Doping liquid xenon with light elements Hugh Lippincott, Fermilab - - PowerPoint PPT Presentation

Doping liquid xenon with light elements

Hugh Lippincott, Fermilab COFI November 29, 2018

1

FERMILAB-SLIDES-18-140-AE-E This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.

• Limited at low mass by detector threshold
• Limited at high mass by density
• Eventually limited by neutrinos

1 10 100 1000 104 1050 1049 1048 1047 1046 1045 1044 1043 1042 1041 1040 1039 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 WIMP Mass GeVc2 WIMPnucleon cross section cm2 WIMPnucleon cross section pb

8B

Neutrinos Atmospheric and DSNB Neutrinos CDMS II Ge (2009) Xenon100 (2012)

C R E S S T CoGeNT (2012) CDMS Si (2013)

EDELWEISS (2011)

DAMA

SIMPLE (2012) Z E P L I N

• I

I I ( 2 1 2 ) COUPP (2012)

SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) CDMS-II Ge Low Threshold (2011)

SuperCDMS Soudan X e n

• n

1 T LZ L U X ( 2 1 3 ) D a r k S i d e G 2 D a r k S i d e 5 DEAP3600 P I C O 2 5

• C

F 3 I PICO250-C3F8

7Be

Neutrinos

N EU T RIN O C OH ER EN T S CA T TE R I N G N E UT R IN O C O HE REN T S C A T T E R IN G

CDMSlite (2013) SuperCDMS SNOLAB L U X 3

• d

a y S u p e r C D M S S N O L A B

So where are we? (LZ edition)

3

• C. Amole et al., arXiv:1702.07666
• C. Amole et al., arXiv:1702.07666

LUX

LZ <3×10-48 cm2

(XENON nT)

Ge, NaI no discrimination Ge, w/discrim. LXe, w/discrim.

ZEPLIN-III

XENON 1T DEAP

w

Darkside CDMS SCDMS

⌅ ⌅

Z

annihilation cross section < σv >ann≈ 3 × 10−26cm3sec−1 ≈ α2 (200GeV)2

Coupling e.g. to light quarks

⇒ ⇤0 ≈ G2

fµ2

2⇥ ∼ 10−39cm2

?

f f

• direct

collider Indirect time time time

1 10 100 1000 104 1050 1049 1048 1047 1046 1045 1044 1043 1042 1041 1040 1039 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 WIMP Mass GeVc2 WIMPnucleon cross section cm2 WIMPnucleon cross section pb

8B

Neutrinos A t m

• s

p h e r i c a n d D S N B N e u t r i n

• s

CDMS II Ge (2009) Xenon100 (2012)

CRESST CoGeNT (2012) CDMS Si (2013)

EDELWEISS (2011)

DAMA

SIMPLE (2012) Z E P L I N

• I

I I ( 2 1 2 ) COUPP (2012)

SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) CDMS-II Ge Low Threshold (2011)

S u p e r C D M S S

• u

d a n X e n

• n

1 T LZ L U X ( 2 1 3 ) D a r k S i d e G 2 D a r k S i d e 5 D E A P 3 6 P I C O 2 5

• C

F 3 I PICO250-C3F8

7Be

Neutrinos

N EU T R I N O C OH E R E N T S CA T TE R IN G NE UT R IN O C O HE RE N T S CATTERING

CDMSlite (2013) S u p e r C D M S S N O L A B L U X 3

• d

a y S u p e r C D M S S N O L A B

⌅ ⌅

Z

Z-exchange excluded

annihilation cross section < σv >ann≈ 3 × 10−26cm3sec−1 ≈ α2 (200GeV)2

Coupling proportional to mass (e.g. via higgs)

HIGGS MEDIATED

⌅ ⌅

h

g ∼ 1 ⇒ yp ∼ 1 few mp v

⇤0 ∼ 10−39cm2 × 10−6

∼ 10−45cm2

?

f f

• direct

collider Indirect time time time

1 10 100 1000 104 1050 1049 1048 1047 1046 1045 1044 1043 1042 1041 1040 1039 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 WIMP Mass GeVc2 WIMPnucleon cross section cm2 WIMPnucleon cross section pb

8B

Neutrinos A t m

• s

p h e r i c a n d D S N B N e u t r i n

• s

CDMS II Ge (2009) Xenon100 (2012)

CRESST CoGeNT (2012) CDMS Si (2013)

EDELWEISS (2011)

DAMA

SIMPLE (2012) Z E P L I N

• I

I I ( 2 1 2 ) COUPP (2012)

SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) CDMS-II Ge Low Threshold (2011)

S u p e r C D M S S

• u

d a n X e n

• n

1 T LZ L U X ( 2 1 3 ) D a r k S i d e G 2 D a r k S i d e 5 D E A P 3 6 P I C O 2 5

• C

F 3 I PICO250-C3F8

7Be

Neutrinos

N EU T R I N O C OH E R E N T S CA T TE R IN G NE UT R IN O C O HE RE N T S CATTERING

CDMSlite (2013) S u p e r C D M S S N O L A B L U X 3

• d

a y S u p e r C D M S S N O L A B

HIGGS MEDIATED

⌅ ⌅

h

Higgs exchange

• N. Weiner, CIPANP 2015

“This era will answer the question: does the dark matter couple at O(0.1) to the Higgs boson”

⌅ ⌅

Z

Z-exchange excluded

The case for dark matter

8

• We know it interacts

gravitationally

• It is “dark” - should not

interact with light or electromagnetism

• Nearly collision less
• Slow

mDM

mP l

∼ 1019 GeV

∼ 100M

must be composite must be bosonic

∼ 100 eV

∼ 10−20 eV

A sampling of available dark matter candidates

co co d

,*&31)#$,";?(1?$

It’s probably WIMPs, right?

Low Mass Dark Matter (<10 GeV)

9

10 100 1000 ]

2

WIMP mass [GeV/c

LZ sensitivity (1000 live days) Projected limit (90% CL one-sided) expected σ 1 ± expected σ +2 LUX (2017) XENON1T (2017) PandaX-II (2017)

1 neutrino event NS) ν Neutrino discovery limit (CE (MasterCode, 2017) pMSSM11 49 −

10

48 −

10

47 −

10

46 −

10

45 −

10

44 −

10

43 −

10

42 −

10 ]

2

SI WIMP-nucleon cross section [cm

10 100 1000 ]

2

WIMP mass [GeV/c

LZ sensitivity (1000 live days) Projected limit (90% CL one-sided) expected σ 1 ± expected σ +2 LUX (2017) XENON1T (2017) PandaX-II (2017)

1 neutrino event NS) ν Neutrino discovery limit (CE (MasterCode, 2017) pMSSM11 49 −

10

48 −

10

47 −

10

46 −

10

45 −

10

44 −

10

43 −

10

42 −

10 ]

2

SI WIMP-nucleon cross section [cm

10

• [/]
• σ []
• σ []

CRESST-II CDMSLite DS-50 S2-only NEWS-G

Fake neutrino floor

Much less constrained!

Bad news: DM-SM interactions are not obligatory

If nature is unkind, we may never know the right scale

Good news: most discoverable DM candidates are in

thermal equilibrium with us in the early universe

Why is this good news?

DM Prognosis?

mDM

mP l

∼ 1019 GeV

∼ 100M

must be composite must be bosonic

∼ 100 eV

∼ 10−20 eV

DM Prognosis?

11

Courtesy G. Krnjaic

Bad news: DM-SM interactions are not obligatory

If nature is unkind, we may never know the right scale

Good news: most discoverable DM candidates are in

thermal equilibrium with us in the early universe

Why is this good news?

DM Prognosis?

mDM

mP l

∼ 1019 GeV

∼ 100M

must be composite must be bosonic

∼ 100 eV

∼ 10−20 eV

DM Prognosis?

12

Courtesy G. Krnjaic

mDM

∼ 100M

∼ 10−20 eV

too hot too much < 10 keV > 100 TeV

GeV

mZ

MeV

nonthermal nonthermal

mP l ∼ 1019 GeV

“WIMPs”

Direct Detection (Alan Robinson)

{

Light DM

{

Thermal dark matter

13

• “Most discoverable DM candidates are in thermal equilibrium” - G. Krnjaic
• If we can detect it, it’s likely that it was in equilibrium (e.g. interacted enough)
• Thermal dark matter has minimum annihilation rate (to set relic density)
• Doesn’t care about initial conditions (washed out by thermal bath) - makes

modeling easier

• Limited viable mass range (to a range that is basically within reach)

< MeV

Neff / BBN

mDM

∼ 100M

∼ 10−20 eV

too hot too much < 10 keV > 100 TeV

GeV

mZ

MeV

nonthermal nonthermal

mP l ∼ 1019 GeV

“WIMPs”

Direct Detection (Alan Robinson)

{

Light DM

{

18

Thermal dark matter

14

LZ, LAr, PICO, LHC, etc Mature >5 GeV program Wide open

< MeV

Neff / BBN

Are there actual candidates?

15

χ χ W, Z f f

σv ∼ α2m2

χ

m4

Z

∼ 10−29cm3s−1 ⇣ mχ GeV ⌘2

• Annihilation cross section

needed for the relic abundance

• New weak scale particle has to

be heavier than ~a few GeV

• Lee and Weinberg, PRL 39

(1977) 165-168

annihilation cross section < σv >ann≈ 3 × 10−26cm3sec−1

Are there actual candidates?

16

• Light dark matter needs new forces (although we might already be

there in canonical WIMP dark matter anyway)

• Asymmetric DM
• Secluded DM
• Forbidden DM
• SIMP
• ELDER
• Freeze in models

US Cosmic Visions: New Ideas in Dark Matter 2017 : Community Report

Yes!

1707.04591

What do you need for low mass?

• dR

dQ = ρ0 mχ × σ0A2 2m2

p

× F 2(Q) ×

Z vesc

vm

f(v) v dv.

17

10 20 30 40 Ethresh 0.05 0.10 0.50 1.00 ⇧year⇥

Xe Ge Si Ar Ne

R(cts/100kg/yr) for 10-46 cm2, 100 GeV

Energy threshold (keV)

What do you need for low mass?

• dR

dQ = ρ0 mχ × σ0A2 2m2

p

× F 2(Q) ×

Z vesc

vm

f(v) v dv.

18

10 20 30 40 Ethresh 0.05 0.10 0.50 1.00 ⇧year⇥

Xe Ge Si Ar Ne

R(cts/10kg/yr) for 10-45 cm2, 10 GeV

Energy threshold (keV)

10 20 30 40 Ethresh 0.05 0.10 0.50 1.00 ⇧year⇥

Knowing your energy scale and efficiency at threshold are crucial! Xe Ge Si Ar Ne

What do you need for low mass?

• dR

dQ = ρ0 mχ × σ0A2 2m2

p

× F 2(Q) ×

Z vesc

vm

f(v) v dv.

vm =

q

QmN/2m2

r

vesc = 544 km/s (current value)

• Low threshold
• Low mass target (for better kinematic match to the

dark matter mass)

• For given is minimized when

mN is mass of nucleus

mr = mNmχ mN + mχ

mn = mχ

Q, vm

19

10

−2

10

−1

10 10

1

10

2

10

−4

10

−3

10

−2

10

−1

10 10

1

WIMP mass (GeV/c2) Maximum recoil energy (keV) He Ge Xe e−

What do you need for low mass?

• dR

dQ = ρ0 mχ × σ0A2 2m2

p

× F 2(Q) ×

Z vesc

vm

f(v) v dv.

20

For same WIMP mass, He max recoil energy is 20-30x bigger than Xe At same recoil energy, He is sensitive to 5.5x smaller masses than Xe

Light targets less sensitive to halo uncertainty

21 200 400 600 800 |v| [km/s] 1 2 3 4 5 103f(|v|) [km/s]1 SDSS-Gaia DR2 Heliocentric |v| |z| >2.5 kpc d <4.0 kpc Halo Subs Total SHM 101 102 mχ [GeV] 10−47 10−46 10−45 10−44 σχ−n [cm2] Direct Detection Limits Xenon Target Halo Subs Total SHM

1807.02519

• dR

dQ = ρ0 mχ × σ0A2 2m2

p

× F 2(Q) ×

Z vesc

vm

f(v) v dv.

Light targets less sensitive to halo uncertainty

vesc = 544 km/s (current value)

22

200 400 600 10

−3

10

−2

10

−1

Velocity (km/s) Probability Density (a.u.) MB halo (vesc = 544 km/s) MB halo (vesc = 600 km/s) vmin for A = 4 mχ = 8 GeV Q = 3 keV vmin for A = 129

• ×

Z vesc

vm

f(v) v dv.

1 10 100 1000 104 1050 1049 1048 1047 1046 1045 1044 1043 1042 1041 1040 1039 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 WIMP Mass GeVc2 WIMPnucleon cross section cm2 WIMPnucleon cross section pb

Neutrinos Atmospheric and DSNB Neutrinos CDMS II Ge (2009) Xenon100 (2012)

CRESST CoGeNT (2012) CDMS Si (2013)

E D E L W E I S S ( 2 1 1 )

DAMA

S I M P L E ( 2 1 2 ) Z E P L I N

• I

I I ( 2 1 2 ) COUPP (2012)

SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) CDMS-II Ge Low Threshold (2011)

SuperCDMS Soudan X e n

• n

1 T LZ L U X ( 2 1 3 ) D a r k S i d e G 2 D a r k S i d e 5 DEAP3600 P I C O 2 5

• C

F 3 I PICO250-C3F8

Neutrinos

N EU T RIN O C OH E R E N T S CA T TE R ING NE UT R IN O C O HE R E N T S CATTERING

CDMSlite (2013) SuperCDMS SNOLAB L U X 3

• d

a y S u p e r C D M S S N O L A B

What don’t you need for low mass?

• A lot of mass

~10 tonnes Xe ~10 kg He

23

LUX-Zeplin (LZ)

• 7 tonne active LXe TPC
• Heavy target
• Excellent self shielding
• Good discrimination
• Low threshold (<3 keV)
• Huge effort to make it

clean and low background

• >30 institutions, ~200 people
• Now under construction in

Lead, SD

24

Two phase Xenon TPCs

• Interaction in the xenon

creates:

• Scintillation light (~10 ns)
• called S1
• ionization electrons
• Electrons drift through

electric field to liquid/gas surface

• Extracted into gas and

accelerated creating proportional scintillation light - called S2

Two phase Xenon TPCs

• Excellent 3D reconstruction

(~mm)

• Z position from S1-S2

timing

• XY position from hit

pattern of S2 light

• Allows for self shielding,

rejection of edge events

• Ratio of charge (S2) to light

(S1) gives particle ID

• Better than 99.5%

rejection of electron recoil events

7 ton LXe TPC Xe heat exchanger Water tank Gd-loaded liquid scint.

Cathode HV feedthrough Neutron beam pipe

28

10 100 1000 ]

2

WIMP mass [GeV/c

LZ sensitivity (1000 live days) Projected limit (90% CL one-sided) expected σ 1 ± expected σ +2 LUX (2017) XENON1T (2017) PandaX-II (2017)

1 neutrino event NS) ν Neutrino discovery limit (CE (MasterCode, 2017) pMSSM11 49 −

10

48 −

10

47 −

10

46 −

10

45 −

10

44 −

10

43 −

10

42 −

10 ]

2

SI WIMP-nucleon cross section [cm

LUX-Zeplin (LZ)

10 100 1000 ]

2

WIMP mass [GeV/c

LZ sensitivity (1000 live days) Projected limit (90% CL one-sided) expected σ 1 ± expected σ +2 LUX (2017) XENON1T (2017) PandaX-II (2017)

1 neutrino event NS) ν Neutrino discovery limit (CE (MasterCode, 2017) pMSSM11 49 −

10

48 −

10

47 −

10

46 −

10

45 −

10

44 −

10

43 −

10

42 −

10 ]

2

SI WIMP-nucleon cross section [cm

29

Would be nice to extend further down here!

LUX-Zeplin (LZ)

Can we add He or H2 to LXe?

• Dissolve small quantities of He/H2 in liquid xenon
• Extend the reach of a detector like LZ (or XENONnT or PandaX, etc)
• Add new targets to field of direct detection
• No existing experiments using either
• Talk on HeRALD by H. Pinckney next
• NEWS-G gas detector in Canada another contender
• Capitalize on investment in large detectors by adding flexibility

30

Dissolving He/H in LXe?

31 02/01/13 03/01/13 04/01/13 05/01/13 10 10

1

10

2

Date (mm/dd/yy) Concentration (ppb g/g) Helium, Run03 Getter In Getter Out

• Det. Return

PMT Purge Condensation

gas−liquid solubility

Circ Stop

From Bottle Farm

Average He in bulk Xe

From LSB9

• LUX fill data
• Some residual He in

the source bottles

• Data imply 3e-3

mass fraction for 1 atm partial pressure

• He fraction confirmed in

preliminary test at Fermilab

• Achieved 0.1% He in LXe by

mass on first attempt at 1 bar

• f partial pressure
• No data for H2 in xenon, but

scaling by argon data, 25% better than He

0.037 mol He/mol Xe x MHe/MXe ~ 0.1%

32

Dissolving He/H in LXe?

10

−1

10 10

1

10

−1

10 10

1

10

2

10

3

Interaction length [cm] Gamma energy [MeV] Liquid xenon Liquid helium

Backgrounds

• Self shielding is not effective in He/H-only detector
• The longest known radioisotope of He (6He) decays in <1 s
• No new backgrounds introduced (tritium?)

33

Size of LZ Size of 10 kg LHe 150 x 150 cm 30 x 30 cm

Signal detection

• Helium or Hydrogen recoils will interact with xenon atoms and

electrons

• Excitations will be xenon excitations
• Alpha particles for example
• Keep same photon detection scheme!

j.dobson@ucl.ac.uk, IDM2016

Xenon TPC and Skin

9

• 7-tonne active region (cathode → gate), 5.6 tonne FV
• 253 top + 241 bottom 3” φ PMTs (activity ~mBq; high QE)
• TPC lined with high-reflectivity PTFE (RPTFE ≥ 95%)*
• Instrumented “Skin” region optically separated from TPC

146 cm 146 cm

*[Francisco Neves’ Tues. talk]

34

Xenon microphysics

• Xenon recoils in LXe lose a lot of energy to heat (Lindhard

factor)

10 10

1

0.1 0.15 0.2 0.25 Recoil energy [keV] Lindhard factor

• Less than 20% of a ~<7 keV

recoil goes into detectable signal

• The rest goes into nuclear

collisions that lead to heat

• Light nuclei - fewer strong nuclear collisions

Fraction of Xe recoil energy going into signal

35 e-

Not to scale

He Xe e-

Modeling He recoils in LXe (v1)

• Stopping and Range of Ions in Matter (SRIM)
• Calculate the energy lost to nuclear (heat) and electronic (signal)

stopping

36

10 keV Xe in LXe ~100 A ranges 10 keV He in LXe ~1000 A ranges

Modeling He recoils in LXe (v1)

• Stopping and Range of Ions in Matter (SRIM)
• Calculate the energy lost to nuclear (heat) and electronic (signal)

stopping

37

5 10 15 20 0.2 0.4 0.6 0.8 1 Energy [keV] Fraction into signal He e− stopping Xe e− stopping Xe e− stopping with cascades

Modeling He recoils in LXe (v2)

• Noble Element Simulation Technique (NESTv2)
• Data driven model for signal processes in LXe, including alpha

data from LUX and test chambers

• High energies, but at least it’s real He nuclei in LXe

38

Modeling He recoils in LXe (v1+2)

39

1 2 3 4 5 10

1

10

2

Nuclear recoil energy (keV) Total Quanta (e+ph) SRIM He NEST He NEST Xe

Factor >~3 more signal from He

2Xe + hν + e-

Total quanta = +

Modeling H recoils in LXe (SRIM)

40

A key question

• What happens to S2/S1 partitioning?

LUX data PRL 112, 091303

41

Xenon microphysics

• What happens to S2/S1 partitioning?

CRESST data in scintillating bolometers

42

al

• f

.

• e
• NB: Different

microphysical process (heat v. electronic)

What does it look like in LZ?

43

• Put this all together into single model
• Use the LZ Geant4 detector and optical transport model
• See “Projected Sensitivity of LZ” (1802.06039)
• For S1/S2 analysis, threshold is determined by S1
• Partitioning into photons and electrons matters
• Run extreme cases for He - NR-like and ER-like
• Used SRIM for H - looks similar but slightly better

10

−2

10

−1

10 10

1

0.2 0.4 0.6 0.8 1 Energy (keV) Trigger efficiency He S1/S2 (ER−like) He S1/S2 (NR−like) Xe S1/S2

Energy threshold

44

Factor ~>3 lower for ER-like Factor ~2 for S1/S2 (NR-like)

S2-only analysis

45

• Photon detection efficiency (S1) is about 10%
• Electron detection efficiency is (we hope) about 100%
• High gain on S2 channel (80 phd/e-)
• Enables much lower threshold if you look at “S2-only”

1 −

10 × 5 1 2 3 4 5 6 7 8 9 10 ]

2

[GeV/c

χ

M

45 −

10

44 −

10

43 −

10

42 −

10

41 −

10

40 −

10

39 −

10

38 −

10 ]

2

[cm

SI

σ Dark Matter-Nucleon

DarkSide-50 Binomial DarkSide-50 No Quenching Fluctuation NEWS-G 2018 LUX 2017 XENON1T 2017 PICO-60 2017 PICASSO 2017 CDMSLite 2017 CRESST-III 2017 PandaX-II 2016 XENON100 2016 DAMIC 2016 CDEX 2016 CRESST-II 2015 SuperCDMS 2014 CDMSlite 2014 COGENT 2013 CDMS 2013 CRESST 2012 DAMA/LIBRA 2008 Neutrino Floor

• Give up ER/NR

discrimination

• Subject to single

electron noise

• Still very powerful

10

−2

10

−1

10 10

1

0.2 0.4 0.6 0.8 1 Energy (keV) Trigger efficiency He S2−only (ER−like) He S2−only (NR−like) Xe S2−only

Energy threshold

46

Factor ~4.5 lower threshold S2 only

• 3 electron threshold assumed for S2 (>250 photons)

Making projections

• 0.3% loading (1 bar partial pressure) - 15 kg, 20 days for S2-only, 100 days for S1/S2
• Location of LZ Helium lines depends critically on assumed signal yield
• ~225 events/day/pb with S2 only at 100 MeV WIMP with this yield
• Dotted line is 5e- S2-only threshold

47

• [/]
• σ []
• σ []

CRESST-II CDMSLite DS-50 S2-only LUX SuperCDMS Si+Ge HV

LZ Xe

LZ He S2-only, 3e- LZ He S1/S2

LZ He S2-only, 5e-

N E W S

• G

NEWS-G Superfluid LHe proposal

With Hydrogen

48

• Projection from calculating yields with SRIM + LZ detector model
• Definitely to be taken with grain of salt
• 0.0375% H2 (0.1 bar partial pressure), 1.9 kg, 500 days
• [/]
• σ []
• σ []

CRESST-II CDMSLite DS-50 S2-only LUX SuperCDMS Si+Ge HV

LZ Xe

LZ H2 S2-only, 3e- LZ H2 S1/S2

LZ H2 S2-only, 5e-

NEWS-G NEWS-G Superfluid LHe proposal

SD Hydrogen

49 LZ H2 S2-only, 3e- LZ H2 S1/S2

LZ H2 S2-only, 5e- PICO

SuperK PICASSO

• [/]
• σ []
• σ []
• Projection from calculating yields with SRIM + LZ detector model
• Definitely to be taken with grain of salt
• 0.0375% H2 (0.1 partial pressure), 1.9 kg, 500 days

• Helium gas and PMTs are not a good

mix

• Diffusion exponentially suppressed by

temperature (Arrhenius relationship)

• Calculation suggests 500 days at 1 bar/

165 K before tube becomes inoperable

• Exquisitely sensitive to temperature,

and that’s pretty tight…

• Needs to be tested
• Could use SiPMs…

What do I worry about

j.dobson@ucl.ac.uk, IDM2016

Xenon TPC and Skin

9

• 7-tonne active region (cathode → gate), 5.6 tonne FV
• 253 top + 241 bottom 3” φ PMTs (activity ~mBq; high QE)
• TPC lined with high-reflectivity PTFE (RPTFE ≥ 95%)*
• Instrumented “Skin” region optically separated from TPC

146 cm 146 cm

*[Francisco Neves’ Tues. talk]

Rise in PMT internal pressure when exposed to pure helium at 1 atm

Internal Pressure / torr

1.E+07 1.E+08

hours

10 yrs 1 yr

Example for ET9226 PMT

50

• PMT diffusion is suppressed
• Hydrogen is flammable in mine environment
• Purification - getter will take out the H2
• Suppression of S2 production
• Molecular modes can slow down electrons
• Could recover with increased voltage

What do I worry about (H)

51

What do I worry about

52

• This is still fairly speculative
• Henry’s coefficients not comprehensively measured
• Temperature dependence, diffusion, etc?
• Signal yields depend on modeling and MeV scale data

Needs Calibration!

• Monoenergetic neutron scattering experiment is where I would

start

What do I worry about

53

• Cryogenics - what does the presence of the non-condensible

gas do to our cryogenics

• Bubble He/H2 through the bottom of the cryostat?
• Phase separated at weir drain (in LZ design)?
• Should be distilled out fairly efficiently
• Introduction and mixing that worries me the most

He/H doping in LXe

• Physically possible
• Keep low background level achieved in LXe TPC
• Same signal readout with LXe sensitive light detectors
• Increased signal yield from He recoils
• Lower energy thresholds for WIMP-He scattering
• Properties measurable using existing techniques
• Potential reach to well below 1 GeV dark matter
• Depends on properties that need to be measured

54

• [/]
• σ []
• σ []

55 LZ H2 S2-only, 3e- LZ H2 S1/S2

LZ H2 S2-only, 5e- PICO

SuperK PICASSO

• [/]
• σ []
• σ []

Backup

56

57

• Pulsed, monoenergetic beam (at Notre Dame or

elsewhere) to measure response of to nuclear recoils of known energy

• Tunable nuclear recoil energy by changing the

neutron energy and the scattering angle – Neutrons of 100 keV - 1.5 MeV – Recoils of ~1 keV up to 50 keV – Successful measurements in LAr (1406.4825, 1306.5675, SCENE)

Neutron detector TPC Sca0ering angle, Θ Pulsed, mono-energe8c neutrons

Neutron scattering measurement

58

• Time of flight to measure the neutron 8ming
• Pulse shape discrimina8on(PSD) to select

neutrons in the detectors

• Ntof - 8me between beam pulse and neutron

detector

• TPCtof - 8me between beam pulse and LAr

detector

• f90 - PSD in LAr
• Npsd - PSD in neutron detector

Neutron sca0ering in SCENE

Ntof [ns]

• 20

20 40 60 80 100 120 140 160 180 Npsd 0.05 0.1 0.15 0.2 0.25 0.3 5 10 15 20 25 Neutrons Photons (b)

Neutron Detector

TPCtof [ns]

• 40
• 20

20 40 60 80 100 120 Ntof [ns]

• 20

20 40 60 80 100 120 140 160 180 5 10 15 20 25 TPCtof [ns]

• 40
• 20

20 40 60 80 100 120 f90 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 4 6 8 10 Cerenkov Photons Neutrons (a)

LAr-TPC

Number of quanta 100 200 300 400 500 600 700 800 900 1000 Cts/10 quanta 5 10 15 20 25 30

100 keV neutrons, 45 degrees, 13.7 keV He recoils

Helium single scatters All scatters Number of quanta 50 100 150 200 250 300 350 400 450 500 Cts/10 quanta 5 10 15 20 25 30

100 keV neutrons, 22.5 degrees, 3.7 keV He recoils

Helium single scatters All scatters

• In a doping measurement, for a given scattering angle, He recoils

have more energy

• Increased signal on top of that
• Pushes the peak out past the xenon background

Xenon “wall” 3.7 keV He signal Xenon “wall” 14 keV He signal

Neutron scattering with He in LXe

Measures yield and S1/S2 response v. energy!

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