arXiv subjects

T. Koike

Publications and source records attributed to T. Koike.

At least 19 recordsLinked to original sources

arXiv2026

Negative-parity high-spin structure of 105Pd

Negative-parity medium- and high-spin structure of the nucleus 105Pd was studied through the 96Zr(13C,4n)105Pd reaction at incident energies of 51 and 58 MeV, using the EUROBALL IV gamma-ray spectrometer in conjunction with the DIAMANT charged particle array. New bands have been observed and the previously reported bands have been extended to higher energies and spins. Altogether six decoupled bands with E2 transitions and one strongly coupled band with M1 + E2 transitions have been observed. The observed energy spectra and B(M1)/B(E2) ratios are compared with results of quantum particle rotor model calculations. Based on these comparisons, quasiparticle configurations can be assigned to two newly observed decoupled bands as well as to the strongly coupled band. The previously emerged possible interpretation for the third decoupled band as a two-phonon wobbling excitation lacks support. The observations indicate possible gamma-band nature for this band. The strongly coupled band, consistently with the absence of another observed strongly coupled band in this experiment, does not exhibit chirality.

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arXiv2025

Measurement of $\Lambda$ Polarization in the $\pi^{-}p \to K^{0} \Lambda$ Reaction at $p_{\pi^{-}}=1.33$ GeV/$c$ toward a New $\Lambda p$ Scattering Experiment

This paper presents high-precision experimental data of the polarization of the $\Lambda$ hyperon in the $\pi^{-}p \to K^{0} \Lambda$ reaction, measured in the angular range $0.6<\cos \theta ^{CM}_{K0}<1.0$ with a fine bin width of $d\cos \theta ^{CM}_{K0}=0.05$. The data were obtained from the J-PARC E40 experiment at the K1.8 beamline in the J-PARC Hadron Experimental Facility. The observed average polarization of $\Lambda$ in the range $0.60<\cos \theta ^{CM}_{K0}<0.85$ was $0.932 \pm 0.058 \,(\text{stat}) \pm 0.028 \,(\text{syst})$, demonstrating the successful extraction of precise polarization observables. This result provides essential experimental input for partial wave analysis (PWA) of dynamical coupled-channel (DCC) models, which aim to uncover the underlying mechanisms of $N^{*}$ resonances that emerge in intermediate states of $\pi N$ and $\gamma N$ interactions. Besides, it indicates the feasibility of a strongly polarized $\Lambda$ beam suitable for future $\Lambda p$ scattering experiments (e.g., J-PARC E86).

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arXiv2022

Measurement of differential cross sections for $\Sigma^+p$ elastic scattering in the momentum range 0.44-0.80 GeV/c

We performed a novel $\Sigma^+ p$ scattering experiment at the J-PARC Hadron Experimental Facility. Approximately 2400 $\Sigma^+ p$ elastic scattering events were identified from $4.9 \times 10^7$ tagged $\Sigma^+$ particles in the $\Sigma^+$ momentum range 0.44 -- 0.80 GeV/$c$. The differential cross sections of the $\Sigma^+ p$ elastic scattering were derived with much better precision than in previous experiments. The obtained differential cross sections were approximately 2 mb/sr or less, which were not as large as those predicted by the fss2 and FSS models based on the quark cluster model in the short-range region. By performing phase-shift analyses for the obtained differential cross sections, we experimentally derived the phase shifts of the $^3 S_1$ and $^1 P_1$ channels for the first time. The phase shift of the $^3 S_1$ channel, where a large repulsive core was predicted owing to the Pauli effect between quarks, was evaluated as $20^\circ<|\delta_{^3S_1}|<35^\circ$. If the sign of $\delta_{^3S_1}$ is assumed to be negative, the interaction in this channel is moderately repulsive, as the Nijmegen extended-sort-core models predicted.

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arXiv2021

Precise measurement of differential cross sections of the {\Sigma}-p --> {\Lambda} n reaction in momentum range 470-650 MeV/c

The differential cross sections of the {\Sigma}-p --> {\Lambda} n reaction were measured accurately for the {\Sigma}- momentum (p_{{\Sigma}}) ranging from 470 to 650 MeV/c at the J-PARC Hadron Experimental Facility. Precise angular information about the {\Sigma}-p --> {\Lambda} n reaction was obtained for the first time by detecting approximately 100 reaction events at each angular step of {\Delta}cos{\theta} = 0.1. The obtained differential cross sections show slightly forward-peaking structure in the measured momentum regions.The cross sections integrated for -0.7 < cos{\theta} < 1.0 were obtained as 22.5 +- 0.68 (stat.) +- 0.65 (syst.) mb and 15.8 +-0.83(stat.) +- 0.52 (syst.) mb for 470<p_{{\Sigma}}(MeV/c)<550 and 550<p_{{\Sigma}}(MeV/c)<650, respectively. These results show a drastic improvement compared to past measurements of the hyperon-proton scattering experiments. They will play essential roles in updating the theoretical models of the baryon-baryon interactions.

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arXiv2021

Measurement of the differential cross sections of the Sigma-p elastic scattering in momentum range of 470 to 850 MeV/c

A high statistics $\Sigma p$ scattering experiment has been performed at the J-PARC Hadron Experimental Facility. Data for momentum-tagged $\Sigma^{-}$ running in a liquid hydrogen target were accumulated by detecting the $\pi^{-}p \to K^{+}\Sigma^{-}$ reaction with a high intensity $\pi^{-}$ beam of 20 M/spill. Differential cross sections of the $\Sigma^{-}p$ elastic scattering were derived with a drastically improved accuracy by identifying the largest statistics of about 4,500 events from 1.72 $\times$ $10^{7}$ $\Sigma^{-}$. The derived differential cross section shows a clear forward-peaking angular distribution for a $\Sigma^{-}$ momentum range from 470 to 850 MeV/$c$. The accurate data will impose a strong constraint on the theoretical models of the baryon-baryon interactions.

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arXiv2020

Observation of Coulomb-assisted nuclear bound state of $\Xi^-$-$^{14}$N system

In an emulsion-counter hybrid experiment performed at J-PARC, a $\Xi^-$ absorption event was observed which decayed into twin single-$\Lambda$ hypernuclei. Kinematic calculations enabled a unique identification of the reaction process as $\Xi^{-} + ^{14}$N$\ \rightarrow\ ^{10}_\Lambda$Be + $^5_\Lambda$He. For the binding energy of the $\Xi^{-}$ hyperon in the $\Xi^-$-$^{14}$N system a value of $1.27 \pm 0.21$ MeV was deduced. The energy level of $\Xi^-$ is likely a nuclear $1p$ state which indicates a weak ${\Xi}N$-$\Lambda\Lambda$ coupling.

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arXiv2020

Reexamination of $^{6}$Li scattering as a Probe to Investigate the Isoscalar Giant Resonances in Nuclei

Inelastic ${}^{6}$Li scattering at 100 MeV/u on ${}^{12}$C and ${}^{93}$Nb have been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range $0^\circ < \theta_{\text{lab.}}< 2^\circ$. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of ${}^{6}$Li scattering allowed for precise determination of the $E0$ strengths in ${}^{12}$C and ${}^{93}$Nb. It was found that the monopole strength in ${}^{12}$C exhausts $52 \pm 3^\text{(stat.)} \pm 8 ^\text{(sys.)}$\% of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous $\alpha$-scattering experiments. The monopole strength in ${}^{93}$Nb exhausts $92 \pm 4^\text{(stat.)} \pm 10 ^\text{(sys.)}$\% of the EWSR, and it is consistent with measurements of nuclei with mass number of $A\approx90$. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.

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arXiv2019

Experimental Evidence for Transverse Wobbling in $^{105}$Pd

New rotational bands built on the $\nu$$(h_{11/2})$ configuration have been identified in $^{105}$Pd. Two bands built on this configuration show the characteristics of transverse wobbling: the $\Delta$$I$=1 transitions between them have a predominant E2 component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the $A$$\sim$100 mass region.

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arXiv2018

Observation of a Be double-Lambda hypernucleus in the J-PARC E07 experiment

A double-$\Lambda$ hypernucleus, ${}_{\Lambda\Lambda}\mathrm{Be}$, 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 $ {}_{\Lambda\Lambda}^{\;10}\mathrm{Be}$, ${}_{\Lambda\Lambda}^{\;11}\mathrm{Be}$, or ${}_{\Lambda\Lambda}^{\;12}\mathrm{Be}^{*}$ via $\Xi^{-}$ capture in ${}^{16}\mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $\Lambda$ hyperons$\,$($B_{\Lambda\Lambda}$) of these double-$\Lambda$ 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, ${}_{\Lambda\Lambda}^{\;11}\mathrm{Be}$ is the most likely explanation for the observed event.

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arXiv2018

Three-level mixing model for nuclear chiral rotation: Role of planar component

Three- and two-level mixing models are proposed to understand the doubling of states at the same spin and parity in triaxially-deformed atomic nuclei with odd numbers of protons and neutrons. The Particle-Rotor Model for such nuclei is solved using the newly proposed basis which couples angular momenta of two valence nucleons and the rotating triaxial mean-field into left-handed $|\mathcal{L}\rangle$, right-handed $|\mathcal{R}\rangle$, and planar $|\mathcal{P}\rangle$ configurations. The presence and the impact of the planar component is investigated as a function of the total spin for mass A$\approx$130 nuclei with the valence h$_{11/2}$ proton particle, valence h$_{11/2}$ neutron hole and the maximum difference between principle axes allowed by the quadrupole deformation of the mean field. It is concluded that at each spin value the higher-energy member of a doublet of states is built on the anti-symmetric combination of $|\mathcal{L}\rangle$ and $|\mathcal{R}\rangle$ and is free of the $|\mathcal{P}\rangle$ component, indicating that it is of pure chiral geometry. For the lower-energy member of the doublet, the contribution of the $|\mathcal{P}\rangle$ component to the eigenfunction first decreases and then increases as a function of the total spin. This trend as well as the energy splitting between the doublet states are both determined by the Hamiltonian matrix elements between the planar ($|\mathcal{P}\rangle$) and non-planar ($|\mathcal{L}\rangle$ and $|\mathcal{R}\rangle$) subspaces of the full Hilbert space.

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arXiv2017

First Determination of Level Structure of an $sd$-Shell Hypernucleus, $\rm {^{19}_{\Lambda}F}$

We report on the first observation of $\gamma$ rays emitted from an $sd$-shell hypernucleus, $\rm ^{19}_{\Lambda}F$. The energy spacing between the ground state doublet, $1/2^{+}$ and $3/2^{+}$ states, of $\rm ^{19}_{\Lambda}F$ is determined to be $\rm 315.5 \pm 0.4 (stat) ^{+0.6}_{-0.5} (syst)~keV$ by measuring the $\gamma$-ray energy from the $M1(3/2^{+} \rightarrow 1/2^{+})$ transition. In addition, three $\gamma$-ray peaks were observed and assigned as $E2(5/2^{+} \rightarrow 1/2^{+})$, $E1(1/2^{-} \rightarrow 1/2^{+})$, and $E1(1/2^{-} \rightarrow 3/2^{+})$ transitions. The excitation energies of the $5/2^{+}$ and $1/2^{-}$ states are determined to be $\rm 895.2 \pm 0.3 (stat) \pm 0.5 (syst)~keV$ and $\rm 1265.6 \pm 1.2 (stat) ^{+0.7}_{-0.5} (syst)~keV$, respectively. It is found that the ground state doublet spacing is well described by theoretical models based on existing $s$- and $p$-shell hypernuclear data.

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arXiv2017

Brachistochrone of Entanglement for Spin Chains

We analytically investigate the role of entanglement in time-optimal state evolution as an appli- cation of the quantum brachistochrone, a general method for obtaining the optimal time-dependent Hamiltonian for reaching a target quantum state. As a model, we treat two qubits indirectly cou- pled through an intermediate qubit that is directly controllable, which represents a typical situation in quantum information processing. We find the time-optimal unitary evolution law and quantify residual entanglement by the two-tangle between the indirectly coupled qubits, for all possible sets of initial pure quantum states of a tripartite system. The integrals of the motion of the brachistochrone are determined by fixing the minimal time at which the residual entanglement is maximized. Entan- glement plays a role for W and GHZ initial quantum states, and for the bi-separable initial state in which the indirectly coupled qubits have a nonzero value of the 2-tangle.

quant-ph↗

arXiv2016

First application of superconducting transition-edge-sensor microcalorimeters to hadronic-atom x-ray spectroscopy

High-resolution pionic-atom x-ray spectroscopy was performed with an x-ray spectrometer based on a 240-pixel array of superconducting transition-edge-sensor (TES) microcalorimeters at the piM1 beam line of the Paul Scherrer Institute. X-rays emitted by pionic carbon via the 4f->3d transition and the parallel 4d->3p transition were observed with a full-width-at-half-maximum energy resolution of 6.8 eV at 6.4 keV. Measured x-ray energies are consistent with calculated electromagnetic values which considered the strong-interaction effect assessed via the Seki-Masutani potential for the 3p energy level, and favor the electronic population of two filled 1s electrons in the K-shell. Absolute energy calibration with an uncertainty of 0.1 eV was demonstrated under a high-rate hadron beam condition of 1.45 MHz. This is the first application of a TES spectrometer to hadronic-atom x-ray spectroscopy and is an important milestone towards next-generation high-resolution kaonic-atom x-ray spectroscopy.

physics.ins-det↗

arXiv2015

Observation of Spin-Dependent Charge Symmetry Breaking in $ΛN$ Interaction: Gamma-Ray Spectroscopy of $^4_{Λ}$He

The energy spacing between the ground-state spin doublet of $^4_Λ$He(1$^+$,0$^+$) was determined to be $1406 \pm 2 \pm 2$ keV, by measuring $γ$ rays for the $1^+ \to 0^+$ transition with a high efficiency germanium detector array in coincidence with the $^4$He$(K^-,π^-)$ $^4_Λ$He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus $^4_Λ$H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in $ΛN$ interaction. It is also found that the CSB effect is large in the $0^+$ ground state but is by one order of magnitude smaller in the $1^+$ excited state, demonstrating that the $ΛN$ CSB interaction has spin dependence.

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arXiv2015

Precise determination of $^{12}_Λ$C level structure by $γ$-ray spectroscopy

Level structure of the $^{12}_Λ$C hypernucleus was precisely determined by means of $γ$-ray spectroscopy. We identified four $γ$-ray transitions via the $^{12}$C$(π^{+},K^{+}γ)$ reaction using a germanium detector array, Hyperball2. The spacing of the ground-state doublet $(2^{-}_{1},1^{-}_{1})$ was measured to be $161.5\pm0.3\text{(stat)}\pm0.3\text{(syst)}$\,keV from the direct $M1$ transition. Excitation energies of the $1^{-}_{2}$ and $1^{-}_{3}$ states were measured to be $2832\pm3\pm4$\,keV and $6050\pm8\pm7$\,keV, respectively. The obtained level energies provide definitive references for the reaction spectroscopy of $Λ$ hypernuclei.

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arXiv2014

Near threshold angular distributions of the $^2$H$(γ,Λ)$X reaction

A study of the $^2$H$(γ,Λ)$X reaction was performed using a tagged photon beam at the Research Center for Electron Photon Science (ELPH), Tohoku University. The photoproduced $Λ$ was measured in the $p{π^{-}}$ decay channel by the upgraded Neutral Kaon Spectrometer (NKS2+). The momentum integrated differential cross section was determined as a function of the scatting angle of $Λ$ in the laboratory frame for five energy bins. Our results indicated a peak in the cross section at angles smaller than cos$θ^{LAB}_Λ$ = $0.96$. The experimentally obtained angular distributions were compared to isobar models, Kaon-Maid (KM) and Saclay-Lyon A (SLA), in addition to the composite Regge-plus-resonance (RPR) model. Both SLA(r$K_{1}K_γ$ = $-1.4$) and RPR describe the data quite well in contrast to the KM model, which substantially under predicted the cross section at the most forward angles. With the anticipated finalized data on $Λ$ integrated and momentum dependent differential cross sections of $^2$H$(γ,Λ)$X~\cite{Kaneta_Beckford}, we present our findings on the angular distributions in this report.

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arXiv2014

High-resolution search for the $Θ^{+}$ pentaquark via a pion-induced reaction at J-PARC

The pentaquark $Θ^+$ has been searched for via the $π^-p \to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on the production cross section averaged over the scattering angle from 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame were found to be less than 0.28 $μ$b/sr at the 90\% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10\%. Constraints on the $Θ^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.

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arXiv2014

Multiple chiral doublet bands of identical configuration in 103Rh

Three sets of chiral doublet band structures have been identified in the 103Rh nucleus. The properties of the observed chiral doublet bands are in good agreement with theoretical results obtained using constrained covariant density functional theory and particle rotor model calculations. Two of them belong to an identical configuration, and provide the first experimental evidence for a novel type of multiple chiral doublets, where an "excited" chiral doublet of a configuration is seen together with the "yrast" one. This observation shows that the chiral geometry in nuclei can be robust against the increase of the intrinsic excitation energy.

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