Direct Detection of! sub-gev Dark Matter

Transcription

1 Direct Detection of! sub-gev Dark Matter Rouven Essig C.N. Yang Institute for Theoretical Physics, Stony Brook Sackler Conference, Harvard, May 18, 2014

2 An ongoing program Direct Detection of sub-gev Dark Matter, RE, Mardon, Volansky arxiv: , PRD Semiconductor Probes of Light Dark Matter, Graham, Kaplan, Rajendran, Walters arxiv: , Phys. Dark Univ. First Direct Detection Limits on sub-gev Dark Matter from XENON10, RE, Manalaysay, Mardon, Sorensen, Volansky arxiv: , PRL!! To appear this year:! Prospects for sub-gev DM Detection with Semiconductor Targets, RE, Fernandez-Serra, Mardon, Soto, Volansky, Chiu-Tien Yu Search for sub-gev Dark Matter with XENON100, XENON100 Collaboration w/ RE, Mardon, Volansky Detection of Weakly Interacting Particles via Molecular Excitations, RE, Mardon, Oren Slone, Volansky + ongoing discussions w/ various other experimental groups

3 Outline intro + motivation! strategy & current constraints! future prospects (incl. work in progress)

4 The Future of Direct Detection push lower in cross-section w/ bigger detectors

5 Direct Detection below 1 GeV? Yes, it is possible to go as low as ~1 MeV! 6??

6 The WIMP Paradigm The search for DM is dominated by the search for! Weakly Interacting Massive Particles (WIMPs) ~ GeV theoretically motivated (e.g. appears in SUSY)! naturally have correct relic abundance ( WIMP miracle )! experimentally testable

7 Beyond the WIMP paradigm Let s make sure WIMPs don t get all the attention many new-physics models have non-wimp DM! many other ways to get correct DM abundance! no new physics at the LHC yet We don t know what DM is!! Many other DM candidates exist that we can and should look for!

8 sub-gev Dark Matter (an old idea, e.g. Boehm, Fayet, ) natural, viable candidates exist very rich phenomenology experimental searches often use existing facilities/technology or require only modest amount of additional R&D/expense direct detection! colliders! fixed-target! indirect detection see Natalia s! talk tomorrow

9 sub-gev Dark Matter (an old idea, e.g. Boehm, Fayet, ) natural, viable candidates exist very rich phenomenology experimental searches often use existing facilities/technology or require only modest amount of additional R&D/expense direct detection! colliders! fixed-target! indirect detection This talk:! focus on! direct detection

10 Outline intro + motivation! strategy & current constraints! future prospects (incl. work in progress)

11 Cannot use elastic nuclear recoils for detection Light DM 1 GeV Atom

12 Cannot use elastic nuclear recoils for detection Light DM 1 GeV DM Not enough! energy transfer Can t see! recoiling nucleus

13 Cannot use elastic nuclear recoils for detection limits absent below ~few GeV

14 But DM could also scatter off electrons! DM Atom

15 But DM could also scatter off electrons! DM Atom this can transfer most of DM energy Signal: one or a few electrons

16 Search for DM-electron scattering Noble liquids (xenon, argon, helium)! threshold ~ 10 ev Semiconductor targets (germanium, silicon)! threshold ~ 1 ev (band gap) conduction band! gap valence

17 Search for DM-electron scattering Noble liquids (xenon, argon, helium)! threshold ~ 10 ev sensitive to Done w/ XENON10 data! But significant improvements possible Semiconductor targets (germanium, silicon)! threshold ~ 1 ev (band gap) sensitive to Requires continued R&D to reach low threshold, but very promising

18 Search for DM-electron scattering Noble liquids (xenon, argon, helium)! threshold ~ 10 ev sensitive to Done w/ XENON10 data! But significant improvements possible How? Semiconductor targets (germanium, silicon)! threshold ~ 1 ev (band gap) sensitive to Requires continued R&D to reach low threshold, but very promising

19 The XENON10 experiment PMT s Xe Gas detector! schematic ~E Xe liquid (~14 kg) PMT s two-phase xenon time projection chamber operated for ~1 year in 2006/2007

20 Heavy DM scattering off nuclei Xe! Xe, Xe + produces photons and electrons heavy! Two types of signal: DM e e e e Signal t

21 Heavy DM scattering off nuclei Xe! Xe, Xe + produces photons and electrons Two types of signal: S1: prompt scintillation e e e e Signal S1 t

22 Heavy DM scattering off nuclei Xe! Xe, Xe + produces photons and electrons e e e e Two types of signal: S1: prompt scintillation Signal S1 t

23 Heavy DM scattering off nuclei Xe! Xe, Xe + produces photons and electrons e e e e Two types of signal: S1: prompt scintillation Signal S1 t

24 Heavy DM scattering off nuclei Xe! Xe, Xe + produces photons and electrons Two types of signal: S1: prompt scintillation S2: proportional scintillation! (from ionization) Signal S1 S2 t

25 Sub-GeV DM scattering off electrons on average, a single electron produces about 27 detected photo-electrons DM S1: not measurable e S2: small signal Signal (nothing) S1 S2 t

26 Sub-GeV DM scattering off electrons DM an energetic outgoing e - can ionize other e - 's (estimate w/ semi-empirical model) RE, Manalaysay, Mardon, Sorensen, Volansky e e e S2: proportional to # of e - 's Signal 3e - (nothing) 2e - 1e - S1 S2 t

27 The XENON10 data from published S2-only analysis, (15 kg-days) Counts / 0.1 electrons single electron double electron Best fit Allowed at 90% upper limit triple electron Ionization Signal [electrons] 90% c.l. upper bounds! (counts/kg/day): 1 e - : e - : e - : 0.83 conservative limit: require DM signal < data

28 Proof-of-principle for direct detection! down to DM masses of a few MeV RE, Manalaysay, Mardon, Sorensen, Volansky 2 D Hidden- Photon models Excluded by XENON10 data 1 electron 2 electrons 3 electrons Dark Matter

29 Outline intro + motivation! strategy & current constraints! future prospects (incl. work in progress) noble gases! semiconductors

30 Prospects for noble gases 2 D Cross section Sensitivity and Event Rate Hper kg yearl g D =0.1 g D =10-2 g D =10-3 MeV DM g D =10-4 Excluded by XENON10 Hidden photon F DM HqL = He Ar Xe Ge Event Rate Hse=10-37 cm 2 L XENON10! limit helium xenon argon { Noble gases 1 kg-year Dark Matter XENON100, LUX, DarkSide,! can do this analysis!

31 XENON100 XENON100 Collaboration w/ RE, Mardon, Volansky analysis underway rough trigger efficiency: 100 % 80 % 60 % 40 % 20 % S2 electrons expect improvements in analysis & understanding of backgrounds over XENON10 (which was based on published data)

32 Prospects for semiconductors 2 D Cross section Sensitivity and Event Rate Hper kg yearl g D =0.1 g D =10-2 g D =10-3 MeV DM g D =10-4 Excluded by XENON10 Hidden photon F DM HqL = He Ar Xe Ge assumes experimental Event Rate Hse=10-37 cm 2 L energy threshold is close to band-gap! semiconductors (Ge, but Si similar) 1 kg-year Dark Matter band gap (~1 ev) < atomic ionization energy (~10 ev) =) can potentially reach very low masses!

33 Calculating Rates f(q) 2 ionization form factor X degeneracies h out e i~q ~r bound i 2 Challenging to calculate, especially for semiconductors! analytic approximation how accurate?! Graham et.al. ( ) numerical: adapt existing solid-state codes RE, Mardon, Volansky ( ) RE, Fernandez-Serra, Mardon, Soto, Volansky, Yu (in progress)

34 Recoil energy spectrum Detection Event unitsd mdm = 10 MeV model: heavy dark photon mediator E based on analytic approximation by Graham et.al. Lowering threshold gives HUGE increase in rate

35 Current energy thresholds are! above band-gap of ~1 ev CDMS: >1 kev! CoGENT: ~500 ev! CDMSlite: ~170 ev ( )! CDEX: ~170 ev ( )! DAMIC: ~50 ev ( ) Much work going on to lower energy thresholds down to band-gap (e.g. DAMIC, SuperCDMS) see Tali s talk

36 Some prospects (very preliminary) RE, Fernandez-Serra, Mardon, Soto, Volansky, Chiu-Tien Yu (in progress) (assumes momentum-independent DM form factor) plot from Chiu-Tien Yu 2 D CDMSLite, Eth = 170 ev, 6.3 kg-days Si, Eth = 100 ev, 10 kg-days Si, Eth = 20 ev, 10 kg-days Si, Eth = 10 ev, 10 kg-days XENON10 Si, Eth = 0, 10 kg-days m based on analytic approximation by Graham et.al. Numerical calculation is ongoing

37 Other direct detection avenues! for sub-gev DM ionization! (DM-electron scattering)! excitation! Work in! { progress (DM-electron scattering)! molecular dissociation (DM-nucleon scattering) RE, Mardon, Oren Slone, Volansky

38 Summary Direct detection of DM down to MeV masses is possible! a proof-of-principle exists w/ XENON10 data! significant improvements should be possible w/ upcoming noble gas and semiconductor experiments 6?

39 Backup

40 10-35 F DM = F DM µ 1êq 2 2 D XENON10 ER Massive Dark Photon Planck Neff CRESST He Xe Ar Ge 2 D He Ar Xe Ge XENON10 ER Freeze-In Ultra-light Dark Photon m m 2 D Planck N eff F DM =1 LEP XENON10 ER CMB MDM-DM CRESST XENON10 NR 2 D Planck N eff F DM µ1êq LEP XQC XENON10 ER CRESST EDM-DM XENON10 NR m m

41 Neutrino Background Rates drêdlog 10 E R Hkg -1 year -1 L solid Xe Ge Ar He dotted e - HXeL e - HGeL e - HArL e - HHeL Recoil Energy E R HeVL

42 drêdlog 10 E -1 year -1 D Xe Ar He Electron Ionization Spectrum, s e = cm 2 mdm =10 MeV -- m DM =1000 MeV F DM HqL = 1 n-e - drêdlog 10 E -1 year -1 D Xe Ar He mdm =10 MeV -- m DM =1000 MeV F DM HqL = a 2 m 2 e êq 2 n-e Electron Recoil Energy E