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Register a new userThe KDK (potassium decay) experiment
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Added by
Philippe Di Stefano
Publication date
2017
fields
Physics
and research's language is
English
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Potassium-40 (${}^{40}$K) is a background in many rare-event searches and may well play a role in interpreting results from the DAMA dark-matter search. The electron-capture decay of ${}^{40}$K to the ground state of ${}^{40}$Ar has never been measured and contributes an unknown amount of background. The KDK (potassium decay) collaboration will measure this branching ratio using a ${}^{40}$K source, an X-ray detector, and the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory.
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To measure the main characteristics of radiative neutron decay, namely its relative intensity BR (branching ratio), it is necessary to measure the spectra of double coincidences between beta-electron and proton as well as the spectra of triple coincidences of electron, proton and radiative gamma-quantum. Analysis of double coincidences spectra requires one to distinguish events of ordinary neutron beta decay from the background; analysis of triple coincidences relies on distinguishing radiative neutron decay from background events. As demonstrated in our first experiment, these spectra presented a heterogeneous background that included response peaks related to the registration of electrons and protons by our electronic detection system. The NIST experimental group (emiT group) observed an analogous pattern on the spectrum of double coincidences. The current report is dedicated to the analysis of this heterogeneous background. In particular, this report demonstrates that the use of response function methodology allows to clearly identify radiative neutron decay events and to distinguish them from the background. This methodology enabled us to become the first team to measure the relative intensity of radiative neutron decay B.R.= (3.2+-1.6)*10-3 (where C.L.=99.7% and gamma quanta energy exceeds 35 kev). In addition, the review emphasizes that the background events on the spectrum of double coincidences are caused by ion registration, and demonstrates that one cannot ignore the ionic background, which is why experiment registered the ions and not recoil protons.
Neutrinoless double-beta decay is a key process in particle physics. Its experimental investigation is the only viable method that can establish the Majorana nature of neutrinos, providing at the same time a sensitive inclusive test of lepton number violation. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at developing and testing a new bolometric technology to be applied to future large-scale experiments searching for neutrinoless double-beta decay of the promising nuclei $^{100}$Mo and $^{130}$Te. The limiting factor in large-scale bolometric searches for this rare process is the background induced by surface radioactive contamination, as shown by the results of the CUORE experiment. The basic concept of CROSS consists of rejecting this challenging background component by pulse-shape discrimination, assisted by a proper coating of the faces of the crystal containing the isotope of interest and serving as energy absorber of the bolometric detector. In this paper, we demonstrate that ultra-pure superconductive Al films deposited on the crystal surfaces act successfully as pulse-shape modifiers, both with fast and slow phonon sensors. Rejection factors higher than 99.9% of $alpha$ surface radioactivity have been demonstrated in a series of prototypes based on crystals of Li$_2$MoO$_4$ and TeO$_2$. We have also shown that point-like energy depositions can be identified up to a distance of $sim 1$ mm from the coated surface. The present program envisions an intermediate experiment to be installed underground in the Canfranc laboratory (Spain) in a CROSS-dedicated facility. This experiment, comprising $sim 3times 10^{25}$ nuclei of $^{100}$Mo, will be a general test of the CROSS technology as well as a worldwide competitive search for neutrinoless double-beta decay, with sensitivity to the effective Majorana mass down to 70 meV in the most favorable conditions.
The Gerda experiment designed to search for the neutrinoless double beta decay in 76Ge has successfully completed the first data collection. No signal excess is found, and a lower limit on the half life of the process is set, with T1/2 > 2.1x10^25 yr (90% CL). After a review of the experimental setup and of the main Phase I results, the hardware upgrade for Gerda Phase II is described, and the physics reach of the new data collection is reported.
The aCORN experiment uses a novel asymmetry method to measure the electron-antineutrino correlation (a-coefficient) in free neutron decay that does not require precision proton spectroscopy. aCORN completed two physics runs at the NIST Center for Neutron Research. The first run on the NG-6 beam line in 2013--2014 obtained the result a = 0.1090 +/- 0.0030 (stat) +/- 0.0028 (sys), a total uncertainty of 3.8%. The second run on the new NG-C high flux beam line promises an improvement in precision to <2%.
The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double beta ($0 ubetabeta$) decay in $^{136}$Xe with a target half-life sensitivity of approximately $10^{28}$ years using $5times10^3$ kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the $^{136}$Xe mass, the monolithic and homogeneous configuration of the active medium, and the multi-parameter measurements of the interactions enabled by the time projection chamber. The detector concept and anticipated performance are presented based upon demonstrated realizable background rates.
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