XENONnT andbeyond:Status, prospects and challenges for
direct dark matter detection using
liquid xenon

Florian Jörg
fjoerg@mpi-hd.mpg.deSeminar
Kamioka - November, 27 2023

Outline

1. Direct dark matter detection
2. The XENONnT experiment
3. Latest results
4. The road ahead (DARWIN/XLZD)
5. Radon mitigation for future
detectors

Florian Jörg - XENONnT and beyond

1 / 21

Why to search for (WIMP) dark matter
Evidences for dark matter:▶ Astronomical, astrophysical,
cosmological▶ 5x more dark matter thanbaryonic matter

Weakly interacting massive
particles (WIMPs)▶ Mass in the GeV range,interaction strength of the weakscale▶ Earth (and detector) moving
through DM halo

DMSM

SM

Collider search

Direct search approach:Direct detection
DM

Indirect detection▶ Many candidates from BSM
models▶ Can induce “scattering” eventwith low recoil energy
Florian Jörg - XENONnT and beyond

arXiv: 1904.07915

2 / 21

How can we detect dark matter directly?
WIMPERER ∼ O(10 keV)
Elastic scattering of WIMPs off target nuclei

Florian Jörg - XENONnT and beyond

3 / 21WIMP spectrum and detection efficiency
dRMT ρ0=dErecoilmA mχ

Z vescvminv · f (⃗v )dσχ,Ndv
dERecoil

Astrophysical inputs• Local DM density ρ0 ∼ 0.3GeV/cm3
JCAP10(2014)023• DM velocity distribution f (⃗v)

Florian Jörg - XENONnT and beyond▶ Assumption: DM is collisionlesswith isotropic velocity distribution▶ Isothermal sphere (MaxwellBoltzmann distribution)

4 / 21WIMP spectrum and detection efficiency
dRMT ρ0=dErecoilmA mχ

Z vescvminv · f (⃗v )dσχ,Ndv
dERecoil

Astrophysical inputs• Local DM density ρ0 ∼ 0.3GeV/cm3• DM velocity distribution f (⃗v)

▶ Assumption: DM is collisionlesswith isotropic velocity distribution▶ Isothermal sphere (MaxwellBoltzmann distribution)
Florian Jörg - XENONnT and beyond

4 / 21WIMP spectrum and detection efficiency
dRMT ρ0=dErecoilmA mχ

Z vescvminv · f (⃗v )dσχ,Ndv
dERecoil

Astrophysical inputs• Local DM density ρ0 ∼ 0.3GeV/cm3• DM velocity distribution f (⃗v)

Particle physics• WIMP - nucleon cross section σχ,NdσmN  SI 22σ0 FSI + σ0SD FSD=
22dER2µ v
4µ22[Zfp + (A − Z )fn ]π∝ A2σ0SI =▶ FSI & FSD are nuclear form factors(material specific)▶ At low momentum transfer: A2scaling due to coherence
Florian Jörg - XENONnT and beyond

4 / 21WIMP spectrum and detection efficiency
dRMT ρ0=dErecoilmA mχ

Z vescAstrophysical inputsvminv · f (⃗v )dσχ,NdvdERecoil

J. Phys. G43 (2016) 013001• Local DM density ρ0 ∼ 0.3GeV/cm3• DM velocity distribution f (⃗v)

Particle physics• WIMP - nucleon cross section σχ,NFlorian Jörg - XENONnT and beyond

4 / 21WIMP spectrum and detection efficiency
dRMT ρ0=dErecoilmA mχ

Z vescvminv · f (⃗v )dσχ,Ndv
dERecoil

Astrophysical inputs• Local DM density ρ0 ∼ 0.3GeV/cm3

PRL 131, 041003 (2023)

1.0Particle physics

Detector physics• Target material: atomic mass mA andtotal mass MT• Energy threshold: vmin
Florian Jörg - XENONnT and beyond

0.8Efficiency• WIMP - nucleon cross section σχ,NDetection

0.6Selection
ROIWIMP0.4
0.2
0.0 050 G 2
eV/c 2 00 GeV 2/c10 GeV/c2

204060
Nuclear recoil energy [keVNR]

Normalized rate [a.u.]• DM velocity distribution f (⃗v)

80
4 / 21XENONnTDual-phase TPC principle▶ Electron drift time ⇒ z-position▶ Distribution of S2 signal ⇒ x-y-position▶ S1/S2 ratio ⇒ signal discrimination
Florian Jörg - XENONnT and beyond

5 / 21

Background mitigation
Cosmogenicµν

3400 mwe, µVeto
None

RadiogenicγnFiducialization
nVeto222

Internal85RnKr & 37 Ar

Cosmogenicμ ν ν
WIMP

ER/NR separation
distillation

Florian Jörg - XENONnT and beyondγLiquidXenonγ

From: Robert Hammann

αβnInternal

Nature (2012), 435–438

Radiogenicn

6 / 21

The XENON-family▶ 170 scientists▶ 29 institutions▶ 12 countries

Florian Jörg - XENONnT and beyond

7 / 21

The XENON family-tree

Florian Jörg - XENONnT and beyond

8 / 21

The XENON family-tree

102Fiducial mass (ton)10101
11000.1
10 10.01

10 22010

20152020

ER background (events/keV/ton/day)

Moore's law of liquid xenon detectors

2025

YearBigger detector ⇒ less background ⇒ better sensitivity!
Florian Jörg - XENONnT and beyond

8 / 21

Some new subsystems in XENONnTDual-phase TPC
JCAP11(2020)031 & arXiv: 2007.08796

Florian Jörg - XENONnT and beyond

9 / 21

Some new subsystems in XENONnTDual-phase TPC
JCAP11(2020)031 & arXiv: 2007.08796

Neutron veto

Florian Jörg - XENONnT and beyond9 / 21

Some new subsystems in XENONnTDual-phase TPC
JCAP11(2020)031 & arXiv: 2007.08796

LXe purification

EPJC 82 (2022) 860 arXiv: 2205.07336

Neutron veto

Florian Jörg - XENONnT and beyond

9 / 21

Some new subsystems in XENONnTDual-phase TPC
JCAP11(2020)031 & arXiv: 2007.08796

LXe purification

EPJC 82 (2022) 860 arXiv: 2205.07336

Neutron vetoRadon distillation
EPJC82(2022)12,1104 & arXiv:2205.11492

Florian Jörg - XENONnT and beyond

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Some new subsystems in XENONnTDual-phase TPCJCAP11(2020)031 & arXiv: 2007.08796

LXe purification

EPJC 82 (2022) 860 arXiv: 2205.07336

Neutron vetoRadon distillation
EPJC82(2022)12,1104 & arXiv:2205.11492

Florian Jörg - XENONnT and beyond

9 / 21

First science data from XENONnTOther operations
83mKr
220Rn

Getter bypass
mode37Ar

AmBe
Search data

100

Livetime [days]

80
60
40
20-12
20
21-11-1020
21

Date (UTC)2021-09
20
21-08
20
21-07
20
2120
21-060▶ Livetime: 97.1 days
▶ Drift field: ∼23 V/cm

▶ Light and charge yield: stable within 2%▶ Investigate electronic recoil excess (XENON1T)▶ Special Tritium enhanced mode at the end
Florian Jörg - XENONnT and beyond

10 / 21

Calibration of ER/NR response
Electronic recoil band10

• Calibrated by mixing 220 Rn
into the LXe

4cS2 [PE]• Continuous β-spectrum
from 212 Pb
10• Additional: 37 Ar at end ofSR0• Low energy mono-energetic
X-ray at 2.8 keV

310 keV ER

50 keV NR

40 keV NR

30 keV NR

20 keV NR

10 keV NR

1020204060
cS1 [PE]PRL 131, 041003 (2023)

Florian Jörg - XENONnT and beyond

80100120

Nuclear recoil band
• External AmBe neutronsource• Utilization of the neutron
veto for coincidence
selection
11 / 21

Backgrounds for WIMP searchElectronic recoils (ER)• Dominated by 214 Pb (from 222 Rn)• Suppressed by ER/NR separation

Expected Background events:
ER
134

Florian Jörg - XENONnT and beyond

12 / 21

Backgrounds for WIMP searchElectronic recoils (ER)• Dominated by 214 Pb (from 222 Rn)• Suppressed by ER/NR separation

Accidental coincidences (AC)• Random pairing of isolated S1/S2• Suppressed by analysis cuts

Expected Background events:

Florian Jörg - XENONnT and beyond

ERAC

134

4.3 ± 0.2

12 / 21

Backgrounds for WIMP searchElectronic recoils (ER)• Dominated by 214 Pb (from 222 Rn)• Suppressed by ER/NR separation

Accidental coincidences (AC)• Random pairing of isolated S1/S2• Suppressed by analysis cuts

Surface• 210 Pb plate-out during construction• Radial selection

Florian Jörg - XENONnT and beyond

Expected Background events:
ERACSurface

134

4.3 ± 0.2

14 ± 312 / 21

Backgrounds for WIMP searchElectronic recoils (ER)• Dominated by 214 Pb (from 222 Rn)• Suppressed by ER/NR separation

Accidental coincidences (AC)• Random pairing of isolated S1/S2• Suppressed by analysis cutsSurface• 210 Pb plate-out during construction

Expected Background events:• Radial selection

ERACSurface

Nuclear recoils (NR)134

4.3 ± 0.2

14 ± 3

Neutrons

CEνNSTotal+0.6
1.1−0.5

0.23 ± 0.06

154

• Radiogenic neutrons: fission & (α, n)• CEνNS: Solar & atmospheric neutrinos
Florian Jörg - XENONnT and beyond12 / 21

WIMP Result▶ 152 events in ROI▶ 16 events in blinded region▶ No significant excess▶ ∗) Assuming a 200 GeV WIMP and abest-fit σ = 2.5 × 10−47 cm2
PRL 131, 041003 (2023)

Expectation
ROI

Florian Jörg - XENONnT and beyond

Best Fit
Signal region

ERNeutrons
CEνNSAC
Surface134+0.6
1.1−0.5
0.23 ± 0.06
4.3 ± 0.2
14 ± 3135+12−111.1 ± 0.4
0.23 ± 0.06
4.32 ± 0.15
12+0−40.86 ± 0.07
0.42 ± 0.17
0.022 ± 0.011
0.366 ± 0.013+0.010.35−0.11Total
WIMP∗)

154-

152 ± 122.6

2.0 ± 0.2
1.3

Observed-152

313 / 21

WIMP limits
10 43

2 sensitivity

10 4410 45018)
N1T (2XENOk)
is worh(tNnT 47 MGeV/c )XEN=O6.08×10 (10010 46

DM

10 47
10 48

2UL

10102
WIMP Mass MDM [GeV/c2]

XENONnT: PRL 131, 041003 (2023)
XENON1T: PRL 121, 111302 (2018)▶ 90% C.L. Power-Constrained Limit▶ Use 50% median rejection power as
constraintFlorian Jörg - XENONnT and beyond

WIMP-proton cross-section SDp [cm2]

WIMP-nucleon cross-section SI[cm2]

1 sensitivity

10 37

WIMP-neutron cross-section SDn [cm2]Spin dependent limits

Spin independent limits

10 38

1 sensitivity

2 sensitivity

10 38018)
N1T (2XENOrk)
is wonT (th M V/c )NO
XEN ×10 40 (100 Ge

10 39

DM

10 40
10 41

UL

102= 3.26102
WIMP Mass MDM [GeV/c2]
1 sensitivity

2 sensitivity

10 39
10 4018)
T (20ON1ork)
XEN
his wM V/c )(tTONn 42 (100 Ge
XEN 10.61×1010 41DMUL

10 42

102=102
WIMP Mass MDM [GeV/c2]
14 / 21

Comparison with other LXe experiments

140

WIMP-nucleon cross-section SI[cm2]

PRL 129, 161804 (2022)
PRD 102, 072004 (2020)
arXiv: 2207.03764 (2022)
PRL 129, 161805 (2022)
PandaX-4T

Events/(t y keVee )

120

100

XENON1T
80

60

40

LZ

XENONnT

200
0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

Energy [keVee ]

10 43
10 44
10 45021)
X-4T (2 18)
PanNdOa N1T (20XErk)
ow(this 022)
ONnT LZ (210 46XEN

10 47
10 48

10102
WIMP Mass MDM [GeV/c2]▶ Factor 5 reduction in ER background XENON1T ⇒ XENONnT▶ Further reduction is possible (222 Rn distillation using LXe & GXe).
▶ No excesses found in electronic/nuclear recoil region in XENONnT▶ ⇒ Placing competitive limits
Florian Jörg - XENONnT and beyond

15 / 21

The road ahead:

Future of liquid xenon dark matter searchesGlobal picture of the WIMP search100

NEWS-G (2017)

10 38
CRESST (2019)

10 40

10 42

CDMSLite (2018)

10 2

DAMIC (2017)
DAMA (Na)EDELWEISS-III (2016)

10 4

DAMA (I)

DarkSide-50 (2018)

10 67)
MS (201SuperCD00 (2019)
DEAP-36

XENON1T (2019)10 44

10 82)LZ (202
PandaX-4T (2021)

10 46

nT/LZ

Neutrino coherent scattering

XENONnT (2023)

Bagnaschi
2016

10 48

10 50

10 10

XENONy) 10(200 t·DARWIN

100

101

102

12

SI DM-nucleon cross section [pb]

SI DM-nucleon cross section [cm²]

10 36

10 14103m (GeV)
PDG (2019) (modified)
Florian Jörg - XENONnT and beyond

16 / 21

A glance into the future
4.0Radon Removal System:
GXe-only modeRadon Removal System:
GXe+LXe mode

3.0

37Ar calibration and removal
RRS improvements and restart

222Rn Activity Concentration [µBq/kg]

3.5

1.8 µBq/kg

2.5
2.0
1.5
1.0

First science data

Norm. Res.

0.5

Future of XENONnT▶ Target exposure of 20 t×yr

Now

▶ Unlock full potential ofradon distillation plant

0.8 µBq/kg▶ Surpass design goal of
1 µBq/kg

2.5
0.0
2.5
0204060+80

100120340

Time since 01 July 2021 [d]+360

380

400

420440▶ Gd-loaded neutron veto:
Higher neutron tagging
efficiency=
www.xlzd.org▶ 300+ Scientists from 60+ Institutions▶ Goal: Enter the neutrino phase▶ Build a ≥ 50 t LXe detector
2nd meeting April 2023 UCLA ←Florian Jörg - XENONnT and beyond

17 / 21

Why do we need to reduce the radon...
▶ Low energy β decay of 214 Pb▶ 222 Rn distributes
homogeneously: No
fiducialization possible
Darwin/XLZD: Solar νdominated. ⇒ Reduce
222
Rn conc. by 10!

Figure courtesy: Masaki Yamashita
Florian Jörg - XENONnT and beyond

18 / 21

... and how to achieve this!
• Methods that prevent radon fromentering the active volume• Material pre-selection, radon barriers,
new detector designs• Active removal of radon that has
already entered the detector• Distillation (XENONnT/PandaX-4T)
and/or adsorption (LZ)

• Rejection of radon-induced low
energy events in the analysis• ER/NR separation and/orconvection-based veto
⇒ Optimal combination needed!
Florian Jörg - XENONnT and beyond

19 / 21

EPJC82(2022)12,1104 & arXiv:2205.11492

Some of the ongoing R&D efforts▶ LowRAD distillation plant (Münster)▶ New radon detectors (U. Freiburg, MPIK)▶ Cold radon emanation facility (RAL, UK)▶ Cross-calibration and book-keeping▶ Sealed TPC: Freiburg, Nagoya, San Diego▶ Solid Xenon TPC (CrystaLiZe)▶ Coating-based radon barriers (MPIK)
Florian Jörg - XENONnT and beyond

20 / 21More science than WIMP dark matter!

Backup slides

Energy calibration in XENONnT▶ Weekly PMT calibrations via LEDs
▶ Internal source:
37Ar, 83m Kr, 192m Xe, 131m Xe, 220 Rn▶ External sources and materialradioactivity▶ Used to determine scintillation (g1)and ionization (g2) gains
Florian Jörg - XENONnT and beyond

1/3

Basic concept and results▶ Recoil emanation
4.9 MeV 222▶ α-decay: 226 Ra =====⇒Rn▶ 86 keV recoil energy⇒ ∼ 14 nm (steel)Radon mitigation with coatings▶ Diffusion-driven emanation
Requirement for coating:Thick, Tight, Radiopure

Florian Jörg - XENONnT and beyond

2/3

Basic concept and results▶ Recoil emanation
4.9 MeV 222▶ α-decay: 226 Ra =====⇒Rn▶ 86 keV recoil energy⇒ ∼ 14 nm (steel)Radon mitigation with coatings▶ Diffusion-driven emanation
Requirement for coating:Thick, Tight, Radiopure

Tested coating techniques & resuslts
MethodMaterialSputtering
Plasma spraying
Epoxy resin
Chem. vapor dep.
Electrochem. plating

Titanium
CopperStycastCarbonCopperFlorian Jörg - XENONnT and beyond

Thickness[µm]
0.4 - 0.8
3
≈ 200
15Reduction
222RnRn
4.5
2.1 ± 0.722≥ 74
3
1.4 ± 0.413015002202/3

Best results: electrochemical plating

2cm1

1. Sample: 226 Ra-implanted stainlesssteel. 2 Bq emanation of 222 Rn−2. Deposition: Cu2+aq + 2 · e → Cus2from solution 10 mA/cm
3. Reduction: By ×1500 with 5 µm
copper.

2 cm2 Bq
Appl.Radiat.Isot. 194 (2023) 110666 & arXiv: 2205.15926

U₀2+ -3I(t)
SO₄²⁻
Cu²⁺

SampleholderWork
piece

Counter
electrode

Heater & Stirrer
Florian Jörg - XENONnT and beyond

1.3 mBq
3/3

Best results: electrochemical plating

2cm

1

1. Sample: 226 Ra-implanted stainlesssteel. 2 Bq emanation of 222 Rn−
2. Deposition: Cu2+
aq + 2 · e → Cus
2from solution 10 mA/cm
3. Reduction: By ×1500 with 5 µm
copper.

2 cm2 Bq

Very promising! Only first step...

Appl.Radiat.Isot. 194 (2023) 110666 & arXiv: 2205.15926

U₀2+ -3I(t)SO₄²⁻Cu²⁺Sample
holderWork
piece

Counter
electrode

Heater & Stirrer
Florian Jörg - XENONnT and beyond

1.3 mBq
3/3