The Majorana Demonstrator calibration system Abgrall, N.; Arnquist, I.J.; Avignone III, F.T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2017, Letnik:
872, Številka:
C
Journal Article
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The Majorana Collaboration is searching for the neutrinoless double-beta decay of the nucleus 76Ge. The Majorana Demonstrator is an array of germanium detectors deployed with the aim of implementing ...background reduction techniques suitable for a 1-ton 76Ge-based search. The ultra low-background conditions require regular calibrations to verify proper function of the detectors. Radioactive line sources can be deployed around the cryostats containing the detectors for regular energy calibrations. When measuring in low-background mode, these line sources have to be stored outside the shielding so they do not contribute to the background. The deployment and the retraction of the source are designed to be controlled by the data acquisition system and do not require any direct human interaction. In this paper, we detail the design requirements and implementation of the calibration apparatus, which provides the event rates needed to define the pulse-shape cuts and energy calibration used in the final analysis as well as data that can be compared to simulations.
We present the performances of two 92% enriched 130TeO2 crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of 130Te. The ...crystals, 435 g each, show an energy resolution, evaluated at the 2615 keV γ-line of 208Tl, of 6.5 and 4.3 keV FWHM. The only observable internal radioactive contamination arises from 238U (15 and 8 μBq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, 226Ra and 228Th, are both evaluated as <3.1 μBq/kg for one crystal and <2.3 μBq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by β/γ particles by means of Neganov–Luke bolometric light detectors we were able to perform an event-by-event identification of β/γ events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for α particles.
P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We ...have characterized a PPC detector’s response to
α
particles incident on the sensitive passivated and p
+
surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the
Majorana
Demonstrator
experiment, a search for neutrinoless double-beta decay (
0
ν
β
β
) in
76
Ge.
α
decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of
α
identification, reliably identifying
α
background events on the passivated surface of the detector. We demonstrate effective rejection of all surface
α
events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the
0
ν
β
β
region of interest window by an order of magnitude in the
Majorana
Demonstrator
and will be used in the upcoming LEGEND-200 experiment.
The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay ( Formula omitted) in the isotope Formula omitted. In this work we present ...the latest results on two searches for the double beta decay (DBD) of Formula omitted to the first Formula omitted excited state of Formula omitted: the Formula omitted decay and the Standard Model-allowed two-neutrinos double beta decay ( Formula omitted). Both searches are based on a 372.5 kg Formula omittedyr TeO Formula omitted exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90% Credible Interval (C.I.) of the given searches were estimated as Formula omitted for the Formula omitted decay and Formula omitted for the Formula omitted decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at Formula omitted C.I. on the decay half lives is obtained as: Formula omitted for the Formula omitted mode and Formula omitted for the Formula omitted mode. These represent the most stringent limits on the DBD of Formula omittedTe to excited states and improve by a factor Formula omitted the previous results on this process.
Abstract
The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay (
$$0\nu \beta \beta $$
0
ν
β
β
) in the isotope
$$\mathrm ...{^{130}Te}$$
130
Te
. In this work we present the latest results on two searches for the double beta decay (DBD) of
$$\mathrm {^{130}Te}$$
130
Te
to the first
$$0^{+}_2$$
0
2
+
excited state of
$$\mathrm {^{130}Xe}$$
130
Xe
: the
$$0\nu \beta \beta $$
0
ν
β
β
decay and the Standard Model-allowed two-neutrinos double beta decay (
$$2\nu \beta \beta $$
2
ν
β
β
). Both searches are based on a 372.5 kg
$$\times $$
×
yr TeO
$$_2$$
2
exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90% Credible Interval (C.I.) of the given searches were estimated as
$$\mathrm {S^{0\nu }_{1/2} = 5.6 \times 10^{24} \, \mathrm {yr}}$$
S
1
/
2
0
ν
=
5.6
×
10
24
yr
for the
$${0\nu \beta \beta }$$
0
ν
β
β
decay and
$$\mathrm {S^{2\nu }_{1/2} = 2.1 \times 10^{24} \, \mathrm {yr}}$$
S
1
/
2
2
ν
=
2.1
×
10
24
yr
for the
$${2\nu \beta \beta }$$
2
ν
β
β
decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at
$$90\%$$
90
%
C.I. on the decay half lives is obtained as:
$$\mathrm {(T_{1/2})^{0\nu }_{0^+_2} > 5.9 \times 10^{24} \, \mathrm {yr}}$$
(
T
1
/
2
)
0
2
+
0
ν
>
5.9
×
10
24
yr
for the
$$0\nu \beta \beta $$
0
ν
β
β
mode and
$$\mathrm {(T_{1/2})^{2\nu }_{0^+_2} > 1.3 \times 10^{24} \, \mathrm {yr}}$$
(
T
1
/
2
)
0
2
+
2
ν
>
1.3
×
10
24
yr
for the
$$2\nu \beta \beta $$
2
ν
β
β
mode. These represent the most stringent limits on the DBD of
$$^{130}$$
130
Te to excited states and improve by a factor
$$\sim 5$$
∼
5
the previous results on this process.
The MAJORANA DEMONSTRATOR is a leading experiment searching for neutrinoless double-beta decay with high purity germanium (HPGe) detectors. Machine learning provides a new way to maximize the amount ...of information provided by these detectors, but the data-driven nature makes it less interpretable compared to traditional analysis. An interpretability study reveals the machine’s decision-making logic, allowing us to learn from the machine to feed back to the traditional analysis. In this work, we present the first machine learning analysis of the data from the MAJORANA DEMONSTRATOR; this is also the first interpretable machine learning analysis of any germanium detector experiment. Two gradient boosted decision tree models are trained to learn from the data, and a game-theory-based model interpretability study is conducted to understand the origin of the classification power. By learning from data, this analysis recognizes the correlations among reconstruction parameters to further enhance the background rejection performance. Here, by learning from the machine, this analysis reveals the importance of new background categories to reciprocally benefit the standard MAJORANA analysis. This model is highly compatible with next-generation germanium detector experiments like LEGEND since it can be simultaneously trained on a large number of detectors.
Abstract The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) in the isotope $$\mathrm ...{^{130}Te}$$ 130 Te . In this work we present the latest results on two searches for the double beta decay (DBD) of $$\mathrm {^{130}Te}$$ 130 Te to the first $$0^{+}_2$$ 0 2 + excited state of $$\mathrm {^{130}Xe}$$ 130 Xe : the $$0\nu \beta \beta $$ 0 ν β β decay and the Standard Model-allowed two-neutrinos double beta decay ( $$2\nu \beta \beta $$ 2 ν β β ). Both searches are based on a 372.5 kg $$\times $$ × yr TeO $$_2$$ 2 exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90% Credible Interval (C.I.) of the given searches were estimated as $$\mathrm {S^{0\nu }_{1/2} = 5.6 \times 10^{24} \, \mathrm {yr}}$$ S 1 / 2 0 ν = 5.6 × 10 24 yr for the $${0\nu \beta \beta }$$ 0 ν β β decay and $$\mathrm {S^{2\nu }_{1/2} = 2.1 \times 10^{24} \, \mathrm {yr}}$$ S 1 / 2 2 ν = 2.1 × 10 24 yr for the $${2\nu \beta \beta }$$ 2 ν β β decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at $$90\%$$ 90 % C.I. on the decay half lives is obtained as: $$\mathrm {(T_{1/2})^{0\nu }_{0^+_2} > 5.9 \times 10^{24} \, \mathrm {yr}}$$ ( T 1 / 2 ) 0 2 + 0 ν > 5.9 × 10 24 yr for the $$0\nu \beta \beta $$ 0 ν β β mode and $$\mathrm {(T_{1/2})^{2\nu }_{0^+_2} > 1.3 \times 10^{24} \, \mathrm {yr}}$$ ( T 1 / 2 ) 0 2 + 2 ν > 1.3 × 10 24 yr for the $$2\nu \beta \beta $$ 2 ν β β mode. These represent the most stringent limits on the DBD of $$^{130}$$ 130 Te to excited states and improve by a factor $$\sim 5$$ ∼ 5 the previous results on this process.
We report on a search for double beta decay of Formula omitted to the first Formula omitted excited state of Formula omitted using a Formula omitted exposure of Formula omitted collected with the ...CUORE-0 experiment. In this work we exploit different topologies of coincident events to search for both the neutrinoless and two-neutrino double beta decay modes. We find no evidence for either mode and place lower bounds on the half-lives: Formula omitted and Formula omitted ( Formula omitted). Combining our results with those obtained by the CUORICINO experiment, we achieve the most stringent constraints available for these processes: Formula omitted and Formula omitted ( Formula omitted).
Abstract
We report on a search for double beta decay of
$$^{130}\hbox {Te}$$
130
Te
to the first
$$0^{+}$$
0
+
excited state of
$$^{130}\hbox {Xe}$$
130
Xe
using a
$$9.8\,\hbox {kg}\cdot \hbox {yr}$$
...9.8
kg
·
yr
exposure of
$$^{130}\hbox {Te}$$
130
Te
collected with the CUORE-0 experiment. In this work we exploit different topologies of coincident events to search for both the neutrinoless and two-neutrino double beta decay modes. We find no evidence for either mode and place lower bounds on the half-lives:
$$T^{0\nu }_{0^+_1}>7.9\cdot 10^{23}\hbox {yr}$$
T
0
1
+
0
ν
>
7.9
·
10
23
yr
and
$$T^{2\nu }_{0^+_1}>2.4\cdot 10^{23}\hbox {yr}$$
T
0
1
+
2
ν
>
2.4
·
10
23
yr
(
$$90\%\,\hbox {CL}$$
90
%
CL
). Combining our results with those obtained by the CUORICINO experiment, we achieve the most stringent constraints available for these processes:
$$T^{0\nu }_{0^+_1}>1.4\cdot 10^{24}\hbox {yr}$$
T
0
1
+
0
ν
>
1.4
·
10
24
yr
and
$$T^{2\nu }_{0^+_1}>2.5\cdot 10^{23}\hbox {yr}$$
T
0
1
+
2
ν
>
2.5
·
10
23
yr
(
$$90\%\,\hbox {CL}$$
90
%
CL
).
A brief discussion of the early history of unconventional uses of Ge detectors is given, followed by a more detailed discussion focusing on their uses for axion searches. The main purpose of this ...discussion is to explore the possibility of pushing the envelope of sensitivity of solar axion searches with future large Ge detector arrays applied to searches employing coherent Bragg-Primakoff conversion, as well as the axio-electric effect.
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