1. Studies of the m-induced neutron background in LSM:
detector concept & status of the installation
Valentin Kozlov
(Forschungszentrum Karlsruhe)
for the EDELWEISS collaboration
DM search principle of Edelweiss
Muons & neutron background
Simulations
Neutron counter in LSM
1 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

2. Edelweiss: Ge heat and ionization detectors
WIMP
Scatt. WIMP
Recoil
nucleus  ER
discrimination g/n > 99.9% for Er> 15keV
 Simultaneous measurement
 17 mK with Ge/NTD thermometer
 few V/cm with Al electrodes
 Evt by evt identification of the recoil by ratio Q=Eionization/Erecoil
 Q=1 for electron recoil
 Q0.3 for nuclear recoil
=> talk of Xavier Defay, 19/08
2 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

3. What‘s about background?
a, b, g : => Improvement of detector technology; => Radiopurity of the materials; => Passive shielding;
neutrons :
Radioactivity in the surrounding => Passive shielding: cm Pb + 50cm PE shielding
Muon induced neutrons produced :
In the detector material => active m-vetoing + Simulations;
In the surrounding rock (high-E n!) => Simulations;
Need explicit m-n coincidence measurement!
LSM: muon flux ~ 103 m-2 y-1
3 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

4. Fréjus safety tunnel (LSM) extension: approved!
68%
Ruiz de Austri, Trotta & Roszkowski (2006)
CDMS
95%
EURECA, LSM extension
See talk of Prof. H.Kraus, 19/08
# To probe 10−8 ÷10−10 pb; # 1 tonne Cryo detector; # ~10-5 evts / (kg day)
Fréjus safety tunnel (LSM) extension: approved!
4 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

5. 3He detector (JINR) for the ambient neutrons
1 – guard ring;
2 – signal wire;
3 – body;
4 – glass isolators
covered inside by μm Teflon &
1μm electrolytic Cu against
alpha background
n +3He -> p +T (p=5333(7) b)
Q=764 keV
5 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

6. Data for n peak energy (660-830 keV)
<rate> ~ 150 cpd, 70% - fast n, 30% - therm. n;
flux ~ n/cm2/s
14/06/2007
From 11:20 – 14:20
Not documented (but known to be) operation with neutron source
16/07/2007
5-12/01/2007
15/06/2007
7-8/03/2007
Dilution OFF
(?)
1600V V
6 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

7. Simulations: µ’s in LSM
Veto Ge n
Gestein
Blei Pb
Polyethylen
rock
Polyethylene
p,π,α ´
Cu (Cryostat)
valley (N-S)
mountain range
7 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

8. Simulations: µ-induced signal
DM: n mimic WIMP recoils (~ few keV);
0nbb: n (>MeV) => g rays (inelast. scatt); n (therm.) => g rays (capture);
CnH2n
GEANT4 (CnH2n)
g®N
p®N
p- abs
n®N
m®N
others
8 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

9. Coincidences in µ-veto system and Ge bolometers
1keV<Edep<250keV
Candidates for coincident veto-bolometer events
Accidental coincidences
Selection of coincident candidates:
> 1 veto module hit
15 ms < Δt < 35 ms
Geant 4 simulation of µ-induced Ge-hits
Expected from Geant4 simulation: ~0.03 events/kg.d
Measured: events/kg.d
Erecoil < 250 keV
Erecoil > 250 keV
measured events 16 28
expected accidentals
3.7 ± 0.2
2.9 ± 0.2
excess coincidences
12.3 ± 4.2
25.1 ± 5.5
signal/background
3.3 ± 1.4
8.7 ± 2.4
preliminary
9 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

10. Neutron counter (NC) principle
Dimensions (H x W x L):
(50 x 100 x 200 cm)
paraffin
Gd-loaded scintillator (Pseudocumene based)
8 LED‘s,
l=420 nm
n´s
Pb bricks
8x2 8“ PMTs (neutrons) + 3x2 2“ PMTs (µ)
157Gd(n,g)158Gd Eg=8 MeV =2.54e+5 b
Neutron count rate: ~1 /day (m), ~8000 /day (radioactivity)
Signature: m-n coincidence or multiple n‘s
10 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

11. NC prototype in Karlsruhe
Geometry
PMT1
liquid scintillator
PMT2
paraffin
11 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

12. Test measurements DAQ Logic card tests PMT signal vs. U(LED)
ADC gate
Veto discr.
PMT signal vs. U(LED)
signal
DAQ Logic card tests
TDC comm. stop
PMT=-1300 V
PMT=-900 V
PMT signal vs. t(LED)
Afterpulse studies
12 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

13. GEANT4: interaction & light propogation
n penetration in scintillator
13 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

14. Neutron counter in Karlsruhe (May’08)
14 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

15. Safety control of the neutron counter
Temperature
Sensors (x2)
Liquid level meter
Liquid leak sensor (x2)
Pseudocumene vapour sensor (+1)
15 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

16. Improvement in sensitivity = better control of the background;
Summary
Improvement in sensitivity = better control of the background;
Neutrons constitute highly important background component;
Monitoring of the ambient neutron background in operation since July 2006;
Muon-induced neutrons:
GEANT4 muon simulations;
Muon-Veto is operating for EDW II;
Neutron counter, operation in LSM: autumn 2008;
DFG
16 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

17. The EDELWEISS collaboration
 CEA Saclay (DAPNIA & DRECAM) Detectors, background, analysis, electronics, acquisition
E. Armengaud, O. Bessida, M. Chapellier, G. Chardin, G. Gerbier, H. Deschamps,
M. Fesquet, M. Gros, S. Hassani, S. Hervé, M. Karolak, X-F. Navick, P.Pari, B. Paul
Post-doc: R. Lemrani, F. Schwamm Thesis : E. Grémion, A. Chantelauze (cotutelle FZK)
 CSNSM Orsay Detectors, cabling, cryogenics, analysis
L. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin, A. Juillard, F. Lalu, S. Marnieros
Post-doc: Emilano Olivieri Thesis : O. Crauste, X. Defay, Y. Dolgorouki, C. Nones
 IPN Lyon Electronics, background, analysis, detectors
F. Charlieux, M. De Jésus, P. Di Stefano, J. Gascon, M. Stern, V. Sanglard, L. Vagneron
Thesis : M. Luca, S. Scorza
 IAP Paris Low radioactivity, analysis
C. Goldbach, G. Nollez
 CRTBT Grenoble Cryogenics, electronics
A. Benoit, M. Caussignac, H. Rodenas
 FZK/ Uni Karlsruhe (TH) Vetos, background
N. Bechtold, J. Blümer, K. Eitel, V. Kozlov Thesis : A. Chantelauze (cotutelle CEA), H. Kluck, M. Horn (Imperial College)
 JINR Dubna Background
E. Yakushev, A. Smolnikov Thesis : A. Lubashevski, L. Perevozchikov
  50 persons (30 FET), 11 PhD theses, 3 post-docs
17 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

18. ADDITIONAL SLIDES Additional slides
18 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

19. Muons flux: sea level and underground lab
Log10 (Muon Flux) (m-2s-1)
LSM (France)
Depth (meters water equivalent)
LSM level ~ 103 m-2 y-1
Sea level m-2 y-1
Mainly from:
19 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

20. Neutron yield as function of Atomic weigth
H. Araújo et al., NIM A545 (2005) p
V. Kudryavtsev et al., NIM A505 (2003), p
H. Wulandari, Ph.D. Thesis, Techn. Uni München (2003)
20 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

21. Safety: control system and alarms
KA-CS computer
NI 6221
16 analog
10 digit.
Blinking light, audio signal etc.
LSM alarm system
Liquid level meas.
Web-cam
Temp. sensor (paraf.)
Temp. sensor (ext.)
PT100, °C
Vapour sensor (int.)
Vapour sensor (ext.)
Dräger, Type XTR0010
Liquid sensor 1
Liquid sensor 2
Optical sensors, EGE UGFS 075
21 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008