Search

The J-PARC E56 experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). In order to examine the feasibility of the experiment, we measured the background rates of different detector candidate sites, which are located at the third floor of the MLF, using a detector consisting of plastic scintillators with a fiducial mass of 500 kg. The result of the measurements is described in this article. The gammas and neutrons induced by the beam as well as the backgrounds from the cosmic rays were measured., Comment: submitted to PTEP. arXiv admin note: substantial text overlap with arXiv:1502.02255: Revision on 2015-April-22

At the 17th J-PARC PAC, which was held on September 2013, we proposed the sterile neutrino search at J-PARC MLF. After reviewing the proposal, PAC recommended to have a background measurement at the detector's candidate site location in their report to investigate whether the background rates can be manageable for the real experiment or not. Therefore, we have performed the background measurements (MLF; 2013BU1301 test experiment) during the summer of 2014, also following the 18th J-PARC PAC recommendations, and the measurements results are described here.

Effects of electron doping on the BiS$_2$-based superconductors Sr$_{1-x}$La$_x$FBiS$_2$ ($0\le x\le 0.6$) have been investigated using the systematically synthesized polycrystals. The pristine compound is a band insulator with the BiS$_2$ layer, which accommodates electron carriers through the La substitution for Sr, as evidenced by the change in x-ray absorption spectra reflecting the occupancy of Bi 6$p$ orbitals. With increasing the carrier density, the resistivity progressively decreases and a bad metallic state appears for $x\ge0.45$, where bulk superconductivity manifests itself below approximately 3 K. The value of $T_{\rm c}$ gradually increases with decreasing $x$ from 0.6 to 0.45 and immediately decreases down to zero at the critical concentration of $x\sim 0.4$, resulting in an insulator-superconductor transition highly sensitive to the carrier density. Thermodynamic measurements furthermore have revealed the possible enhancement of the superconducting coupling strength as the insulating phase is approached. The obtained superconducting phase diagram is markedly different from the broad dome-shaped superconducting phase previously reported for $R$O$_{1-x}$F$_x$BiS$_2$ ($R$: rare-earth ion), suggesting a strong influence of the blocking layer on the superconductivity. Instead all these features are similar to those observed in Li-intercalated ZrNCl superconductor, except for the critical electron concentration of as low as 6% in the latter compound. For the present superconductor, notably, the existence of hole-type carriers has been indicated in the normal state from the Hall effect measurements. The Sr$_{1-x}$La$_x$FBiS$_2$ system providing the phase diagram for the rigid-band doping in the BiS$_2$ layer would be another prototypical example of superconductivity derived from a doped layered band insulator, hosting both hole-like and electron-like Fermi surfaces., Comment: 19 pages, 8 figures, accepted for publication in J. Phys. Soc. Jpn

We propose a definite search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). With the 3 GeV Rapid Cycling Synchrotron (RCS) and spallation neutron target, an intense neutrino beam from muon decay at rest (DAR) is available. Neutrinos come from \mu+ decay, and the oscillation to be searched for is (anti \nu \mu -> anti \nu e) which is detected by the inverse \beta decay interaction (anti \nu e + p -> e+ + n), followed by a gamma from neutron capture. The unique features of the proposed experiment, compared with the LSND and experiments using horn focused beams, are; (1) The pulsed beam with about 600 ns spill width from J-PARC RCS and muon long lifetime allow us to select neutrinos from \mu DAR only. (2) Due to nuclear absorption of \pi- and \mu-, neutrinos from \mu- decay are suppressed to about the $10^{-3}$ level. (3) Neutrino cross sections are well known. The inverse \beta decay cross section is known to be a few percent accuracy. (4) The neutrino energy can be calculated from positron energy by adding ~1.8 MeV. (5) The anti \nu \mu and \nu e fluxes have different and well defined spectra. This allows us to separate oscillated signals from those due to \mu- decay contamination. We propose to proceed with the oscillation search in steps since the region of \Delta m^2 to be searched can be anywhere between sub-eV^2 to several tens of eV^2. We start to examine the large \Delta m^2 region, which can be done with short baseline at first. At close distance to the MLF target gives a high neutrino flux, and allows us to use relatively small detector. If no definitive positive signal is found, a future option exists to cover small \Delta m^2 region. This needs a relatively long baseline and requires a large detector to compensate for the reduced neutrino flux.

We have grown the new uranium compound URhIn$_5$ with the tetragonal HoCoGa$_5$-type by the In self flux method. In contrast to the nonmagnetic ground state of the isoelectronic analogue URhGa$_5$, URhIn$_5$ is an antiferromagnet with antiferromagnetic transition temperature $T_{\rm N}$ = 98 K. The moderately large electronic specific heat coefficient $\gamma$ = 50 mJ/K$^2$mol demonstrates the contribution of 5$f$ electrons to the conduction band. On the other hand, magnetic susceptibility in the paramagnetic state roughly follows a Curie-Weiss law with a paramagnetic effective moment corresponding to a localized uranium ion. The crossover from localized to itinerant character at low temperature may occur around the characteristic temperature 150 K where the magnetic susceptibility and electrical resistivity show a marked anomaly., Comment: 7 pages, 7 figures

A complete set of analyzing powers for the dd->3Hp reaction at the kinetic beam energy of 200 MeV has been measured in the full angular range in the c.m. frame. The observed signs of the tensor analyzing powers Ayy, Axx, and Axz at forward and backward directions have clearly demonstrated the sensitivity to the ratio of the D- and S-wave components of the triton and deuteron, respectively. The new high-precision data are compared with the prediction of the relativistic multiple-scattering model by using standard wave functions of the three-nucleon bound state and of the deuteron.

Vector analyzing powers for proton elastic scattering from 8He at 71 MeV/nucleon have been measured using a solid polarized proton target operated in a low magnetic field of 0.1 T. The spin-orbit potential obtained from a phenomenological optical model analysis is found to be significantly shallower and more diffuse than the global systematics of stable nuclei, which is an indication that the spin-orbit potential is modified for scattering involving neutron-rich nuclei. A close similarity between the matter radius and the root-mean-square radius of the spin-orbit potential is also identified., Comment: 6 pages, 4 figures, accepted for publication in Physical Review C Rapid Communication

The vector Ay and tensor analyzing powers Ayy and Axx for dp- elastic scattering were measured at Td = 880 MeV over the c.m. angular range from 60 to 140 degrees at the JINR Nuclotron. The data are compared with predictions of different theoretical models based on the use of nucleon-nucleon forces only. The observed discrepancies of the measured analyzing powers from the calculations require the consideration of additional mechanisms., Comment: 5 pages,3 figures

The investigation of the d, 3H and 3He spin structure has been performed at the RIKEN(Japan) accelerator research facility and VBLHEP(JINR) using both polarized and unpolarized deuteron beams. The experimental results on the analyzing powers studies in dp- elastic scattering, d(d,3H)p and d(d,3He)n reactions are presented. The vector and tensor analyzing powers for dp-elastic scattering at 880 and 2000 MeV are obtained at the Nuclotron(VBLHEP). The result on the analyzing powers Ay, Ayy of the deuteron at 2000 MeV are compared with relativistic multiple scattering model calculations. The data on the tensor analyzing powers for the d(d,3H)p and d(d,3He)n reactions obtained at Ed = 200 and 270 MeV demonstrate the sensitivity to the 3H, 3He and deuteron spin structure. The essential disagreements between the experimental results and the theoretical calculations within the one-nucleon exchange model framework are observed. The wide experimental program on the study of the polarization effects in dp- elastic scattering, dp-nonmesonic breakup, d(d,3He)n, d(d,3H)p and d(3He,4He)p reactions using internal and extracted beam at Nuclotron is discussed., Comment: 4 pages, 6 figures, XIV International Conference on Hadron Spectroscopy, HADRON2011, 13-17 June 2011, Munchen

Magnetically-driven ferroelectric atomic displacements of the order of 10$^{-3} Angstrom have been observed in orthorhombic (perovskite like) YMnO$_3$ by a single-crystal synchrotron x-ray diffraction. The refined polar structure shows the characteristic bond alternation driven by the exchange striction in staggered Mn-O-Mn arrays with $\uparrow\uparrow\downarrow\downarrow$ type ordering, giving rise to a spontaneous polarization along a-axis. First-principles calculations based on the Berry phase method as well as on the experimentally refined crystal structure can reproduce the observed polarization value., Comment: 8 pages, 5 figures, 2 tables

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a 6He nucleus. An optical model analysis revealed that the spin-orbit potential for 6He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with a alpha+n+n cluster folding model suggests that the interaction between a proton and the alpha core is essentially important in describing the p+6He elastic scattering. The data are also compared with fully microscopic analyses using non-local optical potentials based on nucleon-nucleon g-matrices., Comment: 20 pages, 20 figures, accepted by Physical Review C

A complete high precision set of deuteron analyzing powers for elastic deuteron-proton ($dp$) scattering at 250 MeV/nucleon (MeV/N) has been measured. The new data are presented together with data from previous measurements at 70, 100, 135 and 200 MeV/N. They are compared with the results of three-nucleon (3N) Faddeev calculations based on modern nucleon-nucleon (NN) potentials alone or combined with two models of three nucleon forces (3NFs): the Tucson-Melbourne 99 (TM99) and Urbana IX. At 250 MeV/N large discrepancies between pure NN models and data, which are not resolved by including 3NFs, were found at c.m.\ backward angles of $\theta_{\rm c.m.}\gtrsim 120^\circ$ for almost all the deuteron analyzing powers. These discrepancies are quite similar to those found for the cross section at the same energy. We found small relativistic effects that cannot resolve the discrepancies with the data indicating that other, short-ranged 3NFs are required to obtain a proper description of the data., Comment: submitted to Phys. Rev. C

Inhomogeneous electronic states resulting from entangled spin, charge, and lattice degrees of freedom are hallmarks of strongly correlated electron materials; such behavior has been observed in many classes of d-electron materials, including the high-Tc copper-oxide superconductors, manganites, and most recently the iron-pnictide superconductors. The complexity generated by competing phases in these materials constitutes a considerable theoretical challenge-one that still defies a complete description. Here, we report a new manifestation of electronic inhomogeneity in a strongly correlated f-electron system, using CeCoIn5 as an example. A thermodynamic analysis of its superconductivity, combined with nuclear quadrupole resonance measurements, shows that nonmagnetic impurities (Y, La, Yb, Th, Hg and Sn) locally suppress unconventional superconductivity, generating an inhomogeneous electronic "Swiss cheese" due to disrupted periodicity of the Kondo lattice. Our analysis may be generalized to include related systems, suggesting that electronic inhomogeneity should be considered broadly in Kondo lattice materials., Comment: 27 pages

We have performed low-temperature specific heat $C$ and thermal conductivity $\kappa$ measurements on the Ni-pnictide superconductors BaNi$_2$As$_2$ ($T_\mathrm{c}$=0.7 K and SrNi$_2$P$_2$ ($T_\mathrm{c}$=1.4 K). The temperature dependences $C(T)$ and $\kappa(T)$ of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual $\kappa$ for BaNi$_2$As$_2$ rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba$_{0.6}$La$_{0.4}$Ni$_2$As$_2$ shows a mild suppression of $T_\mathrm{c}$ and $H_\mathrm{c2}$ relative to BaNi$_2$As$_2$., Comment: 5 pages, 3 figures, to be published in J. Phys.: Conf. Ser

The proportionality between differential cross sections at vanishing linear momentum transfer and Gamow-Teller transition strength, expressed in terms of the \textit{unit cross section} ($\hat{\sigma}_{GT}$) was studied as a function of target mass number for ($t$,$^{3}$He) and ($^{3}$He,$t$) reactions at 115 $A$MeV and 140 $A$MeV, respectively. Existing ($^{3}$He,$t$) and ($t$,$^{3}$He) data on targets with mass number $12\leq A\leq 120$ were complemented with new and reevaluated ($t$,$^{3}$He) data on proton, deuteron, $^{6}$Li and $^{12}$C targets. It was found that in spite of the small difference in beam energies between the two probes, the unit cross sections have a nearly identical and simple dependence on target mass number $A$, for $A\geq 12$: $\hat{\sigma}_{GT}=109/A^{0.65}$. The factorization of the unit cross sections in terms of a kinematical factor, a distortion factor and the strength of the effective spin-isospin transfer nucleus-nucleus interaction was investigated. Simple phenomenological functions depending on mass number $A$ were extracted for the latter two. By comparison with plane and distorted-wave Born approximation calculations, it was found that the use of a short-range approximation for knock-on exchange contributions to the transition amplitude results in overestimated cross sections for reactions involving the composite ($^{3}$He,$t$) and ($t$,$^{3}$He) probes., Comment: 14 pages, 10 figures

We report results of $^{59}$Co nuclear magnetic resonance measurements on a single crystal of superconducting PuCoGa5 in its normal state. The nuclear spin-lattice relaxation rates and the Knight shifts as a function of temperature reveal an anisotropy of spin fluctuations with finite wave vector q. By comparison with the isostructural members, we conclude that antiferromagnetic XY-type anisotropy of spin fluctuations plays an important role in mediating superconductivity in these heavy fermion materials., Comment: Published in Phys. Rev. Lett

Variation of magnetocaloric (MC) effects has been systematically investigated for colossal magnetoresistive (CMR) manganites R0.6Sr0.4MnO3 (R=La-Gd). As the one-electron bandwidth is reduced, the temperature profile of MC effect, i.e., field-induced entropy change, exhibits a steeper drop below the ferromagnetic transition temperature due to its first-order nature promoted by a competing charge-orbital ordering instability. For these small-bandwidth systems adjacent to the metal-insulator phase boundary, a rectangular-shaped profile for the entropy change emerges with an anomalously wide temperature range and a considerable magnitude. Model calculations have indicated that the fluctuation enhanced in the phase-competing region has a strong impact on such MC features, which can be extensively controlled by the chemical composition., Comment: 5 pages, 4 figure

Single crystals of electron-doped SrMnO3 with a cubic perovskite structure have been systematically investigated as the most canonical (orbital-degenerate) double-exchange system, whose ground states have been still theoretically controversial. With only 1-2% electron doping by Ce substitution for Sr, a G-type antiferromagnetic metal with a tiny spin canting in a cubic lattice shows up as the ground state, where the Jahn-Teller polarons with heavy mass are likely to form. Further electron doping above 4%, however, replaces this isotropic metal with an insulator with tetragonal lattice distortion, accompanied by a quasi-one-dimensional 3z^2-r^2 orbital ordering with the C-type antiferromagnetism. The self-organization of such dilute polarons may reflect the critical role of the cooperative Jahn-Teller effect that is most effective in the originally cubic system., Comment: 5 pages, 4 figures

Vector analyzing power for the proton-6He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target working at low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The alpha-core distribution in 6He is suggested to be a possible key to understand the nuclear structure sensitivity., Comment: 5 pages, 3 figures, accepted for publication as a Rapid Communication in Physical Review C

A deuteron beam polarimeter has been constructed at the Internal Target Station at the Nuclotron of JINR. The polarimeter is based on spin-asymmetry measurements in the d-p elastic scattering at large angles and the deuteron kinetic energy of 270 MeV. It allows to measure vector and tensor components of the deuteron beam polarization simultaneously., Comment: 15 pages, 9 figures

We report $^{121,123}$Sb NQR studies on single crystals of the narrow gap semiconductor Ce3Au3Sb4. The temperature dependence of the nuclear quadrupole frequency ($\nu_Q$), as well as the magnetic susceptibility, is well explained by crystal electric field effects. The nuclear spin-lattice relaxation rate ($T_1^{-1}$) of both $^{121}$Sb and $^{123}$Sb increases rapidly with decreasing temperature. The ratio of $T_1^{-1}$ for the two Sb isotopes is constant at high temperature but it decreases at low temperatures, indicating the important role of quadrupole fluctuations of the Ce ions. We propose that quadrupole fluctuations could be the origin of the large specific heat at low temperature via phonon-quadrupole moment coupling., Comment: accepted in PRB as a regular article

$^{235}$U nuclear spin-lattice ($T_1^{-1}$) and spin-spin ($T_2^{-1}$) relaxation rates in the itinerant antiferromagnet USb$_2$ are reported as a function of temperature in zero field. The heating effect from the intense rf pulses that are necessary for the $^{235}$U NMR results in unusual complex thermal recovery of the nuclear magnetization which does not allow measuring $T_1^{-1}$ directly. By implementing an indirect method, however, we successfully extracted $T_1^{-1}$ of the $^{235}$U. We find that the temperature dependence of $T_1^{-1}$ for both $^{235}$U and $^{121}$Sb follows the power law ($\propto T^n$) with the small exponent $n=0.3$ suggesting that the same relaxation mechanism dominates the on-site and the ligand nuclei, but an anomaly at 5 K was observed, possibly due to the change in the transferred hyperfine coupling on the Sb site., Comment: 5 pages, 4 figures, accepted for publication in PRB as a regular article

Precision data are presented for the break-up reaction, $^2{\rm H}(\vec p,pp)n$, within the framework of nuclear-force studies. The experiment was carried out at KVI using a polarized-proton beam of 190 MeV impinging on a liquid-deuterium target and by exploiting the detector, BINA. Some of the vector-analyzing powers are presented and compared with state-of-the-art Faddeev calculations including three-nucleon forces effect. Significant discrepancies between the data and theoretical predictions were observed for kinematical configurations which correspond to the $^2{\rm H}(\vec p,^2$He$)n$ channel. These results are compared to the $^2{\rm H}(\vec p,d)p$ reaction to test the isospin sensitivity of the present three-nucleon force models. The current modeling of two and three-nucleon forces is not sufficient to describe consistently polarization data for both isospin states., Comment: 4 pages, 3 figures, submitted to PRL

Gamow-Teller and dipole transitions to final states in 13B were studied via the 13C(t,3He) reaction at Et = 115 AMeV. Besides the strong Gamow-Teller transition to the 13B ground state, a weaker Gamow-Teller transition to a state at 3.6 MeV was found. This state was assigned a spin-parity of 3/2- by comparison with shell-model calculations using the WBP and WBT interactions which were modified to allow for mixing between nhw and (n+2)hw configurations. This assignment agrees with a recent result from a lifetime measurement of excited states in 13B. The shell-model calculations also explained the relatively large spectroscopic strength measured for a low-lying 1/2+ state at 4.83 MeV in 13B. The cross sections for dipole transitions up to Ex(13B)= 20 MeV excited via the 13C(t,3He) reaction were also compared with the shell-model calculations. The theoretical cross sections exceeded the data by a factor of about 1.8, which might indicate that the dipole excitations are "quenched". Uncertainties in the reaction calculations complicate that interpretation., Comment: 11 pages, 6 figures

We report 209Bi NMR and NQR measurements on a single crystal of the Kondo insulator U3Bi4Ni3. The 209Bi nuclear spin-lattice relaxation rate ($T_1^{-1}$) shows activated behavior and is well-fit by a spin gap of 220 K. The 209Bi Knight shift (K) exhibits a strong temperature dependence arising from 5f electrons, in which K is negative at high temperatures and increases as the temperature is lowered. Below 50 K, K shows a broad maximum and decreases slightly upon further cooling. Our data provide insight into the evolution of the hyperfine fields in a fully gapped Kondo insulator based on 5f electron hybridization., Comment: 4 pages, 4 figures, submitted to Phys. Rev. B

Heat capacity, magnetic susceptibility, NMR, and resistivity of SrNi2P2 single crystals are presented, illustrating a purely structural transition at 325 K with no magnetism. Bulk superconductivity is found at 1.4 K. The magnitude of the transition temperature T_c, fits to the heat capacity data, the small upper critical field $H_{c2}$ = 390 Oe, and Ginzburg-Landau parameter $\kappa$ = 2.1 suggests a conventional fully gapped superconductor. With applied pressure a second structural phase transition occurs which results in an 8% reduction in the c/a ratio of lattice parameters. We find that superconductivity persists into this high pressure phase, although the transition temperature is monotonically suppressed with increasing pressure. Comparison of these Ni-P data as well as layered Fe-As and Ni-As superconductor indicates that reduced dimensionality can be a mechanism for increasing the transition temperature., Comment: 6 pages, 7 figures, New Title, minor changes, published in PRB as an editor's suggestion

We searched for the neutrino-less double beta decay(0nbb) of 48Ca by using CaF2(Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q-value region for the data of 3394 kg days. It gives a lower limit (90% confidence level) of T > 2.7 x 10^22 year for the half life of 0nbb of 48Ca. Combined with our previous data for 1553 kg days, we obtained more stringent limit of T > 5.8 x 10^22 year., Comment: submitted to PRC

Versatile features of impurity doping effects on perovskite manganites, $R_{0.6}$Sr$_{0.4}$MnO$_{3}$, have been investigated with varying the doing species as well as the $R$-dependent one-electron bandwidth. In ferromagnetic-metallic manganites ($R$=La, Nd, and Sm), a few percent of Fe substitution dramatically decreases the ferromagnetic transition temperature, leading to a spin glass insulating state with short-range charge-orbital correlation. For each $R$ species, the phase diagram as a function of Fe concentration is closely similar to that for $R_{0.6}$Sr$_{0.4}$MnO$_{3}$ obtained by decreasing the ionic radius of $R$ site, indicating that Fe doping in the phase-competing region weakens the ferromagnetic double-exchange interaction, relatively to the charge-orbital ordering instability. We have also found a contrastive impact of Cr (or Ru) doping on a spin-glass insulating manganite ($R$=Gd). There, the impurity-induced ferromagnetic magnetization is observed at low temperatures as a consequence of the collapse of the inherent short-range charge-orbital ordering, while Fe doping plays only a minor role. The observed opposite nature of impurity doping may be attributed to the difference in magnitude of the antiferromagnetic interaction between the doped ions., Comment: 7 pages, 6 figures