The Majorana Project: A Next-Generation Neutrino

Mass ProbeCraig Aalseth

for

The Majorana Collaboration

NDM03, Nara, JapanJune 9, 2003

The Majorana CollaborationBrown 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, NCEric Adles, Rakesh Kumar Jain, Jeremy Kephart, Ryan Rohm, Albert Young

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

Pacific Northwest National Laboratory, Richland, WAHarry Miley, Co-spokespersonCraig 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, WAPeter Doe, Victor Gehman, Kareem Kazkaz, Hamish Robertson, John Wilkerson

http://majorana.pnl.govhttp://majorana.pnl.gov

Outline

Introduction and OverviewReference Concept Backgrounds and Mitigation– Pulse-Shape Discrimination– Detector Segmentation

Experiment SensitivityProgress and StatusConclusions

Germanium Basics

“Internal Source Method” from Fiorini76Ge: Endpoint = 2039 keV– Energy above many contaminants– Except: 208Tl, 60Co, 68Ge…

FWHM = 3-4 keV around 2 MeV (~0.2%)Long experience with Ge decay– Previous efforts found 2 at T1/2 ~1021 y

– Expect 0 at T1/2 ~ 4 x 1027 y

Ready to go!– Essentially no R&D needed

Majorana OverviewGOAL: Sensitive to effective Majorana mass as low as 0.02-0.07 eV0-decay of 76Ge potentially measured at 2039 keVBased 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

n

n

p+ p+

e-

e-

e

Reference ConfigurationReference Configuration

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 configurationSegmentation (6x2) results in2500 individual 200g segments210 2.35 kg crystals

Starting Background Estimate

International Germanium Experiment (IGEX) achieved between 0.1-0.3 counts/keV/kg/yDocumented experiences with cosmic secondary neutron production of isotopes

Spallation Isotope

T1/2 (d) Rate from [Bro95]

After Construction

Rate During Experiment

Total in ROI

After PSD Rejection

After Seg Rejection

68Ge 270.82 0.1562 0.03702 3.93E-03 70.15 18.59 2.57 56Co 77.27 0.0238 0.00212 6.43E-05 1.15 0.30 0.04 60Co 1925.2 0.0177 0.01294 7.15E-03 127.55 33.80 4.66 58Co 70.82 0.0024 0.000202 5.60E-06 0.10 0.03 0.00

cts/keV/kg/y cts/keV/kg/y cts/keV/kg/y Counts Counts Counts

Total 0.2 0.0523 0.0112 198.95 52.72 7.28

Calculated

Experimental

[Bro95] R. L. Brodzinski, et al, Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 193, No. 1 (1995) 61-70.

Single-site interaction example

Monte-Carlo 2038-keV deposition from 0-decay of 76Ge

Multiple-site interaction example

Monte-Carlo 2038-keV deposition from multi-Compton of 2615-keV 208Tl

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)

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)

Improves T1/2 limit by 56%

Experimental Data

Original spectrum

Scaled PSD

result

Detector Segmentation

Sensitive to axial and azimuthal separation of depositionsreference design with six azimuthal and two axial contacts is low riskThis level of segmentation gives good background rejectionThis segmentation gives us ~2500 segments of 200 g or 40 cc

0 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

Sensitivity vs. TimeSlow Production: Gradual ramp to 100 kg/y - total 500 kg 85% 76Ge Fast Production: 200 kg/y (No ramp) Present 76Ge T1/2 limit rapidly surpassed (T1/2 > 1.9 1025

y)

0

H

alf

-Lif

e

Based on early IGEX background levels with reasonable background reduction and cutting methods appliedBased on early IGEX background levels with reasonable background reduction and cutting methods applied

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 detectorsAll enriched/segmentedMulti-crystal modules

1 to 5 Crystals

First enriched, segmented detector in testing!

Additional tests being planned for other segmented systems

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

Figure-Of-Merit vs. Axial & Azimuthal Segmentation

for internal 60Co background

SEGA crystal initial test cryostat

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 anticipatedSensitive to ~1e4 short-lived atoms

Recent Crystal Packaging Test(MEGA)

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

Progress and StatusLow-Background Electroformed

Copper

Can be easily formed into thin, low-mass partsRecent designs reduce MCu/MGe x5UG Electroforming can reduce cosmogenicsPre-processing can reduce U-ThRecent results suggest cleaner than thought

Electroformed cups shown have wall thickness of only 250 m!

ConclusionsUnprecedented 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

Thank YouNDM03, Nara