1 of 57

First Results from the

LUX-ZEPLIN Dark Matter Experiment

PATRAS 2023

Jim Dobson* for the LZ Collaboration

* STFC Ernest Rutherford Fellow, King’s College London

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

2 of 57

Direct detection of Dark Matter

2

(University of California, Berkeley)

Standard Halo Model

Isothermal sphere of DM, ρ ∝ r^-2
Local density ρ₀ ~ 0.3 GeV/cm3
Maxwellian (truncated) velocity distribution
Characteristic velocity v₀=220 km/s → non-relativistic!

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

3 of 57

Direct detection of Dark Matter

2

(University of California, Berkeley)

Standard Halo Model

Isothermal sphere of DM, ρ ∝ r^-2
Local density ρ₀ ~ 0.3 GeV/cm3
Maxwellian (truncated) velocity distribution
Characteristic velocity v₀=220 km/s → non-relativistic!

E_R^max = 5-50 keV for m_χ = 10-100 GeV

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

4 of 57

Liquid Xenon Time Projection Chambers

3

(SLAC National Accelerator Laboratory)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

5 of 57

Liquid Xenon Time Projection Chambers

3

(SLAC National Accelerator Laboratory)

Key features: excellent charge/light yields, σ ∝ A², lack of long-lived radioisotopes, fiducialisation →highly scalable.

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

6 of 57

Background suppression in LXe-TPC

4

3D position: σ_xy= O(cm), σ_z ~ O(mm) → fiducialisation + single-scatter ID

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

7 of 57

Background suppression in LXe-TPC

4

Self-shielding: here showing low-energy neutron single scatters

3D position: σ_xy= O(cm), σ_z ~ O(mm) → fiducialisation + single-scatter ID

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

8 of 57

Background suppression in LXe-TPC

4

Self-shielding: here showing low-energy neutron single scatters

3D position: σ_xy= O(cm), σ_z ~ O(mm) → fiducialisation + single-scatter ID

Electron-recoils (ER) [internal betas, auger/x-rays, external gammas]

Nuclear-recoils (NR) [WIMP scatters, single-scatter neutrons]

LZ WIMP Sensitivity paper: Phys.Rev.D 101 (2020) 5, 052002

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

9 of 57

Leading technology above a ~few GeV

5

PANDAX-II

580 kg (362 kg)

LUX

250 kg (100 kg)

XENON1T

2,000 kg (1,042 kg)

ZEPLIN-III

12 kg (7 kg)

XENON100

62 kg (34 kg)

2008 2013 2016 2017 2018

7,000 kg (5,600 kg)

LUX-ZEPLIN

2022-25

circa 2021

?

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

10 of 57

6

LZ (LUX-ZEPLIN) Collaboration, 37 Institutions

250 scientists, engineers, and technical staff

Black Hills State University
Brookhaven National Laboratory
Brown University
Center for Underground Physics
Edinburgh University
Fermi National Accelerator Lab.
Imperial College London
King’s College London
Lawrence Berkeley National Lab.
Lawrence Livermore National Lab.
LIP Coimbra
Northwestern University
Pennsylvania State University
Royal Holloway University of London
SLAC National Accelerator Lab.
South Dakota School of Mines & Tech
South Dakota Science & Technology Authority
STFC Rutherford Appleton Lab.
Texas A&M University
University of Albany, SUNY
University of Alabama
University of Bristol
University College London
University of California Berkeley
University of California Davis
University of California Los Angeles
University of California Santa Barbara
University of Liverpool
University of Maryland
University of Massachusetts, Amherst
University of Michigan
University of Oxford
University of Rochester
University of Sheffield
University of Sydney
University of Texas at Austin
University of Wisconsin, Madison

US UK Portugal Korea Australia

Thanks to our sponsors and participating institutions!

https://lz.lbl.gov/

@lzdarkmatter

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

11 of 57

The LUX-ZEPLIN Detector

7

1.456 m

TPC key stats:

1.456 m between cathode and gate grid
7 tonne active region
494 Hamamatsu R11410-22 3” PMTs
High reflectivity PTFE for light collection

Nucl.Instrum.Meth.A 953 (2020) 163047

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

12 of 57

Multi-detector active veto system

8

Optically separated Xe Skin detector + Outer Detector (OD) with 17 tonnes of Gd-doped LS → BG suppression and in-situ characterisation

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

13 of 57

Multi-detector active veto system

8

Optically separated Xe Skin detector + Outer Detector (OD) with 17 tonnes of Gd-doped LS → BG suppression and in-situ characterisation

≈10 events/5.6 tonne FV/1000d

6-30 keV nuclear recoils before veto cut…

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

14 of 57

Multi-detector active veto system

8

Optically separated Xe Skin detector + Outer Detector (OD) with 17 tonnes of Gd-doped LS → BG suppression and in-situ characterisation

≈10 events/5.6 tonne FV/1000d

6-30 keV nuclear recoils before veto cut…

≈1 events/5.6 tonne FV/1000d

…after veto cut

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

15 of 57

Backgrounds, backgrounds, backgrounds

9

Radiopurity is key:

Xe purification with chromatography
Extensive radioassay campaign > 1000 assays
Strict cleanliness controls

2) Take 1 mile underground

Ultra-radio pure materials and construction

3) Run until background limited

See Eur.Phys.J.C 80 (2020) 11

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

16 of 57

Backgrounds, backgrounds, backgrounds

9

Radiopurity is key:

Xe purification with chromatography
Extensive radioassay campaign > 1000 assays
Strict cleanliness controls

2) Take 1 mile underground

Ultra-radio pure materials and construction

3) Run until background limited

See Eur.Phys.J.C 80 (2020) 11

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

17 of 57

LUX-ZEPLIN Construction - a few highlights

10

2018

2019

HV grids production at SLAC, see Nucl.Instrum.Meth.A 1031 (2022) 165955

Bottom PMT array after assembly at Brown University

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

18 of 57

LUX-ZEPLIN Construction - a few highlights

11

Offsite Kr removal of 10 tonnes of LXe at SLAC

Completed outer detector tank at Reynolds Polymer Technology - USCB

In total, OD tanks will contain w/17 tonnes Gd-LS produced at BNL

Gas chromatography:

→ natKr reduced to 0.1 ppt g/g

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

19 of 57

TPC Assembly at SURF surface laboratory

12

2019

Dust and Rn exposure control critical → assembly in Rn-reduced surface lab cleanroom

Fully assembled TPC at SURF surface lab

Mating of the extraction region to central TPC

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

20 of 57

Moving to the Davis Campus

13

2021

TPC inside inner cryostat vessel (ICV) being transported underground

ICV being lowered into the outer vessel inside the water tank

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

21 of 57

Fully assembled 1 mile UG in Davis Campus

14

2021

Fully assembled detector

- OD ready for GdLS + water fill (at same time)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

22 of 57

Fully assembled 1 mile UG in Davis Campus

14

2021

Fully assembled detector

- OD ready for GdLS + water fill (at same time)

Commissioning complete late 2021 -

& first science run started December

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

23 of 57

Detector state and stability

15

Gas extraction field of 7.3 kV/cm

(~60 phd/extracted electron)

193 V/cm between cathode-gate

(951 μs drift time)

Liquid-level stable within 10 μm

LXe: 174.1 K and 1.791 bar(a) [stable within 0.2%]

Composite overlay courtesy of Nicolas Angelides, Imperial

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

24 of 57

Detector state and stability

15

Gas extraction field of 7.3 kV/cm

(~60 phd/extracted electron)

193 V/cm between cathode-gate

(951 μs drift time)

Liquid-level stable within 10 μm

LXe: 174.1 K and 1.791 bar(a) [stable within 0.2%]

Xe continuously purified through hot Zirconium getter → 3.3 tonnes/day to remove electronegative impurities

Composite overlay courtesy of Nicolas Angelides, Imperial

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

25 of 57

Light and Charge collection

16

e-

γ^{178 nm}

Xe microphysics → light and charge signals are anti-correlated:

Where:

g1 = photon detection efficiency

g2 = electron gain phd/e-

W = work function = 13.5 eV/quanta

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

26 of 57

Detector response - monoenergetic sources

Noble Element Scintillation Technique (NEST) 2.3.7
Tuned to reconstruct ER mono-energetic sources:

^83mKr (41.5 keV)
^129mXe (236 keV)
^131mXe (164 keV)

Detector (g1, g2) and Xe response parameters varied

17

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

27 of 57

Detector response - ER/NR bands

NEST simultaneously tuned to reproduce ER band mean and widths
Tuned parameters propagated into NR model
Consistent at 1% with neutron calibration data (DD and AmLi)

18

5343 tritium tagged methane (CH3T). β with Q value 18.6 keV

6324 DD neutron gun events - 2.45 MeV neutrons

Fitted det. parameters: g₁ = 11.4% and g₂ = 47.1 phd/liquid electron

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

28 of 57

Science Run 1 (SR1)

19

23rd December 2021 to 11th May 2022

Remove DAQ deadtime (3%), anomalous trigger rates (7%) → 89 live-days left

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

29 of 57

Time hold-off following large S2s

20

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

30 of 57

Time hold-off following large S2s

20

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

31 of 57

Time hold-off following large S2s

20

S2-size dependent hold-off period following large S2s. Results in 60 live-days remaining.

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

32 of 57

SR1 WIMP-search data before analysis cuts

60 live-days and 5.5 tonne fiducial volume cut

21

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

33 of 57

SR1 WIMP-search data before analysis cuts

60 live-days and 5.5 tonne fiducial volume cut

21

Then analysis cuts to:

Remove poorly reconstructed/noisy events
Removal “accidentals”
Veto events with coincident signal in Skin or OD

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

34 of 57

Nuclear Recoil Efficiency - all cuts

DD neutron data to evaluate trigger and reconstruction efficiency
CH3T for S1-cuts
AmLi(S2) + CH3T(S1) for S2-cuts
50% signal efficiency at 5.5 keV

22

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

35 of 57

WIMP-search events surviving all cuts

60 live-days and 5.5 tonne fiducial volume cut

23

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

36 of 57

WIMP-search events surviving all cuts

60 live-days and 5.5 tonne fiducial volume cut

23

= inside FV; = outside F

= vetoed by skin; = vetoed by OD

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

37 of 57

WIMP-search events surviving all cuts

60 live-days and 5.5 tonne fiducial volume cut

23

= inside FV; = outside F

= vetoed by skin; = vetoed by OD

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

38 of 57

Backgrounds: pre-and post-fit

Profile likelihood fit (in S1 vs S2 observable space)
Pre-constraints on BGs (high-energy sideband, mass spec, OD tagged)

24

“Background Determination for the LUX-ZEPLIN (LZ) Dark Matter Experiment” (11/2022), arxiv/2211.17120

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

39 of 57

Backgrounds: pre-and post-fit

Profile likelihood fit (in S1 vs S2 observable space)
Pre-constraints on BGs (high-energy sideband, mass spec, OD tagged)

24

Post-fit model vs data

“Background Determination for the LUX-ZEPLIN (LZ) Dark Matter Experiment” (11/2022), arxiv/2211.17120

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

40 of 57

Spin-independent WIMP-nucleon

Data consistent with the background-only hypothesis
2-sided PLR test statistic with power constraint (-1σ)

25

“First Dark Matter Search Results from the LUX-ZEPLIN (LZ) Experiment” (07/2022) (arxiv/2207.03764)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

41 of 57

Spin-independent WIMP-nucleon

Data consistent with the background-only hypothesis
2-sided PLR test statistic with power constraint (-1σ)

25

Most stringent limit of 9.2 x 10^-48 cm² for a 36 GeV/c² WIMP

“First Dark Matter Search Results from the LUX-ZEPLIN (LZ) Experiment” (07/2022) (arxiv/2207.03764)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

42 of 57

Not just WIMPs

26

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

43 of 57

Not just WIMPs

26

ER band searches: mirror dark matter, ALPs, hidden photons Phys.Rev.D 104, 092009, 2021

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

44 of 57

Not just WIMPs

26

ER band searches: mirror dark matter, ALPs, hidden photons Phys.Rev.D 104, 092009, 2021

8B CEvNS; SN neutrinos

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

45 of 57

Not just WIMPs

26

ER band searches: mirror dark matter, ALPs, hidden photons Phys.Rev.D 104, 092009, 2021

8B CEvNS; SN neutrinos

High energy NR/EFT (up to 400 keV)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

46 of 57

Not just WIMPs

26

ER band searches: mirror dark matter, ALPs, hidden photons Phys.Rev.D 104, 092009, 2021

8B CEvNS; SN neutrinos

High energy NR/EFT (up to 400 keV)

0νββ (2.45 MeV/0.83 MeV) and 2vDEC (2.86 MeV)

Phys. Rev. C 102, 014602, 2020 and Phys. Rev. C 104, 065501 202

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

47 of 57

Not just WIMPs

26

ER band searches: mirror dark matter, ALPs, hidden photons Phys.Rev.D 104, 092009, 2021

8B CEvNS; SN neutrinos

High energy NR/EFT (up to 400 keV)

0νββ (2.45 MeV/0.83 MeV) and 2vDEC (2.86 MeV)

Phys. Rev. C 102, 014602, 2020 and Phys. Rev. C 104, 065501 202

LZ Sensitivity to 0νββ decay of 136Xe

Phys.Rev.C 102 (2020) 1, 014602

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

48 of 57

Not just WIMPs

26

ER band searches: mirror dark matter, ALPs, hidden photons Phys.Rev.D 104, 092009, 2021

8B CEvNS; SN neutrinos

High energy NR/EFT (up to 400 keV)

0νββ (2.45 MeV/0.83 MeV) and 2vDEC (2.86 MeV)

Phys. Rev. C 102, 014602, 2020 and Phys. Rev. C 104, 065501 202

LZ Sensitivity to 0νββ decay of 136Xe

Phys.Rev.C 102 (2020) 1, 014602

Stay tuned. 60 live-days is <10% of eventual dataset.

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

49 of 57

XLZD - a next-generation LXe observatory

Consortium of XENON, LUX-ZEPLIN & DARWIN → MOU July 2021
Explore electro-weak parameter space to neutrino fog in the 2030s

27

Scale-up: 7t → 40-80t

https://xlzd.org

Credit: Ciaran O'Hare

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

50 of 57

A broad range of physics with 300+ tonne.years

28

J Aalbers et al 2023 J. Phys. G: Nucl. Part. Phys.

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

51 of 57

In summary:

29

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

52 of 57

In summary:

29

LZ has released leading WIMP constraints with 60 live-days

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

53 of 57

In summary:

29

LZ has released leading WIMP constraints with 60 live-days
Now collecting data towards 1000 live-days → exploring new parameter space
Watch this space for WIMP & other BSM searches

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

54 of 57

In summary:

29

LZ has released leading WIMP constraints with 60 live-days
Now collecting data towards 1000 live-days → exploring new parameter space
Watch this space for WIMP & other BSM searches
Momentum building for XLZD next-gen LXe observatory (https://xlzd.org)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

55 of 57

In summary:

29

Thanks to our sponsors and 37 participating institutions!

U.S. Department of Energy Office of Science

LZ has released leading WIMP constraints with 60 live-days
Now collecting data towards 1000 live-days → exploring new parameter space
Watch this space for WIMP & other BSM searches
Momentum building for XLZD next-gen LXe observatory (https://xlzd.org)

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

56 of 57

Backups - SD results

56

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23

57 of 57

Spin-dependent WIMP-p(n)

Structure functions from Hoferichter et al [Phys. Rev. D 102, 074018 (2020)]
Gray band → uncertainty from range of theory models

57

Most stringent limit for SD-n of 1.49 x 10^-42 cm² at 36 GeV/c²

jim.dobson@kcl.ac.uk – 18th PATRAS - 3/7/23