The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of Formula omittedMo to the ground state of Formula omittedRu, Formula omitted ...year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of Formula omitted events and a signal-to-background ratio of Formula omitted 80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of Formula omitted, as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.
In this study, we evaluated and compared the pulse shape discrimination (PSD) performance of a typical photomultiplier tube (PMT) with that of multipixel photon counters (MPPCs), also known as ...silicon photomultipliers (SiPMs). We used CsI(Tl) scintillators for both setups and mainly evaluated the PSD performance in the <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula> separation. We used the charge comparison method, that is, identifying the particle type based on the ratio of the charges collected in two time gates: Short gate (SG) for the delayed part and long gate (LG) for the entire digitized waveform. With the same LG = 2250 ns, the PMT setup showed a better PSD performance with the figure of merit (FOM) being 3.33 (in <inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula> separation), whereas the FOM of the MPPC setup was 2.26. This inferior performance of the MPPC setup was due to its slow response, mainly the slow decay time in the waveform of one photoelectron (p.e.) of the MPPCs. This study aimed to determine the relationships of the PSD performance with the number of p.e. collected and the time characteristics of the scintillator-photosensor coupling. From these relationships, we estimated the SG to obtain <inline-formula> <tex-math notation="LaTeX">\text {FOM}_{\text {max}} </tex-math></inline-formula> and afterward confirmed a method to further increase the PSD performance. The estimated SG gave a comparable FOM without an extensive search for the optimized SG for obtaining the actual <inline-formula> <tex-math notation="LaTeX">\text {FOM}_{\text {max}} </tex-math></inline-formula> in analysis. To further increase the PSD performance of the MPPC setup, we used a new data acquisition (DAQ) system and extended the LG to 8000 ns to collect more p.e. and mitigate the slow response of the MPPCs. Using the new DAQ system, we obtained an FOM of 3.91 for the MPPC setup, that is, an increase by a factor of 1.7.
The NEMO-3 results for the double-
β
decay of
150
Nd to the 0
1
+
and 2
1
+
excited states of
150
Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope
150
Nd are used in the ...analysis. The signal of the
2
ν
β
β
transition to the 0
1
+
excited state is detected with a statistical significance exceeding 5
σ
. The half-life is measured to be
T
1
/
2
2
ν
β
β
(
0
1
+
)
=
1
.
11
-
0.14
+
0.19
stat
-
0.15
+
0.17
syst
×
10
20
year, which is the most precise value that has been measured to date. 90% confidence-level limits are set for the other decay modes. For the
2
ν
β
β
decay to the 2
1
+
level the limit is
T
1
/
2
2
ν
β
β
(
2
1
+
)
>
2.42
×
10
20
year
. The limits on the
0
ν
β
β
decay to the 0
1
+
and 2
1
+
levels of
150
Sm are significantly improved to
T
1
/
2
0
ν
β
β
(
0
1
+
)
>
1.36
×
10
22
year
and
T
1
/
2
0
ν
β
β
(
2
1
+
)
>
1.26
×
10
22
year
.
The energy calibration system for CANDLES using (n,γ) reaction Iida, T.; Mizukoshi, K.; Ohata, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2021, Letnik:
986
Journal Article
Recenzirano
Odprti dostop
Calcium fluoride for the study of Neutrinos and Dark matters by Low-energy Spectrometer (CANDLES) searches for neutrino-less double-beta decay of 48Ca using a CaF2 scintillator array. A high Q-value ...of 48Ca at 4268 keV enabled us to achieve low background, however, at the same time it causes difficulties in calibrating the detector’s Q-value region because of the absence of a standard high-energy γ-ray source. Therefore, we have developed a novel calibration system based on γ-ray emission by neutron capture on 28Si, 56Fe, and 58Ni nuclei. In this paper, we report the development of the new calibration system as well as the results of energy calibration in CANDLES up to 9 MeV.
JSNS
2
(J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment that is searching for sterile neutrinos via the observation of
ν
¯
μ
→
ν
¯
e
appearance oscillations ...using muon decay-at-rest neutrinos. Before dedicated data taking in the first-half of 2021, we performed a commissioning run for 10 days in June 2020. Using the data obtained in this commissioning run, in this paper, we present an estimate of the correlated background which imitates the
ν
¯
e
signal in a sterile neutrino search. In addition, in order to demonstrate future prospects of the JSNS
2
experiment, possible pulse shape discrimination improvements towards reducing cosmic ray induced fast neutron background are described.
In a neutrinoless double-beta decay (<inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula>) experiment, energy resolution is important to distinguish between ...<inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula> and background events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the <inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula> of 48 Ca using a CaF 2 scintillator as the detector and source. Photomultiplier tubes (PMTs) collect scintillation photons. At the <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value of 48 Ca, the current energy resolution (2.6%) exceeds the ideal statistical fluctuation of the number of photoelectrons (1.6%). Because of CaF 2 's long decay constant of 1000 ns, a signal integration within 4000 ns is used to calculate the energy. The baseline fluctuation (<inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula>) is accumulated in the signal integration, thus degrading the energy resolution. This article studies <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula> in the CANDLES detector, which severely degrades the resolution by 1% at the <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value of 48 Ca. To avoid <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula>, photon counting can be used to obtain the number of photoelectrons in each PMT; however, a significant photoelectron signal overlapping probability in each PMT causes missing photoelectrons in counting and reduces the energy resolution. "Partial photon counting" reduces <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula> and minimizes photoelectron loss. We obtain improved energy resolutions of 4.5%-4.0% at 1460.8 keV (<inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray of 40 K) and 3.3%-2.9% at 2614.5 keV (<inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray of 208 Tl). The energy resolution at the <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value is estimated to be improved from 2.6% to 2.2%, and the detector sensitivity for the <inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula> half-life of 48 Ca can be improved by 1.09 times.
We have studied the neutrino-less double beta decay(0νββ) of 48Ca with the CANDLES III system, which consists of CaF2(pure) scintillators. Rejection analyses for background events from radioactive ...contaminations in the CaF2(pure) scintillators were effective to reduce backgrounds in Qββ-value region. As the results, no events were observed in the region for the data of 131 days × 86 kg. It gave a lower limit 6.2 × 1022 year (90 % C.L.) for the half-life of 0νββ of 48Ca. For higher sensitive measurement of 48Ca 0νββ, we have developed new techniques for 48Ca enrichment and CaF2 scintillating bolometer. In this paper, we will also show current status of these techniques.
The photo-production of ϕ mesons from Li, C, Al, and Cu at forward angles has been measured at Eγ=1.5–2.4GeV. The number of events for incoherent ϕ photo-production is found to have a target mass ...number dependence of A0.72±0.07 in the kinematical region of |t|⩽0.6GeV2/c2. The total cross section of the ϕ–nucleon interaction, σϕN, has been estimated as 35−11+17mb using the A-dependence of the ϕ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than σϕN in free space, suggesting that the ϕ properties might change in the nuclear medium.
Modifications of an in-air microbeam system at the Wakasa Wan Energy Research Center designed to improve its performance are described. In the previous setup, a silicon nitride membrane (area: ...1×1mm2; thickness: 100nm) was used for the beam exit window and the distance between the window and the sample was restricted to ⩾1.7mm. Due to this restriction, the beam spot size obtained using the previous setup was 13×13μm2. To reduce the beam spot size, the beam exit window was replaced by a silicon nitride membrane (area: 3 (horizontal)×2 (vertical)mm2; thickness: 200nm). In this setup, the sample can be moved as close as 0.7mm to the window, enabling a beam spot size of 7×6μm2 to be achieved. An additional Si-PIN X-ray detector was installed to estimate the relative number of beam particles. It detects X-rays from the beam exit window. The number of the X-rays from the beam exit window (which is proportional to the number of beam particles) is used for quantitative analysis and for online monitoring of the beam current. This system has the potential to be used for simultaneous particle-induced X-ray emission (PIXE) and particle-induced gamma-ray emission (PIGE) measurements and for studying dental medicine.
The observation of neutrino-less double beta decay (0vßß) would be the most practical way to prove the Majorana nature of the neutrino and lepton number violation. CANDLES studies 48Ca double beta ...decay using CaF2 scintillator. The main advantage of 48Ca is that it has the highest Q-value (4.27 MeV) among all the isotope candidates for 0vßß. The CANDLES III detector is currently operating with 300kg CaF2 crystals in the Kamioka underground observatory, Japan. In 2014, a detector cooling system and a magnetic cancellation coil was installed with the aim to increase light emission of CaF2 scintillator and photo-electron collection efficiency of the photo-multipliers. After this upgrade, light yield was increased to 1000 p.e./MeV which is 1.6 times larger than before. According to data analysis and simulation, main background source in CANDLES is turned out to be high energy external gamma-ray originating neutron capture on the surrounding materials, so called (n,γ). Upgrading the detector by installing neutron and gamma-ray shield can reduce the remaining main backgrounds by two order magnitude. In this report, we discuss the detail of (n,γ) and background reduction by additional shielding.
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