1. Surface Sensitive Bolometers (SSB): last development MARISA PEDRETTI INFN - Milano

2. Outline recap of the SSB idea brief summary of previous SSB tests and results new test: detector set up and results future tests

3. The SSB idea The idea is to use auxiliary thin Ge bolometers to control surface contamination Classical pulse Fast high and saturated pulse TeO 2 thermistor VV If we make a scatter plot of the pulse amplitude (pulse amplitude obtained with thermistor on Ge crystal versus those obtained with thermistor on TeO 2 crystal) we obtain two well separated behaviours

4. Previous test Work done in the IDEA framework small prototypes in order to test the idea  R&D in Como (above ground lab) Germanium alfa peaks 224 Ra 220 Ra 216 Po 212 Po Rise Time [ms]

5. TeO 2 shieldsGe shieldsSi shields small prototypes in order to test the idea probe different materials and thermal connections  R&D in Como (above ground lab) Previous test Work done in the IDEA framework

6. 4 large SSB detectors silicon slabs in parallel read-out goal: to check the technical feasibility no attention on cleaning procedure  R&D at LNGS – First test Previous test Work done in the IDEA framework

7. 4 large SSB detectors silicon slabs in parallel read-out goal: to check the technical feasibility no attention on cleaning procedure  R&D at LNGS – First test Previous test Work done in the IDEA framework Surface events Bulk events Mixed events

8. 4 large SSB detectors silicon slabs in parallel read-out goal: to check the technical feasibility no attention on cleaning procedure  R&D at LNGS – First test Previous test Work done in the IDEA framework detector with slabs (SSB) Amplitude on main bolometer Decay time on main bolometer anomalous events Bkg result compatible with the Cuoricino one

9. SLAB 1 Small prototype TeO2 slabs radioactive source between slab and main goal: understanding structures in scatter plots  R&D at LNGS – Second test Previous test Work already done in IDEA framework D3 SLAB 2MAIN implanted slab clean slab

10. R&D at LNGS – Third test New test: set up New test with 4 SSB detectors shielded with TeO 2 slabs 2 SSB have 6 actively shielding bolometers read out independently 2 SSB have 5 passively shielding bolometers and an active one the slabs don’t cover completely the main detector (~75%)

11. Marisa Pedretti Some pictures SSB slabs module Standard module for background comparison RAD = detectors with lower background obtained in R&D work

12. New test: problems we lost an electric channel on each detector -> we don’t have a totally active SSB detector SSB Active slabs Passive slabs TeO 2 slabs were not cleaned as main detectors low performance detectors and problems cause d by very noisy measurements

13. Marisa Pedretti THERE ARE TWO POSSIBLE WAYS TO ANALYZE THIS DATA USING ALL SSB AS PASSIVE DETECTORS (THEN REJECTING PULSES DEPENDING ON PULSE SHAPE PARAMETERS SUCH AS DECAY TIME ON THE MAIN BOLOMETER) USING ALL THE POTENTIALITY OF SLABS, i.e. USING INFORMATION COMING FROM ACTIVE SLABS. THIS APPROACH ALLOWS US TO CHECK THE EFFICIENCY OF THE PREVIOUS METHOD

14. SSB: Decay Time vs Amplitude on main bolometers 5 passive slabs 5 active slabs

17. DETECTOR2700 - 32003400 – 3900 Detector without slabs in the same run0.16 ± 0.040.11 ± 0.03 SSB (as passive) SSB (as active) 0.11 ± 0.03 0.07 ± 0.02 0.14 ± 0.03 0.04 ± 0.02 RAD0.06 ± 0.010.08 ± 0.02 VERY PRELIMINARY!!!!!!! Background Results WHY ISN’T THERE A BIGGER BACKGROUND REDUCTION USING SSB? Possible answer: no clean slabs lost channels no total main detector coverage increase of the amount of Teflon (not covered by slabs) poor quality measurements PAY ATTENTION: WE ARE SPEAKING OF A VERY SMALL NUMBER OF PULSES

18. Conclusions and future development SSB with active slabs are efficient in order to discriminate background (but the channel number increase is dangerous) the use of pulse-shape parameters to perform bkg discrimination is not optimized (in order to take this option into consideration other R&D work is needed) our model of detector background (surface contamination) still provides the best explanation for all the data collected so far. In order to have decisive confirmation of this model we proposed a diagnostic measurement with 4 SSB that cover totally the main bolometer, made with very clean and active (read-out) slabs we have to test methods to cover also the PTFE and corners we have to find a method to clean reasonably shielding slabs

19. Marisa Pedretti