1. The Majorana Project: A Next- Generation Neutrino Mass Probe Craig Aalseth for The 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, Russia A. Barabash, S. Konovalov, V. Stekhanov, V. Umatov Joint Institute for Nuclear Research, Dubna, Russia V. Brudanin, S. Egorov, O. Kochetov, V. Sandukovsky Lawrence Berkley National Laboratory, Berkley, CA Paul Fallon, I. Y. Lee Lawrence Livermore National Laboratory, Livermore, CA Kai Vetter Los Alamos National Laboratory, Los Alamos, NM Steve Elliott, Andrew Hime New Mexico State University, Carlsbad, NM Joel 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, WA Harry 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, IL Juan Collar, University of South Carolina, Columbia, SC Frank 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 76 Ge: Endpoint = 2039 keV – Energy above many contaminants – Except: 208 Tl, 60 Co, 68 Ge… FWHM = 3-4 keV around 2 MeV (~0.2%) Long experience with Ge  decay – Previous efforts found 2 at T 1/2 ~10 21 y – Expect 0 at T 1/2 ~ 4 x 10 27 y Ready to go! – Essentially no R&D needed

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

6. Majorana Reference Concept 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 3-D model of reference configuration Segmentation (6x2) results in 2500 individual 200g segments 210 2.35 kg crystals

7. Starting Background Estimate International Germanium Experiment (IGEX) achieved between 0.1-0.3 counts/keV/kg/y Documented experiences with cosmic secondary neutron production of isotopes Calculated Experimental [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 0  -decay of 76 Ge

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

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

11. PSD can reject multiple-site backgrounds (like 68 Ge and 60 Co) 228 Ac 1587.9 keV DEP of 208 Tl 1592.5 keV 212 Bi 1620.6 keV Keeps 80% of the single-site DEP (double escape peak) Rejects 74% of the multi-site backgrounds (use 212 Bi peak as conservative indicator) Improves T 1/2 limit by 56% Experimental Data Original spectrum Scaled PSD result

12. Detector Segmentation 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

13. 0  efficiency = 91% internal 60 Co efficiency = 14% Improves T 1/2 limit by 140% Monte-Carlo Example (single crystal) Sensitive to z and phi separation of depositions Segment multiplicity at 2039 keV 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% 76 Ge Fast Production: 200 kg/y (No ramp) Present  76 Ge T 1/2 limit rapidly surpassed (T 1/2 > 1.9 10 25 y) 0  Half-Life Based on early IGEX background levels with reasonable background reduction and cutting methods applied

15. Examples of signal intensity T 1/2 = 1 10 26 y 28 counts 1000 kg-y T 1/2 = 1.5 10 25 y 95 counts 50 kg-y

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

17. Progress and Status SEGA: 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 Figure-Of-Merit vs. Axial & Azimuthal Segmentation for internal 60 Co background SEGA crystal initial test cryostat

18. Progress and Status MEGA: 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

19. Recent Crystal Packaging Test (MEGA)

20. Progress and Status Ultra-Low Level Screening Screening facility – Operating in Soudan (Brown U) Some contamination issues… 207 Bi – 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

21. Progress and Status Low-Background Electroformed Copper Can be easily formed into thin, low-mass parts Recent designs reduce M Cu /M Ge 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  m!

22. 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  track record, many technical resources Neutrino mass sensitivity: – potential for discovery

23. Thank You NDM03, Nara