DarkSide new results and prospects

Stefano Davini - INFN Genovaon behalf of the DarkSide collaboration

La Thuile, March 20, 2018

The DarkSide WIMP-argon program at LNGS

Past Present Future2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

DS-10 DS-50 DS-20ktechnical prototype projected sensitivity

σ (χN) ~ 10-48 cm2 @ WIMP mass 100 GeV/c2

dark matter runs ongoingσ (χN) ~ 10-44 cm2 @

WIMP mass 100 GeV/c2

σ (χN) ~ 10-41 cm2 @ WIMP mass 2 GeV/c2

The DarkSide-50 detector

dark matter detector Time Projection Chamber

50 kg Liquid Argonfrom underground source

low in radioactive 39Ar

neutron veto 30 ton Borated

Liquid Scint

cosmic-ray veto 1 kton Water

Cherenkov

The DarkSide-50 signals

S1

S1 primary scintillation signalcollected by 38 PMTs

Powerful Pulse Shapeallows to discriminate between- nuclear recoils (WIMP, neutrons)- electron recoils (β-γ backgrounds)

4

The DarkSide-50 signals

S1

S1

Beta/Gamma

S1

Nuclear Recoil

S1 [PE]50 100 150 200 250 300 350 400 450

90 f

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1) in SCENEn,pLi(7 AmBe in DarkSide-50241

]nrEnergy [keV20 40 60 80 100 120 140 160 180 200

Nuclear recoil (WIMP signals)

β/γ (backgrounds)

β/γ

Nuclear recoils

The DarkSide-50 signals

S1

! e-

e-e-e-e-

e-e- e- S2

S2 secondary electroluminescence signalone extracted e- -> S2~23 PE in central PMTallows for lower threshold analysis

S2-S1 drift time -> vertical positionS2 pattern on top PMTs -> horizontal positionS1 & S2 -> 3D position reco

drift time

S1

S2

top S2

6

WIMP search - A blind analysis

WIMP blind box DON’T LOOK HERE!

7

WIMP search - A blind analysis

0 100 200 300 400 500 600S1 [PE]

0

0.2

0.4

0.6

0.8

1

90f

1

10

210

310

410

510

S1 [PE]

f 90 no cuts - previous 71 days search data - PRD 93 (2016) 081101

WIMP BLIND BOX (final choose)

test regions

Goal - design WIMP analysis with < 0.1 background in box Using test regions to test bkg model prior to unblinding

WIMP search - 532 days

0

100

200

300

400

500

0 50 100 150 200 250 300 350 400 450S1 [PE]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

90f

50%

99%

1%

0 20 40 60 80 100 120 140 160 180 200]nrEnergy [keV

arXiv: 1802.07198

WIMP search - 532 days

1.1×10%&&()*

@100 GeV/(*3.8×10

%&& ()*

@1 TeV/(*

3.4×10%&.()*

@10 TeV/(*

arXiv: 1802.07198

WIMP-nucleon Spin Indep.

STD Halo Model

90% C.L. exclusion plot

Low mass WIMP search

arXiv: 1802.06994

!" =$%2'(

≤ 2*+(% ,%'(

≃ 50123 '+100523

% 100523'(

'(67~37GeVFor '+ = 10GeV !"~1.4KeV

Below threshold for S1 production (~6 123D7) but S2 has threshold ~0.4 123D7

Nuclear recoils from low mass WIMPdetectable 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

S2

e-

χ

Low mass WIMP search

arXiv: 1802.06994

Low mass WIMP search

arXiv: 1802.06994binomial fluctuation

no quenching fluctuation

DarkSide-50

Light DM on electron

arXiv: 1802.06998

S2

e-

χ

!" = $⃗ & '⃗ − $)2+,-

~12 12×4,512

For 4, = 100MeV !"~50eV

!"#$ ∼ 16.08eV, !"#, ∼ 34.76eV,!"0$ ∼ 260.45 eV,!"0, ∼ 335.30eV,!"3, ∼ 3227.51 eV

Use lightness of electronto investigate light mass DM

Recoil energy comparable with binding energies

in argon atoms

Same S2-only analysisbut very different interpretation

LDM on electron - scattering rate

arXiv: 1802.06998

min. velocity for Eer in bounded electrons

LDM form factorionization form factor

!"# $% = 1: “heavy mediator” !"# $% ∝ 1 $%⁄ : “light mediator”

LDM on electron - DS-50 constraints

arXiv: 1802.06998

!"# $% = 1: “heavy mediator” !"# $% ∝ 1 $%⁄ : “light mediator”

The Future

DS-20k GADMC

DarkSide - OutlookDarkSide-50 at LNGS: a successful 3-year underground argon run lead to

new dark matter constraints

DarkSide-50 532 day Dark Matter Search with Low-Radioactivity Argon 1802.07198

Low-mass Dark Matter Search with the DarkSide-50 experiment 1802.06694

Constraints on sub-GeV Dark Matter Electron Scattering from the DarkSide-50 experiment 1802.06998

DarkSide-20k and GADMC, the next tyrants in the dark matter argon community

Backup Slides

S1 [PE]

0 1000 2000 3000 4000 5000 6000

s]

× kg

×Events / [80 PE

8−10

7−10

6−10

5−10

4−10

3−10

2−10

1−10

AAr (200 V/cm, LSV anti-coinc.)

UAr (200 V/cm, LSV anti-coinc.)

Ar (from global fit)39

Kr (from global fit)85

atmospheric and underground argon at 200 V/cm

< 1/300< 1/1000

39Ar in UAr < 1 mBq/kg85Kr in UAr ~ 2 mBq/kg

DarkSide-50 γ-rays

DarkSide-50 alphas

30 35 40 45

310×

S1 [PE]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8310×

Events / [250 PE]

Data

Po210

Rn222

Po218

4 4.5 5 5.5 6 6.5Energy [MeV]

Full-energy:In LAr

Degraded:Under TPB

×1000

many with small or no S2, surface decays in TPB (wavelength shifter) additional rejection

because of long light emission tail

DarkSide-50 neutrons n + 10B → a + 7Li

n + 10B → a + 7Li* + g

neutron veto, calibration with 241Am13C source efficiency 0.9964 +- 0.0004

for LAr TPC single site nuclear recoils

DarkSide-50 backgrounds Background Est. Survive

Surface α decays 1Cosmogenic n <0.0003Radiogenic n <0.005ER S1+Cherenkov 0.08*

Total 0.09±0.04

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

90f

1−10

1

10

210

310

410

]90

Events / [0.01 f

Single-Scatter

Unresolved Multi-Scatter

Scintillation + Fused-Silica Cherenkov

Scintillation + PTFE Cherenkov

100 150 200 250 300 350 400 450S1 [PE]

0.65

0.7

0.75

0.8

0.85

90

f

Radiogenic

Cosmogenic

Fission candidate

50% NR acceptance

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14 16 18 20Reconstructed radius [cm]

50

100

150

200

250

300

350

s]

µDrift time [

DarkSide-50 electron recoil charge yield

37Ar 2.8 keV

37Ar 0.27 keV

Ne=47.9

37Ar

Even

ts/[

0.05

Ne×kg×day

]

Ne

Argon and Xenon charge yieldQ y

[e− /ke

V nr]

e (Lindhard reduced energy)

DarkSide-50 single electron spectrum

NeEven

ts/[

0.05

Ne×kg×day

]

Fiducialization

× Trigger efficiency

× S2 Identification (f90 < 0.15)

S2 [PE]

Acce

ptan

ce

DarkSide-50 S2-based analysis acceptance