Скачать презентацию EDELWEISS-II Status and first results A new
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EDELWEISS-II : Status and first results A new generation of background-free bolometers for WIMP search Véronique SANGLARD Université Lyon 1 CNRS/IN 2 P 3/IPNLyon sanglard@ipnl. in 2 p 3. fr http: //edelweiss. in 2 p 3. fr
Outline § Reminder on dark matter direct search § From EDELWEISS-I to EDELWEISS-II § New Inter. Digit detectors § Some current results § Outlook TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 2
WIMPs direct search § WIMPs forming our Galactic halo • • v ~ 200 km/s 10 - 1000 Ge. V/c² mass exponential spectrum SUSY neutralino prediction < 1 coll/kg/month WIMP Xe Ge Scatt. WIMP § Experimental challenges • Low energy threshold ~ few ke. V’s • Large mass ~ 1 ton • Low background < 102 /kg/day Recoil nucleus § Principle • Detection of the energy • deposition in a target Nuclear recoil : 10 -50 ke. V § radioactivity (electron recoils) § radioactivity (surface electron § recoils) Neutron scatterings (nuclear recoils) TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 3
EDELWEISS-I : Heat-Ionization NTD sensors § Ionization measurement @ few V/cm § Heat measurement (NTD sensor) @ 20 m. K § Discriminating variable between electronic and nuclear recoils : « Q » ~ ionization/heat § « Edelweiss-I » detectors « NTD » type detectors : plain Al electrodes Guard ring Center electrode m=320 g Neutrons 73 Ge(n, n', γ) Gammas Ionization threshold TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 4
EDELWEISS-I results (2005) § Charge collection deficit of electron like events : « surface » events § 210 Pb surface contamination can explain observed alphas at high energy and betas at low energy PRD 71, 122002 (2005) 210 Pb Astro. Part. 28, 143 (2007) β 210 Po 206 Pb a Bad charge collection TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 5
The EDELWEISS-II collaboration § CEA Saclay (IRFU and IRAMIS) Detectors, electronics, acquisition, background, analysis E. Armengaud, O. Besida, G. Gerbier, M. Gros, X-F. Navick, B. Paul, S. Hervé, M. Karolak, (M. Chapellier), P. Pari Post-doc: M Hannewald Thesis : A. Chantelauze (cotutelle FZK), J Domange BDI § CNRS, CSNSM Orsay Detectors, cabling, cryogenics, analysis L. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin, , F. Lalu, S. Marnieros Post-doc : E. Olivieri Thesis : O. Crauste, J Domange BDI § CNRS IPN Lyon Electronics, background, analysis, detectors C Augier, F. Charlieux, M. De Jésus, P. Di Stefano, J. Gascon, A. Juillard, V. Sanglard, L. Vagneron Thesis : M-A. Verdier, S. Scorza § CNRS I Néel Grenoble Cryogenics, electronics A. Benoit § FZ/ Universität Karlsruhe J. Blümer, K. Eitel Post doc : V Koslov § JINR Dubna E. Yakushev, S. Semikh § Oxford University H Kraus, S Henry Muon Veto and neutron counter, background Thesis : H. Kluck, A. Chantelauze (cotutelle FZK) Monitoring of neutron and radon backgrounds Thesis : A. Lubashevski, L. Perevozchikov High impedance sensors, wiring Thesis : S Kierkby, TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 6
The EDELWEISS-II experiment § Operated at the Underground § Laboratory of Modane (4μ/d/m 2) Shieldings : • • • Clean room + Radon-free air Active muon veto (> 98% coverage) PE shield 50 cm Lead shield 20 cm background reduced by ~2 wrt EDW 1 Polyethelene shield Pb shield cryostat § Cryogenic installation (~ 20 m. K) : • Reversed geometry cryostat • Use of pulse tubes § Can House up to 40 kg of detectors § Facilities : • Remotely controlled sources for • calibrations + regenerations Detector storage & repair within the clean room § 12 cool-downs already operated Muon Veto TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique Neutron counter 7
The issue of surface interactions § GGA 1 « NTD type » detector equiped with 210 Pb nano source : • Incomplete charge collection y • « Leakage » down to the nuclear recoil i ar n region lim re P EDELWEISS-II 93. 5 kgd § EDW-II 2008 data : • • • 11 detectors with < 30 ke. V thresholds 93. 5 kg. d in 4 months Threshold chosen a priori 3 events in nuclear recoil band Beta bkg reduced wrt EDW-I but still insufficient to reach 10 -8 pb TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 8
Rejecting surface events with interleaved electrodes The “ID” (Inter. Digit) detector ‘b’ electrodes (+2 V) collecting ‘a’ electrodes (-1 V) field shapping « VETO » Surface Volume ‘d’ (-2 V) Guard § Keep the EDW-I phonon detector § Modify the E field near the § surfaces with interleaved electrodes Use ‘a’ and ‘c’ signals as vetos against surface event ‘c’ (+1 V) § First detector built 2007 § 1 x 200 g + 3 x 400 g tested in 2008 § 10 x 400 g running since spring 2009 TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 9
An outstanding surface event discrimination « single-side » surface events E 1=0 Beta calibration (210 Pb) 200 g detector « 3 -electrodes » surface events 46 ke. V gamma-ray line ry na i lim e Pr fiducial volume events E 1=E 2 § A combination of cuts is made on the signals of electrodes § Example : cut on the difference of signals between 2 collecting electrodes § Surface and volume events are ½( ) ½ ( ) completely separated ! § From β calibration : overall rejection ~ 1/105 TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 10
ID fiducial volume § Approx. ~ 20 kg. d of background data 400 g detector background runs ry na i § with two 400 g detectors (2008 data) Cosmogenic lines : 68 Ge and 65 Zn lines at ~ 10 ke. V lim σion = 300 e. V re P 8. 98 ke. V ½( ) Fiducial volume cut 10. 37 ke. V Preliminary § Background electron recoils are § § distributed homogeneously in the volume of the cristal Fiducial volume = 160 g, primarily limited by the guard regions Result confirmed with neutron calibration measurements TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 11
IDs : overall background rejection performances ar. Xiv: 0905. 0753 -equivalent to ~103 kgd 0 ev -equivalent to 3 x 104 kgd ent s TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 12
ID 401+ID 3 18. 3 kgd WIMP-nucleon cross-section (pb) Physics runs with IDs § 2008 : • 86 live days / 4 months / 2 x 400 g detectors • 18. 3 kg. d with < 15 ke. V threshold, ~50% efficiency y ar in lim re P WIMP mass (Ge. V/c²) at 10 ke. V § 2009 : physics run ongoing • 10 x 400 g detectors running • x 20 improvement by 2010 : 4 x 10 -8 pb • Additional new detectors with increased fiducial volume ( « FIDs » 400 g, 800 g) 9 kg fiducial mass end 2010) TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 13
The muon veto in action § Interactions in detectors due to muon-induced neutrons inside the shield § Geant 4 • evts/kg. d < 250 ke. V Mostly nuclear recoils below 50 ke. V § Measured detector - muon veto § coincidence rate : ~ 0. 04 evts/kg. d The ionization yield distribution of coincidences is consistent with muon-induced events Ionization/recoil energy • Expected : ~0. 03 2007 -2008 data (280 kg. d - no cut) § In addition: neutron detector installed to study µ induced n TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 14
Summary § Edelweiss-II now aiming at ~ 10 -8 pb § Neutron shield and muon veto designed for < 10 -8 pb § New generation of « ID » detectors are validated • • Robust fabrication and operation Thresholds <15 ke. V Electron recoil rejection and surface event rejection (~1/105) Good fiducial volume fraction - with improvments ongoing § ID detectors are well-fitted for future 100 kg / ton-scale bolometric dark matter searches TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 15
The future : EURECA § EURECA: beyond 10 -9 pb, major efforts in background control and detector development § Joint effort from teams from EDELWEISS, CRESST, ROSEBUD, CERN, +others… § >>100 kg cryogenic experiment, multitarget : scintillators and Germanium § Part of ASPERA European Roadmap § Preferred site: 60 000 m 2 extension of present LSM (4 /m 2/d), to be dig in 2011 -2012 § Design study start by the end of the year § Start installation by 2013 EURECA : 2 cryostats in water tanks TAUP 09 - Roma - 07/03/2009 - SANGLARD Véronique 16
Coincidences in µ-veto system and Ge bolometers 1 ke. V