2,371 research outputs found
Double Beta Decay
The motivation, present status, and future plans of the search for the
neutrinoless double beta decay are reviewed. It is argued that, motivated by
the recent observations of neutrino oscillations, there is a reasonable hope
that neutrinoless double beta decay corresponding to the neutrino mass scale
suggested by oscillations, of about 50 meV, actually exists. The
challenges to achieve the sensitivity corresponding to this mass scale, and
plans to overcome them, are described.Comment: 34 pages, 3 figures included, Submitted to Annu. Rev. Nucl. Part.
Sci., vol.5
Ge Detectors and : The Search for Double Beta Decay with Germanium Detectors: Past, Present and Future
High Purity Germanium Detectors have excellent energy resolution; the best
among the technologies used in double beta decay. Since neutrino-less double
beta decay hinges on the search for a rare peak upon a background continuum,
this strength has enabled the technology to consistently provide leading
results. The Ge crystals at the heart of these experiments are very pure; they
have no measurable U or Th contamination. The added efforts to reduce the
background associated with electronics, cryogenic cooling, and shielding have
been very successful, leading to the longevity of productivity. The first
experiment published in 1967 by the Milan group of Fiorini, established the
benchmark half-life limit yr. More recently, the \MJ\ and
GERDA collaborations have developed new detector technologies that optimize the
pulse waveform analysis. As a result, the GERDA collaboration refuted the claim
of observation with a revolutionary approach to shielding by immersing the
detectors directly in radio-pure liquid argon. In 2018, the \MJ\ collaboration,
using a classic vacuum cryostat and high-Z shielding, achieved a background
level near that of GERDA by developing very pure materials for use nearby the
detectors. Together, GERDA and \MJ\ have provided limits approaching
yr. In this article, we elaborate on the historical use of Ge detectors for
double beta decay addressing the strengths and weaknesses. We also summarize
the status and future as many \MJ\ and GERDA collaborators have joined with
scientists from other efforts to give birth to the LEGEND collaboration. LEGEND
will exploit the best features of both experiments to extend the half-life
limit beyond yr with a ton-scale experiment.Comment: Invited submission to Frontiers in Physic
The Gallium Anomaly
In order to test the end-to-end operations of gallium solar neutrino
experiments, intense electron-capture sources were fabricated to measure the
responses of the radiochemical SAGE and GALLEX/GNO detectors to known fluxes of
low-energy neutrinos. Such tests were viewed at the time as a cross-check,
given the many tests of Ge recovery and counting that had been routinely
performed, with excellent results. However, the four Cr and Ar
source experiments yielded rates below expectations, a result commonly known as
the Ga anomaly. As the intensity of the electron-capture sources can be
measured to high precision, the neutrino lines they produce are fixed by known
atomic and nuclear rates, and the neutrino absorption cross section on
Ga is tightly constrained by the lifetime of Ge, no simple
explanation for the anomaly has been found. To check these calibration
experiments, a dedicated experiment BEST was performed, utilizing a neutrino
source of unprecedented intensity and a detector optimized to increase
statistics while providing some information on counting rate as a function of
distance from the source. The results BEST obtained are consistent with the
earlier solar neutrino calibration experiments, and when combined with those
measurements, yield a Ga anomaly with a significance of approximately
, under conservative assumptions. But BEST found no evidence of
distance dependence and thus no explicit indication of new physics. In this
review we describe the extensive campaigns carried out by SAGE, GALLEX/GNO, and
BEST to demonstrate the reliability and precision of their experimental
procedures, including Ge recovery, counting, and analysis. We also
describe efforts to define uncertainties in the neutrino capture cross section.
With the results from BEST, an anomaly remains.Comment: Invited submission to Progress in Particle and Nuclear Physic
Experiments for Double-Beta Decay
The recent neutrino oscillation experimental results indicate that at least
one neutrino has a mass greater than 50 meV. The next generation of double-beta
decay experiments will very likely have a sensitivity to an effective Majorana
neutrino mass below this target. Therefore this is a very exciting time for
this field of research as even null results from these experiments have the
potential to elucidate the nature of the neutrino.Comment: 15 pages, Invited Talk: "Neutrino and Implications for Physics beyond
the Standard Model", Repaired reference in V2, added ref in V
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