arXiv subjects

Y. Yamaguchi

Publications and source records attributed to Y. Yamaguchi.

At least 37 records · Page 2Linked to original sources

arXiv2022

Development of Ultra-pure Gadolinium Sulfate for the Super-Kamiokande Gadolinium Project

This paper reports the development and detailed properties of about 13 tons of gadolinium sulfate octahydrate, $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, which has been dissolved into Super-Kamiokande (SK) in the summer of 2020. We evaluate the impact of radioactive impurities in $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ on DSNB searches and solar neutrino observation and confirm the need to reduce radioactive and fluorescent impurities by about three orders of magnitude from commercially available high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$. In order to produce ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, we have developed a method to remove impurities from gadolinium oxide, Gd$_2$O$_3$, consisting of acid dissolution, solvent extraction, and pH control processes, followed by a high-purity sulfation process. All of the produced ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ is assayed by ICP-MS and HPGe detectors to evaluate its quality. Because of the long measurement time of HPGe detectors, we have employed several underground laboratories for making parallel measurements including LSC in Spain, Boulby in the UK, and Kamioka in Japan. In the first half of production, the measured batch purities were found to be consistent with the specifications. However,in the latter half, the $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ contained one order of magnitude more $^{228}$Ra than the budgeted mean contamination. This was correlated with the corresponding characteristics of the raw material Gd$_2$O$_3$, in which an intrinsically large contamination was present. Based on their modest impact on SK physics, they were nevertheless introduced into the detector. To reduce $^{228}$Ra for the next stage of Gd loading to SK, a new process has been successfully establised.

physics.ins-det↗

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↗

arXiv2022

First application of mass measurement with the Rare-RI Ring reveals the solar r-process abundance trend at A=122 and A=123

The Rare-RI Ring (R3) is a recently commissioned cyclotron-like storage ring mass spectrometer dedicated to mass measurements of exotic nuclei far from stability at Radioactive Isotope Beam Factory (RIBF) in RIKEN. The first application of mass measurement using the R3 mass spectrometer at RIBF is reported. Rare isotopes produced at RIBF, $^{127}$Sn, $^{126}$In, $^{125}$Cd, $^{124}$Ag, $^{123}$Pd, were injected in R3. Masses of $^{126}$In, $^{125}$Cd, and $^{123}$Pd were measured whereby the mass uncertainty of $^{123}$Pd was improved. This is the first reported measurement with a new storage ring mass spectrometery technique realized at a heavy-ion cyclotron and employing individual injection of the pre-identified rare nuclei. The latter is essential for the future mass measurements of the rarest isotopes produced at RIBF. The impact of the new $^{123}$Pd result on the solar $r$-process abundances in a neutron star merger event is investigated by performing reaction network calculations of 20 trajectories with varying electron fraction $Y_e$. It is found that the neutron capture cross section on $^{123}$Pd increases by a factor of 2.2 and $β$-delayed neutron emission probability, $P_\mathrm{1n}$, of $^{123}$Rh increases by 14\%. The neutron capture cross section on $^{122}$Pd decreases by a factor of 2.6 leading to pileup of material at $A=122$, thus reproducing the trend of the solar $r$-process abundances. The trend of the two-neutron separation energies (S$_\mathrm{2n}$) was investigated for the Pd isotopic chain. The new mass measurement with improved uncertainty excludes large changes of the S$_\mathrm{2n}$ value at $N=77$. Such large increase of the S$_\mathrm{2n}$ values before $N=82$ was proposed as an alternative to the quenching of the $N=82$ shell gap to reproduce $r$-process abundances in the mass region of $A=112-124$.

nucl-ex↗

arXiv2021

$P_c(4312)^+$ and $P_c(4337)^+$ as interfering $Σ_c\bar{D}$ and $Λ_c\bar{D}^{*}$ threshold cusps

The recent LHCb data on $B_s^0\to J/ψp\bar{p}$ revealed a new pentaquark-like $P_c(4337)^+$ structure, while finding no evidence for $P_c(4312)^+$ discovered earlier in $Λ_b^0\to J/ψp K^-$. Though puzzling, the data actually offer an important hint to understand the nature of the pentaquark candidates. We develop a model to analyze the $B_s^0\to J/ψp\bar{p}$ data. We find that a $Σ_c\bar{D}$ one-loop mechanism causes a threshold cusp that fits well the $P_c(4337)^+$ peak. Also, the $Σ_c\bar{D}$ and $Λ_c\bar{D}^{*}$ threshold cusps interfere with each other to reproduce an oscillating behavior in the proton helicity angle distribution. These results combined with our earlier analysis on $Λ_b^0\to J/ψp K^-$ indicate that $P_c(4312)^+$ and $P_c(4337)^+$ are created by different interference patterns between the $Σ_c\bar{D}$ and $Λ_c\bar{D}^{*}$ (anomalous) threshold cusps. The proposed scenario consistently explains why the $P_c(4312)^+$ and $P_c(4337)^+$ peaks appear in $Λ_b^0\to J/ψp K^-$ and $B_s^0\to J/ψp\bar{p}$, respectively, but not vice versa or both.

hep-ph↗

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↗

arXiv2020

Proposal: JSNS$^2$-II

This article describes the goal and expected sensitivity of the JSNS$^2$-II experiment at J-PARC Materials and Life Science Experimental Facility (MLF). The JSNS$^2$-II experiment is the second phase of the JSNS$^2$ experiment (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) with two detectors which are located in 24 m (an existing detector) and 48 m (new one) baselines to improve the sensitivity of the search for sterile neutrinos, especially in the low $Δm^2$ region, which has been indicated by the global fit of the appearance mode. The new second detector has a similar structure as the existing JSNS$^2$ detector, which is already working. To compensate for the reduction of the neutrino flux due to the distance from the mercury target, the target mass of the Gd-loaded liquid scintillator which is the Linear AlkylBenzene (LAB) based liquid scintillator inside the acrylic vessel is 35 tons. To keep the same photo-coverage of the detector as the first detector, we will surround the acrylic vessel with 240 PMTs. With this experimental setup and 5 years (times 1 MW beam power) exposure, the sensitivity of the JSNS$^2$-II is significantly improved compared to the current JSNS$^2$, especially in the low $Δm^2$ oscillation parameter region. The JSNS$^2$-II can also confirm or refute the most of the oscillation parameters' space preferred by the previous experiments with 3 sigma C.L.. Considering these situations and world wide status of the sterile neutrino searches, we are eager to start the data taking with the two detector configuration from 2023. The fund to build the second detector was already secured.

hep-ex↗

arXiv2020

Development and operation of an electrostatic time-of-flight detector for the Rare RI storage Ring

An electrostatic time-of-flight detector named E-MCP has been developed for quick diagnostics of circulating beam and timing measurement in mass spectrometry at the Rare-RI Ring in RIKEN. The E-MCP detector consists of a conversion foil, potential grids, and a microchannel plate. Secondary electrons are released from the surface of the foil when a heavy ion hits it. The electrons are accelerated and deflected by 90$^\circ$ toward the microchannel plate by electrostatic potentials. A thin carbon foil and a thin aluminum-coated mylar foil were used as conversion foils. We obtained time resolutions of 69(1) ps and 43(1) ps (standard deviation) for a $^{84}$Kr beam at an energy of 170 MeV/u when using the carbon and the aluminum-coated mylar foils, respectively. A detection efficiency of approximately 90% was obtained for both foils. The E-MCP detector equipped with the carbon foil was installed inside the Rare-RI Ring to confirm particle circulation within a demonstration experiment on mass measurements of nuclei around $^{78}$Ge produced by in-flight fission of uranium beam at the RI Beam Factory in RIKEN. Periodic time signals from circulating ions were clearly observed. Revolution times for $^{78}$Ge, $^{77}$Ga, and $^{76}$Zn were obtained. The results confirmed successful circulation of the short-lived nuclei inside the Rare-RI Ring.

physics.ins-det↗

arXiv2020

Design and Implementation of Detector Control System for Muon Forward Tracker at ALICE

ALICE is the experiment at the CERN LHC devoted to study heavy-ion collisions. An upgrade program of the ALICE detector is ongoing toward the LHC Run 3 starting in 2022 together with the upgrade of the data acquisition system and the detector control system (DCS). One of the main projects of the current ALICE upgrade program is the addition of the muon forward tracker (MFT), a new silicon pixel detector located at forward rapidity. In this paper, we describe the DCS of the MFT detector which is entirely controlled via a finite state machine in a hierarchical system.

physics.ins-det↗

arXiv2020

ALMA 26 arcmin$^2$ survey of GOODS-S at one-millimeter (ASAGAO): millimeter properties of stellar mass selected galaxies

We make use of the ASAGAO, deep 1.2 mm continuum observations of a 26 arcmin$^2$ region in the GOODS-South field obtained with ALMA, to probe dust-enshrouded star formation in $K$-band selected (i.e., stellar mass selected) galaxies, which are drawn from the ZFOURGE catalog. Based on the ASAGAO combined map, which was created by combining ASAGAO and ALMA archival data in the GOODS-South field, we find that 24 ZFOURGE sources have 1.2 mm counterparts with a signal-to-noise ratio $>$ 4.5 (1$σ\simeq$ 30 - 70 $μ$Jy beam$^{-1}$ at 1.2 mm). Their median redshift is estimated to be $z_\mathrm{median}=$ 2.38 $\pm$ 0.14. They generally follow the tight relationship of the stellar mass versus star formation rate (i.e., the main sequence of star-forming galaxies). ALMA-detected ZFOURGE sources exhibit systematically larger infrared (IR) excess (IRX $\equiv L_\mathrm{IR}/L_\mathrm{UV}$) compared to ZFOURGE galaxies without ALMA detections even though they have similar redshifts, stellar masses, and star formation rates. This implies the consensus stellar-mass versus IRX relation, which is known to be tight among rest-frame-UV-selected galaxies, can not fully predict the ALMA detectability of stellar-mass-selected galaxies. We find that ALMA-detected ZFOURGE sources are the main contributors to the cosmic IR star formation rate density at $z$ = 2 - 3.

astro-ph.GA↗

arXiv2019

A dominant population of optically invisible massive galaxies in the early Universe

Our current knowledge of cosmic star-formation history during the first two billion years (corresponding to redshift z >3) is mainly based on galaxies identified in rest-frame ultraviolet light. However, this population of galaxies is known to under-represent the most massive galaxies, which have rich dust content and/or old stellar populations. This raises the questions of the true abundance of massive galaxies and the star-formation-rate density in the early universe. Although several massive galaxies that are invisible in the ultraviolet have recently been confirmed at early epochs, most of them are extreme starbursts with star-formation rates exceeding 1000 solar masses per year, suggesting that they are unlikely to represent the bulk population of massive galaxies. Here we report submillimeter (wavelength 870um) detections of 39 massive star-forming galaxies at z > 3, which are unseen in the spectral region from the deepest ultraviolet to the near-infrared. With a space density of about $2 \times 10^{-5}$ per cubic megaparsec (two orders of magnitudes higher than extreme starbursts) and star-formation rates of 200 solar masses per year, these galaxies represent the bulk population of massive galaxies that have been missed from previous surveys. They contribute a total star-formation-rate density ten times larger than that of equivalently massive ultraviolet-bright galaxies at z >3. Residing in the most massive dark matter halos at their redshifts, they are probably the progenitors of the largest present-day galaxies in massive groups and clusters. Such a high abundance of massive and dusty galaxies in the early universe challenges our understanding of massive-galaxy formation.

astro-ph.GA↗

arXiv2019

Masses of ground and isomeric states of $^{101}$In and configuration-dependent shell evolution in odd-$A$ indium isotopes

We report first precision mass measurements of the $1/2^-$ isomeric and $9/2^+$ ground states of $^{101}$In. The determined isomeric excitation energy continues a smooth trend of odd-$A$ indium isotopes up to the immediate vicinity of $N=50$ magic number. This trend can be confirmed by dedicated shell model calculations only if the neutron configuration mixing is considered. We find that the single particle energies are different for different states of the same isotope. The presented configuration-dependent shell evolution, type II shell evolution, in odd-$A$ nuclei is discussed for the first time. Our results will facilitate future studies of single-particle neutron states.

nucl-ex↗

arXiv2019

Masses of neutron-rich $^{\operatorname{52-54}}$Sc and $^{54,56}$Ti nuclides: The $N=32$ subshell closure in scandium

Isochronous mass spectrometry has been applied in the storage ring CSRe to measure the masses of the neutron-rich $^{\operatorname{52-54}}$Sc and $^{54,56}$Ti nuclei. The new mass excess values $ME$($^{52}$Sc) $=$ $-40525(65)$ keV, $ME$($^{53}$Sc) $=$ $-38910(80)$ keV, and $ME$($^{54}$Sc) $=$ $-34485(360)$ keV, deviate from the Atomic Mass Evaluation 2012 by 2.3$σ$, 2.8$σ$, and 1.7$σ$, respectively. These large deviations significantly change the systematics of the two-neutron separation energies of scandium isotopes. The empirical shell gap extracted from our new experimental results shows a significant subshell closure at $N = 32$ in scandium, with a similar magnitude as in calcium. Moreover, we present $ab$ $initio$ calculations using the valence-space in-medium similarity renormalization group based on two- and three-nucleon interactions from chiral effective field theory. The theoretical results confirm the existence of a substantial $N = 32$ shell gap in Sc and Ca with a decreasing trend towards lighter isotones, thus providing a consistent picture of the evolution of the $N = 32$ magic number from the $pf$ into the $sd$ shell.

nucl-ex↗

arXiv2019

Improving the resolving power of Isochronous Mass Spectrometry by employing an in-ring mechanical slit

Isochronous Mass Spectrometry (IMS) in heavy-ion storage rings is an excellent experimental method for precision mass measurements of exotic nuclei. In the IMS, the storage ring is tuned in a special isochronous ion-optical mode. Thus, the mass-over-charge ratios of the stored ions are directly reflected by their respective revolution times in first order. However, the inevitable momentum spread of secondary ions increases the peak widths in the measured spectra and consequently limits the achieved mass precision. In order to achieve a higher mass resolving power, the ring aperture was reduced to 60 mm by applying a mechanical slit system at the dispersive straight section. The momentum acceptance was reduced as well as better isochronous conditions were achieved. The results showed a significant improvement of the mass resolving power reaching $5.2 \times 10^{5}$, though at the cost of about 40\% ion loss.

nucl-ex↗

arXiv2018

Isochronous mass measurements of $T_z=-1$ $fp$-shell nuclei from projectile fragmentation of $^{58}$Ni

Atomic masses of seven $T_z=-1$, $fp$-shell nuclei from $^{44}$V to $^{56}$Cu and two low-lying isomers, $^{44m}$V ($J^π=6^+$) and $^{52m}$Co ($J^π=2^+$), have been measured with relative precisions of $1-4\times 10^{-7}$ with Isochronous Mass Spectrometry (IMS) at CSRe. The masses of $^{56}$Cu, $^{52g,52m}$Co, and $^{44m}$V were measured for the first time in this experiment. The Mass Excesses ($ME^{\prime}$s) of $^{44}$V, $^{48}$Mn, $^{50}$Fe, and $^{54}$Ni are determined with an order of magnitude improved precision compared to the literature values. $^{52g,52m}$Co and $^{56}$Cu are found to be $370$~keV and $400$~keV more bound, respectively, while $^{44g,44m}$V are $\sim 300$~keV less bound than the extrapolations in the Atomic-Mass Evaluation 2012 (AME$^{\prime}$12). The masses of the four $T_z=-1/2$ nuclei $^{45}$V, $^{47}$Cr, $^{49}$Mn, and $^{51}$Fe are re-determined to be in agreement, within the experimental errors, with the recent JYFLTRAP measurements or with the previous IMS measurements in CSRe. Details of the measurements and data analysis are described, and the impact of the new $ME$ values on different aspects in nuclear structure are investigated and discussed.

nucl-ex↗

arXiv2018

The Masses of the $T_z=-3/2$ Nuclei $^{27}$P and $^{29}$S

Isochronous mass spectrometry has been applied in the storage ring CSRe to measure the masses of the $T_z=-3/2$ nuclei $^{27}$P and $^{29}$S. The new mass excess value $ME$($^{29}$S) $=-3094(13)$~keV is 66(52)~keV larger than the result of the previous $^{32}$S($^3$He,$^{6}$He)$^{29}$S reaction measurement in 1973 and a factor of 3.8 more precise. The new result for $^{29}$S, together with those of the $T=3/2$ isobaric analog states (IAS) in $^{29}$P, $^{29}$Si, and $^{29}$Al, fit well into the quadratic form of the Isobaric Multiplet Mass Equation IMME. The mass excess of $^{27}$P has been remeasured to be $ME(^{27}$P$)=-685(42)$ keV. By analyzing the linear and quadratic coefficients of the IMME in the $T_z=-3/2$ $sd$-shell nuclei, it was found that the ratio of the Coulomb radius parameters is $R\approx0.96$ and is nearly the same for all $T=3/2$ isospin multiplets. Such a nearly constant $R$-value, apparently valid for the entire light mass region with $A>9$, can be used to set stringent constraints on the isovector and isotensor components of the isospin non-conserving forces in theoretical calculations.

nucl-ex↗

arXiv2018

Mass Measurements of Neutron-Deficient Y, Zr, and Nb Isotopes and Their Impact on $rp$ and $νp$ Nucleosynthesis Processes

Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of $^{82}$Zr and $^{84}$Nb were measured for the first time with an uncertainty of $\sim 10$ keV, and the masses of $^{79}$Y, $^{81}$Zr, and $^{83}$Nb were re-determined with a higher precision. %The latter differ significantly from their literature values. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low $α$ separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr-Nb cycle in the $rp$-process unlikely. The new proton separation energy of $^{83}$Nb was determined to be 490(400)~keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the $p$-nucleus $^{84}$Sr relative to the neutron-deficient molybdenum isotopes in the previous $νp$-process simulations.

nucl-ex↗

arXiv2017

ALMA Twenty-six arcmin$^2$ Survey of GOODS-S at One-millimeter (ASAGAO): X-ray AGN Properties of Millimeter-Selected Galaxies

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin$^2$ (12 sources at a 1.2-mm flux-density limit of $\approx$0.6 mJy), supplemented by the deeper but narrower 1.3-mm survey of a part of the ASAGAO field by Dunlop et al.\ (2017). Fourteen out of the total 25 millimeter galaxies have Chandra counterparts. The observed AGN fractions at $z=1.5-3$ is found to be 90$^{+8}_{-19}$\% and $57^{+23}_{-25}$\% for the ultra/luminous infrared galaxies with $\log L_{\rm IR}/L_{\odot} = 12-12.8$ and $\log L_{\rm IR}/L_{\odot} = 11.5-12$, respectively. The majority ($\sim$2/3) of the ALMA and/or Herschel detected X-ray AGNs at $z=1.5-3$ appear to be star-formation dominant populations, having $L_{\rm X}$/ $L_{\rm IR}$ ratios smaller than the "simultaneous evolution" value expected from the local black-hole mass to stellar mass ($M_{\rm BH}$-$M_*$) relation. On the basis of the $L_{\rm X}$ and stellar mass relation, we infer that a large fraction of star-forming galaxies at $z=1.5-3$ have black hole masses smaller than those expected from the local $M_{\rm BH}$-$M_*$ relation. This is opposite to previous reports on luminous AGN at same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGN. Our results are consistent with an evolutionary scenario that star formation occurs first, and an AGN-dominant phase follows later, in objects finally evolving into galaxies with classical bulges.

astro-ph.HE↗

arXiv2017

ALMA Deep Field in SSA22: Blindly Detected CO Emitters and [CII] Emitter Candidates

We report the identification of four millimeter line emitting galaxies with the Atacama Large Milli/submillimeter Array (ALMA) in SSA22 Field (ADF22). We analyze the ALMA 1.1 mm survey data, with an effective survey area of 5 arcmin$^2$, a frequency range of 253.1--256.8 and 269.1--272.8 GHz, angular resolution of 0".7 and RMS noise of 0.8 mJy beam$^{-1}$ at 36 km s$^{-1}$ velocity resolution. We detect four line emitter candidates with significance levels above $6 σ$. We identify one of the four sources as a CO(9-8) emitter at $z = 3.1$ in a member of the proto-cluster known in this field. Another line emitter with an optical counterpart is likely a CO(4-3) emitter at $z = 0.7$. The other two sources without any millimeter continuum or optical/near-infrared counterpart are likely to be [CII] emitter candidates at $z = 6.0$ and $6.5$. The equivalent widths of the [CII] candidates are consistent with those of confirmed high-redshift [CII] emitters and candidates, and are a factor of 10 times larger than that of the CO(9-8) emitter detected in this search. The [CII] luminosity of the candidates are $4-7 \times 10^8~\rm L_\odot$. The star formation rates (SFRs) of these sources are estimated to be $10-20~\rm M_{\odot}~yr^{-1}$ if we adopt an empirical [CII] luminosity - SFR relation. One of them has a relatively low-S/N ratio, but shows features characteristic of emission lines. Assuming that at least one of the two candidates is a [CII] emitter, we derive a lower limit of [CII]-based star formation rate density (SFRD) at $z~\sim~6$. The resulting value of $> 10^{-2}$ $\rm M_\odot yr^{-1} Mpc^{-3}$ is consistent with the dust-uncorrected UV-based SFRD. Future millimeter/submillimeter surveys can be used to detect a number of high redshift line emitters, with which to study the star formation history in the early Universe.

astro-ph.GA↗