1. LUCIFER a potentially background-free approach to the search for 0  Claudia Nones CSNSM/CNRS-Orsay NOW2010 – September 4 th - 11 th, 2010 – Conca Specchiulla, Italy

2. Outline  Background and sensitivity in the search for 0   The LUCIFER project  The R&D activities @ LNGS and @ CSNSM-Orsay  Perspectives & Conclusions

3. The size of the challenge 1 – 10 counts/ y ton 100 – 1000 counts/ y ton 0.1 – 1 counts/ y ton 50 meV 15 meV Goal: b= 10 -3 – 10 -4 c/keV/kg/y with a high energy resolution detector 76 Ge claim

4. The LUCIFER recipe How to approach a 0 background experiment: High energy resolution (no background from 2  ) 1 1 Make irrelevant the  background 2 2 Discrimination between  and  particles 3 3 A bolometer with embedded a high Q-value 0  isotope that also scintillates Bolometers Isotope with a high Q value 130 Te 76 Ge 100 Mo 116 Cd Environmental “underground” Background: 238 U and 232 Th trace contaminations 82 Se CUORICINO background Energy-degraded  above 2615 keV

5. Double read-out bolometers: heat + light Alphas emit a different amount of light with respect to beta/gamma of the same energy (normally lower → a QF < 1, but not in all cases). A scatter plot light vs. heat separates alphas from betas / gammas. V lig ht V heat Scintillating crystal under test Copper frame Reflecting foil Ge disk A device able to measure simultaneously the phonon (heat) excitations and the photon (scintillation) excitations generated in a crystal by the same nuclear event can efficiently discriminate alphas from betas / gammas. Original idea Milano group mid 1990’s CaF 2 scintillating bolometer beta alpha The experimental basis for LUCIFER is the R&D activity performed by Stefano Pirro at LNGS, in the framework of the programs:  BOLUX, funded by INFN – CSN5  ILIAS-IDEA funded by the European Commission (WP2-P2) The experimental basis for LUCIFER is the R&D activity performed by Stefano Pirro at LNGS, in the framework of the programs:  BOLUX, funded by INFN – CSN5  ILIAS-IDEA funded by the European Commission (WP2-P2)

6. LUCIFER Low-background Underground Cryogenics Installation For Elusive Rates Principal Investigator: Fernando Ferroni Co-Investigator : Andrea Giuliani ERC-2009-AdG 247115 Double Beta Decay pilot project based on scintillating bolometers

7. NucleusI. A. Q-value Materials successfully tested as bolometers [%] [keV] in crystalline form 76 Ge7.82039Ge 136 Xe8.92479NONE 130 Te33.82527TeO 2 116 Cd7.52802CdWO 4, CdMoO 4 82 Se9.22995ZnSe 100 Mo9.63034PbMoO 4, CaMoO 4, SrMoO 4, CdMoO 4, SrMoO 4, ZnMoO 4, Li 2 MoO 4, MgMoO 4 96 Zr2.83350ZrO 2 150 Nd5.63367NONE → many attempts 48 Ca0.1874270CaF 2, CaMoO 4 Four high Q-value candidates ( 116 Cd – 100 Mo – 82 Se – 48 Ca) can be studied as scintillating bolometers Underlined compounds are good scintillators Candidate isotopes in scintillating bolometers

8. The choice of the isotope There are 3 main candidates The baseline: ZnSe Active isotope: 82 Se Decay: 82 Se -> 82 Kr + 2e - Q-Value: 2995 keV Abundance: 9% Q-value [keV] Useful material LY [keV/MeV] QF  Enrichment [€/g] CdWO 4 280932%340.19> 150-200 ZnMoO 4 303444%1.40.1650-80 ZnSe299556%7.44.250-80 Cons Pros Transition energy does not indicate a preference 113 Cd beta emitter 113 Cd high neutron cross-section

9. Results @ LNGS (1)   4 cm, 1.7 cm height, 120 g  2 cm, 3 cm height, 39 g  QF > 1: alphas give more light than gammas → risk of leakage in the beta/gamma region? Q-value of 82 Se   2615 keV: the end of  radioactivity Background free area Just an example

10. Results @ LNGS (2) Pulse shape discrimination in light detector (very preliminary) Spring 2010 There are no enough data to conclude that pulse shape discrimination is sufficient to reject alphas at the desired level, but it is surely crucial to investigate this opportunity. Final surprise: pulse shape discrimination in the heat signal

11. ZnSe optical properties Preliminary Sample: 1x1x1 cm 3 - ZnSe From preliminary measurements performed on ZnSe bolometric and scintillation characteristics:  very promising results on the amplitude of scintillation signal  very promising capability to discriminate between  and  particles Nevertheless Quite large spread of characteristics (even among samples delivered by the same producer) Quenching factor > 1 Study of optical properties (optical trasmission and luminescence) Study of the effect of impurities and local defect on the optical properties of ZnSe crystals

12. Study of ZnSe optical properties @ CSNSM Courtesy of O. Plantevin

13. Photo-luminescence measurements @ CSNSM Preliminary July 2010 Preliminary July 2010 emission band E [eV] [nm] A2.02613.86 B1.27976.38 C0.951305.3 D0.761631.6 A B C D Next steps: photoluminescence @ low temperatures

14. LUCIFER detector structure Single module: 4 ZnSe crystals and 1 light detector Tower: 12 single modules Preliminary Possible location: ex-Cuoricino cryostat @ LNGS LUCIFER is a demonstrator…

15. From the LUCIFER proposal: CrystalIsotope weightUseful material Half Life limit (10 26 y) Sensitivity* to m ee (meV) CdWO 4 116 Cd 15.1 kg32%1.1565-80 ZnMoO 4 100 Mo 11.3 kg44%1.2767-73 ZnSe [baseline] 82 Se 17.6 kg56%2.3152-65 ZnSe [option 1] 82 Se 20.5 kg56%2.5949-61 ZnSe [option 2] 82 Se 27.8 kg56%3.2044-55 * The 1  sensitivity is calculated with the Feldman Cousins approach for 5 y running and a background index d  b /dE = 10 -3 c/keV/Kg/y. The matrix elements come from the two most recent QRPA calculations [ME08]; the energy window is taken as 5 keV, compatible with the resolution achieved in TeO 2 macrobolometers and in scintillating-bolometer R&D. Optimistic evaluation, assuming full success for several difficult tasks:  negotiate a good contract for enrichment → Zelenogorsk (Russia), URENCO (NL)  get radiopure and chemically pure isotope after enrichment  efficient crystallization → Institute for Single Crystals, Kharkov, Ukraina  optimize bolometric performance of ZnSe crystals The physics reach …but has a remarkable sensitivity by itself More realistic evaluation: 10 kg of isotope ~100 meV as sensitivity More realistic evaluation: 10 kg of isotope ~100 meV as sensitivity

16. LUCIFER next steps Cristal growth optimization Procurement of the enriched material Optimization of light detectors Optimization of ZnSe scintillating bolometers LUCIFER Assembly NEXT STEPS LUCIFER Kick-off LUCIFER Kick-off Data taking First physics results 2014

17. Conclusions & Perspectives  A 0 background approach is mandatory to reach sensitivities useful to scan completely the inverted hierarchy region.  Double read-out detectors (heat+light) are a powerful tool.  LUCIFER is the first full demonstrator of this technique.  An intense R&D programme is going on.  LUCIFER data taking: 2014.

18. BACK-UP

19. N. Starzhinskiy et al, IEEE Trans. Nucl. Science, 55, 1542 (2008)