Search

We present a catalog of optical and infrared identifications (ID) of X-ray sources in the AKARI North Ecliptic Pole (NEP) Deep field detected with Chandra covering $\sim 0.34\,{\rm deg^{2}}$ with 0.5-2 keV flux limits ranging $\sim 2 \mathrm{-} 20\times 10^{-16}\,{\rm erg\,s^{-1}\,cm^{-2}}$. The optical/near-infrared counterparts of the X-ray sources are taken from our Hyper Suprime Cam (HSC)/Subaru and Wide-Field InfraRed Camera (WIRCam)/Canada-France-Hawaii Telescope (CFHT) data because these have much more accurate source positions due to their spatial resolution than that of {Chandra} and longer wavelength infrared data. We concentrate our identifications in the HSC $g$ band and WIRCam $K_{\rm s}$ band-based catalogs. To select the best counterpart, we utilize a novel extension of the likelihood-ratio (LR) analysis, where we use the X-ray flux as well as $g - K_{\rm s}$ colors to calculate the likelihood ratio. Spectroscopic and photometric redshifts of the counterparts are summarized. Also, simple X-ray spectroscopy is made on the sources with sufficient source counts. We present the resulting catalog in an electronic form. The main ID catalog contains 403 X-ray sources and includes X-ray fluxes, luminosities, $g$ and $K_{\rm s}$ band magnitudes, redshifts, and their sources, optical spectroscopic properties, as well as intrinsic absorption column densities and power-law indices from simple X-ray spectroscopy. The identified X-ray sources include 27 Milky-Way objects, 57 type I AGNs, 131 other AGNs, and 15 galaxies. The catalog serves as a basis for further investigations of the properties of the X-ray and near-infrared sources in this field. (Abridged), Comment: 16 pages, 9 figures, Three electronic (fits) tables are included in src. Accepted to Astronomy and Astrophysics

We present a search for neutrinoless double-beta ($0\nu\beta\beta$) decay of $^{136}$Xe using the full KamLAND-Zen 800 dataset with 745 kg of enriched xenon, corresponding to an exposure of $2.097$ ton yr of $^{136}$Xe. This updated search benefits from a more than twofold increase in exposure, recovery of photo-sensor gain, and reduced background from muon-induced spallation of xenon. Combining with the search in the previous KamLAND-Zen phase, we obtain a lower limit for the $0\nu\beta\beta$ decay half-life of $T_{1/2}^{0\nu} > 3.8 \times 10^{26}$ yr at 90% C.L., a factor of 1.7 improvement over the previous limit. The corresponding upper limits on the effective Majorana neutrino mass are in the range 28-122 meV using phenomenological nuclear matrix element calculations., Comment: arXiv admin note: text overlap with arXiv:2203.02139

We have established a method to measure picograms-per-gram (pg g$^{-1}$) levels of $^{238}$U and $^{232}$Th in scintillation films by combining the dry ashing method and inductively coupled plasma mass spectrometry. Trace amounts of $^{238}$U and $^{232}$Th were measured in up to 2~g of the scintillation film with almost 100% collection efficiency. This paper details the experimental procedure, including the pretreatment of the samples and labware, detection limit of the method, collection efficiencies of $^{238}$U and $^{232}$Th, and measurement of $^{238}$U and $^{232}$Th in a polyethylene naphthalate film. This method is also applicable to $^{238}$U and $^{232}$Th measurements in other low-background organic materials for rare event search experiments.

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.

Particle dark matter could belong to a multiplet that includes an electrically charged state. WIMP dark matter ($\chi^{0}$) accompanied by a negatively charged excited state ($\chi^{-}$) with a small mass difference (e.g. $<$ 20 MeV) can form a bound-state with a nucleus such as xenon. This bound-state formation is rare and the released energy is $\mathcal{O}(1-10$) MeV depending on the nucleus, making large liquid scintillator detectors suitable for detection. We searched for bound-state formation events with xenon in two experimental phases of the KamLAND-Zen experiment, a xenon-doped liquid scintillator detector. No statistically significant events were observed. For a benchmark parameter set of WIMP mass $m_{\chi^{0}} = 1$ TeV and mass difference $\Delta m = 17$ MeV, we set the most stringent upper limits on the recombination cross section times velocity $\langle\sigma v\rangle$ and the decay-width of $\chi^{-}$ to $9.2 \times 10^{-30}$ ${\rm cm^3/s}$ and $8.7 \times 10^{-14}$ GeV, respectively at 90% confidence level.

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., Comment: 14pages, 16 figures

A new ultra-low background high-purity germanium (HPGe) detector has been installed at the Kamioka underground experimental site. The background count rate in the energy range from 40 keV to 2700 keV is about 25% lower than that of the first HPGe detector installed in 2016, which has the same detector specification and similar shielding geometry. This paper describes the shielding configuration, including the cleaning of the material surface, the comparison of calibration data and simulation, the time variation of the background spectra, the sample measurement procedure, and some results of the radioactivity in the selected samples.

We present the combination of the Canada-France-Hawaii Telescope (CHFT) Large Area $U$-bands Deep Survey (CLAUDS) and the Hyper-Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP) data over their four deep fields. We provide photometric catalogs for $u$, $u^*$ (CFHT--MegaCam), $g$, $r$, $i$, $z$, and $y$ (Subaru--HSC) bands over $\sim 20~{\rm deg}^2$, complemented in two fields by data from the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey and the UltraVISTA survey, thus extending the wavelength coverage toward near-infrared with VIRCAM $Y$, $J$, $H$, and $K_s$ observations over $5.5~{\rm deg}^2$. The extraction of the photometry was performed with two different softwares: the HSC pipeline hscPipe and the standard and robust SExtractor software. Photometric redshifts were computed with template-fitting methods using the new Phosphoros code for the hscPipe photometry and the well-known Le Phare code for the SExtractor photometry. The products of these methods were compared with each other in detail. We assessed their quality using the large spectroscopic sample available in those regions, together with photometry and photometric redshifts from COSMOS2020, the latest version of the Cosmic Evolution Survey catalogs. We find that both photometric data sets are in good agreement in $Ugrizy$ down to magnitude$\sim26$, and to magnitude$\sim24.5$ in the $YJHK_s$ bands. We achieve good performance for the photometric redshifts, reaching precisions of $\sigma_{NMAD} \lesssim 0.04$ down to ${m}_i\sim25$, even using only the CLAUDS and HSC bands. At the same magnitude limit, we measured an outlier fraction of $\eta \lesssim 10\%$ when using the $Ugrizy$ bands, and down to $\eta \lesssim 6\%$ when considering near-infrared data. [abridged], Comment: 25 pages (20+5 Appendices), 17 figures (+4 in appendices), 4 Tables (+2 in appendices), Accepted for publication in A&A

Cosmic-ray muons produce various radioisotopes when passing through material. These spallation products can be backgrounds for rare event searches such as in solar neutrino, double-beta decay, and dark matter search experiments. The KamLAND-Zen experiment searches for neutrinoless double-beta decay in 745kg of xenon dissolved in liquid scintillator. The experiment includes dead-time-free electronics with a high efficiency for detecting muon-induced neutrons. The production yields of different radioisotopes are measured with a combination of delayed coincidence techniques, newly developed muon reconstruction and xenon spallation identification methods. The observed xenon spallation products are consistent with results from the FLUKA and Geant4 simulation codes.

We report a measurement of the strange axial coupling constant $g_A^s$ using atmospheric neutrino data at KamLAND. This constant is a component of the axial form factor of the neutral-current quasielastic (NCQE) interaction. The value of $g_A^s$ significantly changes the ratio of proton and neutron NCQE cross sections. KamLAND is suitable for measuring NCQE interactions as it can detect nucleon recoils with low-energy thresholds and measure neutron multiplicity with high efficiency. KamLAND data, including the information on neutron multiplicity associated with the NCQE interactions, makes it possible to measure $g_A^s$ with a suppressed dependence on the axial mass $M_A$, which has not yet been determined. For a comprehensive prediction of the neutron emission associated with neutrino interactions, we establish a simulation of particle emission via nuclear deexcitation of $^{12}$C, a process not considered in existing neutrino Monte Carlo event generators. Energy spectrum fitting for each neutron multiplicity gives $g_A^s =-0.14^{+0.25}_{-0.26}$, which is the most stringent limit obtained using NCQE interactions without $M_A$ constraints. The two-body current contribution considered in this analysis relies on a theoretically effective model and electron scattering experiments and requires future verification by direct measurements and future model improvement.

The decay of the primordial isotopes $^{238}\mathrm{U}$, $^{235}\mathrm{U}$, $^{232}\mathrm{Th}$, and $^{40}\mathrm{K}$ have contributed to the terrestrial heat budget throughout the Earth's history. Hence the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth model. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid-Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18-year observation time, and improvements in detector background levels mainly by an 8-year almost rector-free period now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. Herein the KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High-Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2$\sigma$ assuming a homogeneous heat producing element distribution in the mantle., Comment: 13 pages, 2 figures, accepted for publication in Geophysical Research Letters on Aug 4th, 2022

We present the results of a search for core-collapse supernova neutrinos, using long-term KamLAND data from 2002 March 9 to 2020 April 25. We focus on the electron antineutrinos emitted from supernovae in the energy range of 1.8--111 MeV. Supernovae will make a neutrino event cluster with the duration of $\sim$10 s in the KamLAND data. We find no neutrino clusters and give the upper limit on the supernova rate as to be 0.15 yr$^{-1}$ with a 90% confidence level. The detectable range, which corresponds to a >95% detection probability, is 40--59 kpc and 65--81 kpc for core-collapse supernovae and failed core-collapse supernovae, respectively. This paper proposes to convert the supernova rate obtained by the neutrino observation to the Galactic star formation rate. Assuming a modified Salpeter-type initial mass function, the upper limit on the Galactic star formation rate is <(17.5--22.7) $M_{\odot} \mathrm{yr}^{-1}$ with a 90% confidence level., Comment: 10 pages, 4 figures, accepted for publication in Astrophysical Journal

The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta ($0\nu\beta\beta$) 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 $0\nu\beta\beta$ decay half-life of $T_{1/2}^{0\nu} > 2.3 \times 10^{26}$ 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., Comment: 7 pages, 3 figures

We report the results of a search for MeV-scale astrophysical neutrinos in KamLAND presented as an excess in the number of coincident neutrino interactions associated with the publicly available high-energy neutrino datasets from the IceCube Neutrino Observatory. We find no statistically significant excess in the number of observed low-energy electron antineutrinos in KamLAND, given a coincidence time window of $\pm$500s, $\pm$1,000s, $\pm$3,600s, and $\pm$10,000s around each of the IceCube neutrinos. We use this observation to present limits from 1.8 MeV to 100 MeV on the electron antineutrino fluence, assuming a mono-energetic flux. We then compare the results to several astrophysical measurements performed by IceCube and place a limit at the 90% confidence level on the electron antineutrino isotropic thermal luminosity from the TXS 0506+056 blazar., Comment: 12 pages, 5 figures

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 $\mu$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., Comment: To be published in the Proceedings of TAUP2021. (Journal of Physics: Conference Series (JPCS),)

We present the results of a time-coincident event search for low-energy electron antineutrinos in the KamLAND detector with gamma-ray bursts from the Gamma-ray Coordinates Network and Fermi Gamma-ray Burst Monitor. Using a variable coincidence time window of $\pm$500s plus the duration of each gamma-ray burst, no statistically significant excess above background is observed. We place the world's most stringent 90% confidence level upper limit on the electron antineutrino fluence below 17.5 MeV. Assuming a Fermi-Dirac neutrino energy spectrum from the gamma-ray burst source, we use the available redshift data to constrain the electron antineutrino luminosity and effective temperature., Comment: 9 pages, 3 figures

We report on a search for electron antineutrinos ($\bar{\nu}_e$) from astrophysical sources in the neutrino energy range 8.3 to 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% 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 improves on the upper probability limit of $^{8}$B solar neutrinos converting into $\bar{\nu}_e$'s, $P_{\nu_e \rightarrow \bar{\nu}_e} < 3.5\times10^{-5}$ (90% CL) assuming an undistorted $\bar{\nu}_e$ shape. This corresponds to a solar $\bar{\nu}_e$ flux of 60 cm$^{-2}$ s$^{-1}$ (90% CL) in the analysis energy range., Comment: 21 pages, 9 figures, 4 tables, accepted for publication in Astrophysical Journal

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 $\mu$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., Comment: 12 pages, 7 figures, RADIATION DETECTORS AND THEIR USES Proceedings of the 35th Workshop on Radiation Detectors and Their Uses in KEK

We report the result of a search for neutrinos in coincidence with solar flares from the GOES flare database. The search was performed on a 10.8 kton-year exposure of KamLAND collected from 2002 to 2019. This large exposure allows us to explore previously unconstrained parameter space for solar flare neutrinos. We found no statistical excess of neutrinos and established 90% confidence level upper limits of $8.4 \times 10^7$ cm$^{-2}$ ($3.0 \times 10^{9}$ cm$^{-2}$) on electron anti-neutrino (electron neutrino) fluence at 20 MeV normalized to the X12 flare, assuming that the neutrino fluence is proportional to the X-ray intensity., Comment: 13 pages, 9 figures, accepted October 27, 2021

The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta decay of $^{136}$Xe by using $^{136}$Xe-loaded liquid scintillator. The liquid scintillator is enclosed inside a balloon made of thin, transparent, low-radioactivity film that we call Inner Balloon (IB). The IB, apart from guaranteeing the liquid containment, also allows to minimize the background from cosmogenic muon-spallation products and $^{8}$B solar neutrinos. Indeed these events could contribute to the total counts in the region of interest around the Q-value of the double-beta decay of $^{136}$Xe. In this paper, we present an overview of the IB and describe the various steps of its commissioning minimizing the radioactive contaminations, from the material selection, to the fabrication of the balloon and its installation inside the KamLAND detector. Finally, we show the impact of the IB on the KamLAND background as measured by the KamLAND detector itself., Comment: 23 pages, 16 figures, to be submitted to JINST

There are many theories where a dark matter particle is part of a multiplet with an electrically charged state. If WIMP dark matter ($\chi^{0}$) is accompanied by a charged excited state ($\chi^{-}$) separated by a small mass difference, it can form a stable bound state with a nucleus. In supersymmetric models, the $\chi^{0}$ and the $\chi^{-}$ could be the neutralino and a charged slepton, such as the neutralino-stau degenerate model. The formation binding process is expected to result in an energy deposition of {\it O}(1--10 MeV), making it suitable for detection in large liquid scintillator detectors. We describe new constraints on the bound state formation with a xenon nucleus using the KamLAND-Zen 400 Phase-II dataset. In order to enlarge the searchable parameter space, all xenon isotopes in the detector were used. For a benchmark parameter set of $m_{\chi^{0}} = 100$ GeV and $\Delta m = 10$ MeV, this study sets the most stringent upper limits on the recombination cross section $\langle\sigma v\rangle$ and the decay-width of $\chi^{-}$ of $2.0 \times 10^{-31}$ ${\rm cm^3/s}$ and $1.1 \times 10^{-18}$ GeV, respectively (90\% confidence level).

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 $1.2 \pm1.4$ $\mu$Bq/kg and $13\pm4$ $\mu$Bq/kg, respectively. No significant excess in the concentration of $^{210}$Pb was obtained, and the upper limit was 5.7 $\mu$Bq/kg at 90% C. L. The achieved level of radiopurity of NaI(Tl) crystals makes construction of a dark matter detector possible., Comment: 11 pages, 6 figures, accepted to Progress of Theoretical and Experimental Physics

We present the results of a search for MeV-scale electron antineutrino events in KamLAND in coincident with the 60 gravitational wave events/candidates reported by the LIGO/Virgo collaboration during their second and third observing runs. We find no significant coincident signals within a $\pm$ 500 s timing window from each gravitational wave and present 90% C.L. upper limits on the electron antineutrino fluence between $10^{8}$-$10^{13}\,{\mathrm cm^2}$ for neutrino energies in the energy range of 1.8-111 MeV., Comment: 11 pages, 2 figures, 2 tables, Accepted for publication in ApJ

Dusty high-z galaxies are extreme objects with high star formation rates (SFRs) and luminosities. Characterising the properties of this population and analysing their evolution over cosmic time is key to understanding galaxy evolution in the early Universe. We select a sample of high-z dusty star-forming galaxies (DSFGs) and evaluate their position on the main sequence (MS) of star-forming galaxies, the well-known correlation between stellar mass and SFR. We aim to understand the causes of their high star formation and quantify the percentage of DSFGs that lie above the MS. We adopted a multi-wavelength approach with data from optical to submillimetre wavelengths from surveys at the North Ecliptic Pole (NEP) to study a submillimetre sample of high-redshift galaxies. Two submillimetre selection methods were used, including: sources selected at 850$\mathrm{\, \mu m}$ with the Sub-millimetre Common-User Bolometer Array 2) SCUBA-2 instrument and {\it Herschel}-Spectral and Photometric Imaging Receiver (SPIRE) selected sources (colour-colour diagrams and 500$\mathrm{\, \mu m}$ risers), finding that 185 have good multi-wavelength coverage. The resulting sample of 185 high-z candidates was further studied by spectral energy distribution (SED) fitting with the CIGALE fitting code. We derived photometric redshifts, stellar masses, SFRs, and additional physical parameters, such as the infrared luminosity and active galactic nuclei (AGN) contribution. We find that the different results in the literature are, only in part, due to selection effects. The difference in measured SFRs affects the position of DSFGs on the MS of galaxies; most of the DSFGs lie on the MS (60\%). Finally, we find that the star formation efficiency (SFE) depends on the epoch and intensity of the star formation burst in the galaxy; the later the burst, the more intense the star formation.

A high-intensity pulsed muon beam is becoming available at the at the Japan Proton Accelerator Research Complex (J-PARC). Many experiments to study fundamental physics using this high-intensity muon beam are proposed. An experiment to measure the muon magnetic moment anomaly ($g-2$) and the muon electric dipole moment (EDM) is one of these experiments and it requires a tracking detector for positrons from muon decay. Fine segmentation is required in a detector to tolerate the high rate of positrons. The time resolution is required to be much better than the muon anomalous spin precession period while a buffer depth of a front-end electronics needs to be much longer than the accelerated muon lifetime. Requirements of this detector also meet requirements of a measurement of the muonium hyperfine structure interval at the J-PARC and another experiment to measure the proton charge radius at Tohoku University. We have developed a single-sided silicon strip sensor with a 190 $\mu$m pitch, a front-end electronics with a sampling rate of 200 MHz and a buffer memory depth of 8192, and a data acquisition system based on DAQ-Middleware for the J-PARC muon $g-2$/EDM experiment. We have fabricated detector modules consisting of this sensor and the front-end electronics. Performance of fabricated detector modules was evaluated at a laboratory and a beam test using the positron beam at Tohoku University. The detector is confirmed to satisfy all requirements of the experiments except for the time walk, which will be solved by the next version of a front-end electronics., Comment: 18 pages, 17 figures