Germanium Detector Array: Difference between revisions

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{{Underlinked|date=December 2014}}

The GERmanium Detector Array ('''GERDA''') experiment is searching for [[neutrinoless double beta decay]](0vββ) in Ge-76 at the underground [[Laboratori Nazionali del Gran Sasso]] (LNGS). [[Neutrinoless beta decay]] is expected to be a very rare process if possibleit occurs. The collocationcollaboration predicts less than one event each year per kilogram of material, appearing as a narrow spike around 2039 keV in the observed energy spectrum. This means b[[Radiation_protection|Backgroundackground shielding]] is required to detect any rare decays. The LNGS facility has 1400 meters of rock overburden, equivalent to 3000 meters of water shielding, reducing [[Cosmic ray|cosmic radiation]] [[Background radiation|background]].

== Design ==

The experiment uses high purity enriched [[Germanium|Ge]] crystal [[diodes]] (HPGe) as a beta decay source and [[particle detector]]. The detectors from the HdM and Igex experiments were reprocessed and used in GERDAphase 1. The detector array is suspended in a liquid [[argon]] [[cryostat]] lined with copper and surrounded by an ultra-pure water tank. [[Photomultiplier|PMTs]] in the water tank and plastic [[scintillators]] above detect and exclude background [[muons]].

Phase 2 will increase the active mass to 38kg using 30 new HPGe detectors. A magnitude reduction in background is planned to 10^-3/(keV·kg·yr) using cleaner materials. This will increase the half-life sensitivity to 10²⁶ years once 100kg·yr of data is taken and enable evaluation of possible ton-scale expansion.

== Results ==

Phase I collected data November 2011 to May 2013, with 21.6 kg·yr exposure, obtaining a 0vββ 90% CL half-life limit of:

<math>T_{0 \nu \beta \beta} > 2.1*10^{2125} yr </math>. This limit can be combined with previous results, disfavouringdisfavoring the Heidelberg-Moscow experiment detection claim. A double beta decay half-life was also measured: T_2vββ = (1.84^+0.14_−0.10)·10²¹ yr.

Phase II will have additional enriched Ge detectors and reduced background, raising the sensitivity about one order.

== Publications ==