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J. Sato

Publications and source records attributed to J. Sato.

At least 19 recordsLinked to original sources
arXiv2025

Ultracold Neutron Guide-Coating Facility at U.Winnipeg

We report the construction and commissioning of a new ultracold neutron (UCN) guide-coating facility at the University of Winnipeg. The facility employs pulsed laser deposition (PLD) to produce diamond-like carbon (DLC) coatings on cylindrical UCN guides up to 1 m in length with a 200 mm outer diameter. DLC is a promising material for UCN transport and storage due to its high real component of the optical potential, low neutron absorption cross section, and low depolarization probabilities. First coating attempts on a full length aluminum UCN guide and matching blank flange were successfully coated with a carbon film with density of 2.3 g/cm$^3$, corresponding to optical potentials of 200 neV, as measured by X-ray reflectometry (XRR). Coating thicknesses were measured to be 90 nm for the UCN guide and 180 nm for the flange with no evidence of delamination. The implementation of a plasma plume collimator and plasma feed back control via a time of flight in vacuum ion probe produced a film with an XRR measured density of 2.8 g/cm$^3$, corresponding to an optical potential of 240 neV. This 80 nm thick film had poor adhesion to the aluminum tube substrate. These results establish a baseline for the coating facility. Ongoing and future work focuses on improving the diamond content of films and adhesion through plasma plume collimation, TOF ion probe feed back, and pre/post treatment methods with the goal of providing high quality DLC UCN guides for the TUCAN experiment at TRIUMF.

physics.ins-det↗
arXiv2025

Initial results of the TRIUMF ultracold advanced neutron source

We report the first results on ultracold neutron production from a new spallation-driven superfluid $^4$He (He-II) source at TRIUMF, which is being prepared for a new, precise measurement of the neutron electric dipole moment. A total of $(9.3 \pm 0.8)\times 10^{5}$ ultracold neutrons were observed at a proton beam current of \SI{37}{\uA}, when the target was irradiated for a period of \SI{60}{\s}. The results are in fair agreement with expectations based on a detailed simulation of neutron transport and ultracold neutron source cryogenics. There is some indication that the new source might not be as limited by the conduction of heat through the He-II as originally expected. The results indicate that the source is likely to make its ultimate production goals, once the liquid deuterium cold moderator system is completed, with the expectation that $5.7\times 10^7$~UCNs would be detected in the same experiment with full liquid levels. This would, for example, correspond to delivery of $1.4\times 10^6$~UCNs delivered to each of two nEDM measurement cells, and a statistical uncertainty of $1\times 10^{-27}~e$cm on the neutron EDM in 280 days of running.

nucl-ex↗
arXiv2025

Neutron EDM Experiment with an Advanced Ultracold Neutron Source at TRIUMF

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has been developing a high-intensity ultracold neutron (UCN) source aimed at searching for the neutron electric dipole moment (EDM) with a sensitivity goal of $10^{-27}\ e{\rm cm}$. This article reports on recent progress in commissioning of the UCN source and in the development of the neutron EDM spectrometer. In its final configuration, the accelerator-driven super-thermal UCN source will enable a neutron EDM experiment with two orders of magnitude improved statistics compared to the current best experiment. Substantial progress in 2024 allowed the collaboration to operate the complete source system, with the exception of the liquid deuterium cold moderator, resulting in the first production of UCNs. The status of the EDM spectrometer is also presented, with emphasis on UCN handling components and magnetic subsystems relevant to field control, shielding, and magnetometry.

physics.ins-det↗
arXiv2025

Cryogenic systems for the TUCAN EDM experiment

The TUCAN (TRIUMF UltraCold Advanced Neutron) Collaboration is completing a new ultracold neutron (UCN) source. The UCN source will deliver UCNs to a neutron electric dipole moment (EDM) experiment. The EDM experiment is projected to be capable of an uncertainty of $1\times 10^{-27}~e$cm, competitive with other planned projects, and a factor of ten more precise than the present world's best. The TUCAN source is based on a UCN production volume of superfluid helium (He-II), held at 1~K, and coupled to a proton-driven spallation target. The production rate in the source is expected to be in excess of $10^7$~UCN/s; since UCN losses can be small in superfluid helium, this should allow us to build up a large number of UCNs. The spallation-driven superfluid helium technology is the principal aspect making the TUCAN project unique. The superfluid production volume was recently cooled, for the first time, and successfully filled with superfluid helium. The design principles of the UCN source are described, along with some of the challenging cryogenic milestones that were recently passed.

physics.ins-det↗
arXiv2025

Automated segmentation of pediatric neuroblastoma on multi-modal MRI: Results of the SPPIN challenge at MICCAI 2023

Surgery plays an important role within the treatment for neuroblastoma, a common pediatric cancer. This requires careful planning, often via magnetic resonance imaging (MRI)-based anatomical 3D models. However, creating these models is often time-consuming and user dependent. We organized the Surgical Planning in Pediatric Neuroblastoma (SPPIN) challenge, to stimulate developments on this topic, and set a benchmark for fully automatic segmentation of neuroblastoma on multi-model MRI. The challenge started with a training phase, where teams received 78 sets of MRI scans from 34 patients, consisting of both diagnostic and post-chemotherapy MRI scans. The final test phase, consisting of 18 MRI sets from 9 patients, determined the ranking of the teams. Ranking was based on the Dice similarity coefficient (Dice score), the 95th percentile of the Hausdorff distance (HD95) and the volumetric similarity (VS). The SPPIN challenge was hosted at MICCAI 2023. The final leaderboard consisted of 9 teams. The highest-ranking team achieved a median Dice score 0.82, a median HD95 of 7.69 mm and a VS of 0.91, utilizing a large, pretrained network called STU-Net. A significant difference for the segmentation results between diagnostic and post-chemotherapy MRI scans was observed (Dice = 0.89 vs Dice = 0.59, P = 0.01) for the highest-ranking team. SPPIN is the first medical segmentation challenge in extracranial pediatric oncology. The highest-ranking team used a large pre-trained network, suggesting that pretraining can be of use in small, heterogenous datasets. Although the results of the highest-ranking team were high for most patients, segmentation especially in small, pre-treated tumors were insufficient. Therefore, more reliable segmentation methods are needed to create clinically applicable models to aid surgical planning in pediatric neuroblastoma.

cs.CV↗
arXiv2022

The design and performance of the XL-Calibur anticoincidence shield

The XL-Calibur balloon-borne hard X-ray polarimetry mission comprises a Compton-scattering polarimeter placed at the focal point of an X-ray mirror. The polarimeter is housed within a BGO anticoincidence shield, which is needed to mitigate the considerable background radiation present at the observation altitude of ~40 km. This paper details the design, construction and testing of the anticoincidence shield, as well as the performance measured during the week-long maiden flight from Esrange Space Centre to the Canadian Northwest Territories in July 2022. The in-flight performance of the shield followed design expectations, with a veto threshold <100 keV and a measured background rate of ~0.5 Hz (20-40 keV). This is compatible with the scientific goals of the mission, where %-level minimum detectable polarisation is sought for a Hz-level source rate.

astro-ph.IM↗
arXiv2017

A detailed study of the interstellar protons toward the TeV $γ$-ray SNR RX J0852.0$-$4622 (G266.2$-$1.2, Vela Jr.); a third case of the $γ$-rays and ISM spatial correspondence

We present a new analysis of the interstellar protons toward the TeV $γ$-ray SNR RX J0852.0$-$4622 (G266.2$-$1.2, Vela Jr.). We used the NANTEN2 $^{12}$CO($J$ = 1-0) and ATCA & Parkes HI datasets in order to derive the molecular and atomic gas associated with the TeV $γ$-ray shell of the SNR. We find that atomic gas over a velocity range from $V_\mathrm{LSR}$ = $-4$ km s$^{-1}$ to 50 km s$^{-1}$ or 60 km s$^{-1}$ is associated with the entire SNR, while molecular gas is associated with a limited portion of the SNR. The large velocity dispersion of the HI is ascribed to the expanding motion of a few HI shells overlapping toward the SNR but is not due to the Galactic rotation. The total masses of the associated HI and molecular gases are estimated to be $\sim2.5 \times 10^4 $ $M_{\odot}$ and $\sim10^3$ $M_{\odot}$, respectively. A comparison with the H.E.S.S. TeV $γ$-rays indicates that the interstellar protons have an average density around 100 cm$^{-3}$ and shows a good spatial correspondence with the TeV $γ$-rays. The total cosmic ray proton energy is estimated to be $\sim10^{48}$ erg for the hadronic $γ$-ray production, which may still be an underestimate by a factor of a few due to a small filling factor of the SNR volume by the interstellar protons. This result presents a third case, after RX J1713.7$-$3946 and HESS J1731$-$347, of the good spatial correspondence between the TeV $γ$-rays and the interstellar protons, lending further support for a hadronic component in the $γ$-rays from young TeV $γ$-ray SNRs.

astro-ph.HE↗
arXiv2014

A detailed study of non-thermal X-ray properties and interstellar gas toward the γ-ray supernova remnant RX J1713.7-3946

We have carried out a spectral analysis of the Suzaku X-ray data in the 0.4-12 keV range toward the shell-type very-high-energy γ-ray supernova remnant RX J1713.7-3946. The aims of this analysis are to estimate detailed X-rays spectral properties at a high angular resolution up to 2 arcmin, and to compare them with the interstellar gas. The X-ray spectrum is non-thermal and used to calculate absorbing column density, photon index, and absorption-corrected X-ray flux. The photon index varies significantly from 2.1 to 2.9. It is shown that the X-ray intensity is well correlated with the photon index, especially in the west region, with a correlation coefficient of 0.81. The X-ray intensity tends to increase with the averaged interstellar gas density while the dispersion is relatively large. The hardest spectra having the photon index less than 2.4 are found outside of the central 10 arcmin of the SNR, from the north to the southeast (~430 arcmin^2) and from the southwest to the northwest (~150 arcmin^2). The former region shows low interstellar gas density, while the latter high interstellar gas density. We present discussion for possible scenarios which explain the distribution of the photon index and its relationship with the interstellar gas.

astro-ph.HE↗
arXiv2014

Affine and non-affine motions in sheared polydisperse jammed emulsions

We study dense and highly polydisperse emulsions at droplet volume fractions ϕ>= 0.65. We apply oscillatory shear and observe droplet motion using confocal microscopy. The presence of droplets with sizes several times the mean size dramatically changes the motion of smaller droplets. Both affine and nonaffine droplet motions are observed, with the more nonaffine motion exhibited by the smaller droplets which are pushed around by the larger droplets. Droplet motions are correlated over length scales from one to four times the mean droplet diameter, with larger length scales corresponding to higher strain amplitudes (up to strains of about 6%).

cond-mat.soft↗
arXiv2013

Discovery of possible molecular counterparts to the infrared Double Helix Nebula in the Galactic center

We have discovered two molecular features at radial velocities of -35 km/s and 0 km/s toward the infrared Double Helix Nebula (DHN) in the Galactic center with NANTEN2. The two features show good spatial correspondence with the DHN. We have also found two elongated molecular ridges at these two velocities distributed vertically to the Galactic plane over 0.8 degree. The two ridges are linked by broad features in velocity and are likely connected physically with each other. The ratio between the 12CO J=2-1 and J=1-0 transitions is 0.8 in the ridges which is larger than the average value 0.5 in the foreground gas, suggesting the two ridges are in the Galactic center. An examination of the K band extinction reveals a good coincidence with the CO 0 km/s ridge and is consistent with a distance of 8 +/-2 kpc. We discuss the possibility that the DHN was created by a magnetic phenomenon incorporating torsional Alfvén waves launched from the circumnuclear disk (Morris, Uchida & Do 2006) and present a first estimate of the mass and energy involved in the DHN.

astro-ph.SR↗
arXiv2013

Non-thermal X-rays and interstellar gas toward the γ-ray supernova remnant RX J1713.7-3946: Evidence for X-ray enhancement around CO and HI clumps

RX J1713.7-3946 is the most remarkable very-high-energy γ-ray supernova remnant which emits synchrotron X-rays without thermal features. We made a comparative study of CO, HI and X-rays in order to better understand the relationship between the X-rays, and the molecular and atomic gas. The results indicate that the X-rays are enhanced around the CO and HI clumps on a pc scale but are decreased inside the clumps on a 0.1 pc scale. Magnetohydrodynamic numerical simulations of the shock interaction with molecular and atomic gas indicate that the interaction between the shock waves and the clumps excite turbulence which amplifies the magnetic field around the clumps (Inoue et al. 2012). We suggest that the amplified magnetic field around the CO and HI clumps enhances the synchrotron X-rays and possibly the acceleration of cosmic-ray electrons.

astro-ph.GA↗
arXiv2011

A Detailed Study of the Molecular and Atomic Gas Toward the γ-ray SNR RX J1713.7-3946: Spatial TeV γ-ray and ISM Gas Correspondence

RX J1713.7$-$3946 is the most remarkable TeV $γ$-ray SNR which emits $γ$-rays in the highest energy range. We made a new combined analysis of CO and \ion{H}{1} in the SNR and derived the total protons in the interstellar medium (ISM). We have found that the inclusion of the \ion{H}{1} gas provides a significantly better spatial match between the TeV $γ$-rays and ISM protons than the H$_2$ gas alone. In particular, the southeastern rim of the $γ$-ray shell has a counterpart only in the \ion{H}{1}. The finding shows that the ISM proton distribution is consistent with the hadronic scenario that comic ray (CR) protons react with ISM protons to produce the $γ$-rays. This provides another step forward for the hadronic origin of the $γ$-rays by offering one of the necessary conditions missing in the previous hadronic interpretations. We argue that the highly inhomogeneous distribution of the ISM protons is crucial in the origin of the $γ$-rays. Most of the neutral gas was likely swept up by the stellar wind of an OB star prior to the SNe to form a low-density cavity and a swept-up dense wall. The cavity explains the low-density site where the diffusive shock acceleration of charged particles takes place with suppressed thermal X-rays, whereas the CR protons can reach the target protons in the wall to produce the $γ$-rays. The present finding allows us to estimate the total CR proton energy to be $\sim 10^{48}$ ergs, 0.1% of the total energy of a SNe.

astro-ph.GA↗
arXiv2010

Star Forming Dense Cloud Cores in the TeV γ-ray SNR RX J1713.7-3946

RX J1713.7-3946 is one of the TeV γ-ray supernova remnants (SNRs) emitting synchrotron X rays. The SNR is associated with molecular gas located at ~1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C and D, in the SNR in the 12CO(J=2-1) and 13CO(J=2-1) transitions at angular resolution of 90". The most intense core in 13CO, peak C, was also mapped in the 12CO(J=4-3) transition at angular resolution of 38". Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source and has a steep gradient with a r^{-2.2$\pm$0.4} variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X rays are physically associated with the molecular gas (Fukui et al. 2003). We present a scenario where the densest molecular core, peak C, survived against the blast wave and is now embedded within the SNR. Numerical simulations of the shock-cloud interaction indicate that a dense clump can indeed survive shock erosion, since shock propagation speed is stalled in the dense clump. Additionally, the shock-cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to the enhanced synchrotron X rays around dense cores.

astro-ph.GA↗
arXiv2009

Long-Lived Slepton in the Coannihilation Region and Measurement of Lepton Flavour Violation at LHC

When the mass difference between the lightest slepton and the lightest neutralino is smaller than the tau mass, the lifetime of the lightest slepton in the constrained Minimal Supersymmetric Standard Model (MSSM) increases in many orders of magnitude with respect to typical lifetimes of other supersymmetric particles. In a general MSSM, the lifetime of the lightest slepton is inversely proportional to the square of the intergenerational mixing in the slepton mass matrices. Such a long-lived slepton would produce a distinctive signature at LHC and a measurement of its lifetime would be relatively simple. Therefore, the long-lived slepton scenario offers an excellent opportunity to study lepton flavour violation at ATLAS and CMS detectors in the LHC and an improvement of the leptonic mass insertion bounds by more than five orders of magnitude would be possible.

hep-ph↗
arXiv2006

Imprint of Gravitational Lensing by Population III Stars in Gamma Ray Burst Light Curves

We propose a novel method to extract the imprint of gravitational lensing by Pop III stars in the light curves of Gamma Ray Bursts (GRBs). Significant portions of GRBs can originate in hypernovae of Pop III stars and be gravitationally lensed by foreground Pop III stars or their remnants. If the lens mass is on the order of $10^2-10^3M_\odot$ and the lens redshift is greater than 10, the time delay between two lensed images of a GRB is $\approx 1$s and the image separation is $\approx 10 μ$as. Although it is difficult to resolve the two lensed images spatially with current facilities, the light curves of two images are superimposed with a delay of $\approx 1$ s. GRB light curves usually exhibit noticeable variability, where each spike is less than 1s. If a GRB is lensed, all spikes are superimposed with the same time delay. Hence, if the autocorrelation of light curve with changing time interval is calculated, it should show the resonance at the time delay of lensed images. Applying this autocorrelation method to GRB light curves which are archived as the {\it BATSE} catalogue, we demonstrate that more than half light curves can show the recognizable resonance, if they are lensed. Furthermore, in 1821 GRBs we actually find one candidate of GRB lensed by a Pop III star, which may be located at redshift 20-200. The present method is quite straightforward and therefore provides an effective tool to search for Pop III stars at redshift greater than 10. Using this method, we may find more candidates of GRBs lensed by Pop III stars in the data by the {\it Swift} satellite.

astro-ph↗
arXiv2001

Ambiguities of theoretical parameters and CP/T violation in neutrino factories

We study the sensitivity to the CP/T-violation search in the presence of ambiguities of the theoretical parameters. Three generations of neutrinos are considered. The parameters whose ambiguities are considered are the differences of the squared masses, the mixing angles, and the density of matter. We first consider the statistics that are sensitive to the genuine CP-violation effect originating from the imaginary coupling. No ambiguity of the parameters is considered in this part. It is argued that the widely-adopted usual statistics are not necessarily sensitive to the genuine CP-violation effect. Two statistics that are sensitive to the imaginary coupling are proposed. The qualitative difference between these statistics and the usual one are discussed. Next we proceed to the case where the ambiguity of the parameters is present. The sensitivity of the CP-violation search is greatly spoiled when the baseline length is longer than about one thousand kilometers, which turns out to be due to the ambiguity of the matter effect. Thus the CP-violation search by use of CP conjugate channels turns out to require a low energy neutrino and short baseline length. It is also shown that such a loss of sensitivity is avoided by using T-conjugate oscillation channels.

hep-ph↗
arXiv2001

Possible Flavor Mixing Structures of Lepton Mass Matrices

To search for possible textures of lepton mass matrices, we systematically examine flavor mixing structures which can lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data, taking into account phase factors in the mixing matrices. Only six of the patterns can explain the observed data without any tuning of parameters, while the others need particular choices for the phase values. It is found that these six mixing patterns are those predicted by the models which have been proposed to account for fermion mass hierarchies. On the other hand, the others may give new flavor mixing structures of lepton mass matrices and therefore new possibilities of model construction.

hep-ph↗