Transcript Document

Investigating Neutrinoless Double Beta Decay
Status of the GERDA Experiment
Michael Altmann
Max-Planck-Institut für Physik, Munich
Physics
R&D Detectors
Concept
Schedule, etc.
Exp. Setup
Summary
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Physics Motivation :
Nature of the Neutrino
Neutrino masses and lepton flavour mixing
established by oscillation experiments
 Neutrino mass differences known
Still Unknown:
 absolute mass values
 hierarchy scheme
 n = anti-n ?
 Neutrinoless Double Beta Decay
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Physics Goals and
Experimental Requirements
GERDA Sensitivity
Klapdor-Kleingrothaus
positive evidence
Phase 1
Phase 2
Phase-3
For excluding
inverted hierarchy:
Sensitivity on
10 meV level required  ton-scale @ B < 10-4 / keV kg yr
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
GERDA: Germanium Detector Array
Array of HP-Germanium Diodes, made from
isotopically enriched (86% in Ge-76) material
Phase-1:
Use existing diodes from Heidelberg-Moscow and IGEX (  15kg)
0.01 / keV kg yr intrinsic background expected
Goal: verify concept; probe Klapdor-Kleingrothaus‘ evidence
(if no event observed,  1 yr of measuring time needed to disprove at 98% cl)
Phase-2:
Increase mass by adding  20 kg of new enriched Ge-detectors
Goal: 100 kg yr statistics at background level B<10-3 / keV kg yr
T1/2 > 2 * 1026 yr

mneff < 0.09 – 0.29 eV
Phase-3:
(Depending on results of phase-2 and possibly other experiments)
worldwide collaboration for really big experiment;
close contacts and MoU with MAJORANA established
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
GERDA‘s Experimental Concept
Assumption: External background is dominant
• Minimize all impure materials close to Ge diodes
• Operate Ge diodes in ultraclean environment
 cryogenic liquid shield (LN or LAr); graded shielding
• Reject remaining
background (internal and
external) by exploiting
different interaction
topology
(single-site  multi-site; PSA)
Goal: Background index of
0.001 cts / (keV kg y)
at Qbb=2039 keV
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
GERDA Location: Gran Sasso
National Laboratory (LNGS)
Assigned Location for Phases 1 & 2:
LNGS Hall A, next to the CRESST and LVD Experiments
1400 m
~ 3.800 m.w.e
M.Altmann, GERDA Status Report
GERDA
SNOLAB Workshop IV, 15.-17.8.2005
Experimental Setup at LNGS
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
GERDA‘s Cleanroom Facility at
LNGS: LArGe
HD-Moscow‘s KI-detectors
were handed over to
GERDA
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
LArGe‘s Liquid Argon Test Stand
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Detector Arrangement
Modular Detector Arrangement :
- Detector strings
- Hexagonal string
arrangement
- Low mass, low
background crystal
holders and suspension
- Additional strings can
„easily“ be added when
new detectors become
available, with the
vessel remaining cold
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Detector Suspension for Phase-1
- Low mass (bgd index < 10-2 / keV kg y )
- Use only screened materials
with known radioimpurities
(Cu, PTFE, Si)
- Specific ORTEC-type contact
(bottom of bore hole)
- Mount and test every crystal
individually
(LArGe Facility at LNGS)
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Ge-76 Procurement for Phase-2
- Enrichment of 37.5 kg of Germanium ongoing
(ECP, Krasnoyarsk, Russia)
- Delivery procedure tested with natGe:
very smooth, no problems encountered
(20 day trip Krasnoyarsk  Munich,
special shielding container: 10-20 attenuation factor
for cosmogenic production of 68Ge and 60Co)
- ongoing R&D:
 maintaining original purity during enrichment
 optimizing yield of chemical purification
to 6N metal
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Phase-2: Segmented Detectors
Interaction topology of bb-signal and g-background
different  anticoincidence for bgd suppression
„pointlike“, single-site vs. „extended“, multi-site

2 electrons deposit energy
locally (d = O(1 mm))
M.Altmann, GERDA Status Report
60Co:
2 photons (l=O(cm)) 
(multiple) Compton-scattering
SNOLAB Workshop IV, 15.-17.8.2005
Detector Development for Phase-2
R&D on two types of detectors: p-type and n-type
n-type prototypes:
 Naked crystal: available & operated in LN
 Naked crystal, 6fx3z segmented, true coax: on order
p-type prototypes:
 Naked crystal, true coax:
available & operated in LN
 Naked crystal, true coax,
6f x 1z segmented: available
 Naked crystal, true coax,
6f x 3z segmented: on order
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Detector Suspension for Phase-2
18-fold segemented detectors
(true-coaxial, 3x6, n-type)
Kapton
cable
bonded
contacts
Total of 30g mounting material / detector
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Simulation Results on
Segmented Detectors
- Monte Carlo (MaGe: common Majorana-Gerda simulation framework) :
Anticoincidence between segments (18-fold segmentation)
  factor 10 increase in 60Co rejection
- Further improvement (up to  factor 5):
Analysis of pulse shapes and mirror charges (PSA)
( regain signal sitting on segment boundary)
(  0.2 cm spatial resolution)
- R&D ongoing:
 Monte Carlo studies and PSA development
 Laboratory measurements with prototype detectors
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Pulse Shape Simulation
Full simulation of true coaxial 6-fold segmented
detector (only 1 segment hit):
Hit segment:
full energy deposit
electrode
Core signal:
full energy deposit
electrode
core
Charge
Neighbouring
segments:
mirror charges
electrode
electrode
electrode
electrode
Time
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Full Simulation of a True-Coax
18-fold Segmented Detector
Signals seen by the segment electrodes  Position Reconstruction (f and z)
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Simulation Results on
Segmented Detectors
PSA  Information on radius and angle:
Clear correlation between time
of charge collection and radius
of interaction point
M.Altmann, GERDA Status Report
Correlation between
ratio of amplitudes of
neighbouring segments
and angle f of interaction
point
SNOLAB Workshop IV, 15.-17.8.2005
Status & Time Schedule
2004:
• Feb
• Sep
• Oct
2005:
• Feb
• Mar
• May
• Jun
• Jul
• Aug
• Sep
Letter of Intent to LNGS (hep-ex/0404039)
Formation of Collaboration
Funding request approved by MPG; Proposal to LNGS (wwwgerda.mppmu.mpg.de)
GERDA approved by LNGS
Technical proposal to LNGS; 30 kg of enriched Ge-76 for phase-2 ordered
Funding requests approved by INFN
Funding request approved by BMBF
Ge-76 order enlarged to 37.5 kg; safety study for cryostat submitted to LNGS
Expect decision by LNGS on system safety
if OK: tendering for water tank, first orders for cryostat
2006:
• Jun
• ???
Start of water tank installation at LNGS
Installation of cryostat, clean room and lock, muon veto, ...
2007:
• spring
Commissioning, then start of physics run
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
The GERDA Collaboration
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005
Summary and Conclusions
 Approved by LNGS with location
in hall A
 substantially funded by BMBF,MPG,
INFN and Russia (in kind)
 construction at LNGS start 6/06
 in parallel: substantial R&D for and
preparation of phase II
 start of data taking in 2007
phase-1: verify concept, probe KK-evidence for bb0n
phase-2: T1/2 > 2 * 1026 yr  mneff < 0.09 – 0.29 eV
phase-3: t.b.d., depending on results;
ton-scale experiment in worldwide collaboration
M.Altmann, GERDA Status Report
SNOLAB Workshop IV, 15.-17.8.2005