Clear reduction in spin susceptibility and superconducting spin rotation for in the early-stage sample of spin-triplet superconductor UTe

北川 俊作*; 徳永 陽; 酒井 宏典; 神戸 振作; 他11名*

Journal of the Physical Society of Japan, 93(12), p.123701_1 - 123701_5, 2024/11

https://doi.org/10.7566/JPSJ.93.123701

We report the re-measurement of the -axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe with the transition temperature of = 1.6 K. Using Knight-shift measurements along the axis and at a 10-degree tilt from the axis towards the axis, we accurately determined the -axis component without directly measuring the -axis Knight shift. The experiment reveals that the previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead.

Gate-tunable resistance drops related to local superconducting gaps in thin TaS layers on SrTiO substrates

小杉 美央子*; 齊藤 英治; 吉川 貴史*; 他11名*

APL Materials (Internet), 11(8), p.081106_1 - 081106_6, 2023/08

https://doi.org/10.1063/5.0147818

Strontium titanate [SrTiO (STO)], a perovskite oxide with an extremely high gate-tunable dielectric constant () due to quantum paraelectric phases, is attracting considerable attention for yielding various physical phenomena when two-dimensional (2D) layers are integrated. Superconductivity is such a typical phenomenon. However, the influence of the STO substrates on enhancing transition temperatures () for (atomically) thin 2D flakes attached to them has been rarely investigated. Here, we report gate-tunable and gradual four-terminal resistance drops with critical onset () and scanning tunneling spectroscopy (STS) spectra in devices comprising thin TaS flakes attached on monolayer hexagonal boron nitride (hBN) spacer/STO substrates. Observation of STS spectra confirms the presence of local superconducting gaps. (similar to 1.5 meV) with transition ( three-times higher than previous reports of under absent pressure and strong position dependence of . Depending on on back gate voltages () and magnetic fields, there is a strong correlation between and the onset of superconductivity, implying an enhancement of approximately five times compared with the previous highest-onset values without pressure as the applied increases. The high onset and. are discussed based on screening of the long-range Coulomb interaction (CI) due to the high- of SrTiO, while the short-ranged CI remains strong in the 2D limit, causing the superconductivity. Using a monolayer hBN/SrTiO substrate with opens doors to enhancement in thin superconducting layers integrated on it and wide application due to the solid-state high- substrates.

Search for a light Higgs boson in single-photon decays of using tagging method

Jia, S.*; 谷田 聖; Belle Collaboration*; 他211名*

Physical Review Letters, 128(8), p.081804_1 - 081804_9, 2022/02

https://doi.org/10.1103/PhysRevLett.128.081804

We search for a light Higgs boson () decaying into a or pair in the radiative decays of . The production of mesons is tagged by transitions, using 158 million events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant signals in the mass range from the or threshold to 9.2 GeV/ are observed. We set the upper limits at 90% credibility level (C.L.) on the product branching fractions for and varying from to . Our results represent an approximately twofold improvement on the current world best upper limits for the production. For , the upper limits on the product branching fractions for and are at the same level as the world average limits, and vary from to . The upper limits at 90% C.L. on the Yukawa coupling and mixing angle are also given.

High-rate performance of a time projection chamber for an H-dibaryon search experiment at J-PARC

Kim, S. H.*; 市川 裕大; 佐甲 博之; 長谷川 勝一; 早川 修平*; 七村 拓野*; 佐藤 進; 谷田 聖; 吉田 純也; 他11名*

Nuclear Instruments and Methods in Physics Research A, 940, p.359 - 370, 2019/10

https://doi.org/10.1016/j.nima.2019.06.050

We have developed a gas electron multiplier (GEM)-based time projection chamber (TPC) for the H-dibaryon search experiment at J-PARC. High-rate beam particles enter a TPC gas volume of approximately 0.2 m, in a direction perpendicular to the electric field. A long-rectangular hollow section is located inside the TPC volume to accommodate a diamond target. We commissioned the TPC using 230 MeV protons with beam rates of up to 1 MHz. The TPC data acquisition system collected 5768 pad signals in full readout mode, with almost 100% efficiency, at a preset trigger rate of 230 Hz. We operated the TPC in an Ar/CH gas mixture (90/10) without a magnetic field. The spatial resolutions on the pad plane are measured to be 400-700 m, which correspond to 230-300 m in a magnetic field of 1 T. We confirmed high tracking capability at beam rates of up to 1 MHz.

Cross section measurements of Gd(n,) induced by thermal and epithermal neutrons

Mastromarco, M.*; Manna, A.*; Aberle, O.*; Andrzejewski, J.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他116名*

European Physical Journal A, 55(1), p.9_1 - 9_20, 2019/01

https://doi.org/10.1140/epja/i2019-12692-7

Neutron capture cross section measurements on Gd and Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n TOF experimental area EAR1, at 185m from the neutron source, with an array of 4 CD liquid scintillation detectors. At a neutron kinetic energy of 0.0253eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for Gd and Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181eV and 307eV, respectively for Gd and Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2.01(28) 10 and 2.17(41) 10; average total radiative width of 106.8(14)meV and 101.1(20)meV and s-wave resonance spacing 1.6(2)eV and 4.8(5)eV for n + Gd and n + Gd systems, respectively.

Measurements of multiparticle correlations in +Au Collisions at 200, 62.4, 39, and 19.6 GeV and +Au Collisions at 200 GeV and implications for collective behavior

Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他311名*

Physical Review Letters, 120(6), p.062302_1 - 062302_8, 2018/02

AA2018-0511.pdf:0.47MB

https://doi.org/10.1103/PhysRevLett.120.062302

Recently, multiparticle-correlation measurements of relativistic HeAu, Pb, and even collisions have shown surprising collective signatures. Here we present beam-energy-scan measurements of 2-, 4-, and 6-particle angular correlations in Au collisions at =200, 62.4, 39, and 19.6 GeV. We also present measurements of 2- and 4-particle angular correlations in Au collisions at =200 GeV. We find the 4-particle cumulant to be real-valued for Au collisions at all four energies. We also find that the 4-particle cumulant in Au has the opposite sign as that in Au, indicating that the correlations are geometrical and therefore collective in origin. Further we find that the 6-particle cumulant agrees with the 4-particle cumulant in Au collisions at 200 GeV, which indicates that nonflow effects are subdominant and provides strong evidence of collectivity.

Time-of-flight and activation experiments on Pm and Tm for astrophysics

Guerrero, C.*; Lerendegui-Marco, J.*; Domingo-Pardo, C.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他113名*

EPJ Web of Conferences, 146, p.01007_1 - 01007_4, 2017/09

https://doi.org/10.1051/epjconf/201714601007

The neutron capture cross section of several key unstable isotopes acting as branching points in the s-process are crucial for stellar nucleosynthesis studies, but they are very challenging to measure due to the difficult production of sufficient sample material, the high activity of the resulting samples, and the actual (n,) measurement, for which high neutron fluxes and effective background rejection capabilities are required. Capture cross section of Pm and Tm have been measured for time-of-flight measurements at the CERN n_TOF facility using the 19 and 185m beam lines. Activation experiments on the same Pm and Tm targets with a high-intensity 30 keV quasi-Maxwellian flux of neutrons will be performed using the SARAF accelerator and the Liquid-Lithium Target (LiLiT) in order to extract the corresponding Maxwellian Average Cross Section (MACS). The status of these experiments and preliminary results will be presented and discussed as well.

Monte Carlo simulations of the n_TOF lead spallation target with the Geant4 toolkit; A Benchmark study

Lerendegui-Marco, J.*; Corts-Giraldo, M. A.*; Guerrero, C.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他114名*

EPJ Web of Conferences, 146, p.03030_1 - 03030_4, 2017/09

https://doi.org/10.1051/epjconf/201714603030

Monte Carlo (MC) simulations are an essential tool to determine fundamental features of a neutron beam, such as the neutron flux or the ray background, that sometimes can not be measured or at least not in every position or energy range. Until recently, the most widely used MC codes in this field had been MCNPX and FLUKA. However, the Geant4 toolkit has also become a competitive code for the transport of neutrons after the development of the native Geant4 format for neutron data libraries, G4NDL. In this context, we present the Geant4 simulations of the neutron spallation target of the n TOF facility at CERN, done with version 10.1.1 of the toolkit. The first goal was the validation of the intra-nuclear cascade models implemented in the code using, as benchmark, the characteristics of the neutron beam measured at the first experimental area (EAR1), especially the neutron flux and energy distribution, and the time distribution of neutrons of equal kinetic energy, the so-called Resolution Function. The second goal was the development of a Monte Carlo tool aimed to provide useful calculations for both the analysis and planning of the upcoming measurements at the new experimental area (EAR2) of the facility.