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GERDA: GERmanium Detector Array

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GERDA: GERmanium Detector Array. Searching for 0 ... Normal hierarchy or inversed? Nature: Dirac or Majorana? 0 2 decay ... MC package (MaGe) for both ... – PowerPoint PPT presentation

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Title: GERDA: GERmanium Detector Array


1
GERDA GERmanium Detector Array Searching for
0?2? decay
Xiang Liu Max-Planck-Institut für Physik
  • 0?2? introduction
  • GERDA setup
  • detectors
  • 3. Low background
  • high sensitivity
  • RD
  • Conclusion

SNOW 2006, May 2-6th, 2006
2
Neutrino mixing 0?2? decay
  • Open questions
  • Absolute mass scale?
  • Normal hierarchy or inversed?
  • Nature Dirac or Majorana?
  • ? 0?2? decay might address all.


SNOW2006
Page 2
3
Effective Majorana neutrino mass m??
SNOW2006
Page 3
4
GERDA Setup
  • 0?2? rare process
  • Large amount of target mass
  • High efficiency detecting signal
  • Low background

76Ge ?? 8 in nature,need enrichment (reduce
bg) ?? Detector source, gt95 signal effi. ??
Excellent ? (FWHM 2 keV at 1.3 MeV) ,
high Q value (2.04 MeV) ?? existing detectors
experiences from HdMo IGEX.
LNGS Hall A (3800 m.w.e.)
Clean room Lock
Scintillator veto (top of clean room) Cerenkov
veto (PMTs in water tank)
SNOW2006
Page 4
5
Detectors supports
Materials near detectors as little as
possible, as pure as possible.
Phase-I HdMo IGEX detectors, sum 15kg,
non-segmented Phase-IINew detectors, sum 25kg,
18 segments (3z?6?)
SNOW2006
Page 5
6
Status of Existing Phase-I Detectors
  • IGEX detectors testedinside Vacuum storage Can.
  • FWHM 2.2 - 2.3keV at 1332keV
  • HdMo detectors stored at LNGS, all tested.
  • One HdMo detector taken out from Vacuum Can for
    testing.

HdMo Setup
ANG1 Ge crystal
HdMo claim Signal 28.75 ? 6.86 events Bg
level 0.11 cts/keV kg year If claim true,
Phase-I will have Signal 13 events Bg level
lt0.01 cts/keV kg year lt3
events in 10keV window at Q
value.
SNOW2006
Page 6
7
Status of Phase-II Detectors
  • 37.5kg Ge, 87.25 76Ge, purity gt99.9 (in GeO2)
    enriched in Russia,
  • transported to MPI Munich on April 3rd 2006,
  • now stored underground (200m.w.e)
  • Next steps purification, crystal pulling
    detector fabrication.

SNOW2006
Page 2
8
High sensitivity Low background
Exposure kg year bg. Level keV kg year Limit on m?? ev
Phase I 30 10-2 0.5
Phase II 100 10-3 0.2
a) b)
Phase II

Phase I
a) Assessment of uncertainties in QRPA 0?2?-decay
nuclear matrix elements V.A. Rodin, A. Faessler,
F. Simkovic, P. Vogel Nucl-th 0503063 b)
Search for Neutrinoless Double Beta Decay with
Enriched 76Ge in Gran Sasso 1990-2003, H.V.
Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz
and O. Chkvorets, Phys. Lett. B586 (2004) 198-212
SNOW2006
Page 8
9
Use segments to reject background
0?2? signal 2 electrons deposit energy very
localized (lt1mm)
Background ? Mostly Compton scattering 23 cm
mean free path (mostly multi-segment)
Source Reduction factor
208Tl (in Ge) 13
60Co (in Ge) 38
68Ge (in Ge) 18
210Pb (? on Ge surface) 1
208Tl (in holder) 5
60Co (in holder) 157 (?27)
208Tl (in cable) 7
SNOW2006
Page 9
10
MC simulation of bg.
Water tank
  • MC package (MaGe) for both Gerda Majorana.
  • Upper limit on contamination levels for all
    materials calculated.
  • Bg. Index calculated with available materials.

Cryo vessel
(Phase II)
SNOW2006
Page 10
11
RD Ge detector properties
Several test facilities being built with
detectors directly in LN2/LAr.
  • Both n p-type Ge cycled
  • multi times in LN2 LAr
  • ?Similar behavior in LN2/LAr.
  • ?No deterioration of performance.
  • One 18-segment n-type detector is under study.

SNOW2006
Page 11
12
Conclusion
  • Open questions in ? absolute mass? hierarchy?
    Majorana or Dirac?
  • 0?2? might answer all these questions.
  • GERDA searches for 0?2? decay in 76Ge.
  • Ge detectors are submerged directly in LN2/LAr
    (cooling shielding).
  • IGEX HdMo detectors for Phase-I.
  • Segmented Ge detectors for Phase-II.
  • Goal for bg. rate 10-3 cts/keV kg year
    (Phase-II), difficult but feasible.
  • With this bg. rate, sensitivity of 0.2eV on m??
    expected.
  • Several test facilities for GERDA are being
    built.
  • Both n- p-type detectors cycled in LN2/LAr
    without obvious deterioration.
  • Once the GERDA concept is proven, global
    experiment with 1t Ge might be pursued (MoU with
    Majorana exists).

SNOW2006
Page 12
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