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Published on December 10, 2007

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The Majorana Project: A Next-Generation Neutrino Mass Probe:  The Majorana Project: A Next-Generation Neutrino Mass Probe Craig Aalseth for The Majorana Collaboration http://majorana.pnl.gov APS Neutrino WG Meeting, Pasadena, California February 28, 2004 The Majorana Collaboration:  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 Yuen-Dat Chan, Martina Descovich, Paul Fallon, Reyco Henning, Kevin Lesko, Augusto Macchiavelli, Akbar Mokhtarani, Alan Poon, Craig Tull Lawrence Livermore National Laboratory, Livermore, CA Kai Vetter Los Alamos National Laboratory, Los Alamos, NM Ted Ball, Steve Elliott , Victor Gehman, Andrew Hime North Carolina State University, Raleigh, NC Jeremy Kephart, Ryan Rohm, Albert Young Oak Ridge National Laboratory, Oak Ridge, TN Cyrus Baktash, Thomas Cianciolo, Robert Grzywacz, David Radford, Krzysztof Rykaczewshi Osaka University, Osaka, Japan Hiro Ejiri, Ryuta Hazama, Masaharu Nomachi Pacific Northwest National Laboratory, Richland, WA Harry Miley (Project Director), Craig Aalseth, Ronald Brodzinski, Shelece Easterday, Todd Hossbach, David Jordan, Richard Kouzes, William Pitts, Ray Warner Queens University, Kingston, Canada Art McDonald, Aksel Hallin University of Chicago, Chicago, IL Juan Collar, Andrew Sonnenschein University of Tennessee, Knoxville, TN Yuri Efremenko University of South Carolina, Columbia, SC Frank Avignone, George King University of Washington, Seattle, WA Peter Doe, Kareem Kazkaz, R.G. Hamish Robertson, John Wilkerson Outline:  Outline Introduction and Overview Reference Concept Configuration Materials Backgrounds and Mitigation Pulse-Shape Discrimination Detector Segmentation Experiment Sensitivity Progress and Status Conclusions Germanium Basics:  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 Majorana Overview:  Majorana Overview GOAL: Sensitive to effective Majorana n mass near 50 meV 0n bb decay of 76Ge potentially measured at 2039 keV Based on well known 76Ge detector technology plus: Pulse-shape analysis Detector segmentation Requires: Deep underground location 500 kg enriched 86% 76Ge many crystals, segmentation Pulse shape discrimination Time/Spatial Correlation Special low-background materials Ge Acquisition:  Ge Acquisition Purchase enriched, intrinsic 76Ge ECP in Russia supplied previous experiments 86% enrichment Produced at 200 kg/y, delivered quarterly About 4 years of deliveries Need to do full market study Detector Fabrication:  Detector Fabrication Need to build about 50 kg of segmented detectors quarterly About 4-5 years of detector construction Would prefer to grow crystals and fabricate detectors underground Detector Configuration:  Detector Configuration Granularity, low passive mass, are goals Optimization underway of performance and risk Several low-risk designs possible for modular cryostats Many segmentation schemes possible and equally effective Nature of Ge crystals allows repackaging Low-Background Electroformed Copper:  Low-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! Passive Shielding:  Passive Shielding Inner Need about 5 tons of clean, ancient lead PNNL has identified most of this required need Outer About 60 tons of cleaned lead bricks Electroformed Cu will allow roof span External Active Shield:  External Active Shield Plastic scintillator and phototube will provide ~4p coverage 2-4” plastic scintillator May want alternating Pb/plastic layers to improve fast neutron tagging Majorana Reference Concept:  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 Starting Background Estimate:  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. Physics Motivation for Background Rejection:  Physics Motivation for Background Rejection Interaction multiplicity varies with energy, type of radiation Multiple interactions change shape of induced detector current G. F. Knoll. Radiation detection and measurement. John Wiley & Sons, Inc., second edition, 1989. Multi-site events Full-energy gamma signals >500 keV Sum-energy peak signals Single-site events Gamma signals <150 keV 72Ge(n, n’ e-) fast neutrons Double-escape peaks Internal beta-decay (no g) events Backgrounds: 68Ge:  Backgrounds: 68Ge Backgrounds: 60Co:  Backgrounds: 60Co Segmentation & Pulse-Shape Discrimination:  Segmentation & Pulse-Shape Discrimination Allow rejection of multiple-site interactions Effective against projected backgrounds Granularity Costs Money/Should be optimized Different Schemes Being Evaluated Segmented Large N-type Crystals Multiple Small P-type Crystals Segmented Large P-type Crystals Why Now is a good time for PSD….:  Why Now is a good time for PSD…. Commercial digital spectroscopy hardware is available with fast (40 MHz), high-resolution (14-bit) digitization Significant developments in pulse-shape discrimination techniques for HPGe have been made in the past 10 years and are ready to apply to new hardware Full-energy 1621-keV g (top) and 1592-keV DEP (bottom) reconstructed current pulses from 120% P-type Ortec HPGe detector (experimental data) Signal Background Single-site interaction example:  Single-site interaction example Monte-Carlo 2038-keV deposition from 0n bb-decay of 76Ge Multiple-site interaction example:  Multiple-site interaction example Monte-Carlo 2038-keV deposition from multi-Compton of 2615-keV 208Tl g Multi-Parametric Pulse-Shape Discriminator:  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 PSD can reject multiple-site backgrounds (like 68Ge and 60Co):  PSD can reject multiple-site backgrounds (like 68Ge and 60Co) Keeps 80% of the single-site DEP (double escape peak) Rejects 74% of the multi-site backgrounds (use 212Bi peak as conservative indicator) Improves T1/2 limit by 56% Experimental Data Original spectrum Scaled PSD result Detector Segmentation:  Detector Segmentation Sensitive to axial and azimuthal separation of depositions Example design with six azimuthal and two axial contacts in a 2-kg detector This segmentation gives ~2500 segments of 200 g (or 40 cm3) each Many segmentation schemes give equivalent good background rejection Monte-Carlo Example (single crystal):  0nbb efficiency = 91% internal 60Co efficiency = 14% Improves T1/2 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 Electronics:  Electronics Default plan is to use XIA digitizers. Other commercial options exist or are emerging. CAMAC/CPCI/etc. Underground Laboratory:  Underground Laboratory Would prefer NUSEL No “foreign” travel Less customs issues Very deep (fewer fast neutrons) Have had very positive interactions with SNOLab WIPP is available but not as deep as we prefer Sensitivity vs. Time:  Sensitivity vs. Time Slow Production: Gradual ramp to 100 kg/y - total 500 kg 85% 76Ge Fast Production: 200 kg/y (No ramp) Present 0nbb 76Ge T1/2 limit rapidly surpassed (T1/2 > 1.9 1025 y) 0nbb Half-Life Examples of signal intensity:  Examples of signal intensity T1/2 = 1 1026y 28 counts 1000 kg-y T1/2 = 1.5 1025y 95 counts 50 kg-y Collaboration Progress: Optimizations for Full Experiment:  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 Progress and Status SEGA: Segmentation Optimization:  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 underway (USC/PNNL) 40-fold-segmented LLNL detector now available Figure-Of-Merit vs. Axial & Azimuthal Segmentation for internal 60Co background SEGA crystal initial test cryostat Progress and Status Ultra-Low Level Screening:  Progress and Status Ultra-Low Level Screening Screening facility Operating in Soudan (Brown U) 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 Progress and Status MEGA: Cryogenic testing:  Progress and Status MEGA: Cryogenic testing Materials in hand Detectors (20 - 70% HPGe), electronics Assembly and cryogenic testing of two-crystal modules underway (PNNL, UW, NC State) Underground facility (WIPP) in prep (LANL, NMSU) FY 2004 installation anticipated Sensitive to ~104 short-lived atoms MEGA Infrastructure at WIPP:  MEGA Infrastructure at WIPP Steel sub-floor to support many-ton lead shields Cleanroom enclosure with antechamber entry Power, network connectivity MEGA Underground Site:  MEGA Underground Site MEGA will be installed in WIPP 2150 feet of overburden Q Room Alcove LANL providing underground clean room (Steve Elliott and Co.) Module Assembly & Testing:  Module Assembly & Testing (MEGA) Recent Crystal Packaging Test (MEGA):  Recent Crystal Packaging Test (MEGA) Conclusions:  Conclusions Reference Plan meets sensitivity goals Opportunities for enhancements exist Potential for discovery Unprecedented confluence: Enrichment availability/Neutrino mass interest/ Underground facility development High Density: Modest apparatus footprint, no special cavity required Low Risk: Proven technology/ Modular instrument / Relocatable Early results / Incremental deployment Experienced and Growing Collaboration Long bb track record, many technical resources End:  End Majorana and GENIUS:  Majorana and GENIUS If no signal seen: If background (i.e. within Ge mass), then: Leads to emphasis on enrichment balanced mass and time background rejection If we assume background is in structural materials only, B=bT then: Leads to emphasis on minimized structure increased natural mass decreased time Suppressing constants: “Majorana Approach” “GENIUS Approach” Evidence of 68Ge:  Evidence of 68Ge From: NIM A292 (1990) 337-342. Experimental data from two 1.05 kg natural detectors Integral of this spectrum equals integral of this peak. This peak decays with the right half life. Cosmogenics in Ge crystal account for ~all of early IGEX signals at 2039 keV:  Cosmogenics in Ge crystal account for ~all of early IGEX signals at 2039 keV ~70% = 68Ge ~10% = 60Co 77 d 71 d 271 d 5.2 y Early IGEX Data (Computed) From: Journal of Radioanalytical and Nuclear Chemistry, Articles, 193 1 (1995) 61-70 Background in Structural Materials:  Background in Structural Materials We (Jim Reeves) have improved the chemistry for electroformed Cu production U, Th progeny reduced substantially Plan to totally eliminate 60Co NIM A292 (1990) 337-342. Early work showing cosmogenics ~1995 to present Electroformed copper radiochemistry gains: H2SO4 Purity Recrystalized CuSO4 Barium scavenge Results: 226Ra <25 mBq/kg (< 1 part in 71019) (< 2.0 ppt 238U eq.) 228Th 9 mBq/kg (1 part in 31021) (2.2 ppt 232Th eq.) (From Brodzinski et al, Journal of Radioanalytical and Nuclear Chemistry, 193 (1) 1995 pp. 61-70) Worst case estimate today: non-cosmogenics not a show stopper Ge Cu Both What can we do to improve on this?:  What can we do to improve on this? Exploit the single-site (dbd) vs. multi-site (bkg) nature of energy deposition Pulse shape discrimination: works on “R” separation of depositions Segmentation: works on “Z” and/or “f” separation Minimize materials bkg Conventional but hi capacity cryostats <1/5 Cu per Ge as IGEX UG Electroforming Repeated purification Alternative cooling approaches Possibly UG crystal manuf. ~1980 ~1990 Experimental Examples:  Experimental Examples Commercial digital spectroscopy hardware is available with fast (40 MHz), high-resolution (14-bit) digitization Significant developments in pulse-shape discrimination techniques for HPGe have been made in the past 10 years and are ready to apply to new hardware Full-energy 1621-keV g (top) and 1592-keV DEP (bottom) reconstructed current pulses from 120% P-type Ortec HPGe detector (experimental data) Majorana and GENIUS Conclusion:  Majorana and GENIUS Conclusion Both (Maj & Gen) extreme views in background location (crystal and structural materials) are probably somewhat wrong Reducing structural mass is a good idea for Majorana PSD and segmentation help with structural background Structural background concentration can be reduced by UG electroforming (60Co and short lived cosmogenics) Multiple reagent purification steps Re-crystallizing and sub-boiling distillation Many GENIUS risks can be eliminated or minimized by clever design and operation Alternative Packaging:  Alternative Packaging Would boost crystal to crystal background suppression Could take advantage of new shielding opportunities Might use alternative cooling methods Would require methods for progressive commissioning and periodic maintenance <1m <1m Majorana DM Sensitivity Majorana dark matter sensitivity similar to and complementary with CDMS-II :  Majorana DM Sensitivity Majorana dark matter sensitivity similar to and complementary with CDMS-II Projected 95% C.L. Majorana for an assumed low-energy background of 0.005 counts/keV/kg/day, one order of magnitude lower than in present detectors Assumes ionization threshold of 1 keV, and SEGA and MEGA limits are < 1 kg-y Majorana limits are calculated for the total exposure of 5000 kg-y Dots represent plausible supersymmetric neutralino WIMP candidates Signal to noise analysis (SEGA MEGA) Annular Modulation (Majorana)

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