Liquefied Noble Gas Detectors for Low Energy Particle Physics Vitaly Chepel LIP-Coimbra and...

Liquefied Noble Gas Detectors for Low Energy

Particle Physics

Vitaly Chepel

LIP-Coimbra and Department of PhysicsUniversity of Coimbra, Portugal

V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013

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2

Main source of the talk

JINST 8 (2013) R04001

If not given on the slides, see this paper for references


3

Outline

I. Dark Matter (DM) and coherent neutrino scattering (CNS) cases from the detection point of view (very short – much has been said by other speakers already)

II. On physics of the detection processes at low energies: what we knew, what we have discovered and what we still need to learn

III. Short review of DM and CNS experiments using liquefied noble gases

V. ChepelV. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013

5

DM versus CNSDM CNS

Detection: Signal: low energy nuclear recoils

Background reduction is essential

Discrimination from electron recoils

Experiment:

Source is unknown

No external trigger

Source is known and can be controlled

Trigger is possible for some sources

Mass of WIMP – unknown

210-45 cm2 (unknown)

Standard model provides (e.g., for 10 MeV v (Xe)210-39 cm2; (Ar)210-40 cm2

Recoil energy ‘threshold’ ~1 to 10 keV seems OK (for the moment)

Recoils of down to ~100 eV are expected

A few events in the right place may mean discovery

hundreds events are needed for statistically significant pulse height distribution

Target mass ~1,000 kg required Target mass can be ~10 kg


6

Expected integral rates

(thanks to E.Santos)Practical thresholds


7

WIMP Search Technology Zoo

Heat & Ionisation BolometersTargets: Ge,Si

CDMS, EDELWEISScryogenic (<50 mK)

Light & Heat BolometersTargets: CaWO4, BGO, Al2O3

CRESST, ROSEBUDcryogenic (<50 mK)

Light & Ionisation Detectors

Targets: Xe, ArArDM, LUX, WARP,

XENON, ZEPLINcold (LN2)

H phonons

ionisationQ

Lscintillation

ScintillatorsTargets: NaI, Xe, Ar

ANAIS, CLEAN, DAMA, DEAP, KIMS, LIBRA,

NAIAD, XMASS, ZEPLIN-I

Ionisation DetectorsTargets: Ge, Si, CS2, CdTe

CoGeNT, DRIFT, DM-TPCGENIUS, HDMS, IGEX,

NEWAGE

BolometersTargets: Ge, Si, Al2O3, TeO2

CRESST-I, CUORE, CUORICINO

Bubbles & DropletsCF3Br, CF3I, C3F8, C4F10

COUPP, PICASSO, SIMPLE(credit H.Araújo)


11

LNG detectors: a bit of history

First papers:

+ hundreds of further papers

+ achievements in understanding LNG physics

+ technology developments

+ some disappointments

All this has resulted in a series of large scale detectors now working at the cutting edge of science


12

DM double phase detectors: important steps

Foundations of the double-phase technique for particle detection:

First proposal for using double-phase detectors for WIMP search:

Proposed background discrimination by using both scintillation and ionisation signals:


13

First LNG dark matter detectors

DAMA - First single phase detector

ZEPLIN-II - First double phase detector


14

Operation principle of a double-phase electroluminescence detector

Primary scintillation

PMTs

Secondary scintillation(proportional to extracted charge)

S2/S1 ratio – the basis for elctron/nuclear recoil discrimination in double phase detectors


16

Scintillation – a closer lookTwo mechanisms

direct excitation

recombination

field dependent

Similar emission

ionization electrons


17

Scintillation – a closer look

Xe - Xe

Xe – Xe*

Xe - Xe+

Xe2* Xe + Xe + hv


18


Xe - Xe+

Xe – Xe*

E, eV

3 1


19


The transitions

are undistinguishable spectroscopically

but

allowed short lifetime (LXe ~ 2.2 ns; LAr ~5 ns)

forbidden long lifetime (LXe ~ 27 ns; LAr ~1600 ns; LNe ~15 s; LHe ~13 s)

The population of the singlet and triplet states also depends on particle kind

Nuclear recoils can be distinguished from electrons using pulse shape discrimination


20


1600 ns

(45 ns?)

Fast recombination (~1 ns) Slow recombination (~35-45 ns)

Pulse shape discrimination


21

PSD in LXe

XMASS prototype (K. Ueshima, PhD thesis. 2010)

Scintillatuion pulse shape discrimination in LXe (XMASS)

137Cs 252Cf

Prompt/total ph.e. ratio


22

PSD in LXe (XMASS)

Ueshima, e.a., NIMA659(2011)161

4.8-7.2 keVee

9.6-12 keVee

4.8-7.2 keVee


23

PSD in LAr

electron

nuclear

nuclear recoils

electron recoils

(Lippincott e.a., PRC78(2008)035801)

D-D neutron generator

Prompt fraction (F) = Nph(fast) / Nph(total)

90 ns integrationa few s integration

XMASSV. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013

24

Light yield – depends on particle and energy

e-

Electrons escape recombination

Too many excitons bi-excitonic quenching

all excitons recombine

(Doke/Hitachi interpretation)


25

Light yield – different behaviour at low energies

e-

Less light for low energiesLess light for nuclear recoilsdE/dx is not a good parameter for low energies


26

Scintillation yield for electrons and -rays

Data from - Szydagis, e.a., JINST 6(2011)P10002 – evaluated yield (absolute)e - Aprile, e.a., PRD 86(2012)112004 – Compton electrons; relative yield; re-normalized by me at 122 keV

Baudis, e.a., PRD 87(2013)115015 – Compton electrons; relative yield;

Relative yieldAbsolute yield

same data

Anomaly !(9.4 keV ; 83mKr)

Must be careful with detector calibration !

e-

e-

1) e-

2) Anomalous behaviour can happen for some sources

LXe


27

Field dependence of light yield

~10 keV (Baudis, 2013)

1 MeV e- (**)

* Aprile e.a., PRL97(2006)081302** Kubota e.a., PRB20(1979)3486

Ligh

t yi

eld,

a.u

. ZEPLIN-III ~2.8 keV

XENON10 ~2.5 keV

XENON100 ~2.3 keV

XMASS ~1.1 keV

S1 threshold (for electrons)

(estimated in Baudis, 2013)

For nuclear recoils, ~10 keV threshold was used by XENION100 and ZEPLIN-III

122 keV (*)

56.5 keV nucl. recoils (*)

LXe


29

Scintillation efficiency for nuclear recoils in LXe

(Compilation by Horn, e.a. PLB705 (2011) 471)

LXeAt zero field !

1 is for 122 keV -rays (57Co)

γ)(

)(

eff /

/

EN

ENL

ph

nrnrph

or


31

Scintillation efficiency in LAr and LNe

Regenfus e.a., J.Phys:Conf.Ser375(2012)12019

Hitachi’04 (theor.)

Gastler e.a., PRC85(2012)085811

Lippincott e.a. PRC86(2012)015807

LAr

LNe


32

Ws value for LAr and LXe

~5 keV 211

recent

recent

(see Chepel and Araújo 2013 for references)

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Energy partition

Particle energy ionization

excitation

heat

Lindhard’s partition function:

Ions (atoms) lose their energy in electronic and nuclear collisions:

(Platzman equation)Electrons:

0.1–0.2 for Enr 10 keV in LXe

100 – 200 eV with Enr cf 15.6 eV for electrons

(Dahl’2009)

total)(

s)excitation electronic(

E

E

Does W makes sense for nuclear recoils?


36

Ionization yield from nuclear recoils

Aprile e.a.,2006

Notice weak field dependence

0.27 2 kV/cm

0.1 2 kV/cm

200 eV/e-


37

Charge/light vs electric field

Aprile e.a., 2006

light

charge

electrons

nr

nr


38

Field dependence of free charge yield

Notice:1) weak field dependence2) increase of the yield at

low energies

LXe

Extrapolated from E~10 kV/cm using Jaffé model (Obodovski)


39

Nelectrons due to nuclear recoils

LXe

Fundamental limit I=12.13 eV or Eg=9.28 eV SRIM prediction

Exp. data (different fields but dependence on the field is weak)

Compressed gas model

Solid state model

Roughly,i.e. favours low energies

64.0ENe

E

Wnr

The yield is smaller than for electrons even after correction for nuclear collisions

(Dahl’2009)suggested


40

More electrons escape at low E

Bezrukov, e.a. AP35(2011)119

(r – recombining fraction at zero field)

LXe

2 10 20 30 Enr, keV


41

Nuclear recoil tracks in LXe

ER = 100 keV

(simulated with TRIM)

LXe

Electron thermalization length(Mozumder, 1995)


42

Nuclear recoil “track” details

Primary particle

Secondary recoils

Track endpoint

ER = 100 keV

100 nm

LXe


43

Nuclear recoil “track” details

100 nm

Primary particle

Secondary recoils

Track endpoint

ER = 100 keV

LXe


44

Simulated electron tracks

4 m

(PENELOPE 2011)

LXe

Electrons, E=30 keV

thermalization distance 4.5 m

nn

Er

En

th

33

4

Less light and more charge should be observed for lower energies


47

Simulated 0.5 MeV electron tracks

LXe

500

m

Thermalizationsphere

(Courtesy V. Solovov)Simulated with PENELOPE


49

Ionization and drift parameters

~200 eV for nuclear recoils, if Nex/Ni = 1 (assumed Se/Sn0.12)

hole mobility

LXe is “more solid” than LAr


51

Electron emission to gasWorked very well - no big surprises !

Model by Bolozdynya NIMA422(1999)314

Gushchin e.a., JETP55(1982)860Eth

Two emission mechanisms:‘hot’ emission – prompt for e > Vo

‘thermal’ emission – thermal evaporation

Delayed emission observed, more significant in LAr


52

Secondary scintillation in gasWell established linear dependence

(n – number density)

For saturated vapour simple parametrization:


53

Single electron spectrum

ZEPLIN-III: ~300 secondary scintillation photons per extracted electron

Sensitivity of the ionization channel = 1 electron

(if it is extracted from the track, did not get captured by an impurity molecule and succeded to cross the potential barrier on the liquid surface)

This is how ZEPLIN-III sees a single electron


55

Single electron noise - origins

LXe bulk

SE signal correlated with preceding scintillation - Photoionization

cathode wires

Santos e.a., JHEP12(2011)115

SE signals with no apparent correlation with preceding scintillation – possibly delayed emission of electrons trapped under the liquid surface and autoemission from the cathode wires

Time between scintillation and SE pulse

20 s without signals

Rate 5.7 s-1 within the central area of ZEPLIN-III containing 1.3 kg of LXe

Previous irradiation of the detector does affect the rate


56

Single electron noise (cont.)

(Sangiorgio e.a., arXiv1301.4290)

Single electron spectrum in a small LAr chamber (double phase) following accidental discharges - the rate decreased with time


63

Sub-keV electrons in LAr

(Sangiorgio e.a., arXiv1301.4290)

Fit with Thomas-Imel model General comment:Thomas-Imel box model seems to provide useful framework to describe recombination at low energies (there are several other papers in which this parametrization was successfully used)


65

Summary (before going to experiments)Scintillation:

- determines energy threshold in DM search experiments (5-10 keVnr in LXe,

currently)

- provides energy scale for nuclear recoils

- needs to be better studied for low energy (10 keV) electrons and -rays to

understand backgrounds and make feasible in-volume calibration (e.g., with 37Ar

and 83mKr)

Ionization:

- surprise: high charge yield from nuclear recoils, weak field dependence

- need to understand recombination better (e.g., the role of escape electrons) and

initial ionizations/excitations share

- if measured via secondary scintillation in gas may provide sensitivity as low as

few electrons (probably down to ~200 eV for nuclear recoils in LXe)


66

Summary (before going to experiments)

Drift:- sufficient electron life time is routinely achieved- drift velocity well measured

Emission:- Not everything is clear but no troubles in practice

Secondary scintillation in gas:- OK, plenty of light (e.g., 300 ph./electron – in ZEPLIN-III)- provides sensitivity to single electrons extracted from the liquid

Single electron noise:- origins need to be understood- no problem for DM search experiments- trouble for coherent scattering of neutrino


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LXe DM ZEPLIN-III

Planar geometry high field (3–4 kV/cm) with two electrodesScint. threshold - 7 keVnr; ionization – set to 5 electronsElectron recoil rejection efficiency – 99.99% - the best reported for LXeStatus – completedNext: LZ ~7t


69

LXe DM XENON100

Bulk geometry good self-shielding (~5 mdru in 34 kg fiducial)Scint. threshold 6 keVnrElectron recoil rejection efficiency – 99.5%Status – 225 live days DM data published – the best exclusion limitTwo events in the band 6.6-30.5 keVnr, consistent with expected backgroundNext: XENON 1t --- see Alexey Lyashenko’s talk

178 PMTs


70

LXe DM LUX350

Bulk geometry good self-shielding (~0.8 mdru expected in 100 kg fiducial)Thin-wall Ti vessel for low background300 t ultrapure water tank viewed by PMTsStatus – deployed underground Ask Vladimir Solovov for detailsNext: LZ ~7t

61x2 PMTs


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LXe DM XMASS

Spherical geometry, scintillation only; 800 kg of LXe, 100 kg fiduciale/n rejection (PSD) 92% at 5 keVnr, 99.9% at 15 keVnr (at 50% recoil acceptance) 15.9 ph.e./keV at the centre – the highest response Status – runningNext: 20t of LXe

649 PMTs


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LAr DM WARP140

Bulk geometry; 140 kg of isotopicaly pure argon (natural Ar contains long living 39Ar, ~1 s-1 kg-1)TPB wavelength shifter deposited on all surfaces (LAr scintillates at 127 nm) Dual discrimination: S1 pulse shape + S2/S1 ratio very good rejection powerLAr active volume / LAr active shield / LAr coolantStatus – ?

37


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Electron recoil discrimination

LAr

(ZEPLIN-III; thanks to H. Araújo)

S1 pulse shape discrimination

n

(Lippincott e.a., PRC78(2008)035801)

e

n

e

S1

S2

AmBe source

n

CombinedS1 pulse shape + S2/S1 discrimination

(WARP Collab., AP28(2008)495)

S2/S1 ratio

LXeLAr

LAr


75

LAr DM ArDM 1t

Ionization readout with LEMs (Large Electron Multipliers) 850 kg of LAr1 ph.e./keV predicted 30 keVnr threshold for nuclear recoils (on S1)120 cm drift length internal HV generator; 70 kV achieved, aimed at 400 kVStatus – deployed in Canfranc

14 semispherical 8-inch PMTs, TPB wavelength shifter

LEM in gas phase

Greinacher voltage multiplier(Cockroft-Walton)


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LAr DM DEAP-3600

LAr 3600 kg (1000 kg fiducial), plan to use underground source argon

Scintillation only, pulse shape discrimination

Acrylic vessel; long acrylic light guides (~50 cm); ‘warm’ PMTs

Baseline: 8 ph.e./keV, 60 keV threshold; discrimination power 10-10


77

LAr/LNe CNS CLEAR (proposal)

LAr or LNe, interchangable (456 kg and 391 kg, respectively),

Scintillation only, pulse shape discrimination

To be installed at SNS, 60 m form the spallation target; 30 MeV neutrinos

Expect: 600 events/y in LAr at 20 keV threshold; 250 events/y in LNe above 30 keV

LAr/LNe

38 PMTs


78

LAr CNS LLNL proposal

LAr 53 kg

Double phase, single electron counting using secondary scintillation in gas

25 m from a 3.5 GWth reactor core

Expect: 80 events/day at 2 electron threshold

LAr

Hagmann & Bernstein, IEEE TNS51(2004)2151


79

LXe CNS ZEPLIN-III

Double phase LXe, 6kg fiducial,

single electron counting using secondary scintillation in gas; 3 electron threshold

ISIS: 10 m from the spallation source; 10 m from 3 GWth reactor core

Expect at ISIS (10 m from spallation source): ~ 400 ev/y (depends on actual location)

Expect at 10 m from 3 GWth reactor core: ~1,200 ev/y

(H. Araújo)

(see Chepel & Araújo, JINST8(2013)R04001)


80

LXe/LAr CNS RED Collaboration

Double phase, single electron counting using secondary scintillation in gas

SNS: 40 m from the spallation source; 19 m from Kalininskaya power plant reactor core

Expect at SNS: ~1,400 ev/100kg/y (LXe) and ~400 ev/kg/y (LAr) at 2 electron threshold

Expect at 19 m form reactor: ~20 ev/100kg/day (LXe); ~200 ev/100kg/day (LAr)Akimov e.a., arXiv:1212.1938

Ask A Bolozdynya for d

etails

LXe/LAr


82

Conclusion• Liquid noble gas detectors is a well established technology (we use to

say)

• Indeed, there is a number of large scale detectors running (or those

completed their program already); more have been proposed

• However, one can hardly say we know everything about them

• The need for better understanding of the observed signals stimulated

studies of underlying physical processes

• We know understand much better what happens in the liquid at low

particle energies

• Still, there are many interesting things to do for a detector physicists


Thank you !

Liquefied Noble Gas Detectors for Low Energy Particle Physics Vitaly Chepel LIP-Coimbra and...

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