Neutrinoless Double Beta Decay and new Physics Manfred Lindner 8. - - PowerPoint PPT Presentation

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Neutrinoless Double Beta Decay and new Physics Manfred Lindner 8. - - PowerPoint PPT Presentation

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Neutrinoless Double Beta Decay and new Physics Manfred Lindner 8. Mai 2013 M. Lindner, MPIK . 1 Adding Neutrino Masses to the SM Simplest and suggestive possibility: add 3 right handed singlets (1 L ) n R n R n L n R g N x n _ _ c

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SLIDE 1
  • 8. Mai 2013
  • M. Lindner, MPIK

. 1

Manfred Lindner

Neutrinoless Double Beta Decay and new Physics

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SLIDE 2

Adding Neutrino Masses to the SM

  • M. Lindner, MPIK

.

Majorana L

x x

nL nR <f> = v nR nR gN

/

( )

÷ ÷ ø ö ç ç è æ ÷ ÷ ø ö ç ç è æ

R L R D D R L

M m m n n n n

è

_ _ c

c

Simplest and suggestive possibility: add 3 right handed singlets (1L)

like quarks and charged leptons è Dirac mass terms (including NMS mixing) +9 param. & new ingredients: 1) Majorana mass = scales 2) lepton number viol. è SM+ 6x6 block mass matrix block diagonalization MR heavy è 3 light n’s

2

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SLIDE 3
  • M. Lindner, MPIK

. 3

Add scalar triplets (3L) or add fermionic (1L) or (3L)

nL nL èleft-handed Majorana mass term:

MLLLc

_

x x

nL nL

x x

1,3 3

mn=ML - mDMR

  • 1mD

T

è see-saw type II, III

Both nR and new singlets / triplets:

Other Possibilities

Higher dimensional operators: d=5, … è MLLLc

_

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SLIDE 4
  • M. Lindner, MPIK

. 4

Add: more neutrinos, SUSY, extra dimensions, … Radiative neutrino mass generation

è huge number of papers on neutrino masses... ... but we know only two Dm2... (plus mass & unitarity bounds) è neutrino masses can/may solve two of the SM problems:

  • leptogenesis as explanation of BAU (both Majorana and Dirac)
  • keV sterile neutrinos as excellent warm dark matter candidate

even for nR only è BSM physics in many cases connections to LFV, LHC, DM

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SLIDE 5

Double Beta Decay

  • M. Lindner, MPIK

. 5

If neutrinos have Majorana masses è Lepton Number Violation è Neutrinoless Double Beta Decay

BUT: Be careful about the inverted reasoning!

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SLIDE 6
  • M. Lindner, MPIK

. 6

30 31 32 33 34 35 36 37 Z

S

Q

76Zn 76Ga 76Ge 76As 76Se 76Br 76Kr 76Rb

b- b- b- b+ EC b+

  • dd-odd

even-even

Special nuclei:

  • single b decay energetically forbidden
  • double b decay allowed

è GG-nuclei: 76Ge, …

Qbb

bb= 2039 keV

Double b-Decay & Mass Parabolas

76Ge: Only double b decay è SM: 2n+2e- *OR* BSM: 0n+2e-

Further 0nb nbb isotopes… In addition: isotopic composition, backgrounds, costs, NMEs, ...

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SLIDE 7

Majorana

mass

The Standard Picture of Double Beta Decay

2nb nbb decay 0nb nbb decay

2nbb decay seen for diff. isotopes (Kirsten,…) T1/2 = O(1018 - 1021 years) è up to 1011 ⊗ TUniverse

  • observe 2nb

nbb

  • look for 0nb

nbb signal at Qbb

bb

è big amount of 0nb nbb nuclei

  • extreme low backgrounds!

è signal = Majorana mass

  • M. Lindner, MPIK

. 7

2nb nbb 0nb nbb SM T1/2 > O(1025y)

1/ 1/t = G(Q,Z) |Mnucl|2 <mee>2

important: NMEs and their uncertainties…

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SLIDE 8

mee: The Effective Neutrino Mass

  • M. Lindner, MPIK

. 8

Comments:

  • cosmology: m < 0.2-0.3 eV
  • 0nbb

nbb: mee < 0.1-0.3 eV

  • NMEsè unavoidable theory errors
  • known Dm2 from oscillations

è yellow/blue areas è improved sensitivity is very promising!

  • warnings:
  • assumes no *other* DL=2 physics
  • assumes no sterile neutrinos, ...
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SLIDE 9

More general: L Violating Processes

2nb nbb decay 0nb nbb decay

  • exp. search unchanged…
  • M. Lindner, MPIK

. 9

2nb nbb 0nb nbb 0nb nbb SM BSM

some

DL=2

  • perator

T1/2 > O(1025y) …interpretation changes:

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SLIDE 10

Other Double Beta Decay Processes

  • M. Lindner, MPIK

. 10

+

è 2 electrons + 2 neutrinos 2nb nbb Standard Model:

SM+Higgs triplet SUSY

…

SM + Higgs triplet SUSY

Majorana n-masses or other DL=2 physics: è 2 electrons

0nb nbb

important connections to LHC and LFV … sub eV Majorana mass ßà ßà TeV scale physics

Majorana neutrino masses ßà ßà Dirac?

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SLIDE 11

Interference of DL=2 Operators

Usually with interferences

  • M. Lindner, MPIK

. 11

= overall phase space factor ßà determined by parameters of new physics

me ~ (Lnew)-5 m0nb

nbb = 1 eV çè

çè Lnew ~ TeV

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SLIDE 12

Extreme Cases

  • M. Lindner, MPIK

. 12

me

mee from Majorana neutrinos only and no other DL=2 physics

me from other DL=2 physics with Dirac neutrino masses

and anything in-between

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SLIDE 13
  • M. Lindner, MPIK

. 13

me

m’ee interferences growing me for fixed 0nb nbb à shifts of masses, mixings and CP phases à destroys ability to extract Majorana phases à sensitivity to TeV

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SLIDE 14

Does 0nb nbb Decay imply Majorana Masses?

  • Schechter-Valle Theorem è is misleading

Any DL=2 operator which mediates the decay induces via loops Majorana mass terms è unavoidable: Majorana neutrinos…!?

0nb nbbè some DL=2 operator

  • M. Lindner, MPIK

. 14

Dürr, ML, Merle

4 loops è enforce dmn = 10-25 eV è very tiny (academic interest) è cannot explain observed n masses and splitting's Extreme possibility:

  • 0nb

nbb = L violation = other BSM physics

  • neutrino masses = Dirac (plus very tiny Majorana corrections)

+ Dirac leptogenesis, + ...

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SLIDE 15

The experimental Task

  • finite energy resolution

è background from the tail of 2nb nbb

  • extreme low background è does not mean no background è lines…

è need a method to ensure that it is 0nb nbb and not some background 1) two different isotopes 2) isotopic fingerprint

  • M. Lindner, MPIK

. 15

2nb nbb decay 0nb nbb decay

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SLIDE 16

Sensitivity & Background (for a Majorana Mass)

  • M. Lindner, MPIK

. 16

1000 100

NA = Avogadro’s number W = atomic weight of isotope e = signal detection efficiency M = isotope mass t = data taking time

è

without background with background N’ = N + Nbackground

è

c = cts/keV/kg/yr ; DE = ROI

ton-scale à

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SLIDE 17

Which Isotope?

  • M. Lindner, MPIK

. 17

  • Large detector mass

ßà natural abundance

  • r enrichment (cost, time)

ßà ßà detection technology ßà ßà costs, feasibility, …

  • Radio-purity

ßà ultra clean 0nbb source and instrumentation ßà high Qbb ßà ßà less bgd.

  • Good energy resolution

ßà ßà avoid known and unknown backgrounds in ROI: Qbb

bb + DE

  • Uncertainties in nuclear matrix elements + energy resolution

è Germanium is a very good choice è use two different isotopes to confirm a signal …

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SLIDE 18

Consistency Test with one Isotope

  • M. Lindner, MPIK

. 18

ratio is set by nuclear spectra

  • independent of backgrounds!

Duerr, ML, Zuber

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SLIDE 19

The Fight against Background

  • M. Lindner, MPIK

. 19

Extreme rare reaction (T>1025 years >> age of Universe)

Magnitude 1 decay/kg/year Environment ~ 30Bq/kg = 109 /kg/year è 3000/person/second

èavoid single b decay ßà ßà suitable isotopes èavoiding / suppression of environmental radioactivity

  • in the 0nb

nbb detector material

à ultra clean (production, handling) à puls form analysis (identify & reject background)

  • in the detector parts (e.g. holders, signal amplifiers)

à lowest amount of material à ultra pure materials (selection; environmnt = O(100Bq/kg) çè çè µBq/kg ) à extremely helpful: 76Ge source = detector (a big Ge diode)

  • in the environment

à ultra clean room (clean room, …) à avoid Radon (decay of U, Th in the environment à 222Rn-gas) à avoid cosmogenic activation (new isotopes à go underground) à avoid cosmogenic myons, neutrons à go underground

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SLIDE 20

Experimental Realizations

  • M. Lindner, MPIK

. 20

0nb nbb decay is important! èlow background expertise! èlong history and diverse plans for the future Important mile stone: Heidelberg-Moskau-Experiment

(H.V. Klador-Kleingrothaus MPIK)

  • for many years best limts
  • signal?

èGERDA èimportant result

KamLAND-Zen nEXO EXO

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SLIDE 21

The GERDA Collaboration

  • M. Lindner, MPIK

. 21 21

ITEP Moscow Kurchatov Institute

16 institutions ~110 members

http://www.mpi-hd.mpg.de/gerda/

INR Moscow

European Commission Joint Research Centre JRC Geel

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SLIDE 22

Protection against Cosmogenic Radiation

Unterground laboratory è Gran Sasso (Italy)

GERDA

  • M. Lindner, MPIK

. 22

A very special place to work…

1400 m rock as shield (3100 mwe)

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SLIDE 23

The GERDA Detector (original idea by G. Heusser, MPIK)

  • M. Lindner, MPIK

. 23 scale model by A. Lindner

clean room water tank: 590 m3 high purity water neutron moderator/absorber muon Cherenkov veto naked Ge detectors: 3 strings with 9 coax detectors 1 string with 5 BEGe’s lock system very clean liquid Ar cryostat with internal Cu shield plastic scintillator veto

background reduction:

  • material selection
  • screening (g, Rn, …)
  • graded shielding
  • deep underground
  • veto systems
  • water
  • operation in LiAr
  • naked Ge
  • …
  • source = detector
  • puls shape analysis
  • …
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SLIDE 24

MPIK Material g-Screening Facilities

  • Different screening stations@MPIK

underground lab: BRUNO, CORRADO, … (1mBq/kg)

  • 4 GEMPIs

@LNGS (10µBq/kg)

  • New: GIOVE

@MPIK (50µBq/kg) è extensive task for GERDA and other experiments (XENON, …)

  • M. Lindner, MPIK

. 24

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SLIDE 25

Rn Screening Facilities

Gas counting systems @LNGS and @MPIK

222Rn emanation technique

  • sensitivity = few atoms/probe
  • large samples ßà

ßà absolute sensitivity

  • non-trivial; not commonly available; routine @MPIK
  • established numbers:

Nylon (Borexino) < 1µBq/m2 Copper (Gerda): 2µBq/m2 Stainless steel (Borexino): 5µBq/m2 Titanium: (100 + 30) µBq/m2

New: Auto-Ema - automatized Rn screening facility @MPIK è many samples

  • M. Lindner, MPIK

. 25

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SLIDE 26
  • M. Lindner, MPIK

. 26

çaccumulated activity and its decay beware of long-lived isotopes…! BEGe Detector production

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SLIDE 27

GERDA Detector Types

  • M. Lindner, MPIK

. 27

1) Big Ge-diodes è HV è electrical signal 2) re-processed HdM, IGEX and GTF detectors p-type semi-coaxial 3) new p-type BEGe (Broad Energy Ge) detectors

  • n+ conductive Li layer, separated by a grove from

the boron implanted p+ contact

  • perated as ``diode’’: events è pulses
  • SSE/MSE (single/multi site event) discrimination

ç coaxial BEGe ⬇

0νββ signature:

  • point-like energy deposition in detector bulk volume
  • sharp energy peak at 2039 keV (FWHM = 3-4 keV)
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SLIDE 28

Pulse Shape Discrimination

  • M. Lindner, MPIK

. 28

e- e- Ge detector γ γ‘ E1 E2 α-decay

  • Single Site Events (SSE)
  • Multi Site Events (MSE)
  • 0nbb

nbb-decays à localized energy depositionà SSE

  • Compton scattering evt. à background like MSE
  • surface eventsà SSE @ surface
  • SSE by g’s look like events (cannot be rejected)
  • b particles enter via n+ surface à slow pulses
  • a’s @ p+ contact à comparatively high signal

0nbb nbb-decay drift paths E1 γ γ‘ E2

background like multi site event à MSE

1 Current [a.u.] time [µs] E1 E2

signal like single site event à SSE

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SLIDE 29

Backgrounds

  • M. Lindner, MPIK

. 29

Background sources:

  • a decays on the p+ surface
  • b decay of 42K on the surface or close to the

detector from 42Ar (10x more than expected)

  • b decay of 60Co inside detectors
  • g from 208Tl, 214Bi and from various set-

up components

Generic phase I background reduction

  • use cleanest possible material
  • prevent 42K ions from drifting to detectors

using minishrouds

  • cut detector coincidences
  • pulse shape analysis

è Background model ßà from screening è Measured background away from Qbb consistent with expectation from measurement è flat

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SLIDE 30

Phase I: The Region of Interest

  • M. Lindner, MPIK

. 30

expected bg from 5.1 events w/o PSD interpolation: 2.5 events with PSD

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SLIDE 31

Phase I: The Region of Interest

  • M. Lindner, MPIK

. 31

  • bserved

è 7 events w/o PSD è 3 events with PSD expected bg from 5.1 events w/o PSD interpolation: 2.5 events with PSD

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SLIDE 32

Profile Likelihood Fit to PSD Spectrum

  • M. Lindner, MPIK

. 32

profile likelihood fit = hypothesis test: is there a line at Qbb bb signal = a*flat background + b*line è extract coefficients è best fit: N0n = 0 ; upper limit: N0n < 3.5 (90%CL) è half life limit T1/2(0νββ) > 2.1 * 1025 yr (90% C.L.)

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SLIDE 33

GERDA Phase II

  • M. Lindner, MPIK

. 33

Improvement for Phase II:

  • more new BEGe detectors

è ~factor 2 in 76Ge mass

  • active veto (light instrumentation)

è even more background suppresion upgrade è data taking

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SLIDE 34

LAr Scintillation light Veto

  • M. Lindner, MPIK

. 34

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SLIDE 35

Data Taking 2015-2016

  • M. Lindner, MPIK

. 35

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SLIDE 36

Background Suppression @ BEGe

  • M. Lindner, MPIK

. 36

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SLIDE 37

Results

  • M. Lindner, MPIK

. 37

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SLIDE 38

Conclusion / Outlook / Discussion

  • M. Lindner, MPIK

. 38

  • The Majorana nature of neutrinos is a very

important question

  • Now: GERDA, EXO, KamLAND-Zen, CUORE
  • Other projects ...
  • Upscaling:
  • 200kg in GERDA à LEGEND200
  • LEGEND à 1t
  • nEXO à 5t enriched Xe136
  • DARWIN à50t natural Xe (DM+0nb

nbb search)

  • Expectations:
  • global fits tend towards NH
  • cosmology tends towards NH

à we need new ideas to reach the NH