DARK MATTER EXPERIMENTS: QUIET SPACES TO SEARCH FOR BSM PHYSICS HENRIQUE ARAÚJO Imperial College London (LUX & LZ Collaborations) ATOMIC NUCLEI AS LABORATORIES FOR BSM PHYSICS – ECT* TRENTO, APRIL 2019 OUTLINE • Direct dark matter searches • Experimental challenges & opportunities • The noble liquid xenon • Pushing down the energy threshold • The LUX-ZEPLIN (LZ) experiment • Physics from NR and ER interactions Henrique Araújo (Imperial) 2 A DARK UNIVERSE • L-CDM cosmology is a remarkably successful model • Initial conditions photographed at surface of last scatters (CMB) • Left to evolve for 13.7 Gyr under two dark ‘fluids’ – DE and DM • To produce what we see today – normal matter (almost) doesn’t matter { { Henrique Araújo (Imperial) 3 OUR DARK MILKY WAY • Spiral galaxies ‘spin’ too quickly for their observed ‘luminous’ mass • Our Milky Way is no exception: we too are immersed in a DM halo • Direct search experiments probe our galactic DM via elastic scattering • Density near Sun ~0.3 GeV/cm3, mean particle speed v ~ 300 km/s (0.001c) Rubin, et al, 1978, ApJ. Lett. 225, L107 Kafle et al. 2014 ApJ 794 59 Henrique Araújo (Imperial) 4 WEAKLY INTERACTING MASSIVE PARTICLES Main observable: O(keV) nuclear recoils (NR) from elastic WIMP-nucleus scattering Henrique Araújo (Imperial) 5 WIMP-NUCLEUS ELASTIC SCATTERING The ‘spherical cow’ galactic model • DM halo is 3-dimensional, stationary, with no lumps • Isothermal sphere with density profile r ∝ r −2 3 • Local density r0 ~ 0.3 GeV/cm (~1/pint for 100 GeV WIMPs) Maxwellian (truncated) velocity distribution, f(v) • Characteristic velocity v0=220 km/s • Escape velocity vesc=544 km/s • Earth velocity vE=230 km/s Nuclear Recoil (NR) energy spectrum [events/kg/day/keV] v dR r0 A 2 max f (v) dR3 R 4m m F (q) d v 0 eER / E0r , r W T 1 2 v 2 min ~ few keV dER 2m A v dER E0r (mW mT ) Henrique Araújo (Imperial) 6 WIMP-NUCLEON ELASTIC SCATTERING XS • Presenting coupling to p and n more useful than coupling to nucleus • Compare different targets materials, accelerator & indirect searches • Spin-independent (scalar) interaction 2 2 Non-relativistic EFT SI 4A 2 A 2 A (q 0) [Zf p (A Z) fn ] 2 p A p 11 operators for exchange of – A2 enhancement (coherence) – pMSSM within reach spin-0 or spin-1 mediators 6 independent responses • Spin-dependent (axial-vector) interaction contribute to amplitude 2 4 J 1 2 SD(q 0) A SD a S a S A 2 p,n p p n n (Fitzpatrick, Haxton, Anand, et al: p 3 J 1203.3542, 1405.6690) – Nuclear spin J replaces A2 enhancement – less sensitive – Some targets more sensitive to proton, others to neutron scattering Henrique Araújo (Imperial) 7 NUCLEAR RECOIL SPECTRUM WIMP-nucleus SI scattering rate CEnNS scattering (푨ퟐ enhancement) (푵ퟐ enhancement) Henrique Araújo (Imperial) 8 THE (WIDER) DARK MATTER LANDSCAPE US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report (arXiv:1707.04591) Henrique Araújo (Imperial) 9 THE EXPERIMENTAL CHALLENGE • Low-energy detection is easy ;) o Several technologies allow sub-keV NR detection • Rare event searches are also easy ;) o Not a problem at >100 MeV, think neutrinos Key detector requirements • But doing both is hard! • Large mass x time (~tonne∙yr) • Large mass gives exposure & self-shielding • Hard to collect signal ‘carriers’ (threshold) • Low ER threshold (~keV) • Low background (~10-100 DRU) • ER/NR discrimination • By the way: there is no trigger… Henrique Araújo (Imperial) 10 WIMP SEARCH TECHNOLOGY ZOO Ionisation Detectors Targets: Ge, Si, CS2, CdTe CoGeNT, CDEX, D3, DAMIC, DRIFT, Light & Ionisation DM-TPC, GENIUS, IGEX, MIMAC, Detectors NEWAGE, NEWS, TREX Heat & Ionisation Targets: Xe, Ar Bolometers ArDM, Argo, LUX, WARP, Targets: Ge,Si DarkSide, DARWIN, Panda-X, ionisation CDMS, (EDELWEISS) XENON, (ZEPLIN-II/III), Q SuperCDMS, (EURECA) LUX-ZEPLIN cryogenic (<50 mK) cold (LN2) Scintillators Bolometers Targets: NaI, Xe, Ar Targets: Ge, Si, Al O , TeO ANAIS, MiniCLEAN, DAMA, 2 3 2 CRESST-I, CUORE, CUORICINO DEAP-3600, DM-ICE, KIMS, LIBRA, PICOLON, (NAIAD), SABRE, Light & Heat Bolometers Bubbles & Droplets XMASS, (ZEPLIN-I) Targets: CaWO BGO, Al O 4, 2 3 CF Br, CF I, C F , C F CRESST, (ROSEBUD) 3 3 3 8 4 10 COUPP, PICASSO, PICO, cryogenic (<50 mK) Henrique Araújo (Imperial) SIMPLE 11 XENON THE ‘FOREIGNER’… Only 90 ppb in air: Quite “exclusive”… • No nasty radioisotopes, many physics opportunities: dark matter and neutrino physics • Possibility of isotopic manipulation of target (enrichment/depletion) – same detector… Henrique Araújo (Imperial) 12 THE EXPERIMENTAL CHALLENGE OPPORTUNITIES • Large, quiet detectors with low thresholds enable searches 5-10 28 for various rare processes: ≳10 atoms × ≳1 yr exposure tonnes • Nuclear recoil interactions • Dark matter >GeV, including SI and SD LXe • Astrophysical neutrinos via CEnNS, including B-8 and supernova (2020-) • Electron recoil interactions • Dark matter >MeV, ALPs, … • Astrophysical neutrinos via n-e scattering • Neutrinoless double beta decay (demonstrator) • Ultimate “Generation 3” LXe detector 50-100 • “Mopping” the neutrino floor to close the WIMP gap tonnes • Competitive neutrino astrophysics programme • Competitive neutrinoless double beta decay searches LXe Henrique Araújo (Imperial) 13 TWO-PHASE XENON TIME PROJECTION CHAMBER Two signals for every particle interaction: S1: scintillation in liquid phase (prompt) S2: electroluminescence in gas (delayed) S2 • 3D position reconstruction, fiducialisation • Nuclear/electron recoil discrimination S1 S1 S2 Henrique Araújo (Imperial) 14 NR & ER YIELDS IN LIQUID XENON ER NR Henrique Araújo (Imperial) 15 SE S1 quantum SPE S2 quantum Single electron distribution S1 S2 SE ← 3.5 keV electron recoil S1 S2 Henrique Araújo (Imperial) 16 STATE-OF-THE-ART: VANILLA WIMPS LUX PandaX-II XENON1T • 0.25-2 tonnes (active) • ~5 keV NR threshold Henrique Araújo (Imperial) 17 STATE-OF-THE-ART: LIGHT WIMPS CRESST-III • 24 g CaWO4 crystal • 30 eV NR threshold Henrique Araújo (Imperial) 18 MIGDAL EFFECT – DETECTING SUB-keV RECOILS Henrique Araújo (Imperial) 19 MIGDAL EFFECT – DETECTING SUB-keV RECOILS Henrique Araújo (Imperial) 20 MIGDAL EFFECT – DETECTING SUB-keV RECOILS Henrique Araújo (Imperial) 21 MIGDAL EFFECT – SUB-GeV MASS SENSITIVITY Henrique Araújo (Imperial) 22 BACKGROUNDS IN LARGE LIQUID XENON DETECTORS • Nuclear recoils – same signature, possibly irreducible • Neutrons from (a,n) and SF from U/Th trace contamination • Local environment, shields, vessels, components, target material itself • Surface recoils from alpha decay (radon daughter plate-out) • Contamination on detector surfaces (“wall events”) • High energy neutrons from atmospheric muon spallation • Difficult to shield completely even underground • Eventually, coherent elastic neutrino-nucleus scattering (CEnNS) • Electron recoils – discrimination power is finite • Gamma-ray background external to target • U/Th, K-40, Cs-137, from environment, shields, vessels, components,… • Contaminants dispersed within the target • Other noble gases not removed by purification system: Rn-222/220, Ar-39, Kr-85 • Henrique Araújo (Imperial) Eventually, elastic scattering of solar pp neutrinos off electrons 23 neutron and gamma SELF-SHIELDING mean interaction lengths in liquid xenon 100 100 Photoelectric IN NOBLE LIQUIDS Compton Pair production 10 10 Total Liquid 1 1 Elastic mean interaction length, cm length, interactionmean mean interaction length, cm length, interactionmean xenon neutrons in LXe (131Xe) Total gammas in LXe 0.1 0.1 0.01 0.1 1 10 0.01 0.1 1 10 neutron energy, MeV photon energy, MeV single scatters <5 keVee r=3 g/cm3 S2 S1 S2 S2 Henrique Araújo (Imperial) S2 24 ANTI-COINCIDENCE DETECTOR AROUND WIMP TARGET veto Liquid make Xenon thin! Water Cherenkov, passive LXe, bare or loaded scintillator,… Henrique Araújo (Imperial) 25 LUX-ZEPLIN (LZ) 250 scientists from 38 institutes in the US, UK, Portugal, South Korea & Russia Black Hills State University ◊ Bristol University ◊ Brookhaven National Laboratory ◊ Brown University ◊ Center for Underground Physics, Korea ◊ Edinburgh University ◊ Fermi National Accelerator Laboratory ◊ Imperial College London ◊ Lawrence Berkeley National Laboratory ◊ Lawrence Livermore National Laboratory ◊ LIP-Coimbra, Portugal ◊ University of Liverpool ◊ MEPHI Moscow, Russia ◊ Northwestern University ◊ Oxford University ◊ Penn State University ◊ Rutherford Appleton Laboratory ◊ Royal Holloway, University of London ◊ SLAC National Accelerator Laboratory ◊ South Dakota School of Mines & Technology ◊ South Dakota Science and Technology Authority ◊ SUNY University at Albany ◊ Texas A&M University ◊ University of Alabama ◊ University of California Berkeley ◊ University of California Davis ◊ University of California Santa Barbara ◊ University College London ◊ University of Maryland ◊ University of Massachusetts ◊ University of Michigan ◊ University of Rochester ◊ University of Sheffield ◊ University of South Dakota ◊ University of Wisconsin ◊ Washington University Henrique Araújo (Imperial) 26 SANFORD UNDERGROUND RESEARCH FACILITY Former Homestake Mine, Lead, South Dakota Lead and the Open Cut Sturgis Rally Henrique Araújo (Imperial) 27 THE LUX-ZEPLIN (LZ) EXPERIMENT LZ detector(s) • 7t LXe-TPC (494 photomultipliers) • 2t LXe Skin Detector (131 photomultipliers) • 20t Gd-loaded Liquid Scintillator Outer Detector (120 photomultipliers) 100x more sensitive than LUX LZ Technical Design Report: arXiv:1703.09144 LZ Sensitivity: arXiv:1802.06039 2012 2015 2020 2025 DESIGN CONSTRUCTION EXPLOITATION Henrique Araújo (Imperial) 28 LZ DETECTORS n WIMP