arXiv subjects

M. K. Cheoun

Publications and source records attributed to M. K. Cheoun.

At least 19 recordsLinked to original sources

arXiv2026

A study of neutrinoless double electron capture in $^{40}$Ca from the AMoRE experiment

The search for neutrinoless double electron capture ($0\nu\mathrm{2EC}$) provides a sensitive probe of lepton-number violation and the Majorana nature of neutrinos. We investigate the $0\nu\mathrm{2EC}$ decay of $^{40}$Ca using cryogenic detectors equipped with metallic magnetic calorimeters in the AMoRE-I experiment. The analysis is based on a physics dataset corresponding to a total exposure of 7.32 kg$\cdot$yr from thirteen $^{40}$Ca$^{100}$MoO$_4$ crystals. No significant excess is observed, and a lower limit on the half-life is obtained as $T^{0\nu}_{1/2} > 1.7 \times 10^{22}$ yr at 90$\%$ confidence level. An improved sensitivity is expected for the upcoming AMoRE-II experiment. These results demonstrate the potential of CaMoO$_4$ detectors to explore rare decay processes beyond the primary $^{100}$Mo $0\nu\beta\beta$ search program.

nucl-ex↗

arXiv2026

First results from the search for an excess of $\bar{\nu}_{e}$ events in JSNS$^2$

The JSNS$^2$ (J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source) experiment at the Material and Life Science Facility (MLF) of J-PARC is designed to directly test an excess on $\bar{\nu}_{e}$ events which was indicated by LSND (Liquid Scintillator Neutrino Detector). The combination of a short-pulsed proton beam and a gadolinium-loaded liquid scintillator provides an excellent signal-to-noise ratio. In this article, we report the first results of a direct test based on data collected in 2022. After applying all event selection criteria, two events are observed, consistent with the expected background of 2.3$\pm$0.4 events. No excess of $\bar{\nu}_e$ events are seen in this report, however the expected number of events due to LSND anomaly is 1.1$\pm$0.5, thus this result is not yet conclusive. Data taking has been ongoing since 2021 and will continue in future runs. In addition, a new far detector has recently been constructed for the second phase experiment, JSNS$^2$-II, marking an important milestone toward forthcoming measurements.

hep-ex↗

arXiv2025

Muon tagging with Flash ADC waveform baselines

This manuscript describes an innovative method to tag the muons using the baseline information of the Flash ADC (FADC) waveform of PMTs in the JSNS1 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment. This experiment is designed for the search for sterile neutrinos, and a muon tagging is an essential key component for the background rejection since the detector of the experiment is located over-ground, where is the 3rd floor of the J-PARC Material and Life experimental facility (MLF). Especially, stopping muons inside the detector create the Michel electrons, and they are important background to be rejected. Utilizing this innovative method, more than 99.8% of Michel electrons can be rejected even without a detector veto region. This technique can be employed for any experiments which uses the similar detector configurations.

physics.ins-det↗

arXiv2025

The first JSNS$^2$ measurement of electron neutrino flux using $^{12}C(ν_{e},e^{-}) ^{12}N_{g.s.}$ reaction

JSNS$^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment searching for sterile neutrinos through the observation of $\barν_μ \rightarrow \barν_e$ appearance oscillations, using neutrinos produced by muon decay-at-rest. A key aspect of the experiment involves accurately understanding the neutrino flux and the quantities of pions and muons, which are progenitors of (anti-)neutrinos, given that their production rates have yet to be measured. We present the first electron-neutrino flux measurement using $^{12}\mathrm{C}(ν_{e},e^{-}) ^{12}\mathrm{N}_{g.s.}$ reaction in JSNS$^2$, yielding a flux of (6.7 $\pm$ 1.6 (stat.) $\pm$ 1.7 (syst.)) $\times$ 10$^{-9}$ cm$^{-2}$ proton$^{-1}$ at the JSNS$^2$ detector location, located at 24 meters distance from the mercury target. This flux measurement is consistent with predictions from simulations based on hadron models.

hep-ex↗

arXiv2025

PMT calibration for the JSNS2-II far detector with an embedded LED system

The JSNS2-II (the second phase of JSNS2, J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment aimed at searching for sterile neutrinos. This experiment has entered its second phase, employing two liquid scintillator detectors located at near and far positions from the neutrino source. Recently, the far detector of the experiment has been completed and is currently in the calibration phase. This paper presents a detailed description of the calibration process utilizing the LED system. The LED system of the far detector uses two Ultra-Violet (UV) LEDs, which are effective in calibrating all of PMTs at once. The UV light is converted into the visible light wavelengths inside liquid scintillator via the wavelength shifters, providing pseudo-isotropic light. The properties of all functioning Photo-Multiplier-Tubes (PMTs) to detect the neutrino events in the far detector, such as gain, its dependence of supplied High Voltage (HV), and Peak-to-Valley (PV) were calibrated. To achieve a good energy resolution for physics events, up to 10% of the relative gain adjustment is required for all functioning PMTs. This will be achieved using the measured HV curves and the LED calibration. The Peak-to-Valley (PV) ratio values are the similar to those from the production company, which distinguish the single photo-electron signal from the pedestal. Additionally, the precision of PMT signal timing is measured to be 2.1 ns, meeting the event reconstruction requirement of 10 ns.

physics.ins-det↗

arXiv2025

Improved limit on neutrinoless double beta decay of $^{100}$Mo from AMoRE-I

AMoRE searches for the signature of neutrinoless double beta decay of $^{100}$Mo with a 100 kg sample of enriched $^{100}$Mo. Scintillating molybdate crystals coupled with a metallic magnetic calorimeter operate at milli-Kelvin temperatures to measure the energy of electrons emitted in the decay. As a demonstration of the full-scale AMoRE, we conducted AMoRE-I, a pre-experiment with 18 molybdate crystals, at the Yangyang Underground Laboratory for over two years. The exposure was 8.02 kg$\cdot$year (or 3.89 kg$_{\mathrm{^{100}Mo}}\cdot$year) and the total background rate near the Q-value was 0.025 $\pm$ 0.002 counts/keV/kg/year. We observed no indication of $0νββ$ decay and report a new lower limit of the half-life of $^{100}$Mo $0νββ$ decay as $ T^{0ν}_{1/2}>2.9\times10^{24}~\mathrm{yr}$ at 90\% confidence level. The effective Majorana mass limit range is $m_{ββ}<$(210--610) meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.

nucl-ex↗

arXiv2025

Development of MMC-based lithium molybdate cryogenic calorimeters for AMoRE-II

The AMoRE collaboration searches for neutrinoless double beta decay of $^{100}$Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $^{100}$Mo isotope, is under construction. This paper discusses the baseline design and characterization of the lithium molybdate cryogenic calorimeters to be used in the AMoRE-II detector modules. The results from prototype setups that incorporate new housing structures and two different crystal masses (316 g and 517 - 521 g), operated at 10 mK temperature, show energy resolutions (FWHM) of 7.55 - 8.82 keV at the 2.615 MeV $^{208}$Tl $γ$ line, and effective light detection of 0.79 - 0.96 keV/MeV. The simultaneous heat and light detection enables clear separation of alpha particles with a discrimination power of 12.37 - 19.50 at the energy region around $^6$Li(n, $α$)$^3$H with Q-value = 4.785 MeV. Promising detector performances were demonstrated at temperatures as high as 30 mK, which relaxes the temperature constraints for operating the large AMoRE-II array.

physics.ins-det↗

arXiv2025

First Measurement of Missing Energy Due to Nuclear Effects in Monoenergetic Neutrino Charged Current Interactions

We present the first measurement of the missing energy due to nuclear effects in monoenergetic, muon neutrino charged-current interactions on carbon, originating from $K^+ \rightarrow μ^+ ν_μ$ decay at rest ($E_{ν_μ}=235.5$ MeV), performed with the J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source liquid scintillator based experiment. Toward characterizing the neutrino interaction, ostensibly $ν_μn \rightarrow μ^- p$ or $ν_μ$$^{12}\mathrm{C}$ $\rightarrow μ^-$$^{12}\mathrm{N}$, we define the missing energy as the energy transferred to the nucleus ($ω$) minus the kinetic energy of the outgoing proton(s), $E_{m} \equivω-\sum T_p$, and relate this to visible energy in the detector, $E_{m}=E_{ν_μ} (235.5 \mathrm{MeV})-m_μ(105.7 \mathrm{MeV}) + [m_n-m_p (1.3 \mathrm{MeV})] - E_{\mathrm{vis}}$. The missing energy, which is naively expected to be zero in the absence of nuclear effects (e.g. nucleon separation energy, Fermi momenta, and final-state interactions), is uniquely sensitive to many aspects of the interaction, and has previously been inaccessible with neutrinos. The shape-only, differential cross section measurement reported, based on a $(77\pm3)$% pure double-coincidence kaon decay-at-rest signal (621 total events), provides detailed insight into neutrino-nucleus interactions, allowing even the nuclear orbital shell of the struck nucleon to be inferred. The measurement provides an important benchmark for models and event generators at hundreds of MeV neutrino energies, characterized by the difficult-to-model transition region between neutrino-nucleus and neutrino-nucleon scattering, and relevant for applications in nuclear physics, neutrino oscillation measurements,and Type-II supernova studies.

hep-ex↗

arXiv2025

Pulse Shape Discrimination in JSNS$^2$

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 $\barν_μ \rightarrow \barν_e$ appearance oscillations using neutrinos with muon decay-at-rest. For this search, rejecting cosmic-ray-induced neutron events by Pulse Shape Discrimination (PSD) is essential because the JSNS$^2$ detector is located above ground, on the third floor of the building. We have achieved 95$\%$ rejection of neutron events while keeping 90$\%$ of signal, electron-like events using a data driven likelihood method.

physics.ins-det↗

arXiv2025

Evaluation of the performance of the event reconstruction algorithms in the JSNS$^2$ experiment using a $^{252}$Cf calibration source

JSNS$^2$ searches for short baseline neutrino oscillations with a baseline of 24~meters and a target of 17~tonnes of the Gd-loaded liquid scintillator. The correct algorithm on the event reconstruction of events, which determines the position and energy of neutrino interactions in the detector, are essential for the physics analysis of the data from the experiment. Therefore, the performance of the event reconstruction is carefully checked with calibrations using $^{252}$Cf source. This manuscript describes the methodology and the performance of the event reconstruction.

hep-ex↗

arXiv2024

Projected background and sensitivity of AMoRE-II

AMoRE-II aims to search for neutrinoless double beta decay with an array of 423 Li$_2$$^{100}$MoO$_4$ crystals operating in the cryogenic system as the main phase of the Advanced Molybdenum-based Rare process Experiment (AMoRE). AMoRE has been planned to operate in three phases: AMoRE-pilot, AMoRE-I, and AMoRE-II. AMoRE-II is currently being installed at the Yemi Underground Laboratory, located approximately 1000 meters deep in Jeongseon, Korea. The goal of AMoRE-II is to reach up to $T^{0νββ}_{1/2}$ $\sim$ 6 $\times$ 10$^{26}$ years, corresponding to an effective Majorana mass of 15 - 29 meV, covering all the inverted mass hierarchy regions. To achieve this, the background level of the experimental configurations and possible background sources of gamma and beta events should be well understood. We have intensively performed Monte Carlo simulations using the GEANT4 toolkit in all the experimental configurations with potential sources. We report the estimated background level that meets the 10$^{-4}$counts/(keV$\cdot$kg$\cdot$yr) requirement for AMoRE-II in the region of interest (ROI) and show the projected half-life sensitivity based on the simulation study.

physics.ins-det↗

arXiv2024

Study on the accidental background of the JSNS$^2$ experiment

JSNS$^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment which searches for sterile neutrinos via the observation of $\barν_μ \to \barν_{e}$ appearance oscillations using muon decay-at-rest neutrinos. The data taking of JSNS$^2$ have been performed from 2021. In this manuscript, a study of the accidental background is presented. The rate of the accidental background is (9.29$\pm 0.39) \times 10^{-8}$ / spill with 0.75 MW beam power and comparable to the number of searching signals.

hep-ex↗

arXiv2024

Background study of the AMoRE-pilot experiment

We report a study on the background of the Advanced Molybdenum-Based Rare process Experiment (AMoRE), a search for neutrinoless double beta decay (\znbb) of $^{100}$Mo. The pilot stage of the experiment was conducted using $\sim$1.9 kg of \CAMOO~ crystals at the Yangyang Underground Laboratory, South Korea, from 2015 to 2018. We compared the measured $β/γ$ energy spectra in three experimental configurations with the results of Monte Carlo simulations and identified the background sources in each configuration. We replaced several detector components and enhanced the neutron shielding to lower the background level between configurations. A limit on the half-life of $0νββ$ decay of $^{100}$Mo was found at $T_{1/2}^{0ν} \ge 3.0\times 10^{23}$ years at 90\% confidence level, based on the measured background and its modeling. Further reduction of the background rate in the AMoRE-I and AMoRE-II are discussed.

nucl-ex↗

arXiv2023

The acrylic vessel for JSNS$^{2}$-II neutrino target

The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment designed for the search for sterile neutrinos. The experiment is currently at the stage of the second phase named JSNS$^{2}$-II with two detectors at near and far locations from the neutrino source. One of the key components of the experiment is an acrylic vessel, that is used for the target volume for the detection of the anti-neutrinos. The specifications, design, and measured properties of the acrylic vessel are described.

hep-ex↗

arXiv2022

Alpha backgrounds in the AMoRE-Pilot experiment

The Advanced Mo-based Rare process Experiment (AMoRE)-Pilot experiment is an initial phase of the AMoRE search for neutrinoless double beta decay of $^{100}$Mo, with the purpose of investigating the level and sources of backgrounds. Searches for neutrinoless double beta decay generally require ultimately low backgrounds. Surface $α$ decays on the crystals themselves or nearby materials can deposit a continuum of energies that can be as high as the $Q$-value of the decay itself and may fall in the region of interest (ROI). To understand these background events, we studied backgrounds from radioactive contaminations internal to and on the surface of the crystals or nearby materials with Geant4-based Monte Carlo simulations. In this study, we report on the measured $α$ energy spectra fitted with the corresponding simulated spectra for six crystal detectors, where sources of background contributions could be identified through high energy $α$ peaks and continuum parts in the energy spectrum for both internal and surface contaminations. We determine the low-energy contributions from internal and surface $α$ contaminations by extrapolating from the $α$ background fitting model.

physics.ins-det↗

arXiv2022

Conceptual Design Report of DaRveX: Decay at Rest $ν_e$ + Lead Cross Section Measurement at J-PARC MLF

DaRveX stands for "Decay at Rest $ν_e$-Pb cross (X) section measurement". So far, there has not been good target to detect low energy $ν_e$. Lead is expected to be an excellent $ν_e$ target because the cross section is expected to be very large and the delayed coincidence technique can be used using final state neutron(s). However, the cross section have not been measured yet. If it is measured, it opens a new window to the future neutrino research field, such as low energy $ν_e$ oscillation measurements, flavor specific detection of the supernova explosion $ν_e$ and understanding of $ν_e$-nucleus interactions. This report explains a conceptual design of DaRveX experiment, which measures cross section of $ν_e$+Pb charged current interaction, $ν_e$(E~30MeV)+Pb $\to$ $e^-$+$xn$+Bi; ($x$=1 or 2), using $ν_e$ from $μ^+$ decay at rest at J-PARC MLF. The energy and direction of the final state $e^-$ will be measured by using 1-ton scale lead-scintillator sandwich detector. With two years of data taking, the cross section is expected to be measured with 20% of precision.

hep-ex↗

arXiv2022

Characterization of the correlated background for a sterile neutrino search using the first dataset of the JSNS$^2$ experiment

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 $\barν_μ \to \barν_{e}$ 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 $\barν_{e}$ 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.

hep-ex↗

arXiv2021

The JSNS^2 Detector

The JSNS^2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for oscillations involving a sterile neutrino in the eV^2 mass-splitting range. The experiment will search for the appearance of electron antineutrinos oscillated from muon antineutrinos. The electron antineutrinos are detected via the inverse beta decay process using a liquid scintillator detector. A 1MW beam of 3 GeV protons incident on a spallation neutron target produces an intense and pulsed neutrino source from pion, muon, and kaon decay at rest. The JSNS^2 detector is located 24 m away from the neutrino source and began operation from June 2020. The detector contains 17 tonnes of gadolinium (Gd) loaded liquid scintillator (LS) in an acrylic vessel, as a neutrino target. It is surrounded by 31 tonnes of unloaded LS in a stainless steel tank. Optical photons produced in LS are viewed by 120 R7081 Hamamatsu 10-inch Photomultiplier Tubes (PMTs). In this paper, we describe the JSNS^2 detector design, construction, and operation.

physics.ins-det↗