New directions in direct dark matter searches Tongyan Lin UC Berkeley & LBNL April 4, 2017 DM@LHC 2017, UC Irvine
Direct detection of WIMPs target nuclei E recoil Heat, ionization, charge from recoiling nucleus WIMP nucleon cross section [zb] 10 3 10 2 10 1 10 0 10 1 10 2 8 B Lower mass dark matter? Strongest limits from Xenon target (Z=54) experiments: DarkSide 50 2015 XENON100 2016 PandaX II 2016 LUX WS2013 LUX WS2014 16 LUX WS2013+WS2014 16 10 1 10 2 10 3 10 4 10 5 WIMP Mass [GeV/c 2 ] 10 42 10 43 10 44 10 45 10 46 WIMP nucleon cross section [cm 2 ] Established program of WIMP searches. How can we cast a wider net? 2
Dark matter mass scale thermal 10-22 ev mev ev kev MeV GeV TeV = Light bosonic DM WIMP V ( ) coherent light boson searches (e.g. ADMX) Many models + Many proposals for detection SM SM Nuclear recoil in direct detection 3
Dark mediators sub-gev dark matter mass scale of mediator similar to (lighter than) χ! thermal freeze-out possible! (see also, freeze-in) Ω X 1 σv m2 X g 4 X e p g D A /φ e p Freeze-out Dark matter scattering e.g. WIMPless dark matter Feng and Kumar 2008 4
sub-kev bosonic dark matter Candidates: Hidden photon Pseudoscalar (axion) Scalar } very weakly coupled! Coherent field below m ~ ev Occupation number is high: DM 3 db m DM de Broglie = 2 m DM v Non-thermal relic abundance V ( ) DM = 1 2 m2 DM 2 0 0 field value, set by misalignment 5
Mass scale of dark matter? 10-22 ev mev ev kev MeV GeV TeV = Light bosonic DM V ( ) coherent light boson searches (e.g. ADMX) Light thermal Asymmetric SUSY hidden sector helium chemical bonds molecular magnets graphene scintillators semiconductors superconductors WIMP SM SM Nuclear recoil in direct detection 6
Kinematics and thresholds Typical recoil energy kev ev mev Total DM energy Nuclear recoils kev MeV GeV TeV Dark matter mass Energy deposited from WIMP in nuclear recoil: E R µ2 N v2 m N 2 1 100 kev Typical threshold in experiment: > 1 kev nuclear recoil 7
Kinematics and thresholds Typical recoil energy kev Total DM energy ev mev kev MeV GeV TeV Nuclear recoils Dark matter mass Lower mass target nuclei Energy deposited from WIMP in nuclear recoil: E R µ2 N v2 m N 2 1 100 kev Typical threshold in experiment: > 1 kev nuclear recoil 8
3 Typical recoil energy / kev ev / mev hn e i Detecting = low mass dark matter = - hn e i Electron recoils Electron recoils / Total DM energy Nuclear recoils kev MeV GeV TeV Dark matter mass % Goal: sensitivity to ~mev recoils for kev-mev dark matter scattering. = = / % - FIG. 2. Observed number of events versus photoelectrons (PE) in XENON10 (top)[22]andxenon100(bottom)[23]. DM spectra are shown for m = 10 MeV (blue) & 1 GeV (red) with a cross section fixed at our derived 90% C.L. limit (we assume fiducial values for the secondary ionization model). 9 [ ] - - - - - Sensitivity to MeV-scale DM with Xenon10, Xenon100 E th & 12 ev () = / [] FIG. 3. 90% C.L. limit on the DM-electron scattering cross section from XENON10 data (blue) and XENON100 data (red) for F DM =1(top) &F DM = 2 m 2 e/q 2 (bottom). Dotted black lines show XENON10 bounds from [2]. days), including for the figure first from time Essig, events Volansky, with n e Yu & 4, 2017 as well as from XENON100 see data also: [23] 1108.5383, (30 kg-years). 1206.2644 Since
Detecting low mass dark matter Ideas Electron recoils with small gap materials Electronic band structure } ~ev } ~10 ev ~mev in superconductor 10 Hochberg, TL, Zurek 2016/2017; Essig, Mardon, Volansky; Lee, Lisanti, Mishra-Sharma, Safdi Essig, Fernandez-Serra, Mardon, Soto, Volansky, Yu Hochberg, Pyle, Zhao, Zurek; Hochberg, Kahn, Lisanti, Tully, Zurek
Detecting low mass dark matter Ideas Electron recoils with small gap materials Gapless modes (phonons), vibrational modes Long wavelength phonons [~mev]: = c s ~ Q c s 10 5 c s 10 6 in solid in helium vibrational modes [~mev-ev] χ 11 see also: Hochberg, TL, Zurek 2016 Essig, Slone, Mardon, Volansky 2016 Bunting, Gratta, Melia, Rajendran 2017
Detecting low mass dark matter Ideas Electron recoils with small gap materials χ Three-body final states q m v Gapless modes (phonons), vibrational modes Higher order processes. i n f 12 Schutz and Zurek 2016 Knapen, TL, Zurek 2016 McCabe 2017 Kouvaris and Pradler 2016,
Detecting low mass dark matter Backgrounds coherent scattering of solar neutrinos known background of O(1-10)/kg-yr/10 ev (based on DAMIC, SuperCDMS) 1610.00006, 1607.07410 coherent photon scattering O(1-10)/kg-yr/eV 1610.07656 dark counts (fakes) - general challenge. the unknown 13
1. Probing low-mass DM with ev-scale thresholds 2. Towards mev-scale thresholds 14
Semiconductor targets New techniques have led to E th ~50 ev electron recoil. SuperCDMS [Ge, Si] DAMIC, Sensei (Si CCD) E th ~ev (1 or 2 electron sensitivity) can be reached in the near future! Limited by band gap, dark counts. 15
Semiconductor targets e p g D e A e p Kinetically mixed hidden photon A ea 0 µj µ EM couples to electrons, nuclei thermal relic [ ] - - - - - - - beam dump = XENON10 SENSEI, Si 100g-years, 2e - - [] XENON100 current direct detection + colliders [ ] SuperCDMS, Si 10kg-years, 1e - 16 figure from Tien-Tien Yu (see also Essig et al. 2015)
Absorption of hidden photon DM Absorption Reach even lighter (ev-scale) bosonic DM: Hidden photon dark matter A 10 10 10 12 Stellar constraints DAMIC 11.5 g-d Xenon (Si, 0.6 kg-d) DAMIC (Ge, 70 kg-d) CDMSlite Xenon100 10 14 A µ X A 0 µ 10 16 10 18 multi-phonon excitation 10 3 10 2 10 1 10 0 10 1 10 2 10 3 10 4 m A 0 [ev] e excitation 1 kg-yr, Ge 1 kg-yr, Si Hochberg, TL, Zurek 2017 See also: I. Bloch et al. 2016 17 Stellar, Xenon10 constraints: An, Pospelov, Pradler 2013, 2014 Redondo & Raffelt 2013
Scintillators Graphene Band Gap Conduction Bands Exciton Band Scintillation Photons Activator Excited States Activator Ground State er ~ kf e Valence Bands Derenzo, Essig, Massari, Soto, Yu 2016 Aim for detection of single scintillation photons. Hochberg, Kahn, Lisanti, Tully, and Zurek 2016 Idea: use PTOLEMY setup for dark matter. Directionality possible with 2D target. Reach is similar to semiconductors in both cases. Many exciting developments - each proposal has unique advantages 18
1. Probing low-mass DM with ev-scale thresholds 2. Towards mev-scale thresholds 19
Superfluid helium Sensitive to DM-nucleon scattering For low mass dark matter, the possible momentum transfer is Q m v ~ Angstrom -1 for m X = MeV n n At these scales, the relevant degree of freedom is a phonon 20
Superfluid helium Sensitive to DM-phonon scattering For low mass dark matter, the possible momentum transfer is Q m v ~ Angstrom -1 for m X = MeV Quasiparticle At these scales, the relevant degree of freedom is a phonon 21
Superfluid helium 5 4 0.5 1.0 1.5 2.0 2.5 3.0 Measured Quadratic q 2 Phonon / density perturbation in He: [mev] 3 2 2m He Long lived quasiparticles (stable above 0.8 mev) 1 Phonon Roton Zero viscosity for velocities below critical velocity v c 0 0 1 2 3 4 5 6 q [kev]! Possible ~mev thresholds 22
Detector concept calorimeter Evaporation at surface: atom vacuum interface quasiparticle free atom van der Waals binding X ~1 mev 0.62 mev roton LHe vacuum Cal. 10s of mev Threshold for evaporation: 0.62 mev Efficiency: O(10%) T = 10-100 mk 23 S. Hertel (UMass), D. McKinsey (LBL)
Multi-phonon excitations 2-phonon excitation X q m X v Kinematics allows larger energy ω deposited, even for small q Schutz and Zurek 2016 Knapen, TL, Zurek 2016 p [cm 2 ] 10 35 10 36 10 37 10 38 10 39 10 40 10 41 10 42 10 43 10 44 10 45 24 2-phonon Leading order CKL15 Massive mediator X = 10 5,g n = 10 6,m =MeV X = 10 5,g n = 10 6,m =10 MeV Nuclear recoil kg-yr 10 3 10 2 10 1 1 10 10 2 m X [MeV] Extends reach to lower mass DM! (~10 mev resolution)
Light scalar mediator Comparison with other constraints: 10-36 N eff e.g. DM-nucleon coupling via gluon operator sp Hcm 2 L 10-39 5 th Force helium SN1987a 10-42 10-45 PRELIMINARY 10 0 10 1 10 2 10 3 10 4 10 5 m c HkeVL mf m c =10-3 g g 25 Green, Rajendran 2017, Krnjaic 2015 Knapen, TL, Zurek (work in progress)
Superconductor target Dark matter processes break apart Cooper pairs: Long-lived excitations can be collected at the surface X Superconducting Substrate (Al) Insulating layer TES and QP collection antennas (W) = 3 2 T c 0.3 mev SuperConducting Bias Rails (Al) E th ~ mev goal 5 mm 26 Hochberg, Zhao, and Zurek 2015 Hochberg, Pyle, Zhao, and Zurek 2015
Absorption of hidden photon DM 10 10 Stellar constraints DAMIC Kinetic mixing 10 12 10 14 Al, 1 kg-yr Xenon Xenon100 DAMIC CDMSlite 10 16 10 18 A µ X A 0 µ 10 3 10 2 10 1 10 0 10 1 10 2 10 3 10 4 m A 0 [ev] Dark matter mass e excitation 1 kg-yr, Ge 1 kg-yr, Si 27 Hochberg, TL, Zurek 2016
Going Forward Multiple detection targets different systematics, different DM physics. Aim for small-scale experiments (~kg target), in addition to WIMP searches What other materials and processes can be used? What is the full model space and complementarity with other probes of dark matter? 28 see talks @ UMD Cosmic Visions 2017, Dark Sectors 2016 report 1608.08632
Conclusions Current direct detection experiments focus on GeV-TeV scale dark matter. Only scratched the surface for sub-gev. New directions explore many orders of magnitude in mass! mev ev kev MeV GeV TeV DM mass Superconductors Superconducting Substrate (Al) Insulating layer TES and QP collection antennas (W) SuperConducting Bias Rails (Al) Superfluid He and many others Semiconductors 29
Thanks! 30