arXiv subjects
Publications and source records attributed to T. Hashimoto.
Recently, we reported the commissioning of the new cryogenic ion storage ring RICE, which demonstrated potential capabilities for the precise studies of molecular structures and reaction dynamics. In the present article, we describe the status of experimental programs ongoing at RICE with a focus on the laser spectroscopy and merged-beam collision experiments.
Multi-layered materials provide fascinating platforms to realize various functional properties, possibly leading to future electronic devices controlled by external fields. In particular, layered magnets coupled with conducting layers have been extensively studied recently for possible control of their transport properties via the spin structure. Successful control of quantum-transport properties in the materials with antiferromagnetic (AFM) layers, so-called natural spin-valve structure, has been reported for the Dirac Fermion and topological/axion materials. However, a bulk crystal in which magnetic and superconducting layers are alternately stacked has not been realized until now, and the search for functional properties in it is an interesting yet unexplored field in material science. Here, we discover superconductivity providing such an ideal platform in EuSn2As2 with the van der Waals stacking of magnetic Eu layers and superconducting Sn-As layers, and present the first demonstration of a natural spin-valve effect on the superconducting current. Below the superconducting transition temperature (Tc), the electrical resistivity becomes zero in the in-plane direction. In contrast, it, surprisingly, remains finite down to the lowest temperature in the out-of-plane direction, mostly due to the structure of intrinsic magnetic Josephson junctions in EuSn2As2. The magnetic order of the Eu layers (or natural spin-valve) is observed to be extremely soft, allowing one to easy control of the out-of-plane to in-plane resistivities ratio from 1 to infinity by weak external magnetic fields. The concept of multi-functional materials with stacked magnetic-superconducting layers will open a new pathway to develop novel spintronic devices with magnetically controllable superconductivity.
Achieving the highest possible mass resolving power in a multi-reflection time-of-flight mass spectrometer requires very high-stability power supplies. To this end, we have developed a programmable high-voltage power supply that can achieve long-term stability on the order of parts-per-million. Herein we present the design of the stable high-voltage system and bench-top stability measurements up to 1~kV; the stabilization technique can, in principle, be applied up to 15~kV or more.. We demonstrate that in the $\le$1~Hz band the output stability is on the level of 1~part per million (ppm) during one hour, with only slightly more output variation across 3 days. We further demonstrate that the output is largely free of noise in the 1~Hz -- 200~Hz band. We also demonstrate settling to the ppm level within one minute following a 100~V step transition. Finally, we demonstrate that when these power supplies are used to bias the electrodes of a multi-reflection time-of-flight mass spectrograph the measured time-of-flight is stable on the ppm-level for at least one hour.
An important issue for rare-event-search experiments, such as the search for dark matter or neutrinoless double beta decay, is to reduce radioactivity of the detector materials and the experimental environment. The selection of materials with low radioactive impurities, such as isotopes of the uranium and thorium chains, requires a precise measurement of surface and bulk radioactivity. Focused on the first one, an alpha-particle detector has been developed based on a gaseous micro-time-projection chamber. A low-alpha mu-PIC with reduced alpha-emission background was installed in the detector. The detector offers the advantage of position sensitivity, which allows the alpha-particle contamination of the sample to be imaged and the background to be measured at the same time. The detector performance was measured by using an alpha-particle source. The measurement with a sample was also demonstrated and the sensitivity is discussed.
Photometric observations of the spectroscopically confirmed $z\approx 9.1$ galaxy MACS1149-JD1 have indicated the presence of a prominent Balmer break in its spectral energy distribution, which may be interpreted as due to very large fluctuations in its past star formation activity. In this paper, we investigate to what extent contemporary simulations of high-redshift galaxies produce star formation rate variations sufficiently large to reproduce the observed Balmer break of MACS1149-JD1. We find that several independent galaxy simulations are unable to account for Balmer breaks of the inferred size, suggesting that MACS1149-JD1 either must be a very rare type of object or that our simulations are missing some key ingredient. We present predictions of spectroscopic Balmer break strength distributions for $z\approx 7-9$ galaxies that may be tested through observations with the upcoming James Webb Space Telescope and also discuss the impact that various assumptions on dust reddening, Lyman continuum leakage and deviations from a standard stellar initial mass function would have on the results.
The scatter in the relationship between the strength of [CII] 158$μ$m emission and the star formation rate at high-redshift has been the source of much recent interest. Although the relationship is well-established locally, several intensely star-forming galaxies have been found whose [CII] 158$μ$m emission is either weak, absent or spatially offset from the young stars. Here we present new ALMA data for the two most distant, gravitationally-lensed and spectroscopically-confirmed galaxies, A2744\_YD4 at $z=$8.38 and MACS1149\_JD1 at $z=$9.11, both of which reveal intense [OIII] 88$μ$m emission. In both cases we provide stringent upper limits on the presence of [CII] 158$μ$m with respect to [OIII] 88$μ$m. We review possible explanations for this apparent redshift-dependent [CII] deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies.
A double-$Λ$ hypernucleus, ${}_{ΛΛ}\mathrm{Be}$, was observed by the J-PARC E07 collaboration in nuclear emulsions tagged by the $(K^{-},K^{+})$ reaction. This event was interpreted as a production and decay of $ {}_{ΛΛ}^{\;10}\mathrm{Be}$, ${}_{ΛΛ}^{\;11}\mathrm{Be}$, or ${}_{ΛΛ}^{\;12}\mathrm{Be}^{*}$ via $Ξ^{-}$ capture in ${}^{16}\mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $Λ$ hyperons$\,$($B_{ΛΛ}$) of these double-$Λ$ hypernuclei are obtained to be $15.05 \pm 0.11\,\mathrm{MeV}$, $19.07 \pm 0.11\,\mathrm{MeV}$, and $13.68 \pm 0.11\,\mathrm{MeV}$, respectively. Based on the kinematic fitting, ${}_{ΛΛ}^{\;11}\mathrm{Be}$ is the most likely explanation for the observed event.
We construct minimum-uncertainty states and a non-negative quasi probability distribution for quantum systems on a finite-dimensional space. We reexamine the theorem of Massar and Spindel for the uncertainty relationof the two unitary operators related by the discrete Fourier transformation. It is shown that some assumptions in their proof can be justified by the use of the Perron-Frobenius theorem. The minimum-uncertainty states are the ones that saturate this uncertainty inequality. The continuum limit is closely analyzed by introducing a scale factor in the limiting scheme. Using the minimum-uncertainty states, we construct a non-negative quasi probability distribution. Its marginal distributions are smeared out. However, we show that this quasi probability is optimal in the sense that there does not exist a non-negative quasi probability distribution with sharper marginal properties if the translational covariance in the phase space is assumed. Generally, it is desirable that the quasi probability is complete, i.e., it contains full information of the state. We show that the obtained quasi probability is indeed complete if the dimension of the state space is odd, whereas it is not if the dimension is even.
We have fabricated superconductor-normal metal side-junctions with different barrier transparencies out of PdTe$_2$ crystalline flakes and measured the differential conductance spectra. Modeling our measurements using a modified Blonder Tinkham Klapwijk (BTK) formalism confirms that the superconductivity is mostly comprised of the conventional $s$-wave symmetry. We have found that for junctions with very low barrier transparencies, the junctions can enter a thermal regime, where the critical current becomes important. Adding this to the BTK-model allows us to accurately fit the experimental data, from which we conclude that the superconductivity in the $a$-$b$ plane of PdTe$_2$ is dominated by conventional $s$-wave pairing.
Low temperature magnetic properties were investigated on the gold nano particles (GNP) with an average size of 11.5 nm, assembled with molecules of ruthenium complex (Ru0) and phenylboronic acid (B0) by the proton nuclear resonance (1H-NMR) and susceptibility measurements. The temperature dependence of the NMR shift and the uniform susceptibility was described as the sum of the Curie-Weiss term and a positive constant term. From the former, the average number of Ru0 on each GNP was estimated to be 118, which is 23 % of the calculation. The finite positive constant term shows a clear contrast with the well-known fact that the bulk gold is diamagnetic. Finally, a disappearance of the motional narrowing effect in the proton NMR spectra below 60 K indicates that the wavering motion of Ru0 complexes on GNP at room temperature is frozen at low temperatures.
We observed a distinct peak in the $Λp$ invariant mass spectrum of $^{3}{\rm He}(K^-, \, Λp)n$, well below the mass threshold of $m_K + 2 m_p$. By selecting a relatively large momentum-transfer region $q = 350 \sim 650$ MeV/$c$, one can clearly separate the peak from the quasi-free process, $\overline{K}N \rightarrow \overline{K}N$ followed by the non-resonant absorption by the two spectator-nucleons $\overline{K}NN \rightarrow ΛN $. We found that the simplest fit to the observed peak gives us a Breit-Wigner pole position at $B_{\rm {\it Kpp}} = 47 \pm 3 \, (stat.) \,^{+3}_{-6} \,(sys.)$ MeV having a width $Γ_{\rm {\it Kpp}} = 115 \pm 7 \, (stat.) \,^{+10}_{-9} \,(sys.)$ MeV, and the $S$-wave Gaussian reaction form-factor parameter $Q_{\rm {\it Kpp}} = 381 \pm 14 \, (stat.)\,^{+57}_{-0} \,(sys.)$ MeV/$c$, as a new form of the nuclear bound system with strangeness -- "$K^-pp$".
A new active target named MAIKo (Mu-PIC based Active target for Inverse Kinematics$_{\circ}$) has been developed at Kyoto University and Research Center for Nuclear Physics (RCNP), Osaka University. MAIKo is suited for missing-mass spectroscopy of unstable nuclei at forward scattering angles in inverse kinematics. MAIKo consists of a time projection chamber (TPC), which incorporates a micro-pixel chamber ($μ$-PIC) as the electron multiplication and collection system. In MAIKo, the medium gas also plays the role of a reaction target, thus allowing detection of low-energy recoil particles with high position resolution. The MAIKo TPC was commissioned with He(93%)+iso-C$_{4}$H$_{10}$(7%) and He(93%)+CO$_{2}$(7%) mixture gasses at 430 hPa. The gas gain and the angular resolution of MAIKo were evaluated with an alpha source and a $^{4}$He beam at 56 MeV. The TPC was stably operated up to 1000-kcps beam intensity. A tracking algorithm using the Hough transform method has been developed to analyze scattering events. An angular resolution of 1.3$^{\circ}$ was achieved for scattered $^{4}$He particles.
We investigate the performance of discrimination strategy in the comparison task of known quantum states. In the discrimination strategy, one infers whether or not two quantum systems are in the same state on the basis of the outcomes of separate discrimination measurements on each system. In some cases with more than two possible states, the optimal strategy in minimum-error comparison is that one should infer the two systems are in different states without any measurement, implying that the discrimination strategy performs worse than the trivial "no-measurement" strategy. We present a sufficient condition for this phenomenon to happen. For two pure states with equal prior probabilities, we determine the optimal comparison success probability with an error margin, which interpolates the minimum-error and unambiguous comparison. We find that the discrimination strategy is not optimal except for the minimum-error case.
The Lyman alpha (lya) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km/s compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics and correlations with quasar absorption lines when only lya is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the lya line profile. We use spectroscopic observations of Lyman-Alpha Emitters (LAEs) for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z~3 and z~6 as part of various Multi Unit Spectroscopic Explorer (MUSE) Guaranteed Time Observations (GTO). We also include a compilation of spectroscopic lya data from the literature spanning a wide redshift range (z~0-8). First, restricting our analysis to double-peaked lya spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, Vpeak, and the separation of the peaks. Secondly, we find a correlation between Vpeak and the full width at half maximum of the lya line. Fitting formulas, to estimate systemic redshifts of galaxies with an accuracy of +-100 km/s when only the lya emission line is available, are given for the two methods.
The phase point operator $Δ(q,p)$ is the quantum mechanical counterpart of the classical phase point $(q,p)$. The discrete form of $Δ(q,p)$ was formulated for an odd number of lattice points by Cohendet et al. and for an even number of lattice points by Leonhardt. Both versions have symplectic covariance, which is of fundamental importance in quantum mechanics. However, an explicit form of the projective representation of the symplectic group that appears in the covariance relation is not yet known. We show in this paper the existence and uniqueness of the representation, and describe a method to construct it using the Euclidean algorithm.
High-precision mass measurements of $^{63}$Cu, $^{64-66}$Zn, $^{65}$Ga, $^{65-67}$Ge, $^{67}$As, $^{78,81}$Br, $^{80}$Rb, and $^{79}$Sr were performed utilizing a multireflection time-of-flight mass spectrograph combined with the gas-filled recoil ion separator GARIS-II. In the case of $^{65}$Ga, a mass uncertainty of 2.1 keV, corresponding to a relative precision of $δm / m = 3.5\times10^{-8}$, was obtained and the mass value is in excellent agreement with the 2016 Atomic Mass Evaluation. For $^{67}$Ge and $^{81}$Br, where masses were previously deduced through indirect measurements, discrepancies with literature values were found. The feasibility of using this device for mass measurements of nuclides more neutron-deficient side, which have significant impact on the $rp$-process pathway, is discussed.
Background: Type I x-ray bursts are the most frequent thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The $^{30}$S($α$,p) reaction plays a critical role in burst models, yet insufficient experimental information is available to calculate a reliable, precise rate for this reaction. Purpose: Our measurement was conducted to search for states in $^{34}$Ar and determine their quantum properties. In particular, natural-parity states with large $α$-decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of $^{30}$S+$α$ resonant elastic scattering up to a center-of-mass energy of 5.5 MeV using a radioactive ion beam. The experiment utilized a thick gaseous active target system and silicon detector array in inverse kinematics. Results: We obtained an excitation function for $^{30}$S($α$,$α$) near $150^{\circ}$ in the center-of-mass frame. The experimental data were analyzed with an $R$-Matrix calculation, and we observed three new resonant patterns between 11.1 and 12.1 MeV, extracting their properties of resonance energy, widths, spin, and parity. Conclusions: We calculated the resonant thermonuclear reaction rate of $^{30}$S($α$,p) based on all available experimental data of $^{34}$Ar and found an upper limit about one order of magnitude larger than a rate determined using a statistical model. The astrophysical impact of these two rates has been investigated through one-zone postprocessing type I x-ray burst calculations. We find that our new upper limit for the $^{30}$S($α$,p)$^{33}$Cl rate significantly affects the predicted nuclear energy generation rate during the burst.
We present the deepest study to date of the Lya luminosity function (LF) in a blank field using blind integral field spectroscopy from MUSE. We constructed a sample of 604 Lya emitters (LAEs) across the redshift range 2.91 < z < 6.64 using automatic detection software in the Hubble Ultra Deep Field. We calculate accurate total Lya fluxes capturing low surface brightness extended Lya emission now known to be a generic property of high-redshift star-forming galaxies. We simulated realistic extended LAEs to characterise the selection function of our samples, and performed flux-recovery experiments to test and correct for bias in our determination of total Lya fluxes. We find an accurate completeness correction accounting for extended emission reveals a very steep faint-end slope of the LF, alpha, down to luminosities of log10 L erg s^-1< 41.5, applying both the 1/Vmax and maximum likelihood estimators. Splitting the sample into three broad redshift bins, we see the faint-end slope increasing from -2.03+1.42-inf at z ~ 3.44 to -2.86+0.76-inf at z ~ 5.48, however no strong evolution is seen between the 68% confidence regions in L*-alpha parameter space. Using the Lya line flux as a proxy for star formation activity, and integrating the observed LFs, we find that LAEs' contribution to the cosmic SFRD rises with redshift until it is comparable to that from continuum-selected samples by z ~ 6. This implies that LAEs may contribute more to the star-formation activity of the early Universe than previously thought - any additional interglactic medium correction would act to further boost the Lya luminosities. Finally, assuming fiducial values for the escape of Lya and LyC radiation, and the clumpiness of the IGM, we integrated the maximum likelihood LF at 5.00 < z < 6.64 and find we require only a small extrapolation beyond the data (< 1 dex in L) for LAEs alone to maintain an ionised IGM at z ~ 6.