GERDA Test Stands for Segmented Germanium Detectors Iris

GERDA Test Stands for Segmented Germanium Detectors Iris Abt, Allen Caldwell, Manuela Jelen, Kevin Kroeninger, Jing Liu, Xiang Liu, Bela Majorovits, Jens Schubert, Franz Stelzer DPG, March 2007 GERDA 1

Outline Motivation Test Stands with Detectors on Cold Finger Test Stands with Detectors in Cryo-Liquid Conclusions DPG, March 2007 GERDA 2

Motivation counts [arbitrary units] GERDA is looking for 0νββ-decay → n Dirac or Majorana particle? → total mass (upper limit if no discovery) 0νββ: rare process → low background (sum of electron energies)/Qββrequired -3 cnts/kg/y/ke. V) Ge: good energy resolution →(<10 background reduction DPG, March 2007 GERDA 3

Motivation Background reduction: GERDA in underground lab (cosmic rays) Water Tank (neutrons) GERDA Detectors operated directly in LAr (γ-background) Test Stands in Munich: LN 2/LAr and Cold Finger DPG, March 2007 GERDA 4

Segmented Germanium Detectors detector material: high purity Germanium detectors segmented 6 -fold in φ and 3 -fold in height segmentation helps with background rejection signal: 1 segment hit background event: more segments hit DPG, March 2007 GERDA 5

Test Stands with Detectors on Cold Finger classical cryostat ‘Galatea’ LN 2 DPG, March 2007 GERDA 6

Test Stands with Detectors on Cold Finger classical cryostat for first n-type 18 -fold segmented detector cooled indirectly via copper cold finger sources put outside aluminum vacuum tank DPG, March 2007 GERDA 7

Test Stands with Detectors on Cold Finger – Galatea Sources movable 360° in φ- and whole range in z-and rdirection Precision → 3 -D scan; surface and High bulk properties, Tool dead layers no material between source and detector → ideal for α-/ β-sources/laser Segment resolution, segment boundaries and cross-talk → pulse shape studies and background suppression DPG, March 2007 GERDA 8

Test Stands with Detectors in Cryo-Liquid ‘Milchkanne ’ ‘GERDAlinchen II’ LN 2 or LAr DPG, March 2007 GERDA 9

Test Stands with Detectors in Cryo-Liquid detector ‘Milchkanne >30 cooling cycles: ’ 1) submerge crystal in LN 2 or LAr top view 2) measurement (resolution) 3) warm crystal to 300 K and put back in vacuum storage 2 → operational routine → detector stands alternating environments DPG, March 2007 GERDA 10

Test Stands with Detectors in Cryo-Liquid Leakage Current [p. A] ‘GERDAlinchen’ DPG, March 2007 Mounting of a 6 -fold segmented p-type detector 103 102 10 1 Bias Voltage [V] GERDA 11

Test Stands with Detectors in Cryo-Liquid ‘GERDAlinchen II’ DPG, March 2007 GERDA 12

Conclusions Detectors can be operated in vacuum or in cryogenic liquids, LN 2 or LAr n Stable operation of Ge detectors in LN 2/LAr n New vacuum test stand ‘Galatea’: precision tool to scan crystal in 3 -D n New test stand with naked crystal in LN 2 : ‘GERDAlinchen II’ → test for GERDA setup of detector strings n DPG, March 2007 GERDA 13