Double Beta Decay

2: (A,Z) (A,Z+2) + 2e- + 2e(Observed for several nuclei, test of nuclear matrix elem. calculations)

L=2

0: (A,Z) (A,Z+2) + 2e-

d

d

u

u

e-

e-

W-

W- e

e

= G(Q,Z) |Mnucl|2 mee2, mee = |i Uei ² mi |

Range of mee derived from solar and atmospheric oscillation experiments

Goal of next generation experiments:~10 meV

F.Feruglio, A. Strumia, F. Vissani, NPB 637

Inverted hierarchy

Normal hierarchy

Degen

erat

e

Lightest neutrino (m1) in eV

| mee

| in

eV

90% CL

Negligible errors from oscillations;width due toCP phases

Lower bounds!

mee = f(m1, m²sol, m²atm, 12 , 13, -)from oscillation experiments

Experimental status of running experiments

Heidelberg – Moscow: MPIK Heidelberg, Kurchatov Institute Location: Gran Sasso Underground Laboratory Source = detector, 76Ge (10.9 kg isotopically enriched ( 86%)): Q = 2038 keV

NEMO3 (Neutrino Ettore Majorana Observatory): CENBG Bordeaux, Charles Univ. Prague, FNSPE Prague, INEEL, IReS Strasbourg, ITEP Moscow, JINR Dubna, Jyvaskyla Univ., LAL Orsay, LPC Caen, LSCE Gif, Mount Holyoke College, Saga Univ, UCL London

Location: Frejus Underground Laboratory

Source detector study of different nuclei; main target 100Mo (6.9 kg): Q = 3034 keV

CUORICINO (Cryogenic Underground Observatory for Rare Events): Firenze, Gran Sasso, Insubria, LBNL, Leiden, Milano, Neuchatel, South Carolina, Zaragoza

Location: Gran Sasso Underground Laboratory

Source = detector, TeO2 (40 kg) 130Te (13 kg): Q = 2615 keV

NB: More than one nuclei needed to check systematics from nuclear matrix elements

NEMO3

• Tracking volume with Geiger cells

• e+/e- separation by magnetic field

• Plastic scintillators for calorimetry and timing

1 SOURCE

2 TRACKING VOLUME

3 CALORIMETER

• Source in form of foils:

Start data taking February 2003

NEMO3: first resultsFirst results on 100Mo (650 h)

/22 (y) = 7.8 ± 0.09 stat ± 0.8 syst 1018 y

/20 (y) > 6 1022 y

mee < 1.8 – 2.9 eV

Expected final sensitivity: 0.2 – 0.4 eV (6.9 kg)

2spectrum

V. Vasiliev (Nemo coll.)

(C. Augier, ECT Trento)

CUORICINO

2615 keV 208Tl

single escape 208Tl

double escape 208Tl

Start data taking february 2003Energy resolution: 7 keV FWHMTeO2 (40 kg) 130Te (13 kg): Q = 2615 keV

0.8

m Calibration spectrum

(A. Giuliani, Taup03)

CUORICINO: first results

/20 > 5 1023 y

mee < 0.58 – 1.4 eV(90% c.l.)

3 y sensitivity (with present performance): 1 1025 y mee < 0.13 – 0.31 eV

anticoincidence background spectrum,

only 5x5x5 crystalsBackground level

0.23 .04

c/keV/kg/y

(A. Giuliani, Taup03)

New concept under study: Ge in liquid Ar – new ideas

• Replace LN (LN=0.8 g/cm³, 77 K)

by LAr (LN=1.4 g/cm³, 87 K)

LAr/ LN (2.615 MeV) = 0.62

• Scintillation yield: 40,000 photons / MeV Active shielding medium!(4 x organic liquid scintillator) Emission in XUV (~130 nm) – Wavelength shifting required : Organic WLS or Xe addition

• Essential for cosmogenic activities: Co-60, Ge-68, …• What’s about Ar-39, Ar-42 ?

76Ge: sensitivity, exposure and background

HEIDELBERG-MOSCOW Collaboration,Eur. Phys. J. A 12 (2001) 147:

M·T = 35.5 kg y, b = 6 ·10-2 (kg y keV),E ~ 4.2 keV

Sensitivity (with bgd): mee (b E / M T)1/4

0.06 / (kg year keV)

0.01

0.001

0.0001

Basic concepts about 76Ge in liquid N2

• background sources external to crystals

• clean contacts and support can be realized

• minimization of surface contaminations

• purification of liquid nitrogen

Operation of ‘naked’ Ge-detecctors In liquid nitrogen: G. Heusser, Ann. Rev. Nucl. Part. Sci. (1995)

GENIUS proposal: H.V. Klapdor-Kleingrothaus, J. Hellmig, M. Hirsch (1997); H.V. Klapdor–Kleingrothaus, L. Baudis, G. Heusser, B. Majorovits, H. Paes (1999), hep-ph/9910205

LN2 shield against external background radiation

LNGS: ~ 107 /m²/d (2.6 MeV )

LN2

~6 m

10-4 (kg keV y) -1

Space @ LNGS

14.80 m

~14 m

LN/LAr facility: Design study (b)

How small could a tank be?

• Lead layer submersed in LAr

• 232Th activity of lead tank Ø

• Preliminary results 30Bq/kg

Active suppression of internal bgd: example 60Co

Cosmogenic activities:•Production after completion of crystal growth•Exposure to cosmic rays above ground for 10 days: 0.18 Bq/kg [GENIUS]

60Co: no vs. active suppression

,

Reflector (VM2000)Wavelength shifter

Reduction factor ~100

Bgd. in LAr: example 42Ar42Ar / natAr = 3·10-21 (30 Bq/kg) [Barabash et al., LAr-TPC @ LNGS]

42Ar: no vs. active suppression

, 1,2

No issue for DBD even without active suppression!

Reflector (VM2000)Wavelength shifter

External bgd: example 2.615 MeV gamma 232Th (208Tl) in lead shield

Flux from rocks(0.5 Bq / kg) and concrete (5 Bq / kg) @ LNGS: 3.5 ·107 / (m² d) [BOREXINO, Laubenstein]

New lead for shielding under study with GEMPI @ LNGS: <30 Bq / kg

232Th (208Tl): no vs. active suppr.

Lead

Simulation for 30 Bq/kg, inner-Ø: 2m, height: 2 m

Reflector (VM2000)Wavelength shifter

Summary and outlook (1)

• DBD unique tool to study neutrino properties: Majorana vs. Dirac, mass scale, hierarchy, CP phases

• Oscillation data make distinct predictions for mee (NH: 1-4 meV, IV: 14-57 eV, DG: <1 eV (90% CL))

• Second generation experiments (NEMO3, CUORICINO) started data taking; sensitive to check HdM claim within next years: ~ 0.1-0.4 eV