First results on the neutrinoless double beta decay from GERDA twin lock glove box Laura Baudis clean room (for the GERDA collaboration) shutter University of Zurich 3 heat Ω 590 m > 0.17 M m exchanger water tank radon shroud Invisibles workshop Ge detector Durham, July 17, 2013 array copper shield cryostat 3 64 m LAr 66 PMT Cerenkov 2m 5m
The physics • Detect the neutrinoless double beta decay in 76 Ge: ➡ lepton number violation ➡ information on the nature of neutrinos and on the effective Majorana neutrino mass = G 0 ν ( Q, Z ) | M 0 ν | 2 | m ββ | 2 1 Γ 0 ν = T 0 ν m 2 e 1 / 2 arXiv:1305.0056v1 [hep-ph] 30 Apr 2013 10 32 76 Ge Planck1 95 % CL Planck2 95 % CL NH 10 30 H yr L Alonso, Gavela, Isidori, Maiani 10 28 0 n T 1 ê 2 (4x10 25 - 8x10 26 yr) IH arXiv:1306.5927 [hep-ph] 10 26 QD KK 90 % CL HM 90 % CL current sensitivities 10 24 0.001 0.01 0.1 10 - 4 m lightest H eV L Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Experimental requirements • Experiments measure the half life of the decay, T 1/2 1 r M · t h m ββ i / T 0 ν 1 / 2 ∝ a · ✏ · q T 0 ν B · ∆ E 1 / 2 Minimal requirements: Additional tools to distinguish signal from background: large detector masses (M) enriched materials (a) angular distribution ultra-low background noise (B) identification of daughter nucleus excellent energy resolution ( ∆ E) pulse shape information high detection efficiency ... Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
The GERDA experiment at LNGS Eur. Phys. J. C (2013) 73:2330 • Ge detectors directly submersed in LAr ➡ LAr as cooling medium and shielding (U/Th in LAr < 7x10 -4 µBq/kg) ➡ a minimal amount of surrounding materials 590 m 3 H 2 O equipped with PMTs • Phase I ➡ ~18 kg HdM and IGEX detectors • Phase II ➡ additional 20 kg BEGe detectors 16 t Cu � � 64 m 3 LAr Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
The GERDA collaboration http://www.mpi-hd.mpg.de/gerda/ INR Moscow ITEP Moscow Kurchatov Institute 16 institutions ~100 members Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Collaboration meeting in Dubna, June 2013 Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
GERDA detectors arXiv:1307.2610v1 [physics.ins-det] 9 Jul 2013 • Phase I: p-type semi-coaxial • Phase II: p-type, BEGe (broad energy germanium) • n + conductive Li layer, separated by a groove from the boron implanted p + contact • Signal structure allows to distinguish between single site events (SSE) = signal-like and multiple site events (MSE) = background-like 1.0 charge trace [a.u.] GERDA 13-06 0.8 0.6 A single site event SSE 1 multi site event MSE 0.4 A t (A ) t (A ) 2 MSE MSE 2 1 0.2 t (A ) t (A ) SSE SSE 2 1 0.0 time a.u. a.u. 1.0 1.0 SSE MSE 0.8 0.8 Charge 0.6 0.6 Current 0.4 0.4 0.2 0.2 0.0 0.0 81200 81400 81600 81800 82000 81200 81400 81600 81800 82000 t [ns] t [ns] Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
GERDA detectors • From HdM and IGEX experiments: total mass = 17.7 kg ➡ HdM: ANG1, ANG2, ANG3, ANG4, ANG5; IGEX: RG1, RG2, RG3 ➡ Isotopically enriched in 76 Ge: 86% • Two 76 Ge detectors turned off because of high leakage current => m = 14.6 kg • In addition, natural Ge detectors from Genius-TF • And 5 phase II, enriched BEGe detectors added in July 2012 22& Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Overview of physics runs total exposure Phase I, used in neutrinoless double beta analysis: 21.6 kg yr • Blue ‘spikes’: (bi) weekly (215.2 mol yr 76 Ge in active volume) calibrations runs with 3 228 Th yr) sources live time fraction GERDA 13-05 runs 25-32,34-43,44-46 22 × 1.0 exposure (kg 20 • Data in signal region was kept 18 blind: Q ± 20 keV 0.8 16 14 0.6 12 10 0.4 8 6 0.2 4 0 analysis ν β β 2 this analysis 0.0 0 Nov-11 Feb-12 Jun-12 Oct-12 Jan-13 May-13 date data used for background model Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Half life of the 2-neutrino decay mode νββ IOP P UBLISHING J OURNAL OF P HYSICS G: N UCLEAR AND P ARTICLE P HYSICS doi:10.1088/0954-3899/40/3/035110 J. Phys. G: Nucl. Part. Phys. 40 (2013) 035110 (13pp) Measurement of the half-life of the two-neutrino double beta decay of 76 Ge with the GERDA experiment × 10 21 yr 1 . 84 +0 . 09 T 2 ν � � 1 / 2 = − 0 . 08 Uncertainty on T 2 ν 1 / 2 Item (%) Non-identified background components + 5 . 3 Energy spectra from 42 K, 40 K and 214 Bi ± 2 . 1 Shape of the 2 νββ decay spectrum ± 1 + 5 . 8 Subtotal fit model − 2 . 3 Precision of the Monte Carlo geometry model ± 1 Accuracy of the Monte Carlo tracking ± 2 Subtotal Monte Carlo ± 2 . 2 Data acquisition and selection ± 0 . 5 + 6 . 2 Grand total − 3 . 3 Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
GERDA Calibration • Determine energy resolution and stability in time • Energy resolution: ~ 4.5 - 5.1 keV (FWHM) at 2.6 MeV • Mean energy resolution at Q=2039 keV: 4.8 keV and 3.2 keV for coaxial and BEGe (FWHM) 3 10 4.2 keV 4.8 keV ANG2 1 0 500 1000 1500 2000 2500 550 600 2550 2600 3 10 4.2 keV 4.8 keV counts ANG3 1 3 0 500 1000 1500 2000 2500 550 600 2550 2600 10 4.0 keV 4.5 keV ANG4 1 0 500 1000 1500 2000 2500 3 550 600 2550 2600 10 3.6 keV keV 4.5 keV ANG5 1 0 500 1000 1500 2000 2500 550 600 2550 2600 3 10 3.8 keV 4.8 keV RG1 1 0 500 1000 1500 2000 2500 550 600 2550 2600 3 10 4.4 keV keV 5.1 keV RG2 1 0 500 1000 1500 2000 2500 2550 2600 550 600 energy [keV] GERDA draft energy [keV] Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Calibration stability • Mean energy resolution at Q=2039 keV: 4.8 keV and 3.2 keV for coaxial and BEGe (FWHM) Energy&resoluEon&of&coax&detectors&at&2039&keV&& 42 K background line Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Backgrounds arXiv:1306.5084v1 [physics.ins-det] 21 Jun 2013 • main sources considered in the background model counts/(5 keV) yr) enriched coaxials, 16.70 kg yr × GERDA-1305 4 10 2 Bi-214 2204 keV 10 Bi-214 1765 keV Tl-208 2615 keV × kg × cts/(keV 3 10 2 ν β β 10 source location 210 2 Po 10 p + surface 1 210 Po 226 Ra p + surface 226 Ra chain 10 -1 10 222 222 Rn chain LAr in bore hole Rn 218 Po 1 -2 10 n + surface 214 Bi and 3 10 counts/(5 keV) yr) GERDA-1305 enriched BEGes, 1.80 kg yr × 214 Pb mini-shroud K-40 1461 keV K-42 1525 keV × kg detector assembly 3 10 2 10 p + surface × cts/(keV 2 ν β β radon shroud LAr close to p + surface 2 10 10 Q ββ ± 20 keV 208 Tl and detector assembly 10 1 212 Bi radon shroud heat exchanger 1 -1 10 3 10 counts/(5 keV) yr) 228 Ac 4 GERDA-1305 detector assembly GTF 112, 3.13 kg yr 10 × radon shroud × - 39 kg Ar β 2 10 3 10 × cts/(keV 42 K homogeneous in LAr n + surface 10 2 10 p + surface α 1 10 60 Co detectors -1 10 detector assembly 1 0 1000 2000 3000 4000 5000 6000 7000 energy (keV) 2 νββ detectors 40 K detector assembly Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
Three data sets • The BEGe set ; the coaxial data, which is split into gold and silver 0.30 counts/(kg day) GERDA-1305 coaxial diodes, E: 1550-3000 keV 0.25 background rate in the coaxial 0.20 76 Ge detectors versus time 0.15 grey band = silver-coax 0.10 rest = gold-coax 0.05 insertion of BEGe 0.00 Jan-12 Apr-12 Jul-12 Oct-12 Dec-12 Apr-13 date data set detectors exposure E this analysis 0 νββ analysis kg · yr SUM-coax all enriched coaxial 16.70 19.20 GOLD-coax all enriched coaxial 15.40 17.90 SILVER-coax all enriched coaxial 1.30 1.30 detailed exposures for all GOLD-nat GTF 112 3.13 3.98 three data sets GOLD-hdm ANG 2, ANG 3, ANG 4, ANG 5 10.90 12.98 GOLD-igex RG 1, RG 2 4.50 4.93 SUM-bege GD32B, GD32C, GD32D, GD35B 1.80 2.40 Laura Baudis, University of Zurich Invisibles 2013, Lumley Castle, Durham
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