Collaboration, LEGENDAbgrall, NAbt, IAgostini, MAlexander, AAndreoiu, CAraujo, GRIII, FT AvignoneBae, WBakalyarov, ABalata, MBantel, MBarabanov, IBarabash, ASBarbeau, PSBarton, CJBarton, PJBaudis, LBauer, CBernieri, EBezrukov, LBhimani, KHBiancacci, VBlalock, EBolozdynya, ABorden, SBos, BBossio, EBoston, ABothe, VBouabid, RBoyd, SBrugnera, RBurlac, NBusch, MCaldwell, ACaldwell, TSCarney, RCattadori, CChan, Y-DChernogorov, AChristofferson, CDChu, P-HClark, MCohen, TCombs, DComellato, TCooper, RJCosta, IAD'Andrea, VDetwiler, JAGiacinto, A DiMarco, N DiDobson, JDrobizhev, ADurand, MREdzards, FEfremenko, YuElliott, SREngelhardt, AFajt, LFaud, NFebbraro, MTFerella, FFields, DEFischer, FFomina, MFox, HFranchi, JGala, RGalindo-Uribarri, AGangapshev, AGarfagnini, AGeraci, AGilbert, CGold, MGooch, CGradwohl, KPGreen, MPGrinyer, GFGrobov, AGruszko, JGuinn, IGuiseppe, VEGurentsov, VGurov, YGusev, KHacket, BHagemann, FHakenmüeller, JHaranczyk, MHauertmann, LHaufe, CRHayward, CHeffron, BHenkes, FHenning, RAguilar, D HervasHinton, JHodak, RHoffmann, HHofmann, WHostiuc, AHuang, JHult, MMirza, M IbrahimJochum, JJones, RJudson, DJunker, MKaizer, JKazalov, VKermaïdic, YKhushbakht, HKidd, MKihm, TKilgus, KKim, IKlimenko, AKnöpfle, KTKochetov, OKonovalov, SIKontul, IKool, KKormos, LLKornoukhov, VNKorosec, MKrause, PKuzminov, VVLópez-Castaño, JMLang, KLaubenstein, MLeón, ELehnert, BLeonhardt, ALi, ALindner, MLippi, ILiu, XLiu, JLoomba, DLubashevskiy, ALubsandorzhiev, BLusardi, NMüller, YMacko, MMacolino, CMajorovits, BMamedov, FManeschg, WManzanillas, LMarshall, GMartin, RDMartin, ELMassarczyk, RMei, DMeijer, SJMertens, SMisiaszek, MMondragon, EMorella, MMorgan, BMroz, TMuenstermann, DNave, CJNemchenok, INeuberger, MOli, TKGann, G OrebiOthman, GPalušova, VPanth, RPapp, LPaudel, LSPelczar, KPerez, J PerezPertoldi, LPettus, WPiseri, PPoon, AWPPovinec, PPullia, ARadford, DCRamachers, YARansom, CRauscher, LRedchuk, MReine, ALRiboldi, SRielage, KRozov, SRukhadze, ERumyantseva, NRunge, JRuof, NWSaakyan, RSailer, SSalamanna, GSalamida, FSalvat, DJSandukovsky, VSchönert, SSchültz, ASchütt, MSchaper, DCSchreiner, JSchulz, OSchuster, MSchwarz, MSchwingenheuer, BSelivanenko, OShaflee, MShevchik, EShirchenko, MShitov, YSimgen, HSimkovic, FSkorokhvatov, MSlavickova, MSmolek, KSmolnikov, ASolomon, JASong, GStarosta, KStekl, IStommel, MStukov, DSumathi, RRSweigart, DASzczepaniec, KTaffarello, LTagnani, DTayloe, RTedeschi, DTurqueti, MVarner, RLVasilyev, SVeresnikova, AVetter, KVignoli, CVogl, CSturm, K vonWaters, DWaters, JCWei, WWiesinger, CWilkerson, JFWillers, MWiseman, CWojcik, MWu, VH-SXu, WYakushev, EYe, TYu, C-HYumatov, VZaretski, NZeman, JZhitnikov, IZinatulina, DZschocke, A-KZsigmond, AJZuber, KZuzel, G2021-11-172021-11-17https://hdl.handle.net/10161/23993We propose the construction of LEGEND-1000, the ton-scale Large Enriched Germanium Experiment for Neutrinoless $\beta \beta$ Decay. This international experiment is designed to answer one of the highest priority questions in fundamental physics. It consists of 1000 kg of Ge detectors enriched to more than 90% in the $^{76}$Ge isotope operated in a liquid argon active shield at a deep underground laboratory. By combining the lowest background levels with the best energy resolution in the field, LEGEND-1000 will perform a quasi-background-free search and can make an unambiguous discovery of neutrinoless double-beta decay with just a handful of counts at the decay $Q$ value. The experiment is designed to probe this decay with a 99.7%-CL discovery sensitivity in the $^{76}$Ge half-life of $1.3\times10^{28}$ years, corresponding to an effective Majorana mass upper limit in the range of 9-21 meV, to cover the inverted-ordering neutrino mass scale with 10 yr of live time.physics.ins-detphysics.ins-detnucl-exJournal article2021-11-17