How to measure neutrinoless double-beta decay nuclear ...

42
How to measure neutrinoless double-beta decay nuclear matrix elements? Javier Menéndez University of Barcelona Neutrinos ElectroWeak interactions and Symmetries NEWS Colloquium 23 rd April 2021

Transcript of How to measure neutrinoless double-beta decay nuclear ...

Page 1: How to measure neutrinoless double-beta decay nuclear ...

How to measureneutrinoless double-beta decay

nuclear matrix elements?

Javier MenéndezUniversity of Barcelona

Neutrinos ElectroWeak interactions and SymmetriesNEWS Colloquium

23rd April 2021

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Nuclear matrix elements for new-physics searchesNeutrinos, dark matter studied inexperiments using nuclei

Nuclear structure physicsencoded in nuclear matrix elementskey to plan, fully exploit experiments

0νββ:(

T 0νββ1/2

)−1∝ g4

A

∣∣M0νββ∣∣2 m2

ββ

Dark matter:dσχNdq2 ∝

∣∣∣∑i

ci ζi Fi

∣∣∣2CEνNS:

dσνNdq2 ∝

∣∣∣∑i

ci ζi Fi

∣∣∣2M0νββ : Nuclear matrix elementFi : Nuclear structure factor

2 / 37

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Outline

0νββ decay: huge potential, great challenge

Nuclear structure data as test of 0νββ calculations

Double Gamow-Teller transitions and 0νββ decay

γγ transitions and 0νββ decay

2 / 37

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Outline

0νββ decay: huge potential, great challenge

Nuclear structure data as test of 0νββ calculations

Double Gamow-Teller transitions and 0νββ decay

γγ transitions and 0νββ decay

/ 37

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Lepton-number conservationLepton number is conservedin all processes observed

β decay, ββ decay...

Uncharged massive particleslike Majorana neutrinos (ν)allow lepton number violation

Neutrinoless ββ (0νββ) decay3 / 37

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ββ decaySecond order process in the weak interactionOnly observable in nuclei where (much faster) β-decay is forbiddenenergetically due to nuclear pairing interaction

BE(A) = −av A + asA2/3 + acZ (Z − 1)

A1/3+

(A− 2Z )2

A+

−δpairing N,Z even0 A oddδpairing N,Z odd

or where β-decay is very suppressed by ∆J angular momentum change

-76

-74

-72

-70

-68

-66

30 31 32 33 34 35 36 37

Bin

din

g e

nerg

y (

MeV

)

Atomic number, Z

76Se

76Ge

76As

76Br

76Kr

76Ga

β-

β+

β+

β-β

-

48Ca→ 48Ti76Ge→ 76Se82Se→ 82Kr96Zr→ 96Mo100Mo→ 100Ru110Pd→ 110Cd116Cd→ 116Sn124Sn→ 124Te130Te→ 130Xe136Xe→ 136Ba150Nd→ 150Sm

4 / 37

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0νββ decay rate0νββ rate depends on kinematics and physics at very different scales:

1T 0νββ

1/2

(0+

i → 0+f

) = G01 g4A

∣∣M0νββ∣∣2(mββ

me

)2

G01 is the phase space factor, kinematics:accurate calculations; depends on Qββ , charge number Z , electrons...

gA is the coupling to the nucleonhard to compute (lattice QCD) but can be measured in other decays

M0νββ is the nuclear matrix element (NME)nuclear structure of the initial and final nuclei

mββ = |∑U2ek mk |, new physics responsible for lepton-number violation

For 0νββ rate dominated by different new physics, same structuredifferent values of G, g, M and mββ ∼ 1/Λ, v3/Λ3, v5/Λ5

5 / 37

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Next generation experiments: inverted hierarchyDecay rate sensitive toneutrino masses, hierarchymββ = |∑U2

ek mk |T 0νββ

1/2

(0+ → 0+

)−1= G0ν g4

A

∣∣M0νββ∣∣2 m2

ββ

Matrix elements assess ifnext generation experimentsfully explore "inverted hierarchy"

(eV)lightestm4−10 3−10 2−10 1−10

3−10

2−10

1−10

1

IH

NH

A50 100 150

Ca

Ge

SeZr

Mo

CdTe

Te

Xe

Nd

(eV)

m

KamLAND-Zen, PRL117 082503(2016)

6 / 37

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Nuclear matrix elements

Nuclear matrix elements needed in low-energy new-physics searches

〈Final |Lleptons−nucleons| Initial 〉 = 〈Final |∫

dx jµ(x)Jµ(x) | Initial 〉

• Nuclear structure calculationof the initial and final states:Shell model, QRPA, IBM,Energy-density functionalAb initio many-body theoryGFMC, Coupled-cluster, IMSRG...

• Lepton-nucleus interaction:Hadronic current in nucleus:phenomenological,effective theory of QCD

7 / 37

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0νββ decay nuclear matrix elementsLarge difference in nuclear matrix element calculations: factor ∼ 2− 3⟨0+

f

∣∣∑n,m

τ−n τ−m

∑X

HX (r) ΩX∣∣0+

i

⟩ ΩX = Fermi (1), GT (σnσm),TensorH(r) = neutrino potential

0

1

2

3

4

5

6

7

48 76 82 100 116 130 136 150

M0

ν

A

CC

IMSRG

NSM

QRPA

IBM

EDF

Engel, JM, Rep. Prog. Phys. 80 046301 (2017), updated8 / 37

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Uncertainty in physics reach of 0νββ half-lives

0

1

2

3

4

5

6

7

8

M0

ν

SM St-M,Tk

SM Mi

IBM-2

QRPA CH

QRPA Tu

QRPA Jy

R-EDF

NR-EDF

1028

1029

1030

1031

48 76 82 96 100 116 124 130 136 150

T1/20ν m

ββ

2 [y m

eV

2]

A

Nuclear matrix elementtheoretical uncertainty criticalto anticipate mββ sensitivityof future experiments

Order of magnitudeuncertainty in T 0ν

1/2needs to be reduced!

Engel, JM,Rep. Prog. Phys. 80 046301 (2017)

9 / 37

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Pairing correlations and 0νββ decay0νββ decay favoured by proton-proton, neutron-neutron pairing,but it is disfavored by proton-neutron pairing

Ideal case: superfluid nucleireduced with high-seniorities

0

2

4

6

8

10

12

0 4 8 12

M0ν

ββ

sm

A=48A=76A=82

A=124A=128A=130A=136

Caurier et al. PRL100 052503 (2008)

Addition of isoscalar pairingreduces matrix element value

-10

-5

0

5

10

0 0.5 1 1.5 2 2.5 3

M0ν

gT=0/gT=1

GCM SkO′QRPA SkO′GCM SkM*

QRPA SkM*

Hinohara, Engel PRC90 031301 (2014)

Related to approximate SU(4) symmetry of the∑

H(r)σiσjτiτj operator10 / 37

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Outline

0νββ decay: huge potential, great challenge

Nuclear structure data as test of 0νββ calculations

Double Gamow-Teller transitions and 0νββ decay

γγ transitions and 0νββ decay

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Nuclear shell modelNuclear shell model configuration spaceonly keep essential degrees of freedom

• High-energy orbitals: always empty

• Valence space:where many-body problem is solved

• Inert core: always filled

H |Ψ〉 = E |Ψ〉 → Heff |Ψ〉eff = E |Ψ〉eff

|Ψ〉eff =∑α

cα |φα〉 , |φα〉 = a+i1a+

i2...a+iA |0〉

Shell model diagonalization:∼1010 Slater dets. Caurier et al. RMP77 (2005)&1024 Slater dets. with Monte Carlo SM

Otsuka, Shimizu, Y.Tsunoda

Heff includes effects of

• inert core

• high-energy orbitals13 / 37

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Tests of nuclear structureSpectroscopy well described: masses, spectra, transitions, knockout...

Theory Exp0

500

1000

1500

2000

2500

Ex

cita

tio

n e

ner

gy

(k

eV)

4+

6+

0+

3+

4+

6+

2+5

+

2+

0+

2+

4+

2+

6+

3+,4

+6+

2+ 2

+5(4

+)

136Xe

0

0

0.5

1

Ex (

MeV

)

0+2+

4+

6+

8+

0+2+

4+

6+

8+

0+

2+

4+

0+

2+

4+

6+

204

292

325

345

115(2)

175(1)

212(12)

236(11)

98

151

181

55.8(25)

112(12)

Theory Exp. Theory Exp.150Nd 150Sm

Schiffer et al. PRL100 112501(2009)Kay et al. PRC79 021301(2009)...Szwec et al., PRC94 054314 (2016)

Rodríguez et al. PRL105 252503 (2010)...Vietze et al. PRD91 043520 (2015)

14 / 37

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β–decay Gamow-Teller transitions: “quenching”β decays (e− capture): phenomenology vs ab initio

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

T(GT) Th.

T(G

T)

Ex

p.

0.77

0.744

Martinez-Pinedo et al. PRC53 2602(1996)

〈F |∑

i

[gA σiτ−i ]eff |I〉 , [σiτ ]eff ≈ 0.7σiτ

Standard shell modelneeds σiτ “quenching”

Gysbers et al. Nature Phys. 15 428 (2019)

Ab initio calculations includingmeson-exchange currents

do not need any “quenching”15 / 37

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Gamow-Teller strength distributionsGT strength distribution complements β-decay beyond Q-value region

Frekers et al.NPA916 219 (2013)

Iwata et al. JPSCP6 3057 (2015) Caurier et al. PLB711 62 (2012)

dσdΩ

(θ = 0) ∝∑

σiτ±⟨

1+f

∣∣∑geffA σiτ

±i

∣∣0+gs⟩, geff

A ∼ 0.57gA for 136Xe

Similar “quenching” q= 0.57 needed in GT decays in xenon mass regionSmaller “quenching” q= 0.42 needed in 2νββ of 136Xe

16 / 37

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Two-neutrino ββ decay, 2νECEC2νββ decay same initial, final states , similar operator (στ ) as 0νββComparison of predicted 2νββ decay vs data

Shell modelreproduce 2νββ dataincluding “quenching”

Prediction previous to48Ca measurement!Caurier, Poves ZukerPLB 252 13(1990)

M2νββ =∑

k

⟨0+

f

∣∣∑n σnτ

−n∣∣1+

k

⟩ ⟨1+

k

∣∣∑m σmτ

−m∣∣0+

i

⟩Ek − (Mi + Mf )/2

Table 2

The ISM predictions for the matrix element of several 2ν double beta decays

(in MeV−1). See text for the definitions of the valence spaces and interactions.

M2ν (exp) q M2ν (th) INT

48Ca→48Ti 0.047± 0.003 0.74 0.047 kb3

48Ca→48Ti 0.047± 0.003 0.74 0.048 kb3g

48Ca→48Ti 0.047± 0.003 0.74 0.065 gxpf1

76Ge→76Se 0.140± 0.005 0.60 0.116 gcn28:50

76Ge→76Se 0.140± 0.005 0.60 0.120 jun45

82Se→82Kr 0.098± 0.004 0.60 0.126 gcn28:50

82Se→82Kr 0.098± 0.004 0.60 0.124 jun45

128Te→128Xe 0.049± 0.006 0.57 0.059 gcn50:82

130Te→130Xe 0.034± 0.003 0.57 0.043 gcn50:82

136Xe→136Ba 0.019± 0.002 0.45 0.025 gcn50:82

Caurier, Nowacki, Poves, PLB 711 62 (2012)17 / 37

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Two-neutrino ECEC of 124XePredicted 2νECEC half-life:shell model error bar largely dominated by “quenching” uncertainty

SuhonenJPG 40 075102 (2013)

Pirinen, SuhonenPRC 91, 054309 (2015)

Coello Pérez, JM,SchwenkPLB 797 134885 (2019)

Shell model, QRPA and Effective theory (ET) predictionssuggest experimental detection close to XMASS 2018 limit

18 / 37

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Two-neutrino ECEC of 124XePredicted 2νECEC half-life:shell model error bar largely dominated by “quenching” uncertainty

SuhonenJPG 40 075102 (2013)

Pirinen, SuhonenPRC 91, 054309 (2015)

Coello Pérez, JM,SchwenkPLB 797 134885 (2019)

XENON1TNature 568 532 (2019)

Shell model, QRPA and Effective theory (ET) predictionsgood agreement with XENON1T measurement of 2νECEC!

18 / 37

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Effective theory of ββ decay

Effective theory (ET) for ββ decay:spherical core coupled to one nucleon

Couplings adjusted to experimental data,uncertainty given by effective theory(breakdown scale, systematic expansion)

Use β-decay datato predict 2νββ decayGood agreement, large error(leading-order in ET)

Coello-Pérez, JM, SchwenkPRC 98, 045501 (2018)

19 / 37

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Electron spectrum in two-neutrino ββ decayPrecise 2νββ half-life, next term in expansion of energy denominator

(T 2ν1/2)−1 ' g4

A

∣∣(M2νGT )2G2ν

0 + M2νGT M2ν

GT−3G2ν2 + ...

∣∣M2ν

GT =∑

j

〈0+f |∑

l σlτ−l |1

+j 〉〈1

+j |∑

l σlτ−l |0

+i 〉

∆,

M2νGT3 =

∑j

4〈0+f |∑

l σlτ−l |1

+j 〉〈1

+j |∑

l σlτ−l |0

+i 〉

∆3,

∆ = [Ej − (Ei + Ef )/2]/me

Electron differential decay rate:

dΓββ

dTee∼

dG0

dTee+

M2νGT

M2νGT−3

dG2

dTee

Exp. sensitivity to ξ2ν31 = M2ν

GT−3/M2νGT Šimkovic et al.

PRC98 064325 (2018)20 / 37

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Electron spectrum in 136Xe ββ decay

Present 0νββexperiments observe∼10000 2νββ decays,major background

KamLAND-Zen 2νββanalysis excludes largervalues of ξ2ν

31

KamLAND-Zen, PRL122 192501 (2019)21 / 37

Page 24: How to measure neutrinoless double-beta decay nuclear ...

Ratio of leading/subleading ββ matrix elementsShape of ββ spectrum constrains matrix element ratio ξ2ν

31 = M2νGT−3/M2ν

GT

0 0.005 0.01 0.015 0.02 0.025 0.03

M2ν

GT-3

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

gef

f

A

shell model (GCN)

shell model (MC)

QRPA (CD-Bonn)

QRPA (Argonne)

ξ 2ν

31 = 0.26

excluded, KamLAND-Zen

ξ2ν

31 = 0.10

ξ2ν

31 = 0.17(1σ)

(90% C.L.)

ξ 2ν

31 = 0.05

Theory deficiencies in M2νGT

fixed adjusting gA(“quenching”)

ξ2ν31 measurement

test theoretical models

Theory-experiment work withKamLAND-Zen collaborationTheory: JM, Dvornicky, Šimkovic

Shell model ξ2ν31 predictions

consistent with 90% C.L. limitKamLAND-Zen et al.PRL122 192501 (2019)

22 / 37

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Outline

0νββ decay: huge potential, great challenge

Nuclear structure data as test of 0νββ calculations

Double Gamow-Teller transitions and 0νββ decay

γγ transitions and 0νββ decay

/ 37

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Double Gamow-Teller strength distributionMeasurement of Double Gamow-Teller (DGT) resonancein double charge-exchange reactions 48Ca(pp,nn)48Ti proposed in 80’sAuerbach, Muto, Vogel... 1980’s, 90’s

Recent experimental plans in RCNP, RIKEN (48Ca), INFN CataniaTakaki et al. JPS Conf. Proc. 6 020038 (2015)Capuzzello et al. EPJA 51 145 (2015), Takahisa, Ejiri et al. arXiv:1703.08264

Promising connection to ββ decay,two-particle-exchange process,especially the (tiny) transitionto ground state of final state

Shell model calculationShimizu, JM, Yako, PRL120 142502 (2018)

0 20 40 600

20

40

B(D

GT

)

Ex. (MeV)

SDPFMU J=2

SDPFMU J=0

GXPF1B J=2

GXPF1B J=0

B(DGT−;λ; i → f ) =1

2Ji + 1

∣∣∣∣⟨48Ti∣∣∣∣∣∣∣∣[∑

i

σiτ−i ×

∑j

σjτ−j

](λ)∣∣∣∣∣∣∣∣48Cags

⟩∣∣∣∣223 / 37

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Double Gamow-Teller distribution and pairingStudy the sensitivity of Double GT distribution to pairing correlations

Add/remove pairing

H ′ = H + GJT PJT

like-particle (T=1) orproton-neutron (T=0)

Position of theDGT giant resonancevery sensitive tolike-particle pairing

DGT resonance widthprobes isoscalar pairingShimizu, JM, YakoPRL120 142502 (2018) 0 20 40

0

20

40

0

20

40

0

20

40

0 20 400

20

40

G(10)

= +0.5 MeV

Ex (MeV)

Jf=2+

Jf=0+

G(10)

= +0.25 MeV

G(10)

= -0.25 MeV

G(10)

= -0.5 MeV

G(01)

= +0.5 MeV

B(D

GT

)

Ex (MeV)

Jf=2+

Jf=0+

G(01)

= +0.25 MeV

G(01)

= -0.25 MeV

G(01)

= -0.5 MeV

(a) (b)

24 / 37

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Correlation of 0νββ decay to DGT transitionsDouble GT transition to ground state MDGT =

⟨Fgs∣∣∣∣[∑

i σiτ−i ×∑

j σjτ−j

]0∣∣∣∣Igs⟩∣∣2

very good linear correlation with 0νββ decay nuclear matrix elements

0

2

4

6

8

10

0 1 2 3 4 5

42 ≤ A ≤ 238

MD

GT(0

+ gs,i →

0+ g

s,f)

*R(f

m)

M0νββ

(0+gs,i → 0

+gs,f)

QRPA

IBM (MDGT/2.0)

EDF

shell model

Double Gamow-Tellercorrelation with0νββ decay holdsacross nuclear chartShimizu, JM, YakoPRL120 142502 (2018)

Common to shell modelenergy-density functionalsinteracting boson model,disagreement to QRPA

Experiments atRIKEN, INFN, RCNP?access DGT transitions

25 / 37

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Short-range character of DGT, 0νββ decayCorrelation between DGT and 0νββ decay matrix elementsexplained by transition involving low-energy states combined withdominance of short distances between exchanged/decaying neutronsBogner et al. PRC86 064304 (2012)

-0.2

0

0.2

0.4

0.6

0 3 6 9 12 15

(a)

CG

T (

r jk)

[fm

-1]

rjk [fm]

0νββ decay

DGT

0 200 400 600

-0.001

0

0.001

0.002

0.003136

Xe

(b)

CG

T (q

) [MeV

-1]

q [MeV]

0νββ decay matrix elementlimited to shorter range

Short-range part dominantin double GT matrix elementdue to partial cancellationof mid- and long-range parts

Long-range part dominant inQRPA DGT matrix elements

Shimizu, JM, Yako,PRL120 142502 (2018)

26 / 37

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Short-range character of DGT, 0νββ decayCorrelation between DGT and 0νββ decay matrix elementsexplained by transition involving low-energy states combined withdominance of short distances between exchanged/decaying neutronsBogner et al. PRC86 064304 (2012)

JM, JPSCP 23 012036 (2018) Šimkovic et al. PRC 98 064325 (2019)

In contrast to NSM, long-range dominates QRPA DGT matrix elements27 / 37

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Contribution of S = 1 pairs to DGT NMENMEs are dominated by S = 0 pairs

In DGT QRPA, S = 1 pair contributions extremely suppressedlead to small MDGT = MDGT

S=0 + MDGTS=1 = 4MDGT

S=1 (isospin conserved)

In contrast, nuclear shell model MDGTS=1 small but not negligible

even between seniority-zero states (J = 0 pairs, isospin not conserved)

Šimkovic et al. PRC 98 064325 (2019) Linares, JM, in preparation28 / 37

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0νββ decay NMEs in ET of β decayEffective theory of β decay can calculate DGT with uncertainties(similar to calculation of 2νββ, no energy denominator)DGT vs 0nbb correlation⇒ predict 0νββ NMEs with uncertainties

Because ET couplings fitted to β decay and GT strengthscorrect shell model DGT NMEs in correlationby “quenching” factor for these observables: q = 0.42− 0.65

0 0.5 1.0 1.5 2.0 2.5

M0νββ(0+gs,i −→ 0+

gs,f) · A−16

0

0.5

1.0

MD

GT

(0+ gs,

i−→

0+ gs,

f)

44 6 A 6 238fitSM

SM, 44 6 A 6 136

EDF

IBM (MDGT/2.0)

As a result, ET 0νββ NMEs76Ge: M0ν = 0.3− 1.582Se: M0ν = 0.3− 1.6

smaller than mostcalculationslarge uncertainty:LO in ET, fit, “quenching”Brase, Coello Pérez, JM, Schwenkin preparation29 / 37

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Outline

0νββ decay: huge potential, great challenge

Nuclear structure data as test of 0νββ calculations

Double Gamow-Teller transitions and 0νββ decay

γγ transitions and 0νββ decay

/ 37

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γγ decay of the DIAS of the initial ββ nucleusExplore correlation between 0νββ and γγ decays,focused on double-M1 transitions

MγγM1 M1 =

∑k

⟨0+

f

∣∣∑n(g l

nln + gsnσn)IV

∣∣1+k (IAS)

⟩⟨1+

k (IAS)∣∣∑

m(g lmlm + gs

mσm)IV∣∣0+

i (DIAS)⟩

Ek − (Ei + Ef )/2

-75

-74

-73

-72

31 32 33 34 35

76Se

76Ge

76As

76Ge double isobaric analogue state

β-β

- γ γ

Bin

din

g e

nerg

y (

MeV

)

Atomic number, Z

Similar initial and final statesbut both in same nucleusfor electromagnetic transition

M1 and GT operators similar,physics of spin operatorM1 also angular momentum

Different energy denominatorRomeo, JM, Peña-GarayarXiv:2102.11101

30 / 37

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β decays and γ transitions from IASThe relation between electromagnetic decays from IAS and weak oneshas been used and tested many timesEjiri, Suhonen, Zuber, Phys. Rept. 797 1 (2019)Fujita, Rubio, Gelletly, Prog. Part. Nucl. Phys.66, 549 (2011)

And it is certainly not a novel idea...

PRL 21 373 (1968)

31 / 37

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Correlation between M1M1 and 0νββ NMEsα

Mγγ(0 D

IAS

+⟶

0 gs+)[μ

N2Me

V-1 ]

TiCrFe

0

0.5

1.0

1.5

2.0

2.5

46 ≤ A ≤ 60

ZnSeGeKr

TeXeBa

1.0 1.5 2.0 2.5 3.00

0.5

1.0

1.5

2.0

2.5

M0νββ(0gs+ ⟶0gs+ )

72 ≤ A ≤ 136

Good correlation betweenM1M1 and 0νββ NMEs!

Valid across the nuclear chartfor the nuclear shell model

Overall, study ∼ 50 transitionsseveral nuclear interactionsfor each of them

The correlation is slightly differentfor lighter nuclei:effect of energy denominator

Romeo, JM, Peña-GarayarXiv:2102.11101

32 / 37

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Intermediate states of the M1M1 transition

TiCrFeZnSe

GeKrTeXeBa

0.5 1.0 1.5 2.0 2.5 3.0 3.50

2

4

6

8

M0νββ0gs+ ⟶0gs+

αM1

M1(0 D

IAS

+⟶

0 gs+)[μ

N2 ]

46 ≤ A ≤ 136

Dominant intermediate statesat lower energies for lighter nuclei,otherwise similar energies

One or few intermediate statestypically dominate the transition

When energy denominators are(artificially) removed, samecorrelation across the nuclear chart

Romeo, JM, Peña-GarayarXiv:2102.11101

48Ti82Se128Te

5.0 7.5 10.0 12.5 15.0-0.2

0

0.2

0.4

0.6

0.8

En(MeV)

Mγγ(M

1M1)

[μN2

MeV-

1 ]

33 / 37

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Spin, angular momentum decomposition

The numerator NME can be decomposed into

Mss + Mll + Mls

spin, angular momentum and interference components

ss llls

T ss ll ls T ss ll ls T ss ll ls T ss ll ls T0

0.2

0.4

0.6

0.8

Mxx

'γγ[μ

N2 ] 48Ti 72Zn 78Ge 134Xe 136Ba

Spin, angular momentum termsstrikingly similar,always carry same sign

Interference termcan cancel the other twobut always much smaller

Romeo, JM, Peña-GarayarXiv:2102.11101

34 / 37

Page 39: How to measure neutrinoless double-beta decay nuclear ...

Total angular momentum decompositionThe numerator NME can be decomposed into

Mss(J ) + Mll (J ) + Mls(J )

spin, angular momentum and interference componentsand total angular momentum of the nucleons involved in the transition

sslllsT

0 1 2 3 4 5 6 7 8 9 10-0.5

0

0.5

1.0

1.5

Mxx

'γγ(

)[μ

N2 ]

Dominance of J = 0 termsfor spin and orbital contributionsjust like in 0νββ decay

Cancellation from J > 0 termsless pronounced in orbital part

Explains similar behaviour ofspin and orbital components

Romeo, JM, Peña-GarayarXiv:2102.11101

35 / 37

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Experimental feasibility of γγ decay?γγ decays are very suppressed with respect to γ decaysjust like ββ decays are much slower than β decays

γγ decays have been observed recentlyin competition with γ decaysWaltz et al. Nature 526, 406 (2015), Soderstrom et al. Nat. Comm. 11, 3242 (2020)

-75

-74

-73

-72

31 32 33 34 35

76Se

76Ge

76As

76Ge double isobaric analogue state

β-β

- γ γ

Bin

din

g e

nerg

y (

MeV

)

Atomic number, Z

Outlook:

Study in detail leadingdecay channels for M1M1 decayin DIAS of ββ nuclei

Particle emission,M1, E1 decay

Experimental proposal for 48Tiby Valiente-Dobón et al.

Valiente-Dobón, Romeo et al., in prep36 / 37

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Summary

Calculations of 0νββ NMEschallenge nuclear many-body methods

0νββ searches demand reliable NMEsnuclear structure measurements caninform us on their value

Double Gamow-Teller transitionsvery good correlation with 0νββ NMEspotentially accessible in chargeexchange experiments

Electromagnetic M1M1 decayof the DIAS of the initial ββ nucleusgood correlation to 0νββ NMEsfeasibility of measurements in progress

αMγ

γ(0 D

IAS

+⟶

0 gs+)[μ

N2Me

V-1 ]

TiCrFe

0

0.5

1.0

1.5

2.0

2.5

46 ≤ A ≤ 60

ZnSeGeKr

TeXeBa

1.0 1.5 2.0 2.5 3.00

0.5

1.0

1.5

2.0

2.5

M0νββ(0gs+ ⟶0gs+ )

72 ≤ A ≤ 136

37 / 37

Page 42: How to measure neutrinoless double-beta decay nuclear ...

Collaborators

L. Jokiniemi, J. P. Linares, P. Soriano

C. Peña-Garay, B. Romeo

E. A. Coello Pérez

C. Brase, A. Schwenk

N. Shimizu, K. Yako

37 / 37