DarkSide new results and prospects

Transcription

1 DarkSide new results and prospects Stefano Davini - INFN Genova on behalf of the DarkSide collaboration La Thuile, March 20, 2018

2 The DarkSide WIMP-argon program at LNGS Past Present Future DS-10 DS-50 DS-20k technical prototype dark matter runs ongoing σ (χn) ~ cm WIMP mass 100 GeV/c 2 σ (χn) ~ cm WIMP mass 2 GeV/c 2 projected sensitivity σ (χn) ~ cm WIMP mass 100 GeV/c 2

3 The DarkSide-50 detector cosmic-ray veto 1 kton Water Cherenkov neutron veto 30 ton Borated Liquid Scint dark matter detector Time Projection Chamber 50 kg Liquid Argon from underground source low in radioactive 39 Ar

4 The DarkSide-50 signals S1 primary scintillation signal collected by 38 PMTs S1 Powerful Pulse Shape allows to discriminate between - nuclear recoils (WIMP, neutrons) - electron recoils (β-γ backgrounds) 4

5 The DarkSide-50 signals Nuclear recoil Nuclear Recoil (WIMP signals) β/γ Beta/Gamma (backgrounds) S1 S1 f Energy [kev nr ] Li(p,n) in SCENE 241 AmBe in DarkSide-50 S Nuclear recoils β/γ S1 [PE]

6 The DarkSide-50 signals! e - e - e - e - e - e - e - e - S2 drift time S2 secondary electroluminescence signal one extracted e - -> S2~23 PE in central PMT allows for lower threshold analysis S2-S1 drift time -> vertical position S2 pattern on top PMTs -> horizontal position S1 & S2 -> 3D position reco S1 top S2 S2 S1 6

7 WIMP search - A blind analysis WIMP blind box DON T LOOK HERE! 7

8 WIMP search - A blind analysis f 90 f 90 1 no cuts - previous 71 days search data - PRD 93 (2016) WIMP BLIND BOX (final choose) test regions Goal - design WIMP analysis with < 0.1 background in box S1 [PE] Using test regions to test bkg model prior to unblinding S1 [PE] 1

9 WIMP search days Energy [kev nr ] f % 50% 99% S1 [PE] 0 arxiv:

10 WIMP search days %&. () TeV/( * %&& () GeV/( * %&& () TeV/( * WIMP-nucleon Spin Indep. STD Halo Model 90% C.L. exclusion plot arxiv:

11 Low mass WIMP search e - S2! " = $% 2* +( %, % ' ( ' ( ' 67 ( ~37 GeV For ' + = 10 GeV! " ~1.4 KeV ' χ % ' ( Nuclear recoils from low mass WIMP detectable in S2 (charge yield ~6 e - /kevnr, electrolum. yield ~23 PE/e - ) but not detectable in S1 (light yield ~2 PE/keVnr) S2-only low mass WIMP search Below threshold for S1 production (~ D7 ) but S2 has threshold ~ D7 arxiv:

12 Low mass WIMP search arxiv:

13 Low mass WIMP search binomial fluctuation no quenching fluctuation DarkSide-50 arxiv:

14 Light DM on electron! " = $ & ' $) 2+,- ~ , 512 For 4, = 100 MeV! " ~50 ev Use lightness of electron to investigate light mass DM! " #$ ev,!" #, ev,! " 0$ ev,!" 0, ev,! " 3, ev Recoil energy comparable with binding energies in argon atoms e - S2 Same S2-only analysis but very different interpretation χ arxiv:

15 LDM on electron - scattering rate min. velocity for Eer in bounded electrons ionization form factor LDM form factor! "# $ % = 1: heavy mediator! "# $ % 1 $ % : light mediator arxiv:

16 LDM on electron - DS-50 constraints! "# $ % = 1: heavy mediator! "# $ % 1 $ % : light mediator arxiv:

17 The Future DS-20k GADMC

18 DarkSide - Outlook DarkSide-50 at LNGS: a successful 3-year underground argon run lead to new dark matter constraints DarkSide day Dark Matter Search with Low-Radioactivity Argon Low-mass Dark Matter Search with the DarkSide-50 experiment Constraints on sub-gev Dark Matter Electron Scattering from the DarkSide-50 experiment DarkSide-20k and GADMC, the next tyrants in the dark matter argon community

19 Backup Slides

20 s] 10 1 atmospheric and underground argon at 200 V/cm kg Events / [80 PE < 1/300 < 1/1000 AAr (200 V/cm, LSV anti-coinc.) UAr (200 V/cm, LSV anti-coinc.) 39 Ar (from global fit) 85 Kr (from global fit) Ar in UAr < 1 mbq/kg 85Kr in UAr ~ 2 mbq/kg S1 [PE]

21 DarkSide-50 γ-rays

22 DarkSide-50 alphas Energy [MeV] Data Events / [250 PE] Degraded: Under TPB 210 Po 222 Rn 218 Po Full-energy: In LAr S1 [PE] many with small or no S2, surface decays in TPB (wavelength shifter) additional rejection because of long light emission tail

23 DarkSide-50 neutrons n + 10 B a + 7 Li n + 10 B a + 7 Li* + g neutron veto, calibration with 241Am13C source efficiency for LAr TPC single site nuclear recoils

24 DarkSide-50 backgrounds Drift time [µs] Reconstructed radius [cm] Background Est. Survive Surface α decays 1 Cosmogenic n < Radiogenic n <0.005 ER S1+Cherenkov 0.08* Total 0.09± Single-Scatter Unresolved Multi-Scatter 0.85 Scintillation + Fused-Silica Cherenkov Events / [0.01 f90] Scintillation + PTFE Cherenkov f Radiogenic Cosmogenic Fission candidate 50% NR acceptance f S1 [PE]

25 DarkSide-50 electron recoil charge yield Events/[0.05 Ne kg day] 37 Ar 37 Ar 0.27 kev 37 Ar 2.8 kev Ne=47.9 N e

26 Argon and Xenon charge yield Q y [e /kev nr ] e (Lindhard reduced energy)

27 DarkSide-50 single electron spectrum Events/[0.05 N e kg day] N e

28 DarkSide-50 S2-based analysis acceptance Acceptance Fiducialization Trigger efficiency S2 Identification (f 90 < 0.15) S2 [PE]