1. The CRESST Dark Matter Search Status Report
Cryogenic Rare Event Search with Superconducting Thermometers
CRESST is a collaboration of:
Max-Planck-Institut für Physik
Technische Universität München
University of Oxford
Universität Tübingen
Laboratori Nazionali del Gran Sasso

2. Federica Petricca - MPI Project Review 2010
Outline
The CRESST Detector
Status of the experiment
MPI activities
Ongoing run
Analysis
Next run
Light Detectors
Holding of target crystals
Alternative target crystals
Federica Petricca - MPI Project Review 2010

3. CRESST Cryogenic Detectors
Scintillating target crystals
Modular structure
Multi-target possible
CaWO4
h=40mm
∅=40mm
m=300g
W-SPT
Light
absorber
CaWO4
target crystal
reflecting
scintillating
housing
Federica Petricca - MPI Project Review 2010

4. Federica Petricca - MPI Project Review 2010
Outline
The CRESST Detector
Status of the experiment
MPI activities
Ongoing run
Analysis
Next run
Light Detectors
Holding of target crystals
Alternative target crystals
Federica Petricca - MPI Project Review 2010

5. Status of the experiment
CRESST running since spring 2009
9 fully functioning CaWO4 modules
1 fully functioning ZnWO4 module
6 modules with not operational light detector (Tc too low)
1 module with not operational crystal (?)
~750 kg/day of net exposure
Gamma calibration
Neutron calibration
Various test of the shielding
Federica Petricca - MPI Project Review 2010

6. Status of the experiment
CRESST running since spring 2009
(Preliminary) results presented
Module 5 a O W
MPI colloquium –
Visit of the Fachbeirat –
Publication in preparation
Unexpected events in oxygen recoil band
Federica Petricca - MPI Project Review 2010

7. Federica Petricca - MPI Project Review 2010
Outline
The CRESST Detector
Status of the experiment
MPI activities
Ongoing run
Analysis
Next run
Light Detectors
Holding of target crystals
Alternative target crystals
Federica Petricca - MPI Project Review 2010

8. Federica Petricca - MPI Project Review 2010
Analysis of Compound Target Materials The CRESST Dark Matter Search – New Analysis Methods and Recent Results J. Schmaler, PhD thesis, TUM (2010)
WIMPs should mainly scatter off tungsten nuclei
for light WIMPs: W recoils below energy threshold  O and Ca relevant!
new analysis method: takes into account contributions of all nuclei simultaneously
need to work in full 2-D parameter space (energy/light yield)
includes new methods for calculating exclusion limits based on 2-D data
density of expected signal for a 15 GeV WIMP
Federica Petricca - MPI Project Review 2010 8

9. Analysis of Compound Target Materials The CRESST Dark Matter Search – New Analysis Methods and Recent Results J. Schmaler, PhD thesis, TUM (2010)
exclusion limits for elastic WIMP scattering
benefits of new analysis method:
strongly enhanced sensitivity for light WIMPs
two-dimensional: exploits full information of CRESST data to obtain limits robust against unknown backgrounds
Federica Petricca - MPI Project Review 2010

10. Federica Petricca - MPI Project Review 2010
Analysis of Detectors’ Characteristics Optimization of CRESSTII detector modules M. Kiefer, PhD thesis, TUM (in preparation)
Large number of running detector modules
Study characteristics at low temperature
Light emitted
Light detected
Model: distribution of energy in a module
Federica Petricca - MPI Project Review 2010

11. Federica Petricca - MPI Project Review 2010
Analysis of Detectors’ Characteristics Optimization of CRESSTII detector modules M. Kiefer, PhD thesis, TUM (in preparation)
CaWO4 better than ZnWO4
Composite better than conventional
composite
conventional
No large variation in light detection efficiency within the modules
Federica Petricca - MPI Project Review 2010

12. Federica Petricca - MPI Project Review 2010
Outline
The CRESST Detector
Status of the experiment
MPI activities
Ongoing run
Analysis
Next run
Light Detectors
Holding of target crystals
Alternative target crystals
Federica Petricca - MPI Project Review 2010

13. Light Detectors - Production
More detectors running
Production of new LD
Reproducibility of transition
WII-146
WII-132
WII-106
Federica Petricca - MPI Project Review 2010

14. Light Detectors - Production
More detectors running
Production of new LD
Reproducibility of transition
ESD problem
Federica Petricca - MPI Project Review 2010

15. Federica Petricca - MPI Project Review 2010
Light Detectors – Optimization The detectors Parameters Determining the sensitivity of the CRESST-II Experiment P. Huff, PhD thesis, TUM (2010)
Improve event-by-event discrimination
Understanding of the factors determining the width of the bands
 possibility for improvement
Thermometer with separated heater
Two implemented in run32
All newly produced heaters
Black Silicon light absorber
Tested in Munich
Modified thermometer size
Federica Petricca - MPI Project Review 2010

16. Federica Petricca - MPI Project Review 2010
Outline
The CRESST Detector
Status of the experiment
MPI activities
Ongoing run
Analysis
Next run
Light Detectors
Holding of target crystals
Alternative target crystals
Federica Petricca - MPI Project Review 2010

17. Federica Petricca - MPI Project Review 2010
Federica Petricca - MPI Project Review 2010

18. Holding of target crystals
most likely origin of no-light events:
stress relaxation events at contact surface between clamps and crystal
clamps mostly covered with plastic layer
more no-light events than with pure metal clamps
consequence of 2008 run: new clamps for all crystals
no plastic coverage
Federica Petricca - MPI Project Review 2010

19. Holding of target crystals
Module 5
non scintillating clamp a
210Po
206Pb a
High 210Pb content in the clamp material
Federica Petricca - MPI Project Review 2010

20. Holding of target crystals
Reduction of background
Alternative spring material
New reflecting coating (Al)
New scintillating coating (Epo-tek +PPO)
Need testing:
Radiopurity
Production and handling
Low temperature performance
Federica Petricca - MPI Project Review 2010

21. Holding of target crystals
Reduction of background
Alternative spring material
New reflecting coating (Al)
New scintillating coating (Epo-tek +PPO)
CaWO4 balls
Improved holder design
Test facility at GS for studying prototypes
Federica Petricca - MPI Project Review 2010

22. Federica Petricca - MPI Project Review 2010
Outline
The CRESST Detector
Status of the experiment
MPI activities
Ongoing run
Analysis
Next run
Light Detectors
Holding of target crystals
Alternative target crystals
Federica Petricca - MPI Project Review 2010

23. Federica Petricca - MPI Project Review 2010
Al2O3:Ti
Federica Petricca - MPI Project Review 2010

24. Alternative target crystals Light Yield Measurements of CdWO4 and Al2O3:Ti for the CRESST Dark Matter Search R. Kleindienst, Diploma Thesis, TUM (2010)
Cryogenic measurement with small target crystal
CdWO4
Light Yield ~ 2 CaWO4
comparable with LY CaWO4 for large crystals (measured in test cryostat at Gran Sasso)
 Further improvement of crystal quality
Al2O3:Ti (50 to 500 ppm)
Light Yield ~1/2 CaWO4
 Low light yield
W-SPT
Light
absorber
Target crystal
20mm x 10mm x 5mm
reflecting
housing
Federica Petricca - MPI Project Review 2010

25. Alternative target crystals
Cryogenic measurement with small target crystal
CsI
Light Yield ~ 7 CaWO4
Aspects under investigation:
performance as cryogenic calorimeter
possible surface effects
position dependence
intrinsic radioactivity
W-SPT
Light
absorber
Target crystal
20mm x 10mm x 5mm
reflecting
housing
 Needs to be measured in the test facility at Gran Sasso
Federica Petricca - MPI Project Review 2010

26. Federica Petricca - MPI Project Review 2010
Future
Study reproducibility of transitions in light detectors
Investigation of new light absorbers
Black Silicon
Optimization of thermometer size
Characterization of new scintillators
CsI
CdWO4
Federica Petricca - MPI Project Review 2010

27. Federica Petricca - MPI Project Review 2010
Future
Detectors ready
New holders in production
Solution for target crystal holding to be finalized
Conclusion of ongoing run early 2011 approaching 1T/day
Installation of new detectors and maintenance
Start of new run mid 2011
study excess of events in the oxygen band with lower background and higher mass
We want to thank the MPI staff that is involved with the preparation of the new CRESST Run
Federica Petricca - MPI Project Review 2010