Status of theLEGEND experiment
Lomonosov conference
20 Aug 2021
Mariia Redchuk on behalf of the LEGEND collaboration

2

What I want you to remember about

What I want you to remember about LEGEND

3LEGEND = Large Enriched Germanium Experiment for Neutrinoless double beta Decay
1. Neutrinoless double beta decay (0νββ)- create matter without antimatter- lepton number violation- not observed yetnp
W

–W–

νnM

e–e–p

2. Enriched germanium detectors- leading material for 0νββ searches- excellent energy resolution- topological discrimination
3. The LEGEND experiment- indeed large- aims to observe 0νββ in germanium- or push the lower limit on decay half-life- synergy with other neutrino physics experiments
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

4?
Neutrinoless double beta decay
np
e–

W–

νM
Wn–e–pNeutrinoless double beta decay

erumb rved!
nn
leptoot conse rn
atte mmetry!
mtiasyer-anmattBeta decay
npW

Double beta decay (2νββ)
neνNeutrinoless double beta decay (0νββ)np
Wn––eeW–pp
W

ν
ν–eM

ν
76

Ge → 76Se + 2e- [ + 2νe ]nW–ep

Dirac neutrino

Majorana neutrinoν ≠ νν = νIn nature
we only observe
νL and νR

That’s because
they are simply justνL and νR

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk5

Some neutrino physics

6

Neutrino oscillation

Neutrino mixing matrix

flavor change during propagation

mathematical formalism & measurable parameters
new mixing matrixeμτνeνμντee
τeμνequmantu

νμate
propagin spacediceνeν1ν1νeνeν2ν2νμν3ν3na pMajorahasesinteractweakly

Neutrino mass ordering
which mass state is the lightest?

tioncetdecesour

matrixmixingNormalOrdering
(NO)

ντ

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Inverted
Ordering(IO)

Back to neutrinoless double beta decay
Neutrino physics point of viewatrix ases)
mgni
mix orana ph(MajMajorana mass7

Experimental point of view
0νββ signature
suexpo0νββexperiments

Decay half-lifezero background regime

mlightest = ν3
=testlighmmassordering
experiments

ν1

recosmology&neutrino
mass
experiments

vedobsertseven

1σ sensitivity
in presence of background

Connection

droun
gkc
ba
index

nt
ce factor lear matrix elemecphase spaunLomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

yenergution
resol

8✔

?

Neutrinoless double beta decay

Germanium experiment technology

npe–W–νMWn–e–pGermanium detectors

9risetime

amplitude

n+
5000V

76

Ge (depleted)mirror charge on the p+contact → signal●

groundp+●

germanium crystal → semiconductor●

implanted p+ and n+ contacts → diode●crystal fully depleted

particles deposit energy in thecrystal●

reconstruct energy based on
the pulse risetime andamplitude●

electron-hole pairs drift towards
respective contacts●

germanium serves as both detector andsource of 2νββ/0νββ
●76similar trajectories due to E field
profile → position-independet●Ge → 76Se + 2e- [ + 2νe ]Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

ficonroectdetonstiagur

Germanium detectors

10

GERDA experiment (2019)

Spectrum before analysis cutsWindow around Qββ is blinded!
Qββ(76Ge) = 2039.061 ± 0.007 keV

Background index is computed basedon the rest of the spectrum

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Germanium detectors

11

Pulse shape discrimination

signal-like

multi-site

p+ contact

n+ contactLomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Germanium experiments

12sSiPMalopticfibers

GERDA experimentatryostcr
ALo+ vetldr shieetaw(n, γ) renkov+ Che tor (μ)
deteces of Ggnir
ts
tors
detec

PMTs
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Germanium experiments

13All analysis cuts
Quality cuts
● Muon veto
● LAr vetoDetector anti-coincidence● Pulse shape discrimination●GERDA experiment●GERDAexperiment

World leading background index

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Energy resolution

Germanium experiments
GERDA

14

MAJORANA Demonstrator

LEGEND-200 goalmass

44.2 kgmass

29.7 kgmass

200 kgexposure

100 kg yr

exposure

75 kg yr

exposurebkg idx(5.2±1.6)·10-4 cts/(keV kg yr)

bkg idx(4.7±0.8)·10-3 cts/(keV kg yr)

bkg idxx101000 kg yr ↑ x2.5↓
2·10-4 cts/(keV kg yr)

resolution(2.6 ± 0.2) keVresolution(2.53 ± 0.08) keV

resolution

2.5 keV

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

LEGEND-1000 goalmass

1000 kgexposure

x1010 000 kg yr 0↑bkg idx

x510-5 cts/(keV kg yr) 0↓

resolution

2.5 keV✔

✔

?

Neutrinolessdouble beta decay

Germanium
experiment technology

Status of theLEGEND experiment

npe–

W–νM
W

n–e–

p15

LEGEND baseline design

Laboratori Nazionali del Gran Sasso

16

LEGEND-200

LEGEND-1000

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

deepe

largest undergroundresearch centerst underground laboratorycalesr
foLEGEND timeline

17

LEGEND timeline and status
Detector characterization
Transfer of GERDA
infrastructure to LEGEND
9Nov 201

0Feb 202

Preconceptual Design Reportfunding process initiated0
Aug 202

1Aug 202
Jul 2021

9Oct 201

End of GERDA Phase II

LEGEND-200
commissioning
2025
fall 202

Post-GERDA test
@ LNGS, Italy
infrastructure● GERDA, MAJORANA andnew detectors● readout electronics and DAQ● 1 month of physics data &calibrations● ΔE = 2.2 keV @ QE = 2.2 keV @ Qββ●Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

1[LEGEND-1000]

LEGEND prospects in 0νββ
Virtually background free!
freeUnambiguous discovery
even with a handful of counts

18

In case of no discovery,
push lower limit
2 orders of magnitude above current best

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

LEGEND prospects in 0νββ19Discovery potentialLimit settingexposu0↑ rex 10dounrgkbac x x50↓indebackground free regime
massordering
experiments

mlightest = ν3
L1000
L200=testlighν1m

GERDA
Majorana

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

LEGEND goalcosmology&neutrino
mass
experiments

What else can LEGEND do?
Alternative 0νββ mechanisms
Long-range mechanisms e.g. light Majorana
neutrino
Short-range mechanisms = heavy particles●
SUSY particles e.g. gluions or squarks●
right-handed currents with heavy neutrinos
or scalar fields e.g. Higgs●...
Multiple mechanisms at the same time could bepossible
LEGEND can probe short-range mechanisms
beyond what other experiments can do20

Other Beyond Standard Model searches
Fermionic Dark Matter
Fractionally Charged Cosmic-rays
Majoron emission
Exotic Fermion Emission in 0νββ decay
Lorentz violation
Exotic Currents in 2νββ decay

Solar axions
WIMP searches
Bosonic Dark Matter

Electron Decay
Pauli Exclusion Principle
Violation+ BSM physics in 36Ar (ECEC)
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Baryon decayWhat I want you to remember about LEGEND

21LEGEND = Large Enriched Germanium Experiment for Neutrinoless double beta Decay
1. Neutrinoless double beta decay (0νββ)- create matter without antimatter- lepton number violation- not observed yetnp
W

–W–

νn

M

e–
e–

p

2. Enriched germanium detectors- leading material for 0νββ searches- excellent energy resolution- topological discrimination
3. The LEGEND experiment- indeed large- aims to observe 0νββ in germanium- or push the lower limit on decay half-life- synergy with other neutrino physics experiments
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

More about LEGENDLEGEND website
https://legend-exp.org

22

LEGEND Preconceptual Design Reporthttps://inspirehep.net/literature/1892243

Chat with me during the coffee breakContact me if you have questions
mariia.redchuk@pd.infn.it
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

23

THANK YOU!
9 countries • 47 institutions • 260 members

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

24Backup

Dirac vs Majorana neutrino

25“But if ν = ν, does that mean ν can participate in inverse beta decay?„
For Majorana, there is no such thing as ν, just ν, what matters is helicity
DiracMajorana
yes

yes

never

yes but ~0% chancenever
yes but ~0% chance-----

Dirac: so far, we have only observed νL and νR
Majorana: they are simply just νL and νR
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia RedchukDirac vs Majorana neutrino

Dirac: so far, we have only observed νL and νR
Majorana: they are simply just νL and νR
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

26

Neutrino observables

27

Effective Majorana mass
“Incoherent sum” of νe mass eigenstates(“mass of electron neutrino”)
Sum of neutrino masses
cosmological/astrophysical observable

LEGEND goal

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia RedchukTwo-neutrino and neutrinoless double beta decay
35 naturally occurring isotopes which can decay
through 2νβ-β- with forbidden or suppressed βdecay●Only 6 for 2νβ+β+, small Q values and much
longer livetimes●

Limits by present-generation experiments

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk28

Alternative mechanisms for 0νββLong-range mechanisms e.g. light Majorana neutrino
Short-range mechanisms = heavy particles
SUSY particles e.g. gluions or squarks● Right-handed currents with heavy neutrinos or scalar fields e.g. Higgs● ...
●Multiple mechanisms at the same time could be possible
Let’s see if we observe 0νββ!
Possible to see in LHC and determine
dominant (short-range) mechanism

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

29Germanium detectors

30

e- do not contribute much since they drift through avolume of low field strength● n+ → diffused lithium, p+ → ion-implanted boron● >105 e-h pairs / MeV●

PPCup to 1 kg

BEGe

< 1 kgLomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

ICPCup to 3 kgLonger drift times→ optimal PSD

Waveforms

31

Pulse on the p+ contact(simulation)

DAQ waveform(characterization data)

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

Pulse shape analysis

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

32

Pulse shape discrimination
Fits in 30-keV slices– SSE– MSE– total...
→ obtain μ and σ for each slice for each detector
Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk

33The LEGEND experiment

limit setting

34

signal discovery
all Inverted Ordering
region is covered!

L1000

L1000

L200
GERDA
Majorana

L200
GERDA
Majorana

Lomonosov conference • Aug 2021 • Status of the LEGEND experiment • Mariia Redchuk