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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
2
Main source of the talk
JINST 8 (2013) R04001
If not given on the slides, see this paper for references
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
6
Expected integral rates
(thanks to E.Santos)Practical thresholds
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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:
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
13
First LNG dark matter detectors
DAMA - First single phase detector
ZEPLIN-II - First double phase detector
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
16
Scintillation – a closer lookTwo mechanisms
direct excitation
recombination
field dependent
Similar emission
ionization electrons
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
17
Scintillation – a closer look
Xe - Xe
Xe – Xe*
Xe - Xe+
Xe2* Xe + Xe + hv
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
18
Scintillation – a closer look
Xe - Xe+
Xe – Xe*
E, eV
3 1
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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Scintillation – a closer look
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
20
Scintillation – a closer look
1600 ns
(45 ns?)
Fast recombination (~1 ns) Slow recombination (~35-45 ns)
Pulse shape discrimination
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
32
Ws value for LAr and LXe
~5 keV 211
recent
recent
(see Chepel and Araújo 2013 for references)
35
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?
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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-
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
37
Charge/light vs electric field
Aprile e.a., 2006
light
charge
electrons
nr
nr
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
41
Nuclear recoil tracks in LXe
ER = 100 keV
(simulated with TRIM)
LXe
Electron thermalization length(Mozumder, 1995)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
42
Nuclear recoil “track” details
Primary particle
Secondary recoils
Track endpoint
ER = 100 keV
100 nm
LXe
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
43
Nuclear recoil “track” details
100 nm
Primary particle
Secondary recoils
Track endpoint
ER = 100 keV
LXe
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
47
Simulated 0.5 MeV electron tracks
LXe
500
m
Thermalizationsphere
(Courtesy V. Solovov)Simulated with PENELOPE
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
52
Secondary scintillation in gasWell established linear dependence
(n – number density)
For saturated vapour simple parametrization:
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
68
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
71
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
72
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
74
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
76
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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)
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
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
V. Chepel Dark Matter, Dark Energy and their Detection, Novosibirsk, 25 July 2013
Thank you !