The Large Enriched Germanium Experiment for
Neutrinoless
Decay

SEARCH FOR THE NEUTRINOLESSDOUBLE BETA DECAY WITH GERDA
AND LEGEND
Legend-200 Preliminary Design Report

LAURA BAUDISUNIVERSITÄT ZÜRICH
LEGEND-200 Preliminary Design Report for the NSF
Submitted: June 1, 2018

UNIVERSITY OF TOKYOOCTOBER 9, 2019

2

INTRODUCTION: NEUTRINOS(SOME) OPEN QUESTIONS IN NEUTRINO PHYSICS▸ What is the absolute mass of neutrinos?
▸ Are neutrinos their own antiparticles?

nuclear▸ These can be addressed with an extremely rare FUNDAMENTAL
are fundamental particles, whic
decay process: the double beta decay Neutrinos
means that—like quarks and photons andelectrons—they cannot be broken down inany smaller bits.

+ 2
Nucleus A

Nucleus Be

Elektrons+

2⌫(Anti)Neutrinos

3

INTRODUCTION: NEUTRINOS

THE DOUBLE BETA DECAY▸ Predicted by Maria-Goeppert Mayer in 1935
▸ The SM decay, with 2 neutrinos, was observed in 14 nuclei▸ T1/2 > 1018 y; 48Ca, 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 128Te, 130Te, 136Xe, 150Nd, 238U
2⌫
Rate

(A, Z+1)(A, Z)

0⌫(A, Z+2)

Sum energy of the two electronsaspects of neutrinos is that they don’t pickjust one flavor and stick to it. They oscillate
between all three.

ment has succeeded in measuring them. The
masses of other fundamental particles comefrom the Higgs field, but neutrinos might get
their masses another way.

INTRODUCTION: NEUTRINOS

4

THE NEUTRINOLESS DOUBLE BETA DECAY▸ Can only occur if neutrinos have mass and if they are theirown anti-particles; ΔL = 2
DIVERSEMYSTERIOUS

VERY MYSTERIOUS

Neutrinos are created in many processes innature. They are produced in the nuclear
reactions in the sun, particle decays in the
Earth, and the explosions of stars. They arealso produced by particle accelerators andin nuclear power plants.

Neutrinos are mysterious. Experiments seemto hint at the possible existence of a fourth
type of neutrino: a sterile neutrino, which wouldinteract even more rarely than the others.

Scientists also wonder if neutrinos are theirown antiparticles. If they are, they could haveplayed a role in the early universe, right after
the big bang, when matter came to outnumber
antimatter just enough to allow us to exist.

▸ Expected signature: sharp peak at the Q-value of the decayInterested in how the universe works? Read symmetry, an online magazine about particle physics
and its connections to life and other areas of science. Published by Fermi National Accelerator
Laboratory and SLAC National Accelerator Laboratory. symmetrymagazine.org

0⌫
T1/2

Rate

2⌫

> 1024 y

n
νc
ν

0⌫

n
Sum energy of the two electrons

p
ee-

p

5

INTRODUCTION: NEUTRINOS

OBSERVABLE DECAY RATE
Phase
space
factor0⌫<latexit sha1_base64="1w0kwc9+Uj8yrOkgIEd5oaw7smM=">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</latexit>

AxialvectorccNME|hm i|40⌫ 2= 0⌫ = G ⇥ gA ⇥ |M | ⇥
2
T1/2
m
e
Can beDifficult:
1

2

0⌫

calculated: ~ Q5

factor 2-3▸ With the effective Majorana neutrino mass:|hm<latexit sha1_base64="JS2COrAjd/Qi5juqfmz6d6q1nOM=">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</latexit>222i| = |Ue1
m1 + Ue2
m2 ei(↵1 ↵2 ) + Ue3
m3 ei( ↵1 2 ) |▸ a coherent sum over mass ES, with potentially CP violating phases▸ a mixture of m1, m2, m3, proportional to U2

6

INTRODUCTION: NEUTRINOS
Rep. Prog. Phys. 80 (2017) 046301

PHASE SPACE AND MATRIX ELEMENTS"

bottom, a
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= 0⌫ = G (Q, Z)|M |= 0⌫ = G (Q, Z)|M |decay ha
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Rep. Prog. Phys. 80 (2017) 046301
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Matrix elements: vary by a factor of 2- 3 for a given A
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Figure 5. Top panel: nuclear matrix elements (M 0ν) for 0νββ decay
betterrandcalJonathan Engel and Javier
Menéndez
Rep. Prog.
046301 A. All the plotted results
ticle
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as2017a functionofPhys.
mass80number(T ) = G M

m %
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2

7

INTRODUCTION: NEUTRINOSEMPLOYED NUCLEI
Candidate

Q [MeV]

Abund [%]

• Even-even nuclei

48Ca -> 48Ti

4.271

0.187

• Natural abundance is low (except 130Te)

76Ge -> 76Se

2.039

7.8

82Se -> 82Kr

2.995

9.2

96Zr -> 96Mo

3.350

2.8

100Mo -> 100Ru

3.034

9.6

110Pd -> 110Cd

2.013

11.8

116Cd -> 116Sn

2.802

7.5

124Sn -> 124Te

2.228

5.64

130Te -> 130Xe

2.530

34.5

136Xe -> 136Ba

2.479

8.9

150Nd -> 150Sm

3.367

5.6

• Must use enriched material(A, Z+1)(A, Z)(A, Z+2)

February 21, 2013

16:18

WSPC/146-MPLA

S0217732313500211

5–10

0⌫ 4
0⌫ 2 |hm i|= G gA |M |
0⌫
T1/2
m2e

1

ISOTOPES AND SENSITIVITY TO THE DECAY

2<latexit sha1_base64="JqVqVTIpb+b3VTEyTFa/EhCxR3s=">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</latexit>▸ Isotopes have comparable sensitivities in terms of rates per unit mass
Empirical Survey ofDouble Beta Decay Matrix Elements
2 uncertainty|M|NeutrinolessNA 0⌫
4
gA ln(2)GAm2ew.worldscientific.com
or personal use only.

8

INTRODUCTION: NEUTRINOS

gA4 uncertaintyNeffective value for the axial
vector coupling constantgA: ~ 0.6 - 1.269 (free(0) nucleon value)

4
4A
Fig. 1. Mod.
Regionsin theR. G. H. Robertson,
Phys. Lett.
A28 renormalized(2013) 1350021specific phase-space gA H0ν = gA ln(2) Am2e G0ν and matrix
2

9

INTRODUCTION

EXPRIMENTAL REQUIREMENTS▸ Experiments measure the half-life, with a sensitivity (in the caseof non-zero background)0⌫
T1/2 / a · ✏ ·

r

M ·t
B· E

Minimal requirements:
large detector masses
high isotopic abundance
ultra-low background noise
good energy resolution

hm

i/ q

1
0⌫
T1/2

Additional tools to distinguish signal frombackground:

event topology
pulse shape discrimination
particle identification

EXPERIMENTAL TECHNIQUES

Heat

CUORE
CUPID

Energy of thetwo electrons
GERDA
MAJORANALEGEND
SuperNEMO

ChargeLight

KAMLAND-Zen
SNO+

nEXO, NEXTDARWIN(not a complete list)

10

EXPERIMENTAL TECHNIQUES

MAIN CHALLENGES▸ Energy resolution (ultimate background from 2νββ-decay)▸ Backgrounds▸ cosmic rays & cosmogenic activation▸ radioactivity of detector materials (238U, 232Th, 40K, 60Co,
etc: α, β, γ-radiation)▸ anthropogenic (e.g., 137Cs, 110mAg)▸ neutrinos:⌫+e !⌫+e<latexit sha1_base64="nuVYcTH/MPD/BQVRYP4ff3jGgNE=">AAACCHicdVDLSgMxFM34rPVVdenCYBEEcci0xXZ2RTcuK9gHdGrJpGkbmskMSUYpQ5du/BU3LhRx6ye4829MH4qKHrhwOOde7r3HjzhTGqF3a25+YXFpObWSXl1b39jMbG3XVBhLQqsk5KFs+FhRzgStaqY5bUSS4sDntO4PzsZ+/ZpKxUJxqYcRbQW4J1iXEayN1M7seSKGR5BeHUNPsl5fYynDG/iltjNZZLulkosKENkFhArFnCF513VPEHRsNEEWzFBpZ968TkjigApNOFaq6aBItxIsNSOcjtJerGiEyQD3aNNQgQOqWsnkkRE8MEoHdkNpSmg4Ub9PJDhQahj4pjPAuq9+e2PxL68Z626plTARxZoKMl3UjTnUIRynAjtMUqL50BBMJDO3QtLHEhNtskubED4/hf+TWs528nbuopAtn87iSIFdsA8OgQOKoAzOQQVUAQG34B48gifrznqwnq2XaeucNZvZAT9gvX4AbVWYWQ==</latexit>

11

12

COSMIC BACKGROUNDSGO UNDERGROUND▸ Network of undergroundlaboratories

Muon flux [ cm-2 s-1]

10-6

10-7

10-8

Kamioka
SoudanY2L
BoulbyLNGS

XENON100

LSM
SURF

GERDA

LVD
XENON1T

10-9

10-10
1

Borexino
OPERA

SNOLAB
Jin-Ping
2

3

4

5

Depth [ km w.e]

6

7

13

COSMOGENIC BACKGROUNDSAVOID EXPOSURE TO COSMIC RAYS

Jungfraujoch, 3454 m▸ Spallation reactions can produce longlived isotopes▸ Activate and compare with predictions(Activia, Cosmo, etc)

Differential ratekeV -1 day-1]s)]Differential
rate[counts[counts/(keV

10-5

L. Baudis et al., Eur. Phys. J. C75 2015

OFHC copper, pre-activation
OFHC copper, post-activation

58

Co

10-6

Co

Mn

+ -

(e e )

56

Co
46

10-8

Co

46

-7

Sc

48

V

56

Sc

56

10

Copper - after 1 y at
the “top of Europe”

54
56

Co

60

Co

60

59

Fe

Co

48

V

59

Fe

40

56

K

Co

Before
500

1000

1500
Energy [keV]

2000

2500

14

BACKGROUNDS AND SCREENING

MATERIAL SCREENING AND SELECTION
Gator HPGe detector at LNGS

▸ Ultra-low background,
HPGe detectors▸ Mass spectroscopy▸ Rn emanation facilities

L. Baudis et al., JINST 6, 2011

Photosensors
226Ra/228Th: ~1 mBq/PMT
110mAg (T

1/2 = 249.8 d):

up to 1 mBq/PMT

Background
XENON collaboration, EPJ-C 75 (2015) 11

15

DOUBLE BETA DECAY EXPERIMENTS

CURRENT STATUS OF THE FIELD▸ No observation of this extremely rare nuclear decay (so far)▸ Best lower limits on T1/2: 1.07x1026 y (136Xe), 0.9x1026 y (76Ge), 2.7x1024 y (130Te)

0.07 eV  |hm<latexit sha1_base64="+KiSWHR6zPrCNNWSeVDL10Dxhbk=">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</latexit>i|  0.16 eV▸ Running and upcoming experiments (a selection)▸ 130Te: CUORE, SNO+
▸ 136Xe: KAMLAND-Zen, KAMLAND2-Zen, EXO-200, nEXO, NEXT, DARWIN▸ 76Ge: GERDA Phase-II, Majorana, LEGEND (GERDA & Majorana + new groups)▸ 100Mo AMoRE, LUMINEU; 82Se: LUCIFER, CUPID = CUORE with light read-out▸ 82Se (150Nd, 48Ca): SuperNEMO16

GERDA AND LEGENDSEARCH FOR THE NEUTRINOLESS DECAY OF 76GE
▸ HPGe detectors enriched in 76Ge
▸ Source = detector: high detection efficiency▸ High-purity material: no intrinsic backgrounds▸ Semiconductor: energy resolution σ/E < 0.1% at
Qββ (2039.061 ± 0.007 keV)

dN / dE▸ High stopping power: β absorbed within O(1) mm

σ(E) / E = 2.5%

σ(E) / E = 0.5%

σ(E) / E = 0.1%

0ν
2ν
-6
T 1/2 / T1/2 = 10

0ν
2ν
-6
T 1/2 / T1/2 = 10

0ν
2ν
-6
T 1/2 / T1/2 = 10

2ν ββ

2ν ββ

1

σ/E = 2.5%

2ν ββ
0ν ββ

0ν ββ
0.95

0ν ββ

0.95
E / Qββ1σ/E = 0.5%

0.95
E / Qββ1σ/E = 0.1%

E / QββMAJORANA, GERDA AND LEGEND
RATOR

17

FIG. 5. Extended Data Fig 1n HPGe detectors andmodel

EXISTING AND FUTURE GERMANIUM EXPERIMENTSLEGEND-1t
Goal: T1/2 ~ 1 x 1028
y (90% CL)dLocation: tbd

dergroundResearch Facility
MAJORANA at SURF
29.7 kg of 88% enriched
76Ge crystals
2.5 keV FWHM at 2039 keV

GERDA at LNGS
FIG. 6. Extended Data Fig 2

35.6 kg of 86% enriched
76Ge crystals
3.0 keV FWHM at 2039 keV

26 kg y exposure; PRL 120(2018)

58.9 kg y exposure;published in Science 2019

T1/2 > 2.7 x 1025 y (90% CL)

T1/2 > 0.9 x 1026 y (90% CL)

LEGEND-200 at LNGS
200 kg of 76Ge crystals at LNGS
Goal: 1 tonne year exposure
Goal: T1/2 ~ 1 x 1027 y (90% CL)
Start in 2021

18

SMALL HISTORICAL EXCURSION

THE HEIDELBERG-MOSCOW EXPERIMENT▸ Detectors in conventional shield: five 76Ge detectors, mass 10.96 kg▸ Concept to operate directly in cryogenic liquid: Genius - now GERDA

Limits on the Majorana neutrino mass in the 0.1 eV range,
L. Baudis et al., Phys. Rev. Lett. 83, 1999

A first “bare” HPGe detector
GENIUS background and technical studies:
L. Baudis et al, NIM A 426 (1999)

Heidelberg-Moscow detector inconventional shieldSensitivity

T1/2 > 1.6 ⇥ 1025 y 90% C.L.
<latexit sha1_base64="133xiA0JvC7XaiGHbbUYQC7FL3Y=">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</latexit>

19

GERDA OVERVIEWTHE GERDA EXPERIMENT▸ Liquid Ar (64 m3) as coolingmedium and shielding,surrounded by 590 m3 of ultrapure water as muon Cherenkov
veto▸ U/Th in LAr < 7x10-4 µBq/kg▸ A minimal amount ofsurrounding material▸ Phase I: 2011-2014▸ Phase II: 2015-2019

GERDA collaboration, EPJ C78 (2018) no.5

20

GERDA OVERVIEWTHE GERDA PHASE II PROJECT▸ Seven string with 40 detectors (30 BEGe*, 7 coaxial, 3 natural coaxial -> enriched IC)▸ Liquid argon veto, equipped with optical fibres and SiPMs, plus 2 arrays of 3-inch PMTs
8

▸ Science run started in December 2015
▸ Summer 2018: central string replaced with enriched, inverted coaxial detectors
FIG. 5. Extended Data Fig 1

FIG. 6. Extended Data Fig 2* GERDA collaboration, Characterisation of 30 76Ge enriched Broad Energy Ge detectors for GERDA Phase II; arXiv:1901.0650

21

16 INSTITUTES, 132 MEMBERS

THE GERDA COLLABORATION
INR
Moscow

ITEP
Moscow

Kurchatov
Institute16 INSTITUTES, 132 MEMBERS

THE GERDA COLLABORATIONCOLLABORATION MEETING IN ZURICH, JUNE 201922

DETECTORSGERDA PHASE-II DETECTORSGERDA!Phase!II!experimental!setup!at!LNG• BEGe and coaxial• p+ electrodes:• 0.3 μm boron implantation

25-50 mm65-80 mmp+ electrode(read-out)
0V• n+ electrodes:

n+ electrode3-4 kV

Coaxial

New!thickHwindow!BEGe!
detectors!

• Low-mass detector holders (Si,Cu, PTFE)

70-110 mm• 1-2 mm lithium layer(biased up to +4.5 kV)

BEGep-typeGe60-80 mm

Extended Data Fig. 2. Cross section through the germanium detector types (left) and the correspon
p+ electrode is made by a ⇠0.3 µm thin boron implantation. The n+ electrode is a 1-2 mm thick lit
biased with up to +4500 V. The electric field drops to zero in the n+ layer and hence energy depositio

DETECTORSGERDA PHASE-II DETECTORS
Germanium!Phase!II!detector!array!
▸ 7 strings, 40 detectors in total:▸ 7 semi-coax (15.8 kg), 30 BEGe (20 kg), 3 nat semi-coax (7.6 kg) s

Replaced withinverted coax inspring 2018(upgrade)

25

OVERVIEW

PHASE II DATA TAKING
100 kg y, end 2019}
Start Dec 2015

Upgrade58.9 kg y unblind

24.9 kg y in
May 2019 blindOVERVIEW

26

BACKGROUND SUPPRESSION▸ Event topology + anti-coincidence between HPGe
detectors + pulse shape discrimination + liquid argon vetoevent topology

GERDA PHASE II

27

2.5

ENERGY CALIBRATIONCounts / 5 keV

2
600

800 1000

10

8

10

7

10

6

10

5

583 keV▸ Three low neutron-emission 228Th sources in SIS, deployed once every week
861 keV1079 keV

104

893 keV

727 keV785 keV

763 keV▸ FWHM at Qββ: (3.0 ± 0.1) keV for BEGe, (3.6 ± 0.1) keV for coaxial detectors

Custom-made 228Th sources3
encapsulated in stainless steel, on
2 years of calibrations
tantalum holders

10

500

Two position determination systems

1000

L. Baudis et al., JINST 10 (2015) no. 12

GERDA PHASE II

28

2.5

ENERGY CALIBRATIONCounts / 5 keV

2
600

800 1000

10

8

10

7

10

6

10

5

583 keV▸ Three low neutron-emission 228Th sources in SIS, deployed once every week103

861 keV1079 keV

104

893 keV

727 keV785 keV

763 keV▸ FWHM at Qββ: (3.0 ± 0.1) keV for BEGe, (3.6 ± 0.1) keV for coaxial detectors

2 years of calibrations

500

1000

GERDA BACKGROUND DATAENERGY SPECTRA▸ Intrinsic 2νββ-events, 39Ar, 42Ar (Τ1/2 = 33 y) and 85Kr in liquid argon▸ 60Co, 40K, 232Th, 238U in materials, α-decays (210Po) on the thin p+ contact

GERDA collaboration, arXiv:1909.02522

GERDA BACKGROUND DATABACKGROUND MODEL▸ Intrinsic 2νββ-events, 39Ar, 42Ar (Τ1/2 = 33 y) and 85Kr in liquid argon

104

Qββ ± 25 keV

3

10

Enriched detectors - 60.2 kg⋅yr
Bi + 208Tl

214

K

60

Data

Model

212

2νββ

40

42

K

Bi + 214Pb

228

Ac

Co

210

Po

GERDA 19-07

counts / 5 keV▸ 60Co, 40K, 232Th, 238U in materials, α-decays (210Po) on the thin p+ contact

102
10
1
10−1

counts / 5 keV

10−2
103
102
10
1
10−1
10−2
1000

2000

GERDA collaboration, arXiv:1909.02522

3000

4000

5000
energy [keV]GERDA BACKGROUND DATAGERDA collaboration, Nature 544 (2017) 47

PULSE SHAPE DISCRIMINATION▸ Cut based on 1 parameter: max of current pulse (A) normalised to total energy (E) (BEGe)▸ Tuned on calibration data (90% 208Tl DEP acceptance)

Charge (E)Qββ50p+ surface (α)

Single-site

0Multi-site

events after liquid argon (LAr) vetoevents after LAr veto and A/E cut

Counts / 15 keV

− 50

10

PSD parameter: (A/E -1)/σA/E

3enriched BEGe - 30.8 kg⋅yr
after LAr veto and A/E cut

102

50 keV blinding

Mean and resolution corrected for E-dependance
A/E normalised to 1

10

Accept events around (A/E -1)/σA/E =0

1
1000

Current (A)GERDA 18-06(A/E - 1) / σA/E

▸ Acceptance at 0νββ: (87.6±2.5)%

2000

3000

4000

5000
Energy (keV)GERDA BACKGROUND DATALIQUID ARGON VETO
▸ Anti-coincidence with signals in PMTs and SiPMs (0.5 p.e. threshold)▸ Acceptance at 0νββ: (97.7±0.1)%

GERDA PHASE IIGERDA collaboration, Science 365, Sept 2019

DOUBLE BETA DECAY RESULTS▸ Measured T1/2 of the 2νββ-decay: 1.92 x 1021 y▸ LAr veto: factor 5 background suppression at 1525 keV (42K line)▸ Background level: 5.6 x 10-4 events/(keV kg y) in 230 keV window around Q-value
New constraints on the0νββ-decay of 76Ge
0⌫T1/2
> 0.9 ⇥ 1026 y (90%C.L.)m< 0.110.26 eV (90%C.L.)

Median sensitivity0⌫
T1/2> 1.1 ⇥ 1026 y (90%C.L.)GERDA collaboration, Science 365, Sept 2019

GERDA RESULTS

MASS OBSERVABLES▸ Constraints in the mββ parameters space in the 3 light ν scenario▸ GERDA + leading experiments in the fieldm<latexit sha1_base64="e4oNFlI+NN1eQ5LH6bpH7i1Mpjc=">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</latexit>

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NEW DETECTORS IN GERDAUPGRADE: INVERTED COAXIAL DETECTORS▸ Large point-contact detectors with ~ 3 kg mass, excellent PSD performance▸ First 5 enriched IC detectors installed in spring 2018; baseline for LEGENDR.J Cooper et al.,
NIM A 665 (2011) 25

Detector mass
increase: 35.6 kg ->44.2 kg
FWHM at Qββ [keV]: 4.2±0.1 coax; 2.7 ± 0.1 BEGe; 2.9±0.1 IC

BEYOND GERDA

THE LEGEND EXPERIMENT▸ Large enriched germanium experiment forneutrinoless double beta decay

The Large Enriched Germanium Experiment for
October 2016 Decay▸ Collaboration formed inNeutrinoless▸ 2019 members, 48 institutions, 16
Legend-200 Preliminary Design Reportcountries▸ LEGEND-200: 200 kg in existing(upgraded) infrastructure at LNGS
▸ Background goal: 0.6 events/(FWHM t y)
▸ LEGEND-1t: 1000 kg, staged▸ Background goal: 0.1 events/(FWHM t y)

BEYOND GERDALEGEND-200▸ 200 kg HPGe in existing (upgraded)infrastructure at LNGSThe Large Enriched Germanium Experiment for
Neutrinoless
Decay& GERDA &▸ Ge detectors from Majorana
new inverted coaxials

Legend-200 Preliminary Design Report▸ Background reduction: factor 5compared to GERDA (reduce 42K, 214Bi,
208Tl background)▸ Discovery sensitivity:
0⌫27
T1/2 > 10 y

BEYOND GERDALEGEND-200▸ Existing GERDA infrastructure sufficient (800 mm cryostat neck)

The Large
Enriched Germanium Experiment for& feedthroughs▸ New lock system, new cabling
NeutrinolessDecayof theof the Plastic Slide
228Wearing
systemsMeasurementwith multiple
Th sources▸ 19 string, 4 calibrationPrecision

Legend-200
Design Report
I expected movingPreliminary
distance
during the lifetime, assuming
an overestimated 16 m/run:
1 run/week ⇥ 52 week/year ⇥5 year ⇥ 16 m/run = 4160 m

I let the steel band go overthe plastic slide for a total
about 4 km
I measure weight change ofthe slide with 10 5 g
precision scale
I tests is ongoing, willcomplete on Wednesday,
October 9, 2019

GERDA AND LEGENDEXPECTED SENSITIVITY▸ LEGEND-200: 1027y▸ LEGEND-1t: 1028 y▸ mββ = 17 meV (for worst
case ME = 3.5)

LEGEND-1t

Predicted range for 17 meV
LEGEND-200

GERDA

Background
Abgrall et al., The large enriched germanium
experiment for neutrinoless double beta decay. AIP
Conf. Proc. 1894(1), 020027 (2017)

GERDA:
3 events/(ROI t y)
LEGEND-200: 0.6 events/(ROI t y)
LEGEND-1t: 0.1/(ROI t y)

GERDA AND LEGENDTIME SCALE
2018

2019

2020

2021

2022

2023

GERDA (100 kg yr)
MAJORANA (75 kg yr)
LEGEND-200 Purchase Isotope
Fabricate Detectors
Develop/Install New Lock,
Experimental Apparatus

Integration/
Commissioning

LEGEND-200 Data Runs, Goal: 1 t yr (~5-7 y)
Ton-Scale Down-Select Process
LEGEND-1000 Design/Build, ~6yrs, 2021-2027

Earliest LEGEND-1t Data Start: 2025/6

L. BAUDIS: SEARCH FOR THE NEUTRINOLESS DOUBLE BETA DECAY WITH GERDA AND LEGEND; UNIVERSITY OF TOKYO, OCT 2019

SUMMARY▸ Ton-scale experiments are required to probe the IMO scenario▸ 76Ge experiments: excellent resolution and very low background levels▸ GERDA will reach 100 kg y by the end of 201927
▸ LEGEND-200 on track to start in 2021; LEGEND-1t being designed
0.08

3𝜎

70 meV

Current experiments

m𝛽𝛽 (eV)

0.06
2𝜎
0.04

ℐℋ

Future, ton-scale experiments

0.02

10 meV
0.20

𝒩ℋ
0

1𝜎

0.05

2𝜎
0.10

3𝜎
(95% CL)0.15
Σcosm (eV)0.20

OF COURSE, “THE PROBABILITY OF
SUCCESS IS DIFFICULT TO ESTIMATE,
BUT IF WE NEVER SEARCH, THE CHANCEOF SUCCESS IS ZERO”
G. Cocconi & P. Morrison, Nature, 1959

ADDITIONAL MATERIALRESULTSGERDA AND OTHER EXPERIMENTSGERDA DATAGERDA BACKGROUNDS▸ Background levelsin the 3 detector
types before & after
various cuts

BEGe

Coax

IC

LEGEND-200

46

GERMANIUM DETECTOR PRODUCTION▸ GeO2 material from Urenco and ECP▸ Reduction/refinement processing at PPM; diode fabrication: Mirion & Ortec▸ Detector type: p-type IC detectors [R.J. Cooper et al., NIM A 665 (2011)] Li outerelectrode, B implantation for p+ contact▸ Large active mass up to 3 kg
▸ Excellent pulse shape discrimination performance▸ Lower surface to volume ratio▸ Reduced background due to lower number of channels per mass of 76Ge
▸ Production started early 2019, ~60 detectors expected by fall 2021

LEGEND-200

BACKGROUND EXPECTATION
Monte Carlo simulations
based on experimental data
and material assays.
Background rate after anticoin., PSD, LAr veto cuts.
Assay limits correspond to
the 90% CL upper limit. Greybands indicate uncertainties
in overall backgroundrejection efficiency

Qββ BI ≤ (0.7–2.)x10-4 events/(keV kg yr) = 0.2-0.5 events/(FWHM t yr)

LEGEND-200

BACKGROUND EXPECTATION
Monte Carlo simulations
based on experimental data
and material assays.
Background rate after anticoin., PSD, LAr veto cuts.
Assay limits correspond to
the 90% CL upper limit. Greybands indicate uncertainties
in overall backgroundrejection efficiency

Qββ BI ≤ (0.7–2.)x10-4 events/(keV kg yr) = 0.2-0.5 events/(FWHM t yr)

LEGEND-1T

BACKGROUND GOAL
▸ LEGEND-200 background: ~ equal contributions of U/Th, 42Ar, surface α
before analysis cuts
▸ LEGEND-1000: background lower by ~ x6 than LEGEND-200.
▸ U/Th: reduced by optimising array spacing, minimising opaque materials,
larger detectors, better light collection, cleaner materials, improved active
suppression▸ 42Ar: eliminated by using underground sourced Ar▸ Surface α: reduced by improved process control (hypothesis Rn in air at
detector fabrication facility)▸ Larger detectors have a better surface to volume ratio▸ Higher isotope fraction is now cost effective.

DETECTORSGERDA PHASE-II DETECTORSBEGe detectors

GERDA collaboration, arXiv:1901.0650

IC detectors

R.J. Cooper et al., NIM A 665 (2011) 25-32

DETECTORSGERDA PULSE SHAPE DISCRIMINATION(YHQWW\SHVθUD\• Signal-like: Single Site Events (SSE)ηη• Background-like: Multiple Site
Events (MSE)• BEGe detectors: E-field andweighting potential has special
3XOVHVKDSHV
shape: pulse-heightnearly3XOVHVKDSHV
independent of position

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.η

3RĮ

Ɣ 6LJQDOLVDVLQJOHVLWHHYHQW 66(

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Ɣ 'LVFULPLQDWLRQXVLQJWKHHOHFWURQLFVLJQDOVIURPWKHFU\VWD$-=VLJPRQG'3*)U×KMDKUVWDJXQJ0×QVWHUDETECTORSGERDA PULSE SHAPE DISCRIMINATION• A/E: amplitude of the current pulse over energy• Multiple energy depositions: multiple peaks in current pulse => decreasing A/E• p+ surface events: shorter signals => higher A/E$(SDUDPHWHU

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(3-&  TEXTCOSMOGENIC ACTIVATION FOR LEGEND▸ 77Ge production: n-capture by 76Ge
▸ 77Ge: T1/2 = 11.3 h; Qβ-= 2.7 MeV▸ 77mGe: T1/2= 53 s; Qβ-= 2.86 MeV▸