Status of balloon production for KamLAND-Zen 800 kg phase Obara, S.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2017, Volume:
845, Issue:
C
Journal Article
The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (0νββ) decay half-life in ^{136}Xe using a xenon-loaded liquid scintillator. We report an improved search ...using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of ^{136}Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>2.3×10^{26} yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.
We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a ...significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.
Abstract
We report a result of supernova neutrino burst search at KamLAND in a neutrino energy range of 1.8–111 MeV via the inverse-beta decay (IBD). The search was performed using data from 2002 ...March 9th to 2020 July 17th, and the corresponding livetime is 5001.21 days. We searched for two or more sequential IBD events within 10 s as a supernova neutrino burst candidate. The dominant background is the accidental cluster of 2 or more IBD events caused by neutrinos from other sources, though, which are estimated to be almost negligible. We evaluated detectable ranges for some emitted supernova neutrino burst models. The conservative detectable ranges are 38kpc for core-collapse supernova (ccSN) and 42kpc for failed ccSN. We found no significant supernova neutrino burst events and set a 90% upper limit on the supernova neutrino detection rate in KamLAND as 0.178 burst/yr.
A liquid scintillator base experiment KamLAND-Zen has set a lower limit on neutrinoless double beta decay half-life, and upgrade project KamLAND-Zen 800 has started in 2019. Unfortunately this ...project expects some backgrounds, and one of the main backgrounds is β/γ-ray from 214Bi in container of xenon loaded liquid scintillator (mini-balloon). In order to reject the background, we suggest using scintillation film for the future mini-balloon. If we can tag α-ray from 214Po by scintillation detection, we can eliminate 214Bi events by delayed coincidence analysis. Recently, it was reported that polyethylene naphthalate (PEN) can be used as a scintillator with blue photon emission. PEN has chemical compatibility for strong solvent, thus it has a possibility to use in liquid scintillator. In this presentation, we will mention the results for feasibility studies about transparency and emission spectra, light yield, radioactivity, strength of film etc.. We also show the test-sized scintillation balloon with an 800-mm diameter and discussions about how to use the scintillation balloon in KamLAND.
Abstract
We report on a search for electron antineutrinos (
ν
¯
e
) from astrophysical sources in the neutrino energy range 8.3–30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of ...the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60–110 cm
−2
s
−1
(90% confidence level, CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improve on the upper probability limit of
8
B solar neutrinos converting into
ν
¯
e
,
P
ν
e
→
ν
¯
e
<
3.5
×
10
−
5
(90% CL) assuming an undistorted
ν
¯
e
shape. This corresponds to a solar
ν
¯
e
flux of 60 cm
−2
s
−1
(90% CL) in the analysis energy range.
Abstract
We report a search for electron antineutrinos at KamLAND with an 8.3−30.8 MeV energy range via the inverse beta decay. In 6.72 kton-yr of KamLAND data, we found 18 neutrino candidates and no ...significant excess over estimated backgrounds. From data interpretation, with the assumption of some supernova relic neutrino spectrum predictions, we give upper flux limits of 60−110 cm
−2
s
−1
(90% CL) in the analysis range and present a model-independent flux. These upper limits are the most stringent for 8−13 MeV region. We also improve on the upper probability limit of
8
B solar neutrinos converting into antineutrinos via the Resonant Spin Flavor Precession with the neutrino magnetic moment. Besides, we could set limits on the annihilation cross-section for light dark matter pairs to neutrino pairs.
We have developed a dedicated front-end electronics board for a high-pressure xenon gas time projection chamber for a neutrinoless double-beta decay search. The ionization signal is read out by ...detecting electroluminescence photons with silicon photomultipliers (SiPMs). The board reads out the signal from 56 SiPMs and records the waveforms at 5 MS/s with a wide dynamic range up to 4000 photons/200 ns. The SiPM bias voltages are provided by the board. Fine adjustment of the bias voltage for each channel is realized while keeping the dc coupling readout constant, which is indispensable for readout of microsecond-long pulses or at high rate environment. Additional analog-to-digital converters (ADCs) measure one photon-equivalent dark current for calibration and monitoring of the SiPM. The obtained performance satisfies the requirement for a neutrinoless double-beta decay search.
The dynamic characteristics and generation efficiency of a micro-grid structured from 17 houses were examined. A gas engine generator with a power generation capacity of 3
kW installed in a house is ...made to correspond to the base load, and a solid-polymer-membrane-type fuel cell with a power generation capacity of 1
kW is installed in 16 houses. Moreover, when changing the load of a micro-grid, the correspondence takes place by controlling the number of fuel cells. Using numerical analysis, the characteristics of the power quality of a fuel cell micro-grid, and the generation efficiency of the fuel cell were examined. As a result, the relationship between the parameter of the controller and power quality and a fall in generation efficiency by a partial load was clarified.
KamLAND-Zen searches for neutrinoless double-beta decay with an ultra-pure liquid-scintillator (LS) filled with a custom-made clean nylon balloon. The primary backgrounds are radioactive impurities ...such as uranium and thorium series. To reduce them, we studied a self-vetoing balloon-shaped vessel for a future upgrade program, “KamLAND2-Zen”. We selected Polyethylene-Naphthalate (PEN) film which emit fluorescent light and performed the feasibility studies. Owing to its scintillation properties,
214
Bi background could be identified in the KamLAND2-Zen. Moreover, thanks to the different waveforms between the LS and the PEN, we can apply the pulse-shape-discrimination for
212
Bi-Po pileup background. We evaluated its background rejection efficiency as more than 90%. Resulting from these studies, it is possible to remove restrictions on fiducial volume in KamLAND2-Zen.
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