arXiv subjects

R. Hazama

Publications and source records attributed to R. Hazama.

At least 19 recordsLinked to original sources

arXiv2025

Background stability and annual modulation test using PICOLON ultra-pure NaI(Tl) detector

The dark matter observation claimed by the DAMA/LIBRA experiment has been a long-standing puzzle within the particle physics community. NaI(Tl) crystals with radiopurity comparable to DAMA/LIBRA's are essential for adequate verification. Existing experiments using NaI(Tl) target have been hampered by the high radioactivity concentration of NaI(Tl) crystals. PICOLON experiment conducts an independent search for Weakly Interacting Massive Particles using highest purity NaI(Tl) crystals. In 2020, the NaI(Tl) crystal (Ingot#85) reached the same purity level as DAMA/LIBRA crystals. The DAMA/LIBRA group has stressed that verifying their signal requires high-purity NaI(Tl) crystals with long-term stability. Based on a six-month measurement, we have confirmed the long-term stability of its radiopurity. This stability provides a significant advantage for future efforts to adequately verify the DAMA/LIBRA result using NaI(Tl) crystal. In this paper, we present the background stability of purity in the Ingot#94 NaI(Tl) detector, which was produced using the Ingot#85 purification method, along with the first annual modulation search conducted by the PICOLON experiment.

physics.ins-det↗

arXiv2024

Present status of PICOLON project

The existence of cosmic dark matter and neutrino properties are long-standing problems in cosmology and particle physics. These problems have been investigated by using radiation detectors. We will discuss the application of inorganic crystal scintillators to studies on dark matter and neutrino properties. A large volume and high-purity inorganic crystal is a promising detector for investigating dark matter and neutrino.

astro-ph.IM↗

arXiv2023

Radiopurity of NaI(Tl) crystals for PICOLON dark matter experiment

The dark matter observation claim by the DAMA/LIBRA collaboration has been a long-standing puzzle within the particle physics community. Efforts of other research groups to verify the claim have been insufficient by significant radioactivity of present NaI(Tl) crystals. PICOLON (Pure Inorganic Crystal Observatory for LOw-energy Neut(ra)lino) experiment conducts independent search for Weakly Interacting Massive Particles (WIMPs) using NaI(Tl) crystals. Our NaI(Tl) crystal manufactured in 2020 (Ingot #85) reached the same purity level as DAMA/LIBRA crystals. In this report, we describe the radiopurity of the new Ingot #94 crystal produced using the same purification technique as Ingot #85. The $\alpha$-ray events were selected by pulse-shape discrimination method. The impurities in the Ingot #94, $^{232}$Th, $^{226}$Ra and $^{210}$Po radioactivity were $4.6\pm 1.2~\mathrm{\mu Bq/kg}$, $7.9\pm 4.4~\mathrm{\mu Bq/kg}$, and $19\pm 6~\mathrm{\mu Bq/kg}$, which are equivalent to those of the DAMA/LIBRA crystals. The background rate in the energy region of 2-6 keV , was 2-5 events/d/kg/keV without applying a veto trigger.

physics.ins-det↗

arXiv2021

PICOLON dark matter search project

PICOLON (Pure Inorganic Crystal Observatory for LOw-energy Neutr(al)ino) aims to search for cosmic dark matter by high purity NaI(Tl) scintillator. We developed extremely pure NaI(Tl) crystal by hybrid purification method. The recent result of $^{210}$Pb in our NaI(Tl) is less than 5.7 $μ$Bq/kg. We will report the test experiment in the low-background measurement at Kamioka Underground Laboratory. The sensitivity for annual modulating signals and finding dark matter particles will be discussed.

astro-ph.IM↗

arXiv2021

Dark matter search with high purity NaI(Tl) scintillator

A dark matter search project needs and extremely low background radiation detector since the expected event rate of dark matter is less than a few events in one year in one tonne of the detector mass. The authors developed a highly radiopure NaI(Tl) crystal to search for dark matter. The best combination of the purification methods was developed, resulting $^{\mathrm{nat}}$K and $^{210}$Pb were less than 20 ppb and 5.7 $μ$Bq/kg, respectively. The authors will construct a large volume detector system with high-purity NaI(Tl) crystals. The design and the performance of the prototype detector module will be reported in this article.

physics.ins-det↗

arXiv2021

Development of highly radiopure NaI(Tl) scintillator for PICOLON dark matter search project

The highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter. The optimized methods were combined to reduce various radioactive impurities. The $^{40}$K was effectively reduced by the re-crystallization method. The progenies of the decay chains of uranium and thorium were reduced by appropriate resins. The concentration of natural potassium in NaI(Tl) crystal was reduced down to 20 ppb. Concentrations of alpha-ray emitters were successfully reduced by appropriate selection of resin. The present concentration of thorium series and 226Ra were $1.2 \pm1.4$ $μ$Bq/kg and $13\pm4$ $μ$Bq/kg, respectively. No significant excess in the concentration of $^{210}$Pb was obtained, and the upper limit was 5.7 $μ$Bq/kg at 90% C. L. The achieved level of radiopurity of NaI(Tl) crystals makes construction of a dark matter detector possible.

physics.ins-det↗

arXiv2021

Low background measurement in CANDLES-III for studying the neutrino-less double beta decay of $^{48}$Ca

We developed a CANDLES-III system to study the neutrino-less double beta (0$νββ$) decay of $^{48}$Ca. The proposed system employs 96 CaF$_{2}$ scintillation crystals (305 kg) with natural Ca ($^{\rm nat.}$Ca) isotope which corresponds 350\,g of $^{48}$Ca. External backgrounds were rejected using a 4$π$ active shield of a liquid scintillator surrounding the CaF$_2$ crystals. The internal backgrounds caused by the radioactive impurities within the CaF$_2$ crystals can be reduced effectively through analysis of the signal pulse shape. We analyzed the data obtained in the Kamioka underground for a live-time of 130.4\,days to evaluate the feasibility of the low background measurement with the CANDLES-III detector. Using Monte Carlo simulations, we estimated the background rate from the radioactive impurities in the CaF$_{2}$ crystals and the rate of high energy $γ$-rays caused by the (n, $γ$) reactions induced by environmental neutrons. The expected background rate was in a good agreement with the measured rate, i.e., approximately 10$^{-3}$ events/keV/yr/(kg of $^{\rm nat.}$Ca), in the 0$νββ$ window. In conclusion, the background candidates were estimated properly by comparing the measured energy spectrum with the background simulations. With this measurement method, we performed the first search for 0$νββ$ decay in a low background condition using a detector with a Ca isotope, in which the Ca present was not enriched, in a scale of hundreds of kg. The $^{48}$Ca isotope has a high potential for use in 0$νββ$ decay search, and is expected to be useful for the development of a next-generation detector for highly sensitive measurements.

hep-ex↗

arXiv2021

A study on energy resolution of CANDLES detector

In a neutrinoless double-beta decay ($0νββ$) experiment, energy resolution is important to distinguish between $0νββ$ and background events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the $0νββ$ of $^{48}$Ca using a CaF$_2$ scintillator as the detector and source. Photomultiplier tubes (PMTs) collect scintillation photons. At the Q-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 ($σ_{baseline}$) is accumulated in the signal integration, thus degrading the energy resolution. This paper studies $σ_{baseline}$ in the CANDLES detector, which severely degrades the resolution by 1% at the Q-value of $^{48}$Ca. To avoid $σ_{\rm baseline}$, 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 $σ_{baseline}$ and minimizes photoelectron loss. We obtain improved energy resolutions of 4.5-4.0% at 1460.8 keV ($γ$-ray of $^{40}$K), and 3.3-2.9% at 2614.5 keV ($γ$-ray of $^{208}$Tl). The energy resolution at the Q-value is estimated to be improved from 2.6% to 2.2%, and the detector sensitivity for the $0νββ$ half-life of $^{48}$Ca can be improved by 1.09 times.

physics.ins-det↗

arXiv2020

Search for $hep$ solar neutrinos and the diffuse supernova neutrino background using all three phases of the Sudbury Neutrino Observatory

A search has been performed for neutrinos from two sources, the $hep$ reaction in the solar $pp$ fusion chain and the $ν_e$ component of the diffuse supernova neutrino background (DSNB), using the full dataset of the Sudbury Neutrino Observatory with a total exposure of 2.47 kton-years after fiducialization. The $hep$ search is performed using both a single-bin counting analysis and a likelihood fit. We find a best-fit flux that is compatible with solar model predictions while remaining consistent with zero flux, and set a one-sided upper limit of $Φ_{hep} < 30\times10^{3}~\mathrm{cm}^{-2}~\mathrm{s}^{-1}$ [90% credible interval (CI)]. No events are observed in the DSNB search region, and we set an improved upper bound on the $ν_e$ component of the DSNB flux of $Φ^\mathrm{DSNB}_{ν_e} < 19~\textrm{cm}^{-2}~\textrm{s}^{-1}$ (90% CI) in the energy range $22.9 < E_ν< 36.9$~MeV.

hep-ex↗

arXiv2020

The energy calibration system for CANDLES using (n, γ) reaction

CAlcium fluoride for the study of Neutrinos and Dark matters by Low-energy Spectrometer (CANDLES) searches for neutrino-less double beta decay of $^{48}$Ca using a CaF$_2$ scintillator array. A high Q-value of $^{48}$Ca at 4,272 keV enabled us to achieve very low background condition, however, at the same 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 $^{28}$Si, $^{56}$Fe and $^{58}$Ni nuclei. In the paper, we report the development of the new calibration system as well as the results of energy calibration in CANDLES up to 9 MeV.

physics.ins-det↗

arXiv2019

Cosmogenic Neutron Production at the Sudbury Neutrino Observatory

Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of GEANT4 physics models. In addition, the cosmogenic neutron yield, in units of $10^{-4}\;\text{cm}^{2}/\left(\text{g}\cdotμ\right)$, is measured to be $7.28 \pm 0.09\;\text{stat.} ^{+1.59}_{-1.12}\;\text{syst.}$ in pure heavy water and $7.30 \pm 0.07\;\text{stat.} ^{+1.40}_{-1.02}\;\text{syst.}$ in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB.

hep-ex↗

arXiv2019

Measurement of neutron production in atmospheric neutrino interactions at the Sudbury Neutrino Observatory

Neutron production in GeV-scale neutrino interactions is a poorly studied process. We have measured the neutron multiplicities in atmospheric neutrino interactions in the Sudbury Neutrino Observatory experiment and compared them to the prediction of a Monte Carlo simulation using GENIE and a minimally modified version of GEANT4. We analyzed 837 days of exposure corresponding to Phase I, using pure heavy water, and Phase II, using a mixture of Cl in heavy water. Neutrons produced in atmospheric neutrino interactions were identified with an efficiency of $15.3\%$ and $44.3\%$, for Phase I and II respectively. The neutron production is measured as a function of the visible energy of the neutrino interaction and, for charged current quasi-elastic interaction candidates, also as a function of the neutrino energy. This study is also performed classifying the complete sample into two pairs of event categories: charged current quasi-elastic and non charged current quasi-elastic, and $ν_μ$ and $ν_e$. Results show good overall agreement between data and Monte Carlo for both phases, with some small tension with a statistical significance below $2σ$ for some intermediate energies.

hep-ex↗

arXiv2019

Tests of Lorentz invariance at the Sudbury Neutrino Observatory

Experimental tests of Lorentz symmetry in systems of all types are critical for ensuring that the basic assumptions of physics are well-founded. Data from all phases of the Sudbury Neutrino Observatory, a kiloton-scale heavy water Cherenkov detector, are analyzed for possible violations of Lorentz symmetry in the neutrino sector. Such violations would appear as one of eight possible signal types in the detector: six seasonal variations in the solar electron neutrino survival probability differing in energy and time dependence, and two shape changes to the oscillated solar neutrino energy spectrum. No evidence for such signals is observed, and limits on the size of such effects are established in the framework of the Standard Model Extension, including 40 limits on perviously unconstrained operators and improved limits on 15 additional operators. This makes limits on all minimal, Dirac-type Lorentz violating operators in the neutrino sector available for the first time.

hep-ex↗

arXiv2018

Constraints on Neutrino Lifetime from the Sudbury Neutrino Observatory

The long baseline between the Earth and the Sun makes solar neutrinos an excellent test beam for exploring possible neutrino decay. The signature of such decay would be an energy-dependent distortion of the traditional survival probability which can be fit for using well-developed and high precision analysis methods. Here a model including neutrino decay is fit to all three phases of $^8$B solar neutrino data taken by the Sudbury Neutrino Observatory. This fit constrains the lifetime of neutrino mass state $ν_2$ to be ${>8.08\times10^{-5}}$ s/eV at $90\%$ confidence. An analysis combining this SNO result with those from other solar neutrino experiments results in a combined limit for the lifetime of mass state $ν_2$ of ${>1.04\times10^{-3}}$ s/eV at $99\%$ confidence.

hep-ex↗

arXiv2017

The search for neutron-antineutron oscillations at the Sudbury Neutrino Observatory

Tests on $B-L$ symmetry breaking models are important probes to search for new physics. One proposed model with $Δ(B-L)=2$ involves the oscillations of a neutron to an antineutron. In this paper a new limit on this process is derived for the data acquired from all three operational phases of the Sudbury Neutrino Observatory experiment. The search was concentrated in oscillations occurring within the deuteron, and 23 events are observed against a background expectation of 30.5 events. These translate to a lower limit on the nuclear lifetime of $1.48\times 10^{31}$ years at 90% confidence level (CL) when no restriction is placed on the signal likelihood space (unbounded). Alternatively, a lower limit on the nuclear lifetime was found to be $1.18\times 10^{31}$ years at 90% CL when the signal was forced into a positive likelihood space (bounded). Values for the free oscillation time derived from various models are also provided in this article. This is the first search for neutron-antineutron oscillation with the deuteron as a target.

hep-ex↗

arXiv2017

Search for cosmic dark matter by means of ultra high purity NaI(Tl) scintillator

The dark matter search project by means of ultra high purity NaI(Tl) scintillator is now underdevelopment. An array of large volume NaI(Tl) detectors whose volume is 12.7 cm$ϕ\times$12.7 cm is applied to search for dark matter signal. To remove radioactive impurities in NaI(Tl) crystal is one of the most important task to find small number of dark matter signals. We have developed high purity NaI(Tl) crystal which contains small amounts of radioactive impurities, $<4$ ppb of $^{nat}$K, 0.3 ppt of Th chain, 58 $μ$Bq/kg of $^{226}$Ra and 30 $μ$Bq/kg of $^{210}$Pb. Future prospects to search for dark matter by means of a large volume and high purity NaI(Tl) scintillator is discussed.

physics.ins-det↗

arXiv2015

Dark matter search project PICO-LON

The PICO-LON project aims at search for cold dark matter by means of highly radio-pure and large volume NaI(Tl) scintillator. The NaI powder was purifed by chemical processing to remove lead isotopes and selecting a high purity graphite crucible. The concentrations of radioactive impurities of $^{226}$Ra and $^{228}$Th were effectively reduced to 58$\pm$4 $μ$Bq/kg and 1.5$\pm$1.9 $μ$Bq/kg, respectively. It should be remarked that the concentration of $^{210}$Pb, which is crucial for the sensitivity to dark matter, was reduced to 24$\pm$2 $μ$Bq/kg. The total background rate at 10 keVee was as low as 8 keV$^{-1}$kg$^{-1}$day$^{-1}$, which was sufficiently low to search for dark matter. Further purification of NaI(Tl) ingot and future prospect of PICO-LON project is discussed.

astro-ph.IM↗

arXiv2015

The Majorana Parts Tracking Database

The Majorana Demonstrator is an ultra-low background physics experiment searching for the neutrinoless double beta decay of $^{76}$Ge. The Majorana Parts Tracking Database is used to record the history of components used in the construction of the Demonstrator. The tracking implementation takes a novel approach based on the schema-free database technology CouchDB. Transportation, storage, and processes undergone by parts such as machining or cleaning are linked to part records. Tracking parts provides a great logistics benefit and an important quality assurance reference during construction. In addition, the location history of parts provides an estimate of their exposure to cosmic radiation. A web application for data entry and a radiation exposure calculator have been developed as tools for achieving the extreme radio-purity required for this rare decay search.

physics.ins-det↗