GERDA and GeDet Project Review 2010 Fabiana Cossavella for GERDA - PowerPoint PPT Presentation

GERDA and GeDet Project Review 2010 Fabiana Cossavella for GERDA & GeDet groups Max-Planck Institut f¨ ur Physik, M¨ unchen 21 December 2010 Fabiana Cossavella GERDA and GeDet Project Review 2010 1/27

Director : Allen Caldwell Project leaders : B´ ela Majorovits (GERDA), Iris Abt (GeDet) Postdoc : Fabiana Cossavella, Josef Janicsko, Xiang Liu (03/10), Christopher O’Shaughnessy PhD : Neslihan Becerici-Schmidt, Sabine Dinter, Daniel Lenz (03/10), Oleksandr Volynets Diplomand : Hossein Aghaei-Khozani (11/10), Florian Faulstich, Sabine Hemmer (09/10), Annika Vauth (10/10) Group engineer : Hans Seitz, Franz Stelzer Engineering : Karlheinz Ackermann, Sven Vogt Many thanks to the Sonja Boisnel, Reinhard Sedlmeyer, Dominik Wamsler, Alex Wimmer, G¨ unter Winklm¨ uller and the colleagues from electronic & mechanic departments Fabiana Cossavella GERDA and GeDet Project Review 2010 2/27

Search for 0 νββ decay Unknowns about Neutrinos: • Nature of the Neutrino (Dirac - Majorana?) • Absolute mass scale? Inverted/normal hierarchy? Evidence from Heidelberg- • CP phases? Moscow-Experiment n p 90% 90% degeneracy degeneracy F.Feruglio et al., Nucl. F.Feruglio et al., Nucl. CL CL L=2, w- Δ Phys. B 637(2002) Phys. B 637(2002) e - beyond SM Δm 32 < 0 eV Δm 32 < 0 eV e - Δm 32 > 0 eV Δm 32 > 0 eV w- n p If neutrinoless double beta-decay is observed: Neutrino is a Majorana particle Information on absolute mass scale |M nucl | 2 <m ee > 2 1/ τ = G(Q,Z) 0νββ Decay Phase space Matrix Effective Majorana rate factor element Neutrino mass Fabiana Cossavella GERDA and GeDet Project Review 2010 3/27

Search for 0 νββ decay Signature: Sharp peak at Q-value of the decay (2039 keV for 76 Ge) Fabiana Cossavella GERDA and GeDet Project Review 2010 4/27

The GERmanium Detector Array Clean-room Lock system Phase I: Water tank (steel) Use HdMo and Muon veto ( Č ) IGEX detectors (18kg) Cryostat (steel + Cu) Phase II: Liquid argon Use additional detectors from Detector array 37.5kg available enriched material Fabiana Cossavella GERDA and GeDet Project Review 2010 5/27

Deployment of 1st string ◮ infrastructure completed in May 2010 ◮ 1st string of nat Ge installed in June 2010 background measurement ongoing since June 2010 Fabiana Cossavella GERDA and GeDet Project Review 2010 6/27

Deployment of 1st string 4 10 GTF 45 4.4 keV FWHM Counts 2 10 0 10 0 500 1000 1500 2000 2500 3000 3500 Energy (keV) 4 10 GTF 32 4.0 keV FWHM Counts 2 10 0 10 0 500 1000 1500 2000 2500 3000 3500 Energy (keV) 4 10 GTF 112 4.2 keV FWHM Counts 2 10 0 10 0 500 1000 1500 2000 2500 3000 3500 Energy (keV) 228 Th calibration spectrum Fabiana Cossavella GERDA and GeDet Project Review 2010 7/27

GERDA background Distinct peak at 1525 keV s o n r e c t e l m o f r d u n o g r c k a b u s u o n n t i o C ◮ background contributions due to 232 Th, 238 U: < 1 . 2 · 10 − 2 counts / ( kg keV y ) Fabiana Cossavella GERDA and GeDet Project Review 2010 8/27

GERDA background Distinct peak at 1525 keV s o n t r e c e l m o f r d u n o g r c k b a s u u o n n t i o C ◮ 42 K + drift in the electric field ◮ Changing field configuration changes intensities → best background: 8 · 10 − 2 counts / ( kg keV y ) at Q ββ ◮ further studies ongoing Fabiana Cossavella GERDA and GeDet Project Review 2010 8/27

GERDA enriched material Reduction in H 2 atmosphere enr GeO 2 powder enr Ge metal bars Zone refinement enr Ge 6N metal bars suitable for HP enr Ge crystal growth Reduction yield Zone refinement yield 98.5% 95.3% , overall 93.9% Material reduced and purified with yield > 80% (target) Fabiana Cossavella GERDA and GeDet Project Review 2010 9/27

Crystal pulling for n-type HPGe detectors Pulling HPGe crystals is not trivial! Worlwide only three companies. Cooperation with IKZ, Berlin: Czochralski puller procured, Refurbrished and electropolished. Many crystals grown. One crystal with few 10 10 per cm 3 But most crystals with ~10 11 per cm 3 Still one order of magnitude too high 6N Material from PPM is already very clean Fabiana Cossavella GERDA and GeDet Project Review 2010 10/27

The final lock system Outer Lock Cable Feedthrough Inner Lock Motor Feedthrough assembly starts after delivery of the 3-string arm of c-lock Fabiana Cossavella GERDA and GeDet Project Review 2010 11/27

GeDet Project Development of segmented n-type Germaniun detectors for future applications 1 Ton initiative Properties of Ge detectors ◮ push further down sensitivity ◮ study of surface events ◮ normal or inverted hierarchy? induced by α and β ◮ 1 Ton of enr Ge ◮ study of pulse shape details to ◮ background index = 10 − 5 cts identify surface events and multiple interaction → keV − 1 kg − 1 y − 1 background reduction Fabiana Cossavella GERDA and GeDet Project Review 2010 12/27

Test Stands: detector characterization K1 test stand: detector operated in vacuum cryostat (T from 90 K to 120 K), γ scans only task completed → prototype detector for a GERDA scale experiment “Characterization of the first true coaxial 18-fold segmented n-type prototype detector for the GERDA project”, Iris Abt et al., Nucl.Instrum.Meth. A 577 (2007) 574 Fabiana Cossavella GERDA and GeDet Project Review 2010 13/27

Test Stands: detector characterization Gerdalinchen II ◮ able to handle 3 HPGe detectors in LN 2 or LAr ◮ operation at 77 K ”Operation of an 18-fold segmented n-type HPGe detector in liquid nitrogen”, Iris Abt et al., J. Instrum. 4 (2009) p11008 Fabiana Cossavella GERDA and GeDet Project Review 2010 14/27

Pulse Shape simulation Development of a complete package to simulate pulses. Shape of a pulse strongly influenced by: impurity of the crystal ◮ impurities are not homogenous ◮ each crystal is individual ◮ uncertainty ∼ 20% − 30% mobility ◮ e − reasonably well known ◮ holes → available measurements differ inside a factor 2 Fabiana Cossavella GERDA and GeDet Project Review 2010 15/27

Pulse Shape simulation h, outward drift [degree] 10 (a) <100> <110> <100> 40 〈 〉 010 0 0 5 〉 1 110 〉 〈 30 〈 0 20 5 10 10 y [mm] 〈 110 〉 0 120 140 160 180 200 220 240 260 280 -10 -20 -30 (b) -40 -40 -30 -20 -10 0 10 20 30 40 x [mm] ◮ trajectories are bent due to the crystal structure ◮ charge carries slower in the < 110 > than in the < 100 > direction → very clear for the holes trajectories Fabiana Cossavella GERDA and GeDet Project Review 2010 16/27

Pulse Shape simulation 40 1 electron (a) γ hole B 30 20 C A -1 10 10 y [mm] 0 -10 -2 10 -20 -30 -3 -40 10 -40 -30 -20 -10 0 10 20 30 40 x [mm] ◮ electric signals induced on the electrodes by cumulative influence of moving electrons and holes ◮ pulse in segment B + mirror pulses in segments A and C ◮ kinks in core and segment B pulse when e − reach the core Fabiana Cossavella GERDA and GeDet Project Review 2010 17/27

Pulse Shape simulation Data Fitted Simulated Pulse Time scale factor = 0.90 ± 0.01 χ ² /dof = 184/146 ◮ simulated core pulses fitted to measured pulses → simulation describe the general shape very well ◮ overall length of simulated pulse to be adjusted → ρ imp , T, µ Fabiana Cossavella GERDA and GeDet Project Review 2010 18/27

Pulse lenght: T dependence Expectation 550 Rise time [ns] o Core, 0 , <110> axis ◮ if E ∼ const. → DS1, T=77.4 K 500 DS2 shifted for 8.5 K t r ∝ µ eff − 1 DS3 shifted for 10.0 K Fit p +p exp(-p /T) 0 1 2 450 Theoretical calculation ◮ µ eff ∝ T − 3 / 2 400 DS3 Data 350 ◮ Boltzmann-like law: DS2 300 t r ∝ e − k / T DS1 ◮ is something else 250 80 90 100 110 120 130 Temperature [K] T-dependent? ◮ t r core = 290ns, simulation T dependence will be included → in PS simulation package! ◮ t r core = 287ns, data Fabiana Cossavella GERDA and GeDet Project Review 2010 19/27

GALATEA ◮ analysis of surface effects with coaxial Ge detectors ◮ direct irradiation with α and β particles and IR laser Fabiana Cossavella GERDA and GeDet Project Review 2010 20/27

GALATEA first measurements ◮ 60 Co and 228 Th on top of the tank to test functionality ◮ alpha-( 241 Am), beta-( 90 Sr) and gamma sources inside the tank for precision measurements Fabiana Cossavella GERDA and GeDet Project Review 2010 21/27

GALATEA first measurements Th spectrum of segment 7 with background number of events 600 Th228 500 400 FWHM @ 2.6MeV = 3.75 keV 300 200 K40 100 0 500 1000 1500 2000 2500 3000 energy in keV Fabiana Cossavella GERDA and GeDet Project Review 2010 22/27

Background reduction R&D ◮ singly Compton scattered γ s escaping detector → same event topology as signal-like events ◮ use scintillation light to identify event as background ◮ normal PMTs contribute to radioactive background! Fabiana Cossavella GERDA and GeDet Project Review 2010 23/27

Background reduction R&D ◮ 12 SiPMs + 15 m wavelength shifting fibers ◮ successfully operated in anticoincidence with 6-fold segmented HPGe detector ◮ detection efficiency ≈ 90 p.e./MeV energy deposit Fabiana Cossavella GERDA and GeDet Project Review 2010 24/27