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N. Nakajima

Publications and source records attributed to N. Nakajima.

15 recordsLinked to original sources
arXiv2021

Dielectric response of BaTiO3 electronic states under AC fields via microsecond time-resolved X-ray absorption spectroscopy

For the first time, the dielectric response of a BaTiO3 thin film under an AC electric field is investigated using time-resolved X-ray absorption spectroscopy at the Ti K-edge to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge eg peak and shoulder structure just below the main edge increase with an increase in the amplitude of the applied electric field, whereas that of the main peak decreases in an opposite manner. Based on the multiple scattering theory, the increase and decrease of the eg and main peaks are simulated for different Ti off-center displacements. Our results indicate that these spectral features reflect the inter- and intra-atomic hybridization of Ti 3d with O 2p and Ti 4p, respectively. In contrast, the shoulder structure is not affected by changes in the Ti off-center displacement but is susceptible to the effect of the corner site Ba ions. This is the first experimental verification of the dynamic electronic contribution of Ba to polarization reversal.

cond-mat.mtrl-sci↗
arXiv2020

Theoretical studies of equilibrium beta limit in heliotron plasmas

In this study, the MHD equilibrium limit of LHD plasmas is studied using a 3D MHD equilibrium calculation code, HINT, which is an initial value solver based on the relaxation method without the assumption of nested flux surfaces. For finite beta equilibria, flux surfaces become stochastic in the peripheral region. However, though the axis shifts until the conventional limit, the separatrix to limit the equilibrium does not appear. For high beta equilibria, the force balance starts breaking in the stochastic region. To keep the force balance, the pressure gradient in the stochastic region decreases and the fixed profile is reduced. As the result, the volume averaged beta saturates. The beta value, where the force balance starts breaking inside the stochastic region, is proposed as an index of equilibrium beta limit in heliotron plasmas.

physics.plasm-ph↗
arXiv2006

Modified Hagedorn formula including temperature fluctuation - Estimation of temperatures at RHIC experiments -

We have systematically estimated the possible temperatures obtained from an analysis of recent data on $p_t$ distributions observed at RHIC experiments. Using the fact that observed $p_t$ distributions cannot be described by the original Hagedorn formula in the whole range of transverse momenta (in particular above 6 GeV/c), we propose a modified Hagedorn formula including temperature fluctuation. We show that by using it we can fit $p_t$ distributions in the whole range and can estimate consistently the relevant temperatures, including their fluctuations.

hep-ph↗
arXiv2006

On-site underground background measurements for the KASKA reactor-neutrino experiment

On-site underground background measurements were performed for the planned reactor-neutrino oscillation experiment KASKA at Kashiwazaki-Kariwa nuclear power station in Niigata, Japan. A small-diameter boring hole was excavated down to 70m underground level, and a detector unit for $γ$-ray and cosmic-muon measurements was placed at various depths to take data. The data were analyzed to obtain abundance of natural radioactive elements in the surrounding soil and rates of cosmic muons that penetrate the overburden. The results will be reflected in the design of the KASKA experiment.

hep-ex↗
arXiv2006

Letter of Intent for KASKA: High Accuracy Neutrino Oscillation Measurements with anti-nu_es from Kashiwazaki-Kariwa Nuclear Power Station

One of the current most-demanded experiments in neutrino physics is to measure the last mixing angle theta_13. KASKA is an experiment to detect new type of reactor neutrino oscillation and to measure sin^2 2theta_13 accurately using the world's most powerful nuclear reactor complex; Kashiwazaki-Kariwa nuclear power station. KASKA utilizes near and far detectors of identical structure at nearly optimized baselines and underground depths to cancel most of the systematics and reduce backgrounds. The expected sensitivity is sin^2 2theta_13~0.015, which is 10 times better sensitivity than the current upper limit measured by CHOOZ reactor experiment. Extension of KASKA project has potential to accurately measure other anti-nu_e oscillation parameters. Intense and precisely known neutrino flux measured by the KASKA-theta_13 phase can be used to pin down sin^2 2theta_12 at a baseline ~50km and to measure Dm^2_13 for the first time at a baseline ~5km. This Letter of Intent describes physics motivation, detector system and expected performance of the KASKA experiment.

hep-ex↗
arXiv2004

Hadron Physics and Confinement Physics in Lattice QCD

We are aiming to construct Quark Hadron Physics and Confinement Physics based on QCD. Using SU(3)$_c$ lattice QCD, we are investigating the three-quark potential at T=0 and $T \ne 0$, mass spectra of positive and negative-parity baryons in the octet and the decuplet representations of the SU(3) flavor, glueball properties at T=0 and $T \ne 0$. We study also Confinement Physics using lattice QCD. In the maximally abelian (MA) gauge, the off-diagonal gluon amplitude is strongly suppressed, and then the off-diagonal gluon phase shows strong randomness, which leads to a large effective off-diagonal gluon mass, $M_{\rm off} \simeq 1.2 {\rm GeV}$. Due to the large off-diagonal gluon mass in the MA gauge, infrared QCD is abelianized like nonabelian Higgs theories. In the MA gauge, there appears a macroscopic network of the monopole world-line covering the whole system. From the monopole current, we extract the dual gluon field $B_μ$, and examine the longitudinal magnetic screening. We obtain $m_B \simeq$ 0.5 GeV in the infrared region, which indicates the dual Higgs mechanism by monopole condensation. From infrared abelian dominance and infrared monopole condensation, low-energy QCD in the MA gauge is described with the dual Ginzburg-Landau (DGL) theory.

hep-ph↗
arXiv2004

Lambda(1405) and Negative-Parity Baryons in Lattice QCD

We review briefly recent studies of the Lambda(1405) spectrum in Lattice QCD. Ordinary three-quark pictures of the Lambda(1405) in quenched Lattice QCD fail to reproduce the mass of the experimental value, which seems to support the penta-quark picture for the Lambda(1405) such as a Kbar-N molecule-like state. It is also noted that the present results suffer from relatively large systematic uncertainties coming from the finite volume effect, the chiral extrapolation and the quenching effect.

hep-lat↗
arXiv2003

Negative-Parity Baryons in Quenched Anisotropic Lattice QCD

We study negative-parity baryon spectra in quenched anisotropic lattice QCD. The negative-parity baryons are measured as the parity partner of the ground-state baryons. In addition to the flavor octet and decuplet baryons, we pay much attention to the flavor-singlet negative-parity baryon as a three-quark state and compare it with the Lambda(1405) baryon. Numerical results of the flavor octet and decuplet negative-parity baryon masses are close to experimental values of lowest-lying negative-parity baryons, while the flavor-singlet baryon is much heavier than Lambda(1405). This indicates that the Lambda(1405) would be a multi-quark state such as the N-Kbar molecule rather than the flavor-singlet 3 quark state.

hep-lat↗
arXiv2003

Negative-parity baryon spectra in quenched anisotropic lattice QCD

We investigate the negative-parity baryon spectra in quenched lattice QCD. We employ the anisotropic lattice with standard Wilson gauge and O(a) improved Wilson quark actions at three values of lattice spacings with renormalized anisotropy xi=a_sigma/a_tau=4, where a_sigma and a_tau are spatial and temporal lattice spacings, respectively. The negative-parity baryons are measured with the parity projection. In particular, we pay much attention to the lowest SU(3) flavor-singlet negative-parity baryon, which is assigned as the Lambda(1405) in the quark model. For the flavor octet and decuplet negative-parity baryons, the calculated masses are close to the experimental values of corresponding lowest-lying negative-parity baryons. In contrast, the flavor-singlet baryon is found to be about 1.7 GeV, which is much heavier than the Lambda(1405). Therefore, it is difficult to identify the Lambda(1405) to be the flavor-singlet three-quark state, which seems to support an interesting picture of the penta-quark (uds qbar q) state or the N-Kbar molecule for the Lambda(1405).

hep-lat↗
arXiv2002

SU(3) lattice QCD study for octet and decuplet baryon spectra

The spectra of octet and decuplet baryons are studied using SU(3) lattice QCD at the quenched level. As an implementation to reduce the statistical fluctuation, we employ the anisotropic lattice with $O(a)$ improved quark action. In relation to $Λ(1405)$, we measure also the mass of the SU(3) flavor-singlet negative-parity baryon, which is described as a three quark state in the quenched lattice QCD, and its lowest mass is measured about 1.6 GeV. Since the experimentally observed negative-parity baryon $Λ(1405)$ is much lighter than 1.6 GeV, $Λ(1405)$ may include a large component of a $N \bar K$ bound state rather than the three quark state. The mass splitting between the octet and the decuplet baryons are also discussed in terms of the current quark mass.

hep-lat↗
arXiv2001

Analyses of multiplicity distributions at Tevatron by a two-component stochastic model --- No leading particle effect in E735 Experiment ---

Comparisons of multiplicity distributions at sqrt(s) = 1.8 TeV (E735 Experiment and CDF Collaboration) with our predictions by a two-component stochastic model have been made. This stochastic model is described by the pure-birth and Poisson processes. It is found that there are discrepancies among data at the CERN Sp-bar-pS collider and those at the Tevatron collider. The latter data by E735 do not contain the leading particle effect described by the Poisson process, providing that the view of the two-component stochastic model is correct. The data by CDF contain small leading particle effect. The reason is probably attributed to the correction made by E735, which is necessary to make the data of the full phase space from the restricted rapidity |eta|<3.25.

hep-ph↗
arXiv1998

Analyses of multiplicity distributions by means of the Modified Negative Binomial Distribution and its KNO scaling function

We analyze various data of multiplicity distributions by means of the Modified Negative Binomial Distribution (MNBD) and its KNO scaling function, since this MNBD explains the oscillating behavior of the cumulant moment observed in e^+e^- annihilations, h-h collisions and e-p collisions. In the present analyses, we find that the MNBD(discrete distributions) describes the data of charged particles in e^+e^- annihilations much better than the Negative Binomial Distribution (NBD). To investigate stochastic property of the MNBD, we derive the KNO scaling function from the discrete distribution by using a straightforward method and the Poisson transform. It is a new KNO function expressed by the Laguerre polynomials. In analyses of the data by using the KNO scaling function, we find that the MNBD describes the data better than the gamma function.Thus, it can be said that the MNBD is one of useful formulas as well as NBD.

hep-ph↗
arXiv1996

KNO scaling function of modified negative binomial distribution

We investigate the KNO scaling function of the modified negative binomial distribution (MNBD), because this MNBD can explain the oscillating behaviors of the cumulant moment observed in $e^+e^-$ annihilations and in hadronic collisions. By using a straightforward method and the Poisson transform we derive the KNO scaling function from the MNBD. The KNO form of experimental data in $e^{+}e^{-}$ collisions and hadronic collisions are analyzed by the KNO scaling function of the MNBD and that of the negative binomial distribution (NBD). The KNO scaling function of the MNBD describes the data as well as that of the NBD.

hep-ph↗
arXiv1996

Analysis of Cumulant Moments in High Energy Hadron-Hadron Collisions by Truncated Multiplicity Distributions

Oscillatory behavior of cumulant moments obtained from the experimental data in $pp$ collisions and $\bar{p}p$ collisions are analyzed by the modified negative binomial distribution (MNBD) and the negative binomial distribution (NBD). Both distributions well describe the cumulant moments obtained from the data. This fact shows sharp contrast to the result in $e^+e^-$ collisions, which is described by the the MNBD much better than by the NBD.

hep-ph↗