CDMS Status, Upgrades and Plans

1. CDMSStatus, Upgrades and Plans Summary of running at Soudan Cryogenic and Detector Upgrades The Future - SuperCDMS@SNOLAB

2. >2 years of stable data taking at Soudan Maximum livetime = 85% (limited by cryo servicing need for calibration data) DAMA MSSM CDMS (2006) Xenon 10 Gamma Calibration ~10% of livetime CDMS (Feb 2008) Current CDMS sensitivity We now have >1700 kg-days of exposure, sufficient to have world’s best spin-independent WIMP sensitivity for all WIMP masses. Approaching 10 Zeptobarn cross section! Average livetime ~ 75%

3. Cryogenic Upgrades - UPS • Replaced UPS for cryogenics system • Underground diesel generator backs up entire cryogenics system • Aging UPS was used to ‘bridge’ cryogenics control systems • Installed new 30 kVA unit to carry whole cryogenics system • Remote control and monitoring of UPS from the surface Underground diesel generator UPS remote monitoring

4. Cryogenic Upgrades - Replaced Ebox • Have lived for 2 years with small leaks in vacuum bulkhead (Ebox) • Air freezes out on cold surfaces, can cause vacuum bursts • If Helium gets in, it can reach detectors and affect signals • Occasional ~1 week warming to 4-77K has been necessary • Problem was due to custom-design of Ebox • Warping of rectangular box made large o-ring seals difficult • Solution was to buy large commercial vacuum cross • Had vendor weld high-vacuum detector electrical connections into commercial vacuum plates • Decided to warm to room temperature in October to install • Takes about 2 weeks to warm, another 2 weeks to cool down • Actual work at room temperature about 2 weeks

5. Cryogenics Upgrades - Ebox Old ebox (note the black sealant) Stripline detector connections extracted New Ebox being installed Reinstalling the stripline connections

6. Cryogenic Upgrades - Serviced Cryocooler • Cryocooler removes excess heat at 4K and 77K • We cannot run 30 detectors without this • Servicing involves replacing cold head at room temperature • Why did we want to do this now? • Had 150% of recommended hours on the cold head • Valves or piston could begin sticking at some point • No evidence of performance problems but want to run another 2-3 years at Soudan, so this was a good time to do this • Fortunately, the vendor (Sumitomo) can replace the cryocooler head without disturbing the delicate connections to e-stem • Challenge was supporting these connections during the operation • New head should last for length of CDMS operation at Soudan

7. Cryogenic Upgrades - Cryocooler Supporting the cryocooler and estem during the cold head replacement The cryocooler cold head

8. An interesting incident during cooldown • Dilution refrigerator uses 1K pot to condense 3He • 1K pot is filled from He bath via needle valves • Pumping on 4He in pot lowers temperature to 1.4K • At this temperature, liquid Helium is a superfluid • Superfluid Helium tends to creep • Distance it can travel depends on surface roughness • Small amount of air was accidentally introduced in bath • Plated out in needle valves, allowing superfluid Helium connection between 1K pot and 4K bath • Result was a 1K pot temperature >1.9K and very poor condensation of 3He • Had to warm again above 77K and pump away air • Now understand earlier instability with pot temperatures

9. Additional work planned in 2009 • Soudan underground power feed • Near maximum capacity and getting old • Study underway to determine whether upgrades needed • May be possible to run separate feed for water pumps • CDMS would like to install He liquefiers at Soudan • He costs are skyrocketing and availability is an issue • 36% increase in costs this summer • Several recent instances where supply was very tight • CDMS uses about 70l/day • Purchased 3 cryocooler-based liquefiers in FY2008 • Plan phased installation during 2009-2010 • Sufficient capacity to reduce He consumption by x10 • Requires additional power (8 kw/liquefier)

10. Detector Issues • Many detectors have failed in the oldest two towers • These towers are now 6 years old and have seen many thermal cycles • Will do postmortem on failures when towers replaced; most suspected to be cold electronics and wire bonds • Net loss of about 1 kg Ge for the next three months • New issues with Si detectors in this run • Many of our Si detectors show signs of charge leakage through the crystal • Run at reduced charge bias to avoid heating of phonon sensors • Si detectors are no longer crucial for WIMP search

11. Larger detectors to be deployed in 2009 Remove two oldest towers lose 1.5 kg Ge, 0.6 kg Si (mostly not working anyway) New SuperCDMS detectors each 3” dia x 1” => 0.64 kg of Ge with new phonon sensor design to improve fiducial volume

12. SuperCDMS@Soudan • Replace CDMS II detectors with SuperCDMS detectors • 0.25 kg Ge/0.1 kg Si --> 0.64 kg Ge • Each new tower has 5 Ge detectors => ~3 kg mass • Each also has two Ge endcap veto detectors • Improves ability to reject backgrounds from nearby materials • First ‘Supertower’ due in March 2009 • Will bring Ge mass to 6 kg • Remaining 4 supertowers in early 2010 • Total deployed Ge mass will be 15 kg • Two year run will yield x3 sensitivity improvement over the best that CDMS II will produce (x10 better than currently published).

13. The Future: SuperCDMS@SNOLAB • Science goals • Increase sensitivity by x50 (compared with current published) • Reach WIMP-nucleon cross section of 10-46 cm2 • Find WIMP signal and compare with LHC • Technical goals • Increase detector mass in stages up to 100 kg by 2012 • Stay background free • Challenge to deal with existing backgrounds at Soudan • New setup needed at SNOLAB to reduce neutron background • Current status • First Soudan stage funded by DOE/NSF; full 15 kg funding requested • SNOLAB experiment has CD-0 and Stage 1 approval from FNAL Director • DMSAG2 review of the field in 2009 will likely determine funding prospects

14. CDMS is the only DM experiment with demonstrated control of backgrounds Make sure any events here are WIMPS, not background! Expected Background: 0.6 ± 0.5 surface events and < 0.2 neutrons