The Majorana Project: A Next-Generation Neutrino Mass Probe

1. The Majorana Project: A Next-Generation Neutrino Mass Probe Craig AalsethforThe Majorana Collaboration NDM03, Nara, Japan June 9, 2003

2. The Majorana Collaboration Brown University, Providence, RI Rick Gaitskell Duke University, Durham, NC Werner Tornow Institute for Theoretical and Experimental Physics, Moscow, RussiaA. Barabash, S. Konovalov, V. Stekhanov, V. Umatov Joint Institute for Nuclear Research, Dubna, RussiaV. Brudanin, S. Egorov, O. Kochetov, V. Sandukovsky Lawrence Berkley National Laboratory, Berkley, CAPaul Fallon, I. Y. Lee Lawrence Livermore National Laboratory, Livermore, CAKai Vetter Los Alamos National Laboratory, Los Alamos, NMSteve Elliott, Andrew Hime New Mexico State University, Carlsbad, NMJoel Webb North Carolina State University,Raleigh, NC Eric Adles, Rakesh Kumar Jain, Jeremy Kephart, Ryan Rohm, Albert Young Osaka University, Osaka, Japan Hiro Ejiri, Ryuta Hazama, Masaharu Nomachi Pacific Northwest National Laboratory, Richland, WAHarry Miley, Co-spokesperson Craig Aalseth, Dale Anderson, Ronald Brodzinski, Shelece Easterday,Todd Hossbach, David Jordan, Richard Kouzes, William Pitts, Ray Warner University of Chicago, Chicago, ILJuan Collar, University of South Carolina, Columbia, SCFrank Avignone, Co-spokesperson Horacio Farach, George King, John M. Palms, University of Washington, Seattle, WA Peter Doe, Victor Gehman, Kareem Kazkaz, Hamish Robertson, John Wilkerson • http://majorana.pnl.gov

3. Outline • Introduction and Overview • Reference Concept • Backgrounds and Mitigation • Pulse-Shape Discrimination • Detector Segmentation • Experiment Sensitivity • Progress and Status • Conclusions

4. Germanium Basics • “Internal Source Method” from Fiorini • 76Ge: Endpoint = 2039 keV • Energy above many contaminants • Except: 208Tl, 60Co, 68Ge… • FWHM = 3-4 keV around 2 MeV (~0.2%) • Long experience with Ge bb decay • Previous efforts found 2n at T1/2 ~1021 y • Expect 0n at T1/2 ~ 4 x 1027 y • Ready to go! • Essentially no R&D needed

5. e- p+ p+ e- ne n n Majorana Overview • GOAL: Sensitive to effective Majorana n mass as low as 0.02-0.07 eV • 0n bb-decay of 76Ge potentially measured at 2039 keV • Based on well known 76Ge detector technology plus: • Pulse-shape analysis • Detector segmentation • Ready to begin now • Requires: • Deep underground location • 500 kg enriched 85% 76Ge • Many crystals, each segmented • Advanced signal processing • Pulse shape discrimination • Special low background materials • Reference Configuration

6. Segmentation (6x2) results in 2500 individual 200g segments 210 2.35 kg crystals Majorana Reference Concept 3-D model of reference configuration • Optimization underway of performance and risk • Several low-risk designs possible • Many segmentation schemes possible • Alternative packaging, cooling, shielding under consideration • Nature of Ge crystals allows repackaging

7. Starting Background Estimate Calculated Experimental • International Germanium Experiment (IGEX) achieved between 0.1-0.3 counts/keV/kg/y • Documented experiences with cosmic secondary neutron production of isotopes [Bro95] R. L. Brodzinski, et al, Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 193, No. 1 (1995) 61-70.

8. Single-site interaction example Monte-Carlo 2038-keV deposition from 0n bb-decay of 76Ge

9. Multiple-site interaction example Monte-Carlo 2038-keV deposition from multi-Compton of 2615-keV 208Tl g

10. Multi-Parametric Pulse-Shape Discriminator • Extracts key parameters from each preamplifier output pulse • Sensitive to radial location of interactions and interaction multiplicity • Self-calibrating – allows optimal discrimination for each detector • Discriminator can be recalibrated for changing bias voltage or other variables • Method is computationally cheap, requiring no computed libraries-of-pulses

11. 212Bi1620.6 keV DEP of 208Tl1592.5 keV 228Ac1587.9 keV PSD can reject multiple-site backgrounds (like 68Ge and 60Co) Keeps 80% of the single-site DEP (double escape peak) Experimental Data Rejects 74% of the multi-site backgrounds (use 212Bi peak as conservative indicator) Original spectrum Scaled PSD result Improves T1/2 limit by 56%

12. Sensitive to axial and azimuthal separation of depositions reference design with six azimuthal and two axial contacts is low risk This level of segmentation gives good background rejection This segmentation gives us ~2500 segments of 200 g or 40 cc Detector Segmentation

13. Monte-Carlo Example(single crystal) Segment multiplicity at 2039 keV Sensitive to z and phi separation of depositions 0nbb efficiency = 91% internal 60Co efficiency = 14% Improves T1/2 limit by 140% • Next Steps: • T ½ improvement increases to 260% - 620% when including array self-shielding, depending on position of crystal – not included in earlier background estimate • Time-series analysis of background very promising

14. Sensitivity vs. Time • Slow Production: Gradual ramp to 100 kg/y - total 500 kg 85% 76Ge • Fast Production: 200 kg/y (No ramp) • Present 0nbb76Ge T1/2 limit rapidly surpassed (T1/2 > 1.9 1025 y) 0nbb Half-Life • Based on early IGEX background levels with reasonable background reduction and cutting methods applied

15. Collaboration Progress:Optimizations for Full Experiment Multi Element Germanium Assay (MEGA): 16+2 natural Ge MAJORANA: 500 kg Ge detectors All enriched/segmented Multi-crystal modules g Segmented Enriched Germanium Array (SEGA): Segmented Ge 1 to 5 Crystals First enriched, segmented detector in testing! Additional tests being planned for other segmented systems High density Materials qualification Cryogenic design test Geometry & signal routing test Powerful screening tool Full Experiment

16. Progress and StatusSEGA: Segmentation Optimization • First (enriched) 6x2 SEGA operating • Current: Testing (TUNL) • Shallow UG testing at U Chicago LASR facility • Operation in WIPP • Second and third SEGA planning • Funds in hand (LANL, USC) • Alternate segmentation testing in planning (USC/PNNL) • 40-fold-segmented LLNL detector now available SEGA crystal initial test cryostat Figure-Of-Merit vs. Axial & Azimuthal Segmentationfor internal 60Co background

17. Progress and StatusMEGA: Cryogenic testing • Materials in hand • Detectors (20 - 70% HPGe), electronics • Assembly and cryogenic testing of two-packs underway (PNNL, UW, NC State) • UG facility (WIPP) in prep (LANL, NMSU) • Summer installation anticipated • Sensitive to ~1e4 short-lived atoms

18. Recent Crystal Packaging Test(MEGA)

19. Progress and StatusUltra-Low Level Screening • Screening facility • Operating in Soudan (Brown U) • Some contamination issues… 207Bi • Two HPGE detectors (1.05 kg, 0.7 kg) • Planned use for screening • Minor materials used in manufacturing • Improved Cu testing • Small parts qualification • FET, cable, interconnects, etc Dual counter shield: 1.05 and 0.7 kg detectors

20. Progress and StatusLow-Background Electroformed Copper • Can be easily formed into thin, low-mass parts • Recent designs reduce MCu/MGe x5 • UG Electroforming can reduce cosmogenics • Pre-processing can reduce U-Th • Recent results suggest cleaner than thought Electroformed cups shown have wall thickness of only 250 mm!

21. Conclusions • Unprecedented confluence: • Enrichment availability/Neutrino mass interest/ Underground facility development • High Density: • Modest apparatus footprint, no special lab required • Low Risk: • Proven technology/ Modular instrument / Relocatable • Experienced and Growing Collaboration • long bb track record, many technical resources • Neutrino mass sensitivity: • potential for discovery

22. Thank You NDM03, Nara