Stefano Pirro – NuMass 2010 Stefano Pirro Double beta decay searches with enriched and scintillating bolometers - Milano - Bicocca The Future of Neutrino Mass Measurements - NuMass 2010 INT Seattle February 8-11, 2010

Stefano Pirro – NuMass 2010 Background Issues (1)   

Stefano Pirro – NuMass 2010 Background Issues (2) Internal trace contaminations ( 238 U and 232 Th)Surrounding trace contaminations ( 238 U and 232 Th) Neutron induced background: direct and through (n,n’)  Surface  contaminationsLong living  - Emitters 106 Ru  106 Rh (Q=3.5 MeV) (Fission) 110m Ag  (Q=2.9 MeV) (fast n activation) XX

Stefano Pirro – NuMass 2010 Surface and Bulk contaminations CUORICINO  Background Furthermore a not negligible part of the background can arise from high energy neutrons from  -spallation  -region  -region Environmental “underground” Background: 238 U and 232 Th trace contaminations 130 Te 76 Ge 100 Mo 116 Cd 82 Se 136 Xe

Stefano Pirro – NuMass 2010 Some History The first measurement of light and heat in a bolometer was performed in 1992 by the Milano group But this technique, using a silicon PD at low temperatures showed several difficulties  Radioactivity induced by the PD itself  Cold stage charge preamplifier inside the cryostat  Relatively small surface area of the PD For these reasons the technique was abandoned In 2004 we started to develop bolometer as LD (as CRESST and Rosebud Experiments) The activity was then funded by INFN through the BoLux (R&D) Experiment* and by EC * Responsible: Stefano Pirro The CUPIDO R&D* project (INFN) funded for 2010 will go on with R&D on this technique.

Stefano Pirro – NuMass 2010 Principles of operation  =C/G  T=  E/C

Stefano Pirro – NuMass 2010 Light Detectors - Performances Our Light detectors are generally Pure Germanium disks (thickness mm). The Performances of a LD are normally evaluated through the Energy resolution on the 55 Fe doublet (5.9 & 6.5 keV X-Ray) Ge ( Ø = 66 mm) FWHM=550 eV Ge ( Ø = 35 mm) FWHM=250 eV

Stefano Pirro – NuMass 2010 Li 2 MoO 4 ZrO 2 Good Scintillation lightPoor Scintillation light No Scintillation light MgMoO 4 TeO 2 Summary of (almost) all the measured crystals ZnSe PbMoO 4 SrMoO 4 CdMoO 4 CdWO 4 CaF 2 CaMoO 4 ZnMoO 4

Stefano Pirro – NuMass 2010 Undoped 48 CaF 2 There was a lack of an actual calibration due to the “lightness” of the compound; nevertheless the Signal/noise ratio of the CaF 2 was excellent. Calibration ( 232 Th) on a 3x3x3 cm 3 PURE CaF 2 crystal In 2007 we tested a CaF 2 crystal. The light output was “rather poor” but definitively enough to discriminate alpha’s

Stefano Pirro – NuMass 2010 Results on the first array of 116 CdWO 4 crystals (1) CdWO 4 – 3x3x6 4 3x3x3 cm 3 (215 g each) CdWO 4 1 common LD facing the 4 crystals

Stefano Pirro – NuMass 2010 Results on the first array of 116 CdWO 4 crystals (2) The data on the single 420 g 3x3x6 cm 3 crystal is presented here. The obtained scatter plot is shown it corresponds to 1066 hours of background measurement Background-Free area 2615 keV 208 Tl  The MC simulation predicts a background level of c/keV/kg/y in the region of interest 44 days background

Stefano Pirro – NuMass 2010 Zn 100 MoO 4 – A promising Molibdate A 22 g ZnMoO 4 crystal was grown by Institute for Scintillation Materials (Kharkov, Ukraine) In collaboration with by Institute for Nuclear Research (Kiev, Ukraine) 226 Ra, 222 Rn, 218 Po, 214 Bi- 214 Po (56 mBq/kg) 210 Pb (360 mBq/kg)

Stefano Pirro – NuMass 2010 Ln (Light) Zn 82 Se – an extremely Puzzling compound (1) Looking at the coincidences between Heat in ZnSe and “Light” in the light detector, three population appears //  Ionizing particles

Stefano Pirro – NuMass 2010 Calibration with 232 Th and a smeared  source 210 Po Beta region Rejection > 99.5 % Smeared  source Light Zn 82 Se – an extremely promising compound (2) First Results on a 4 cm  5 cm height 337 g ZnSe Crystal 337 g “new” ZnSe Crystal // 

Stefano Pirro – NuMass 2010 “Beyond” Scintillating bolometers Scintillating bolometers are extremely powerful in order to discriminate background. Nevertheless, they require a double readout that implies a dedicated technical and construction effort. This is the “price” one has to pay in order to really “knock down” background. It would be nice to obtain the same w/o this effort…

Stefano Pirro – NuMass 2010 Decay time of the CaMoO 4 crystal – no light detection Rise time of the CaMoO 4 crystal – no light detection [ ms ] [ au ] Results on “large” crystals – 48 Ca 100 MoO 4 CaMoO 4 is not a “perfect candidate” for future DBD Experiment since it contains 48 Ca But this compound did show an extreme interesting feature without Light detection CaMoO 4 Bolometers permits alpha discrimination (99,8%) without Light detection 147 Sm keV The results are obtained on a ~160 g crystal

Stefano Pirro – NuMass 2010 Zn 82 Se – an extremely promising compound (3) This compound shows another very interesting feature:  ’s show different thermal pulse development //   rejection > 97 % without light detection

Stefano Pirro – NuMass 2010 Zn 100 MoO 4 – A promising Molibdate (2) Light- Heat scatter plot No Light information - PSA This seems a characteristic of Molibdate crystals (also observed on other molibdates)

Stefano Pirro – NuMass 2010 Conclusions - I We tested several types of scintillating crystals with interesting  emitters ( 100 Mo, 116 Cd, 82 Se, 48 Ca) Within them CdWO 4 is “ready to use” The “outsider” ZnSe is now, probably, the best candidate, even if some more tests are needed Molibdates need more R&D both for radioactivity and scintillation light This technique is the only one that can be used for several interesting DBD emitters with excellent energy resolution (0.3  1 % FWHM)  Particle Identification through Pulse Shape Analysis could result in a new, unexpected, ally Simulations show that a background level of c/keV/kg/y can be “easily” reached without too much “restrictions” on internal radioactivity. Within few months we plan to test 2 small arrays of CdWO 4 and ZnSe crystals ( O(kg) ) in order to completely test the technique (unexpected “surprises” can always happen)

Stefano Pirro – NuMass 2010 Conclusions-2 Different nuclei HAVE to be investigated by DBD experiments DBD Detectors with Q   >2615 keV can reach background levels  2 orders of magnitude smaller with respect to the others If we think about possible “ III generation experiments” the key point will be (if we consider solved the background issue….) Energy Resolution (  1 %) Scintillating Bolometers are the only detectors that can fulfill all these 3 requirements 130 Te 76 Ge 100 Mo 116 Cd 82 Se 136 Xe Gerda-Majorana CUORE EXO Super-Nemo SNO+