Two Neutrino Double Beta (2 ) Decays into Excited States · 2016. 6. 17. · Two Neutrino Double...

Two Neutrino Double Beta (2νββ) Decays into Excited States

Björn LehnertTU-Dresden, Germany

Carleton University, Canada

International School of Subnuclear Physics54th Course: The new physics frontiers in the LHC-2 eraErice, 17/06/2016

neutron number N

prot

on n

umbe

r Z

Neutrinoless Double Beta (0νββ) Decay

76Ge: 2039 keV

2⌫�� : (Z,A) ! (Z + 2, A) + 2e� + 2⌫̄e0⌫�� : (Z,A) ! (Z + 2, A) + 2e�

(T1/2 = 1.9 x 1021 yr)

(T1/2 > 2.1 x 1025 yr)in 76Ge

- Lepton Number Violation (LNV)- Neutrinos are Majorana particles- Indication of neutrino masswww.nndc.bnl.gov2

Erice, 17/06/16 Bjoern Lehnert 2νββ into Excited States

http://www.nndc.bnl.gov

Standard Mechanism of 0νββ Decay

• Nuclear Matrix Elements (NME) are model dependent and have large theoretical uncertainties (factor 2 - 3)

• Conversion of T1/2 into neutrino mass dominated by uncertainty of NME calculation

measured half-life

effective Majorana

neutrino mass

phase space factor

nuclear matrix element

2⌫�� :⇣T 2⌫1/2

⌘�1= G2⌫ · |M2⌫ |2

0⌫�� :⇣T 0⌫1/2

⌘�1= G0⌫ · |M0⌫ |2 · |mee|2

atomic physics nuclear physics particle physics

arXiv:0812.0479v2 (2009)

mlightest [eV]3

Erice, 17/06/16 Bjoern Lehnert 2νββ into Excited States

light Majorana Higgs triplet SUSY particle right handed currents

Non-Standard Mechanism of 0νββ Decay

• If 0νββ decay is discovered, the LNV mechanism is not clear• Other approaches e.g. LHC• 0νββ observation in multiple isotopes can help to disentangle the mechanism• Strong motivation for different DBD experiments / isotopes• NMEs have to be knows precisely

Possible processes (not exhaustive ) PHYSICAL REVIEW D 83, 113003 (2011)

4Erice, 17/06/16 Bjoern Lehnert 2νββ into Excited States

Improvement of Nuclear Matrix Elements

2⌫�� :⇣T 2⌫1/2

⌘�1= G2⌫ · |M2⌫ |2

0⌫�� :⇣T 0⌫1/2

⌘�1= G0⌫ · |M0⌫ |2 · |mee|2

76Ge

76Se0+

2+1

0+12+2

Qββ=2039.1 keV

0 keV

559.1 keV

1122.3 keV1216.1 keV

559.1

563.2

1216

.1

657.0

64%

36%

2039.1 keV

76As2- 26.3 h

0+

• Measurement of 2νββ decays allow direct test of NME calculations


• Decays into excited states give an additional possibility to test NME calculations and can constrain nuclear model parameters (gA, gpp in QRPA)

• So far 2νββ 0+1 transition discovered in 100Mo (1995) and 150Nd (2004)

76Ge

76Se

76As

0+

2+1

0+12+2

2- 26.3 h

Qββ=2039.1 keV

0 keV

559.1 keV

1122.3 keV1216.1 keV

559.1

563.2

1216

.1

657.0

64%

36%

1480.0 keV

822.0 keV916.8 keV

0+

2⌫�� :⇣T 2⌫1/2

⌘�1= G2⌫ · |M2⌫ |2

0⌫�� :⇣T 0⌫1/2

⌘�1= G0⌫ · |M0⌫ |2 · |mee|2

Improvement of Nuclear Matrix Elements


• Use ratio of NME and PSF which cancels some uncertainties (e.g. gA)

• Then scale with measured ground state T1/2

• Direct theoretical calculation with various nuclear models • Often very inconsistent

2νββ Excited States: Overview

Experimental approaches:


LAr cryostat

HPGe detector

array

water tank

clean room lock system

GERDA = Germanium Detector Array

Phase I:• Nov. 2011 till May 2013

Phase II:• Since Dec. 2015

HPGe detectors in liquid argon (LAr): Shielding, cooling, active scintillation veto


Low background experiment: Reducing environmental radioactivity

Laboratori Nazionali del Gran Sasso in Italy

1400m overburden (3500 m.w.e.)muon flux suppressed by factor 106L’Aquila

outside labunderground labs

GERDA


most probable transition

experimental sensitivity reaches

predictions

Theoretical predictions for 2νββ 0+1Best previous experimental result: 2νββ 0+1: T1/2 > 6.2·1021 yr nuclear model year T1/2

HFB 1994 1.3·1021 yrQRPA 1994 4.0·1022 yrQRPA 1996 4.5·1022 yrQRPA 1996 7.5·1021 yrQRPA 1997 (1.0 - 3.1)·1023 yrQRPA 2014 (1.2 - 5.8)·1023 yrIBM-2 2014 6.4·1024 yrShM 2014 (2.3 - 2.6)·1024 yr

Analysis: 76Ge 2νββ Decay into Excited States

JETP Lett. 72 (2000)


Phase I data set: 2700 2-detector events2-Detector coincidences

2νββ

most probable transition

experimental sensitivity reaches

predictions



Background Monte Carlo


Signal Monte Carlo (Geant4)

• Cut and count analysis (background from sidebands)• Signal selection cuts:

• 1 of 2 detector has one of the ɣ-energies• Other detector above certain threshold

• Background rejection cuts:• Excluding background ɣ-lines (42K, 214Bi, 108mAg)

• Select only detector-detector pairs which contribute to sensitivity• Tuning “ad-hoc” cut parameters to maximize sensitivity


Background Monte Carlo


• Cut and count analysis (background from sidebands)• Signal selection cuts:

• 1 of 2 detector has one of the ɣ-energies• Other detector above certain threshold

• Background rejection cuts:• Excluding background ɣ-lines (42K, 214Bi, 108mAg)

• Select only detector-detector pairs which contribute to sensitivity• Tuning “ad-hoc” cut parameters to maximize sensitivity


Signal Monte Carlo (Geant4)

• 5 events in signal region, 8.5 events expected • No signal observed• Detection efficiency 0.91%, exposure 22.3 kg·yr • Lower half-life limit: T1.2 > 3.7·1023 yr (90% CL)

signal- region

sideband region for

background evaluation

background model

all 2-detector- events



Theoretical predictions for 2νββ 0+1Experimental results


nuclear model year T1/2HFB 1994 1.3·1021 yr

QRPA 1994 4.0·1022 yrQRPA 1996 4.5·1022 yrQRPA 1996 7.5·1021 yrQRPA 1997 (1.0 - 3.1)·1023 yrQRPA 2014 (1.2 - 5.8)·1023 yrIBM-2 2014 6.4·1024 yrShM 2014 (2.3 - 2.6)·1024 yr

decay mode T1/2 (90% CL)

2νββ 2+1 >1.6·1023 yr

2νββ 0+1 >3.7·1023 yr

2νββ 2+1 >2.3·1023 yr

J. Phys. G: Nucl. Part. Phys. 42 (2015) 115201

• Half-life limits improved by 2 orders of magnitude• Most old NME calculations excluded for 0+1 mode

• Sensitivity in Phase II of T1/2 > 1024 yr for 0+1 mode


Conclusions

• 0νββ decay tests LNV and Majorana nature of neutrinos• Standard interpretation: Dominant light Majorana neutrino exchange

• Access to neutrino mass (mee)• Non-standard interpretation: Other LNV processes dominant or mixture

• NMEs crucial to connect T1/2 and mee (or LNV parameter)• Currently large uncertainties for NMEs (factor 2-3)• Improvement with 2νββ decay measurements (ground or excited states)

• Analysis for 76Ge with GERDA Phase I data• 2 orders of magnitude improvement• Many older NME calculations excluded

• New generation of 0νββ will soon discover more 2νββ 0+1 transitions


Backup

18

Cosmology

Beta-decay

Neutrinoless DBD

KATRIN, MARE, EchoLimit: m < 2.3 eV (model independent)

Planck, LSST, ...Limit: m < 0.28 eV (model dependent)

GERDA, EXO, KamLAND-ZEN, ...Limit: m < 0.14 - 0.38 eV (model dependent)

Experimental Overview of Neutrino Masses

19

Schechter Valle

• Standard process: Light Majorana neutrino exchange• There are also other lepton number violating processes that can trigger 0νββ• Schechter-Valle theorem:If 0νββ exists, it can always be interpreted as a neutrino Majorana mass term • Contribution of Majorana mass terms to neutrino mass might be very small

20

NME

only 1+: only GT

all states: GT + Fermi

21

decay final state particles candidates2νβ-β- (Z,A) → (Z+2,A) + 2e- + 2ν 35

2νECEC (Z,A) + 2e- → (Z-2,A) + 2ν 342νβ+EC (Z,A) + e- → (Z-2,A) + e+ + 2ν 192νβ+β+ (Z,A) → (Z-2,A) + 2e+ + 2ν 6

-

Other DBD Isotopes

Isobar A=76

ZnGa

AsGe

protons Z

Se

Rb

Brm

ass

exce

ss (M

eV)

Kr

Sr

22

Effective neutrino mass:

Beyond SM process(particle physics)

matrix element(nuclear physics)

phase space factor(atomic physics)

(only for dominant light Majorana neutrino exchange)

DBD Isotopes

0νββ half-life (mee = 1eV)

PHYSICAL REVIEW C 87, 014315 (2013)

2⌫�� :⇣T 2⌫1/2

⌘�1= G2⌫ · |M2⌫ |2

0⌫�� :⇣T 0⌫1/2

⌘�1= G0⌫ · |M0⌫ |2 · |mee|2

23

0νββ Global Picture

24

Sensitivity: (for Gaussian background)

Advantage 76Ge:• Well known HPGe detector technology• Excellent energy resolution O(0.1%)• Intrinsic low background (Semiconductor)

Sensitivity and Experimental Approaches

Disadvantages 76Ge:• Expensive enrichment (7.8% to 87%)• Difficult to scale• Q-value < 2614 keV of 208Tl

25

The$GERDA$Collabora0on$

ITEP%Moscow%

Kurchatov%%Ins3tute%

16$ins0tu0ons$~100$members$

h5p://www.mpi

GERDA TimelineCommissioning

very early GERDA spectrum

mini-shrouds (MS)

Test with HV potentials on

MS• Larger 42Ar contribution than expected• 1.5 years of commissioning to understand and mitigate 42K background

• Conclusion: • 42K is charged and attracted by HV• Installation of mini-shroud in Phase I

Phase IIPhase I Transition to Phase II

Dec 2015May 2013Nov 20112010

27

High Purity Germanium (HPGe) Detectors

• standard technology since 1980s• 76Ge intrinsic in germanium 7.8%• 76Ge enrichment to 87%• very good energy resolution 0.1%

28

High Purity Germanium Detectors

Semi-coaxial Ge detector:• Standard design for gamma spectroscopy • Major detector for Phase I• Large up to 3 kg• Thick n+ electrode ≈2 mm

Broad Energy Ge (BEGe) detector:• Major detector for Phase II• Small around 600 g• Thin n+ electrode

100Mo 0+1

• 2.6 kg of enriched metallic 100Mo• 600 cm3 HPGe detector• 3.3% efficiency @ 540 keV• Exp [2]: T1/2 = 7.5±1.2·1020 yr• QRPA: T1/2 = (1.6 - 2.2)·1021 yr • IBM-2: T1/2 = 2.2·1022 yr

• Gammas: 539.5 keV and 590.8 keV • [1] First discovered in 1995 by Barabash et al.: Phys. Lett. B, vol. 345, pp. 408–413 (1995)• [2] Latest measurement by NEMO-3 Collaboration: Nucl. Phys. A, vol. 925, pp. 25–36 (2014)

[2]

30

150Nd 0+1• Gammas: 333.9 keV and 406.5 keV• [1] First discovered in 2004 by Barabash et al.: JETP Lett., vol. 79, pp. 10–12 (2004)• [2] Latest measurement by Barabash et al.: Phys. Rev. C, vol. 79, no. 4, p. 045501 (2009)

[2]

[2]

• 3 kg of natural Nd2O3 (153 g 150Nd)• HPGe: 2.3% efficiency @ 334 keV• [2]: T1/2 = 1.33+0.63-0.36·1020 yr• IBM-2: T1/2 = 1.9·1021 yr

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CUORICINO: 130Te

• 11.3 kg of TeO2 bolometers• ɣ: 536 keV and 1257 keV; β 1.3·1023 yr [Phys. Rev. C 85 045503 (2012)]• QRPA: T1/2 = (0.5 - 1.4)·1023 yr • IBM-2: T1/2 = 2.2·1025 yr

EXO-200: 136Xe

• 80 kg liquid enriched Xe TPC• Complicated analysis without segmentation • ɣ: 761 keV and 819 keV; β: 1.2·1023 yr [PhD Thesis Yung-Ruey Yen (2013)]• IBM-2: T1/2 = 2.5·1025 yr

single site multi siteϵ=0.5% ϵ=3.0%

ϵ=1.3%Future CUORE19 towers x 13 floors

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