold plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1726.5.3 P&ID of Recovery/Detector Tie-In . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1736.5.4 Xe Delivery & Recovery system P&ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1746.6.1 Overview of LZ cylinder gas pack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1766.6.2 Location of Xe Storage Room in the Davis campus . . . . . . . . . . . . . . . . . . . . . . . . 1776.6.3 Xe Storage system P&ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1796.7.1 Kr pressure trace for 0.34 ppt (g/g) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806.7.2 P&ID of the LZ online Xe sampling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1816.7.3 SLAC sampling system and coldtrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1826.8.1 Cryogenics installation in the Davis Cavern . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1826.8.2 Cryocooler schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

7.1.1 Illustrations of 83mKr calibrations in LUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1917.1.2 Internal radioisotope source delivery system. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1937.2.1 Recoil spectra from neutron sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1947.2.2 Calibration of Xe Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1957.2.3 Prototype of core of CSD system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1967.2.4 Prototype dummy source capsule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1977.3.1 S1/S2 spectra for 8B solar neutrino coherent scattering . . . . . . . . . . . . . . . . . . . . . . 1987.3.2 Photoneutron pig, various views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1997.4.1 Schematic setup for the utilization of a deuterium-based backscatter reflector . . . . . . . . . . 2017.4.2 LZ DD square wave neutron trigger pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2017.4.3 Solid model of LZ detector with angled neutron tube . . . . . . . . . . . . . . . . . . . . . . . 2027.5.1 Event rate due to all gammas in the active xenon TPC from neutron captures on Gd . . . . . . . 2047.5.2 Event overlap probability as function of event rate . . . . . . . . . . . . . . . . . . . . . . . . 205

8.1.1 TPC PMT signal processing schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2078.1.2 OD PMT signal processing schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2088.1.3 A schematic of the data flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2098.3.1 Simulation of events with >0.25 PHE in two PMTs . . . . . . . . . . . . . . . . . . . . . . . . 2118.3.2 LZ amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2128.3.3 Simulation of S2 response for a 236-keV Xe transition . . . . . . . . . . . . . . . . . . . . . . 2128.3.4 Simulation of S2 response for a 3-MeV Xe energy deposition . . . . . . . . . . . . . . . . . . 212

8.3.5 Dynamic range for S2 signals detected in the top and bottom PMTs . . . . . . . . . . . . . . . 2138.3.6 Dynamic range for S1 signals detected in the bottom PMTs . . . . . . . . . . . . . . . . . . . . 2138.3.7 Flanges and amplifier crate prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2148.3.8 SPHE Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2158.3.9 Amplifier Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2158.3.10 Power and Crosstalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2168.3.11 Results of linearity measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2168.3.12 Lower Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2178.4.1 Digital motherboard used to develop LZ digitizers . . . . . . . . . . . . . . . . . . . . . . . . 2178.4.2 Prototype ADC daughter card with 32 channels . . . . . . . . . . . . . . . . . . . . . . . . . . 2188.5.1 Diagram of the DAQ architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2198.5.2 Detailed depiction of interaction between DAQ elements . . . . . . . . . . . . . . . . . . . . . 2198.5.3 Proposed memory organization of POD waveform storage . . . . . . . . . . . . . . . . . . . . 2208.5.4 Full digital waveform sum creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2238.8.1 Slow control functional diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2278.8.2 An example of a low-level panel in the System Test slow control GUI . . . . . . . . . . . . . . 2308.9.1 Primary interfaces between RC and other LZ subsystems . . . . . . . . . . . . . . . . . . . . . 2318.9.2 Run Control GUI screenshot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2338.10.1 Diagram of the first phase of the Electronics Chain Test Facility . . . . . . . . . . . . . . . . 2358.10.2 Diagram of the Chain Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2358.10.3 Single photoelectron intensity plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2358.10.4 Single photoelectron spectrum at estimated 1.9 × 106 and 3.25 × 106 gain . . . . . . . . . . . 2368.10.5 SPHE timing measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2368.10.6 PMT Base Pulse Shape Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2378.10.7 PMT Base Area Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2378.10.8 DAQScope tool screenshot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2388.10.9 Noise spectrum from LUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2398.10.10 SPHE spectrum obtained at LUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2398.11.1 Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2408.12.1 The LZ Online network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2418.13.1 Location of analog and digital electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2438.13.2 The top breakout box at the mezzanine level . . . . . . . . . . . . . . . . . . . . . . . . . . . 2448.13.3 Details of one elements of the breakout system . . . . . . . . . . . . . . . . . . . . . . . . . . 2458.13.4 Layout of the LZ electronics racks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

9.2.1 ER and NR background in the cryostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

10.1.1 SURF Aerial View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28710.1.2 The Surface Assembly Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28810.1.3 Plan view of additional building to be constructed . . . . . . . . . . . . . . . . . . . . . . . . 28910.1.4 Plan view of RRS Building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28910.1.5 Building constructed for staging LZ detector components . . . . . . . . . . . . . . . . . . . . 29010.2.1 LZ transport method from building to headframe . . . . . . . . . . . . . . . . . . . . . . . . 29110.3.1 Plan view of the Davis Campus at the 4850L . . . . . . . . . . . . . . . . . . . . . . . . . . . 29210.3.2 Overall layout of LZ in the Davis Campus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29310.3.3 LZ and related support systems in the Davis Cavern . . . . . . . . . . . . . . . . . . . . . . . 29410.4.1 LZ surface assembly sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29910.4.2 Underground installation sequence in water tank . . . . . . . . . . . . . . . . . . . . . . . . . 301

11.1.1 Schematic data-flow diagram for LZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30711.5.1 Parallel development workflow in GitLab . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

12.1.1 Engineering drawing and simulation geometry of the outer cryostat . . . . . . . . . . . . . . . 32012.1.2 Engineering drawing and simulation geometry of the TPC . . . . . . . . . . . . . . . . . . . . 32112.1.3 Engineering drawing and simulation geometry of the bottom PMT array . . . . . . . . . . . . 32112.2.1 Top Level LZ Science Requirements Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32612.3.1 Profiles of background and signal in LZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34112.3.2 PLR discrimination statistic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34212.3.3 PLR technique for different masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34212.3.4 Acceptance and rejection for WIMP signals in LZ . . . . . . . . . . . . . . . . . . . . . . . . 34312.3.5 LZ sensitivity projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34412.3.6 LZ discovery potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34512.3.7 Example LZ exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34612.3.8 LZ sensitivity projections for goal, baseline, and reduced parameters . . . . . . . . . . . . . . 34712.3.9 LZ sensitivity projections vs. radon concentration . . . . . . . . . . . . . . . . . . . . . . . . 34812.3.10 LZ sensitivity projections vs. radon concentration . . . . . . . . . . . . . . . . . . . . . . . 34912.3.11 LZ sensitivity projections vs. atmospheric neutrino rate . . . . . . . . . . . . . . . . . . . . 34912.3.12 LZ sensitivity projections vs. S1 photon detection efficiency . . . . . . . . . . . . . . . . . . 35012.3.13 LZ sensitivity projections vs. electron lifetime . . . . . . . . . . . . . . . . . . . . . . . . . 35012.3.14 LZ sensitivity projections vs. electron extraction efficiency . . . . . . . . . . . . . . . . . . 35112.3.15 LZ sensitivity projections vs. electric field . . . . . . . . . . . . . . . . . . . . . . . . . . . 35112.3.16 LZ sensitivity projections vs. trigger coincidence level . . . . . . . . . . . . . . . . . . . . . 35212.3.17 LZ sensitivity projections vs. exposure in days . . . . . . . . . . . . . . . . . . . . . . . . . 352

13.1.1 LZ Project reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35513.1.2 LZ Project organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35613.5.1 Summary of LZ schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

List of Tables

1.2.1 Principal parameters and WBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.6.1 Summary of backgrounds in LZ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.1.1 Key LZ and LUX Assumptions Compared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.1.1 Xenon detector parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573.3.1 Dependence of TPC parameters on cathode HV . . . . . . . . . . . . . . . . . . . . . . . . . . 643.3.2 Safety factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.4.1 Cabling in the xenon space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743.5.1 Optical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783.6.1 Main S2 parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843.6.2 S2 photon detection efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853.6.3 TPC electrode grid parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873.9.1 Monitoring sensors in the xenon space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 983.10.1 LZ System Test planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

4.4.1 The volume and masses of the scintillator vessels . . . . . . . . . . . . . . . . . . . . . . . . . 1204.5.1 Radioactive impurity goals in LAB-based Gd-LS . . . . . . . . . . . . . . . . . . . . . . . . . 1244.6.1 Characteristics of the R5912 PMTs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

5.1.1 Summary of titanium samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1315.1.2 Summary of stainless steel samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1325.3.1 Pressures and temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355.4.1 Vessel-wall thicknesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1365.7.1 External loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

6.4.1 Radon emanation estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1676.8.1 Heat load table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1846.10.1 Solubility and diffusion constants of common impurity species. . . . . . . . . . . . . . . . . . 187

7.0.1 Baseline calibration sources for LZ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1897.5.1 Fraction of neutron scatters in the Xe TPC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

8.2.1 Properties of the PMTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2098.2.2 Calibrations and expected count rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2108.3.1 Summary of the number and type of the 1,359 analog signals. . . . . . . . . . . . . . . . . . . 2138.5.1 Key parameters of the prototype Data Collector. . . . . . . . . . . . . . . . . . . . . . . . . . . 2208.5.2 Summary of the performances of the DAQ links . . . . . . . . . . . . . . . . . . . . . . . . . 2218.5.3 Summary of data collectors expected peak storage and buffering capabilities . . . . . . . . . . 2218.5.4 Summary of three major waveform-selection modes for the central TPC PMTs. . . . . . . . . . 2238.6.1 Details of the PMT HV system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2248.7.1 Information on LZ signal, logic, HV, power, and network cables. . . . . . . . . . . . . . . . . . 225

9.2.1 Table of material radioactivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2529.2.2 Results from the radio-assay of titanium sample TIMET HN3469 . . . . . . . . . . . . . . . . 2559.2.3 Assay results from R11410-20 PMT component materials . . . . . . . . . . . . . . . . . . . . 2569.2.4 Assay results from 3-inch R11410 PMT base component materials . . . . . . . . . . . . . . . . 2579.2.5 Assay results from 1-inch R8520 skin PMT base component materials . . . . . . . . . . . . . . 2579.2.6 NAA measurements of PTFE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2589.2.7 Table of Backgrounds in LZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2609.3.1 Primary material radio-assay techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2629.4.1 The LZ -ray spectroscopy detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2659.5.1 Radon emanation screening facilities available to LZ . . . . . . . . . . . . . . . . . . . . . . . 2719.5.2 Materials in LZ to be assayed for radon emanation . . . . . . . . . . . . . . . . . . . . . . . . 2729.6.1 Expected NR background due to (� ,n) reaction from plate–out activity. . . . . . . . . . . . . . 2789.6.2 Allowable exposure times (days) to reach radon daughter plate-out requirements . . . . . . . . 2789.8.1 Background from laboratory, muon-induced neutrons, and cosmogenic activation . . . . . . . . 281

11.2.1 LZ daily data rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30811.2.2 U.S. and U.K. data center staging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31011.4.1 LZ simulations computing resources needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31411.6.1 Key offline computing milestones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

12.2.1 Top Level Science Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32712.2.2 Level 2 Requirements for WBS 1.2 Xenon Vessel . . . . . . . . . . . . . . . . . . . . . . . . 33012.2.3 Level 2 Requirements for WBS 1.3 Cryogenic System . . . . . . . . . . . . . . . . . . . . . 33112.2.4 Level 2 Requirements for WBS 1.4 Xenon Purification . . . . . . . . . . . . . . . . . . . . . 33212.2.5 Level 2 Requirements for WBS 1.5 Xenon Detector System . . . . . . . . . . . . . . . . . . 33312.2.6 Level 2 Requirements for WBS 1.6 Outer Detector . . . . . . . . . . . . . . . . . . . . . . . 33412.2.7 Level 2 Requirements for WBS 1.7 Calibration System . . . . . . . . . . . . . . . . . . . . . 33412.2.8 Level 2 Requirements for WBS 1.8 Electronics, DAQ, Controls, and Computing . . . . . . . 33612.2.9 Level 2 Requirements for WBS 1.9 Integration and Installation . . . . . . . . . . . . . . . . . 33712.2.10 Level 2 Requirements for WBS 1.10 Cleanliness and Screening . . . . . . . . . . . . . . . . 33812.2.11 Level 2 Requirements for WBS 1.11 Offline Computing . . . . . . . . . . . . . . . . . . . . 33912.3.1 Backgrounds used in the profile likelihood analysis . . . . . . . . . . . . . . . . . . . . . . . 34012.3.2 Key parameters for reduced, baseline, and goal detector performance . . . . . . . . . . . . . . 346

13.1.1 LZ Work Breakdown Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35713.1.2 LZ Work Breakdown Structure (WBS) shown at L2 . . . . . . . . . . . . . . . . . . . . . . . 35913.7.1 LZ Project cost summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366