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

Edelweiss: Ge heat and ionization detectors WIMP Scatt. WIMP Recoil nucleus  ER discrimination g/n > 99.9% for Er> 15keV  Simultaneous measurement  Heat @ 17 mK with Ge/NTD thermometer  Ionization @ 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

What‘s about background? a, b, g : => Improvement of detector technology; => Radiopurity of the materials; => Passive shielding; neutrons : Radioactivity in the surrounding => Passive shielding: 20cm 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

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

3He detector (JINR) for the ambient neutrons 1 – guard ring; 2 – signal wire; 3 – body; 4 – glass isolators covered inside by 50-60 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

Data for n peak energy (660-830 keV) <rate> ~ 150 cpd, 70% - fast n, 30% - therm. n; flux ~ 2 10-6 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 11.01.-7.03.2007 (?) 14.06.-15.07.2007 1600V 1500V 6 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

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

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

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: 0.04 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

Neutron counter (NC) principle Dimensions (H x W x L): (50 x 100 x 200 cm) µ 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

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

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

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

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

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

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

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

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

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 3 109 m-2 y-1 Mainly from: 19 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

Neutron yield as function of Atomic weigth H. Araújo et al., NIM A545 (2005) p.398-411 V. Kudryavtsev et al., NIM A505 (2003), p.688-698 H. Wulandari, Ph.D. Thesis, Techn. Uni München (2003) 20 | V. Kozlov | IDM 2008 | Stockholm, Aug 18-22, 2008

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, 0..100°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