Background suppression in large mass TeO2 bolometers with
Neganov-Luke amplified light detectors
Luca PattavinaINFN-Laboratori Nazionali del Gran Sasso
L. Pattavina 1, N. Casali 2, L. Dumoulin 3, A Giuliani 3, M Mancuso 3, P de Marcillac 3, S Marnieros 3, S.S. Nagorny 6, C. Nones 4, E Olivieri 3, L. Pagnanini 6, S. Pirro 1, D. Poda 3, C. Rusconi 5, K. Schaeffner 1, M. Tenconi 3.
1 INFN – Laboratori Nazionali del Gran Sasso, I-67100 Assergi (AQ), Italy 2 INFN – Sezione di Roma I, I-00185 Roma, Italy 3 CSNSM, Centre de Sciences Nucléaires et de Sciences de la Matière, CNRS/IN2P3, Université Paris-Sud, 91405 Orsay, France 4 CEA, Centre d’Etudes Saclay, IRFU, 91191 Gif-Sur-Yvette Cedex, France 5 INFN – Sezione di Milano-Bicocca I, I-20126 Milano, Italy 6 Gran Sasso Science Institute, I-67100 L’Aquila, Italy
1
OUTLINE• Double-beta decay investigation with TeO2 macro-
bolometers
• TeO2 Cherenkov light emission
• Neganov-Luke amplification in Light Detectors
• Prototype detector
• Conclusions
2
0vββ methods & signature- 0vββ can unveil most of neutrino properties (mass, Nature, hierarchy)
- It occurs only in few natural isotopes: 76Ge, 82Se, 100Mo, 130Te, 136Xe (and not many others).
- Signature: peak at the sum-energy (Q) of the two electrons (2-4 MeV).
Calculated energy spectrum
33
0vββ investigation with TeO2- Particle energy converted to temperature variations
Absorber operated @ cryogenic temperature (~10mK)
- Bolometer features:
high energy resolution O(1/1000)
high detection efficiency (source = detector)
scalable to large masses
fully sensitive device no particle ID in TeO2 bolometers dominant background:
α decays on the detector surfaces
Sens
itive
th
erm
omet
ers:
NTD
ther
mis
tor
�T
=E/C
⇠10
0µK E=2.6 MeV
ΔE=5 keV
4
Energy [keV]2600 2800 3000 3200 3400 3600 3800
Even
t Rat
e [c
ount
s/keV
/kg/
y]
-210
-110
1
10
Cuoricino
CUORE-0
DBD ROI
CUORE-0 background energy spectrum
CUORE coll. Eur. Phys. J. C 74, 2956 (2014)
-> See Lucia Canonica T4.4
-> See Carlo Ligi T4.5
4
Background suppression in TeO2T. Tabarelli in Eur. Phys. J. C (2010) 65: 359–361 proposed for the first time: background
ID in TeO2 calorimeter using Cherenkov light emission from beta rays.
Cherenkov thresholdEe- > 50 keV
Eα > 400 MeV
@ 130Te Qββ (2.5 MeV)
~220 Cherenkov photons (300-900 nm) ➞ 600 eV
No Cherenkov photons from natural radioactivity
A positive tagging of 0vββ is possible by means of a proper Light Detector
facing a TeO2 calorimeter
Radio-pureLarge Area
Low thresholdOperated at low T
➞ low bkg investigation➞ high efficiency➞ large signal ➞ …
Bolometric Light Detector5
First detection of light from TeO2
25 g TeO2 “Scintillation” light : 125 eV @ 2.6 MeV
in 2003
6
State of the art for large TeO2TeO2mass
Reflector/Diffusor
Light Detector
β/γ light in eV @ 2615 keV
Baselineσ [eV]
DiscriminationPower @ ROI ref.
750 g PTFEGe +
NTD105 74 1.5 Eur.Phys.J. C75
(2015) 1, 12
750 g 3M VM2002Ge +
NTD101 72 1.5 Eur.Phys.J. C75
(2015) 1, 12
285 g 3M VM2002SOS
+ W-TES
129 23 3.7 Astropart.Phys. 69 (2015) 30-36
117 g 3M VM2002Ge +
NTD195 97 1.4 Astropart. Phys. 35
(2012) 558
Expected light signal from a 750 g TeO2 ~200 eV
Observed light signal O(100 eV) ➞ low noise LD are needed➞ large area detector
Light trapping inside the crystallarge mass crystals = higher sensitivity
smaller crystal = more light A compromise is needed
7
NTD-based LD with Neganov-Luke effect:
Photons:- Electron-hole pairs- Drift by applied voltage- Additional phonons- Amplification
Total energy deposited in the absorber with applied field V:
ETOT =E
✏eV + E
Drifting charges produce phonons
Neganov-Luke effect
Ec Voltage
Amplification factor:
G = 1 +eV
✏
B. Neganov, V. Trofimov. 1985. Otkryt. Izobret. 146, 215
P.N. Luke. 1988. J. Appl. Phys. 64, 6858
8
Light detector produced at CSNSM (France)
Neganov-Luke effect on LD
0.00#
50.00#
100.00#
150.00#
200.00#
250.00#
300.00#
350.00#
0# 5000# 10000# 15000# 20000# 25000# 30000# 35000#
RMS$filtered$no
ise$[eV]$
Vluke$[mV]$
Baseline Noise
0.00#
1.00#
2.00#
3.00#
4.00#
5.00#
6.00#
0# 5000# 10000# 15000# 20000# 25000# 30000# 35000#
Norm.&A
mplifica.o
n&
Vluke[mV]&
Amplification
Entries 1310
Mean 5.99
RMS 0.6093
Integral 1310
Energy [eV]4 4.5 5 5.5 6 6.5 7 7.5 8
coun
ts /
0.1
0
20
40
60
80
100
Entries 1310
Mean 5.99
RMS 0.6093
Integral 1310
Kα
Kβ
Baseline energy resolution @ 0 keVσ = 185 eV
Signal amplitudeA = 1 uV/keV
55FeVgrid=0V
• HP-Ge wafer (44 mm X 180 um)• Al electrodes (EDELWEISS-like)• IR LED faced to LD• 55Fe X-ray calib. source• Thermal sensor: Ge-NTD
9
Experimental set-up
TeO2 5x5x5 cm3
pictures
LD + TeO2
10
GeLuke baseline σ: 0.48 mV Light @ 2615 keV: 0.24 mV
Vgrid OFF
Gain = 1
preliminary
11 S/N = 0.5
β/𝛾 events
α events
GeLuke baseline σ: 0.56 mV Light @ 2615 keV: 1.01 mV
Ligh
t am
plitu
de [a
.u.]
Vgrid ON : 30 V
preliminary
12
Gain = 4.2S/N = 1.8
β/𝛾 events
α events
GeLuke baseline σ: 0.63 mV Light @ 2615 keV: 1.64 mV
Ligh
t am
plitu
de [a
.u.]
Vgrid ON : 50 V
preliminary
13
Gain = 6.8S/N = 2.6
β/𝛾 events
α events
GeLuke baseline σ: 0.65 mV Light @ 2615 keV: 2.33 mV
Ligh
t am
plitu
de [a
.u.]
Vgrid ON : 90 V
preliminary
14
Gain = 9.7S/N = 3.6
β/𝛾 events
α events
GeLuke baseline σ: 0.65 mV Light @ 2615 keV: 2.33 mV
Ligh
t am
plitu
de [a
.u.]
Vgrid ON : 90 V
Gain = 9.7Baseline energy resolution
@ 0 V σ = 185 eV@ 90 V σ = 19 eV
preliminary
15
β/𝛾 events
α events
α β/γpreliminary
Light Yield [a.u.]
Vgrid ON : 90 V
Discrimination power: 2.7 σ
preliminary
16
• TeO2 bolometers proved to be suitable detectors for ββ investigation
• Cherenkov light detection is an excellent technique for background suppression in TeO2 crystals
• NTD-based Neganov-Luke amplified LD is a simple but a highly effective technology for particle identification
• low energy threshold -> NL-amplification
• robust, stable and reproducible performances -> NTD thermistors
• There is still room for improvements: LD coating for increasing light collection efficiency, lower baseline energy, crystal shape optimization.
Conclusions
17
Amplification characterizationEntries 1310
Mean 5.99
RMS 0.6093
Integral 1310
Energy [eV]4 4.5 5 5.5 6 6.5 7 7.5 8
coun
ts /
0.1
0
20
40
60
80
100
Entries 1310
Mean 5.99
RMS 0.6093
Integral 1310Kα
Kβ
Vgrid = 0 V Vgrid = 30 V Vgrid = 90 V
Whe
re is
the
55Fe
? Po
sitio
n de
pend
ence
in
tera
ctio
ns in
the
dete
ctor
RMS baseline noise: 0.65 [mV]LED Amplitude: 430.20 [mV]
RMS baseline noise: 0.48 [mV]LED Amplitude: 68.02 [mV]
RMS baseline noise: 0.56 [mV]LED Amplitude: 350.10 [mV]
LED Vgrid = 30 V
LED Vgrid = 90 V
LED
Vgrid = 0 V
55Fe
LED
19
20
5000
*
21