Majorana Neutrinoless Double-Beta Decay Experiment

GERDA Collaboration Meeting

June 28, 2005

Dubna, Russia

Brown University, Providence, Rhode IslandInstitute for Theoretical and Experimental Physics, Moscow, RussiaJoint Institute for Nuclear Research, Dubna, RussiaLawrence Berkeley National Laboratory, Berkeley, CaliforniaLawrence Livermore National Laboratory, Livermore, CaliforniaLos Alamos National Laboratory, Los Alamos, New MexicoOak Ridge National Laboratory, Oak Ridge, TennesseeOsaka University, Osaka, Japan

Pacific Northwest National Laboratory, Richland, WashingtonQueen's University, Kingston, OntarioTriangle Universities Nuclear Laboratory, Durham, North Carolina and Physics Departments at Duke University and North Carolina State UniversityUniversity of Chicago, Chicago, IllinoisUniversity of South Carolina, Columbia, South CarolinaUniversity of Tennessee, Knoxville, TennesseeUniversity of Washington, Seattle, Washington

The Majorana 76Ge 0-Decay Experiment

• Based on Ge crystals– 180 kg 86% 76Ge– Enriched via centrifugation

• Modules with 57 crystals each– Three modules for 180 kg– Eight modules for 500 kg!

• Maximal use of copper electroformed underground

• Background rejection methods– Granularity– Pulse Shape Discrimination– Single Site Time Correlation– Detector Segmentation

• Underground Lab– 6000 mwe– Class 1000

57 Detector Module

Veto Shield

Sliding Monolith

LN Dewar

Inner Shield

Conceptual Design of 57 Crystal Module

• Conventional vacuum cryostat made with electroformed Cu• Three-crystal tower is a module within a module• Allows simplified detector installation & maintenance• Low mass of Cu and other structural materials per kg Ge

CapCap

Tube (0.007” wall thickness)Tube (0.007” wall thickness)

Ge(62mm x 70 mm)Ge(62mm x 70 mm)

Tray(Plastic, Si, etc)Tray(Plastic, Si, etc)

Cold PlateCold Plate

1.1 kg Crystal 1.1 kg Crystal

Thermal Shroud

Vacuum jacketVacuum jacket

Cold Finger

Bottom Closure1 of 19 Towers

40 cm x 40 cm Cryostat

Shield Design

• Allows modular deployment, early results• 40 cm bulk Pb, 10 cm ULB shielding• 4 veto shield• Sliding 5 ton doors (prototype under ME test)

Veto Detector

Sliding Monolith

LN Dewar

Inner Shield

57 Detector Module

Veto Detector

Sliding Monolith

LN Dewar

Inner Shield

57 Detector Module

Background Goals and Demonstrated Levels

• Simulation connects activity to expected count rate• Background target: ~1 count/ROI/ton-year• Three years’ run time with this level (~0.5 ton-year) ~5 x 1026 y

BkgLocation

Purity IssueActivation

RateTarget

ExposureRef.

Ge Crystals 68Ge & 60Co1

atom/kg/day100 d [Avi92]

Target Mass

Target PurityAchieved

Assay

Inner Mount

232Th

2 kg

1 Bq/kg 2-4 Bq/kg

[Arp02]&

more recentwork

Cryostat 38 kg

Cu Shield 310 kg

Small Parts 1 g/crystal 1 mBq/kg 1 mBq/kg [Mil92]

Ge Exposure Timeline

• Conservative estimate of 100 days exposure taken• Doubling this or spallation rate (1 atom/kg/day @

surface) adds only 3% to total rateProcess Step Minimum

EstimatedTime

Effective Time(with shield)

Enrichment: (ECP Zelenogorsk) ~90 days ~1 day

Shipping: Zelenogorsk to Oak Ridge

32 days 3.2 days

Production of metal and initial refinement:

11 days 11 days

Manufacturer’s zone refinement 14 days 14 days

Crystal growth: 4 days 4 days

Mechanical preparation 3 days 3 days

Detector Fabrication 7 days 7 days

Total 161 days 44.2 days

Shipping Concept: 2m cube

Storage Concept: 4m cube

Granularitydetector-to-detector rejection

• Simultaneous signals in two detectors cannot be 0

• Requires tightly packed Ge

• Successful against:– 208Tl and 214Bi

• Supports/small parts (~5x)• Cryostat/shield (~2x)

– Some neutrons– Muons (~10x)

• Simulation and validation with Clover

~ 40 cm

Pulse Shape Discrimination

• Excellent rejection for internal 68Ge and 60Co (x4)

• Moderate rejection of external 2615 keV (x0.8)

• Shown to work well with segmentation

• Demonstrated capability– Central contact

– External contacts

• Requires ~25 MHz BW

Central contact (radial) PSD

Time Correlations

• 68Ge is worst initial raw background– 68Ge -> 10.367 keV x-ray, 95% eff– 68Ga -> 2.9 MeV beta

• Cut for 3-5 half-lives after signals in the 11 keV X-ray window reduces 68Ga spectrum substantially

• Independent of other cuts

No cut

3 , 5 t1/2 cut

QEC = 2921.1

Crystal Segmentation

• Segmentation– Multiple conductive contacts– Additional electronics and

small parts– Rejection greater for more

segments• Background mitigation

– Multi-site energy deposition• Simple two-segment rejection• Sophisticated multi-segment

signal processing

• Demonstrated with– GEANT4 (MaGe) calculations– MSU experiment

60Co

(“Low” Energy)

(“High” Energy)

Segmentation Study Experiment and Simulation

60Co on the side of the detector

Simple multiplicity cuts – No PSD

Experiment

GEANT

Crystal

1x8

4x8

Cou

nts

/ ke

V /

106

deca

ys

Crystal

1x84x8

Ultra-Pure Electroformed Cu

• Th chain purity is key– Ra and Th must be eliminated– Successful Ra ion exchange [C]– Th ion exchange under

development

• Demonstrated >8000 Th rejection via electroplating from A->B

• Starting stock [A] <9 Bq/kg 232Th

• Intensive development of assay to achieve 1 Bq/kg 232Th of A, B, and C, and, possibly much less– Based on ICPMS of nitric etch soln– Would allow QA of each part

Electroforming copper

A B

C

A B

C

30 cm x 30 cm Cryostat30 cm x 30 cm Cryostat

Small Parts: Low-background Front-end Electronics Package

LFEP

Material Mass (grams)

Circuit Board (PTFE, Cu, Au)

0.32974

JFET 1.5E-4

RhO2 Resistor 5.9E-4

Al wirebond wire

~2E-5

Silver-Loaded Epoxy

~1E-4

ORTEC LFEP3 (IGEX)

LFEP4

Design DriversAnalog Performance Needed for PSD

• Commercial digital spectroscopy hardware used for current PNNL PSD has 40 MHz, 14-bit digitization

• Sampling rate is good match with “easily-achievable” HPGe preamp bandwidth

Full-energy 1621-keV (top) and 1592-keV DEP (bottom) reconstructed current pulses from 120% P-type

Ortec HPGe detector (experimental data)Response of Ortec HPGe 237P preamplifier

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

An old demonstrated result with 12 bit 40 MHz digitization rate

228Ac1587.9 keV

DEP of 208Tl

1592.5 keV

212Bi1620.6 keV

Keeps 80% of the single-site DEP (double escape peak)Rejects 74% of the multi-site backgrounds (use 212Bi peak as conservative indicator)

Experimental Data

Original spectrum

Scaled PSD

result

Previous Front-End Results

Detector typeRise-time with pulser input (10%-90%)

Commercial HPGe detector, 30% relative efficiency, Princeton Gamma-Tech.

30.0 ns

Low-background detector and cryostat with original IGEX cooled FET assembly, 30% relative efficiency.

43.0 ns

Low-background detector and cryostat with final IGEX cooled FET assembly, 30% relative efficiency.

37.5 ns

IGEX low-background detector and cryostat with original cooled FET assembly and internal wiring.

70 ns

IGEX low-background detector and cryostat with final IGEX cooled FET assembly and Beldin type 8700 coaxial cable for signal connections.

32.5 ns

Rise-times for various experimental configurations. The pulser rise-time for these tests was ~15 ns.

All tests used PGT RG-11 as preamp back-end

Disasters Do Happen

• We didn’t really like that FET anyway…

Punishment for yielding 120 ns 10% - 90% performance

Current LFEP Module Performance(2N4356 FET w/92cm leads)

input powe

r

output

power

input pulse

output

pulse

25 MHz

40 ns 10-

90%

Background Goals

Gross and Net Rates for Important Isotopes

Total Est. Background

(per t-y)

Background Source

Counts in ROI per t-y Counts in ROI 68Ge 60Co Germanium Gross 2.54 1.22

Net 0.01 0.02 0.03 208Tl 214Bi 60Co

Gross 0.12 0.03 0.26 Inner Mount Net 0.01 0.00 0.00 0.01

Gross 0.77 0.16 0.58 Cryostat Net 0.22 0.04 0.00 0.26

Gross 2.28 0.30 0.02 Copper Shield Net 0.64 0.06 0.00 0.70

Gross 0.18 0.04 0.34 Small Parts Net 0.02 0.01 0.00 0.03

muons

cosmic activity

(,n)

Gross 0.03 1.33 0.003

External Sources

Net 0.003 0.18 0.003 0.18 2-decay < 0.01

TOTAL SUM 1.21

Dominated by 232Th in Cu

At this level, we might not get a count in a 3 year run!

Cuts vs. Background Estimates

0

2

4

6

8

10

12

14

16

Raw 0vbb Final 0vbb Raw Granularity PSD SSTC Segmentation

Co

un

ts /

RO

I /

ty

0vbb

External

Small parts

Cu Shield

Cryostat

Inner Mount

Crystals

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

RawConstruction

Raw Granularity Segmentation PSD TimeCorrelation

External

Small parts

Cu Shield

Cryostat

Inner Mount

Crystals

Construction vs. Operations

0

2000

4000

6000

8000

10000

12000

0 365 730 1095 1460 1825 2190 2555 2920

kg/quarter

atoms 68

68Ge build up and decay

Ops Begins

80% of total 68Ge has decayed

Majorana Sensitivity vs. Time

• 180 kg 86% 76Ge operated for 3 years• 0.46 t-y of 76Ge or 0.54 t-y total Ge

Effect of background

0 cts/ROI/ty: Ideal1 cts/ROI/ty: target8 cts/ROI/ty: certain(IGEX levels with new data cuts applied)

Used five 76Ge crystals, with a total of 10.96 kg of mass, and 71 kg-years of data.1/2 = 1.2 x 1025 y0.24 < mv < 0.58 eV (3 sigma)

A Recent Claim

Background level depends on intensity fit to other peaks.

Klapdor-Kleingrothaus H V, Krivosheina I V, Dietz A and Chkvorets O, Phys. Lett. B 586 198 (2004).

Expected signal in Majorana(for 0.456 t-y)

135 counts

With a background Goal: < 1 cnt in the ROI (Demonstrated < 8 cnts in the ROI)

Year 0 Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Year 11

Proposal/CD-0 Package

CD-0/Approve Mission Need

R&D module

Conceptual Design

Site Selection

CD-1/Approve Preliminary Baseline Range

Preliminary Design (PED)

CD-2/3a/Approve Baseline/Long-Lead Procurement

3a: Prepare and Ship Ge

Site Preparation

CD-3 Start Construction

Receive Ge

Fabricate Detectors

Electroforming Production Cryostats

Assemble Experimental Apparatus/Shielding

Assemble Detectors into Cryostat/Shield

Pre-Operational Testing

CD-4/Start of Operations

Full Detector Operations

Decommissioning

Reference Schedule

R&D Module

EnrichedGe

Module 1Testing

Module 2Testing

Module 3Testing

Operations

Construction

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

Majorana Sensitivity: Realistic runtime

GERDA Relationship

• GERDA Collaboration using 20 kg of existing (IGEX+HM) 76Ge crystals (Phase 1) and ~35kg new Ge (Phase 2) to achieve sensitivity past KKDC

• New approach for Phase 1 & 2 – Ge immersed in cryogen in large tank in LNGS

• Signed MOU to cooperate in early years and merge for unified ultimate thrust, using most effective technologies and concepts

• Continued careful cooperation and coordination very important!

GERDA P1 20 kg

GERDA P2 35 kg

Majorana 180 kg

Joint experiment ~1000 kg

Majorana Summary

• As in Gerda, backgrounds are key

• We have begun proposing a modular plan for intermediate (180 kg) scale with potential for expansion to ton scale

• The NuSAG Committee is expected to recommend a double-beta decay research plan by mid to late July

Brown University, Providence, Rhode IslandMichael Attisha, Rick Gaitskell, John-Paul Thompson

Institute for Theoretical and Experimental Physics, Moscow, Russia

Alexander Barabash, Sergey Konovalov, Igor Vanushin, Vladimir Yumatov

Joint Institute for Nuclear Research, Dubna, RussiaViktor Brudanin, Slava Egorov, K. Gusey, S. Katulina, Oleg

Kochetov, M. Shirchenko, Yu. Shitov, V. Timkin, T. Vvlov, E. Yakushev, Yu. Yurkowski

Lawrence Berkeley National Laboratory, Berkeley, CaliforniaYuen-Dat Chan, Mario Cromaz, Martina Descovich, Paul Fallon,

Brian Fujikawa, Bill Goward, Reyco Henning, Donna Hurley, Kevin Lesko, Paul Luke, Augusto O. Macchiavelli, Akbar

Mokhtarani, Alan Poon, Gersende Prior, Al Smith, Craig Tull

Lawrence Livermore National Laboratory, Livermore, CaliforniaDave Campbell, Kai Vetter

Los Alamos National Laboratory, Los Alamos, New MexicoMark Boulay, Steven Elliott, Gerry Garvey, Victor M. Gehman, Andrew Green, Andrew Hime, Bill Louis,

Gordon McGregor, Dongming Mei, Geoffrey Mills, Larry Rodriguez, Richard Schirato, Richard Van de Water,

Hywel White, Jan Wouters

Oak Ridge National Laboratory, Oak Ridge, TennesseeCyrus Baktash, Jim Beene, Fred Bertrand, Thomas V. Cianciolo,

David Radford, Krzysztof Rykaczewski

Osaka University, Osaka, JapanHiroyasu Ejiri, Ryuta Hazama, Masaharu Nomachi

Pacific Northwest National Laboratory, Richland, WashingtonCraig Aalseth, Dale Anderson, Richard Arthur, Ronald

Brodzinski, Glen Dunham, James Ely, Tom Farmer, Eric Hoppe, David Jordan, Jeremy Kephart, Richard T. Kouzes, Harry Miley,

John Orrell, Jim Reeves, Robert Runkle, Bob Schenter, Ray Warner, Glen Warren

Queen's University, Kingston, OntarioMarie Di Marco, Aksel Hallin, Art McDonald

Triangle Universities Nuclear Laboratory, Durham, North Carolina and Physics Departments at Duke University and

North Carolina State UniversityHenning Back, James Esterline, Mary Kidd, Werner Tornow,

Albert Young

University of Chicago, Chicago, IllinoisJuan Collar

University of South Carolina, Columbia, South CarolinaFrank Avignone, Richard Creswick, Horatio A. Farach, Todd

Hossbach, George King

University of Tennessee, Knoxville, TennesseeWilliam Bugg, Yuri Efremenko

University of Washington, Seattle, WashingtonJohn Amsbaugh, Tom Burritt, Jason Detwiler, Peter J. Doe, Joe Formaggio, Mark Howe, Rob Johnson, Kareem Kazkaz, Michael

Marino, Sean McGee, Dejan Nilic, R. G. Hamish Robertson, Alexis Schubert, John F. Wilkerson

The Majorana Collaboration