[show abstract][hide abstract] ABSTRACT: A systematic search for superfragments (charmed nuclei) has been performed in 22 200 neutrino–emulsion interactions obtained with the CHORUS experiment making use of automatic off-line image analysis. The absence of candidates provides an upper limit for the superfragment production rate of 1.9×10−4 (90% C.L.) relative to neutrino charged-current interactions at an average neutrino energy of 27 GeV. In the same analysis 28 hyperfragment decays were found. For the first time, a production rate of hyperfragments in neutrino–emulsion interactions was obtained. The value of the hyperfragment production rate relative to the neutrino charged-current cross-section was found to be (2.0±0.4(stat)±0.3(syst))×10−3.
[show abstract][hide abstract] ABSTRACT: During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy. In total about 100 000 charged-current neutrino interactions were located in the nuclear emulsion target and fully reconstructed. A high-statistics sample of neutrino interactions with a D0 in the final state was collected. Using the decay mode D*+→D0π+ a production cross-section measurement of the D*+ in neutrino–nucleon charged-current interactions was performed. The low Q-value of the decay was used to isolate a sample of candidate events containing a positive hadron with a small pT with respect to the D0 direction. A signal of events was obtained. The D*+ production cross-section relative to the D0 production cross-section, σ(D*+)/σ(D0), was estimated to be 0.38±0.09(stat)±0.05(syst). From this result, the fraction of D0's produced via the decay of a D* was deduced to be 0.63±0.17. The D*+ production cross-section relative to the νμ charged-current interaction, σ(D*+)/σ(CC), was estimated to be [1.02±0.25(stat)±0.15(syst)]%.
[show abstract][hide abstract] ABSTRACT: We report results of nuclear magnetic resonance (NMR) experiments on
39K and 87Rb nuclei in the new superconductors
AOs2O6 (A=K or Rb). These compounds crystallize in
the β-pyrochlore structure. In the superconducting phase, we found
a small peak in 1/(T1T) for 87Rb slightly below
the superconducting transition temperature (T) but no peak
for 39K. In the normal state of KOs2O6,
we observed a clear pseudogap behavior similar to what has been observed
in high T cuprates.
Physica B Condensed Matter 04/2005; · 1.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report results of nuclear magnetic resonance (NMR) experiments on 39K and 87Rb nuclei in the new superconductors AOs2O6 (A=K or Rb). These compounds crystallize in the β-pyrochlore structure. In the superconducting phase, we found a small peak in 1/(T1T) for 87Rb slightly below the superconducting transition temperature (Tc) but no peak for 39K. In the normal state of KOs2O6, we observed a clear pseudogap behavior similar to what has been observed in high Tc cuprates.
Physica B Condensed Matter 01/2005; 359:488-490. · 1.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy. In total about 100 000 charged-current neutrino interactions were located in the nuclear emulsion target and fully reconstructed. From this sample of events which was based on the data acquired by new automatic scanning systems, 1048 charged-current interactions with a D0 in the final state were selected by a pattern recognition program and confirmed as neutral-particle decays through visual inspection. The ratio of decay branching fractions of the D0 into four charged particles to two charged particles was measured to be B(D0→V4)/B(D0→V2)=0.207±0.016±0.004. The inclusive measurement of the observed production rate of the D0 with a decay into four charged prongs in combination with external measurements of this topological branching ratio was used to determine the total D0 production rate by neutrinos without additional assumption on the branching fractions. The value of this rate relative to the charged-current cross-section was found to be σ(D0)/σ(CC)=0.0269±0.0018±0.0013. In addition, the same normalization method was used to deduce the inclusive topological decay rate into final states with neutral particles only. A value of 0.218±0.049±0.036 was found for this branching fraction. From an observed number of three charged six-prong events the branching ratio into six charged particles was determined to be . A measurement of the energy dependence of the D0 production by neutrinos relative to the total charged-current cross-section is also reported. This measurement was used to deduce for mc, the effective charm-quark mass, a value of .
[show abstract][hide abstract] ABSTRACT: This Letter reports on a study of trimuon events induced by neutrino interactions in the CHORUS calorimeter exposed to the CERN SPS wide-band νμ beam. Among the multimuon events produced in the calorimeter, 42 μ−μ−μ+ events were selected and their kinematical properties investigated. In the past, several groups collected a sample of about one hundred events of this type but their source was largely unknown. Taking advantage of experimental data presently available on the production and muonic branching ratios of light neutral mesons and resonances, we make absolute predictions for the expected rates in our experiment. Detailed Monte Carlo simulations described in this article show that more than half of the trimuon events can be attributed to this source. Muons from π− and K− decays in charm dimuon events are responsible for an additional ≈25% contribution to the total μ−μ−μ+ rate. The remaining 25% of events are likely to come from the internal bremsstrahlung of virtual photons into a muon pair. Associated-charm production with subsequent decays of both charmed particles into muons is a negligible source of trimuon events.
[show abstract][hide abstract] ABSTRACT: The two-dimensional spin-gap system SrCu2(BO3)2 shows unique physical properties due to the strong quantum fluctuations that follow from its low-dimensionality and its very special topology. The magnetic properties of this material, e.g. dimer singlet ground state, an almost localized triplet and magnetization plateaux, are well described by a spin-1/2 antiferromagnetic Heisenberg model on the orthogonal dimer lattice. Recently, an unusual angular dependence of the shifts at the B sites with the external magnetic field rotated in the (110) plane, which indicates the presence of a field-induced staggered moment, has been observed by nuclear magnetic resonance. Such a behaviour cannot be explained by the Heisenberg model alone. We include an intra-dimer Dzyaloshinsky–Moriya interaction as well as an anisotropic gyromagnetic tensor in the orthogonal dimer model, and we show that the observed field-induced staggered moment can be very well described with physically reasonable values of the parameters.
[show abstract][hide abstract] ABSTRACT: Low-Z impurity (7Be) on the JT-60U divertor tiles was analyzed to study the impurity behavior in the divertor region. The amount of the 7Be increased approximately one hundred times after B4C-tile installation in the outer divertor. The 7Be was probably produced by 10B(p,α)7Be nuclear reaction on the divertor tiles in the hydrogen experiment with ion cyclotron range of frequency heating. The 7Be was distributed asymmetrically in the poloidal and the toroidal direction. The highest 7Be concentration was found at the inner divertor whose boron content (B/(B+C)∼20%) was lower than the B4C tiles (B/(B+C)∼80%) of the outer divertor. This result may imply impurity transport from the outer divertor to the inner divertor.
Journal of Nuclear Materials - J NUCL MATER. 01/2004; 329:845-848.
[show abstract][hide abstract] ABSTRACT: During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS. In total about 100 000 charged-current neutrino interactions were located in the nuclear emulsion target and fully reconstructed. From this sample of events which was based on the data acquired by new automatic scanning systems, 1048 D0 events were selected by a pattern recognition program. They were confirmed as neutral-particle decays through visual inspection. Fragmentation properties of deep-inelastic charm production were measured using these events. Distributions of the D0 momentum, Feynman x (xF), z and tanθout, the transverse angle out of the leptonic plane defined by the muon and the neutrino, are presented. The mean value of z was measured to be 〈z〉=0.63±0.03(stat)±0.01(syst). From fits to the z distribution, values for the Peterson parameter εP=0.108±0.017(stat)±0.013(syst) and the Collins–Spiller parameter are found. For the average value of xF we find 〈xF〉=0.38±0.04(stat)±0.03(syst) and for the forward–backward asymmetry A=0.79±0.14(stat)±0.05(syst). The distribution of tanθout was measured with an average value 〈tanθout〉=0.030±0.002.
[show abstract][hide abstract] ABSTRACT: 133Cs-NMR experiments on the S=12 quasi-two-dimensional antiferromagnet Cs2CuBr4 have been performed up to magnetic fields of 15.9T, which covers the field range for the 13 magnetization plateau. Outside the plateau region, the NMR spectrum at T=0.5K shows a double-horn type broad line shape characteristic of an incommensurate spin structure. On the other hand, discrete two peaks were observed in the plateau phase, indicating a commensurate up–up–down spin structure.
Journal of Magnetism and Magnetic Materials - J MAGN MAGN MATER. 01/2004; 272:861-862.
[show abstract][hide abstract] ABSTRACT: The experimental apparatus used for the first direct observation of the tau neutrino (the DONUT experiment) is described. Its main features consisted of a target system composed of nuclear emulsion targets and scintillation fiber trackers, a magnetic charged-particle spectrometer and detectors for lepton identification. This paper will concentrate on the description of the electronic detectors and their performance in selecting neutrino interactions, making the vertex predictions necessary for locating events in the emulsion target and lepton identification.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 01/2004;
[show abstract][hide abstract] ABSTRACT: Detailed tritium profiles on the JAERI Tokamak-60U (JT-60U) W-shaped divertor and the first wall tiles were examined by a tritium imaging plate technique (TIPT) and full combustion method. The highest tritium level (60 kBq/cm2) was observed at the dome top tiles. The tritium level of the divertor target was lower (2 kBq/cm2). The result of the triton deposition simulation using orbit following Monte-Carlo code was consistent with the tritium distribution obtained by TIPT and full combustion method. These results indicate that the tritium distribution of the JT-60U W-shaped divertor reflects mainly the distribution of the energetic triton impinging on the wall. According to the simulation, the tritium atoms produced by D–D nuclear reaction in JT-60U are not loosing completely their initial energy of 1 MeV and around 1/3 of them are implanted into the wall.
Journal of Nuclear Materials - J NUCL MATER. 01/2003; 313:514-518.
[show abstract][hide abstract] ABSTRACT: During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the CERN-SPS Wide Band Neutrino Beam. The improvements of the past few years in the automatic emulsion scanning systems allowed a sample of events located in emulsion to be used for studies of charm production. Based on a sample of charged-current interactions analysed so far, we find a value of Bμ=0.093±0.009(stat.)±0.009(syst.) for the semi-leptonic branching fraction of charm hadrons. The result for events with visible energy larger than 30 GeV, Bμ=0.102±0.016(stat.)±0.010(syst.), can be combined with the existing measurements of the dimuon rate to yield a value of 0.219±0.022 for the magnitude of the Cabibbo–Kobayashi–Maskawa matrix element |Vcd|.
[show abstract][hide abstract] ABSTRACT: Improvement of an enhanced confinement state in a high poloidal beta (βp) regime without sawtooth activity has been achieved in JT-60U. A confinement mode has been demonstrated where both the edge and the core confinement are improved. The attainable βp was also extended to higher values in this improved mode, because of its broader pressure profile. As a result of the improvement in confinement and in attainable βp, the highest value of the fusion triple product has been extended by a factor of 2.5 over that achieved in the 1992 experiments; it has reached (1.1 ± 0.3) × 1021 m-3.s.keV with a central ion temperature of about 37 keV. The D-D neutron emission rate has also been doubled in these experiments and has reached (5.6 ± 0.6) × 1016 s-1
[show abstract][hide abstract] ABSTRACT: We report results of nuclear quadrupole resonance (NQR) experiments on the Re sites in the pyrochlore superconductor Cd2Re2O7. A discontinuous change of the NQR spectrum was observed near T s2 = 120 K, confirming the first-order structural transition in addition to the already known second-order transition at T s1 = 200 K. The spin–lattice relaxation rate at the Re sites shows a steep increase above T s2, in contrast to the reported results for the Cd sites, suggesting changes of orbital fluctuations.
[show abstract][hide abstract] ABSTRACT: A measurement of Λc+ production in neutrino nucleon charged-current interactions is presented. In a subsample of about 50 000 interactions located in the emulsion target of the CHORUS detector, exposed to the wide band neutrino beam of the CERN SPS, candidates for decays of short-lived particles were identified using new automatic scanning systems and later confirmed through visual inspection. Criteria based on the flight length allowed a statistical separation among the different charm species thus enabling a sample particularly rich in Λc+ to be defined. At an average neutrino energy of 27 GeV, the product σ(Λc+)/σ(CC)×BR(Λc+→3p) was measured to be (0.37±0.10(stat)±0.02(syst))×10−2, while the values of (1.54±0.35(stat)±0.18(syst))×10−2 and of 0.24±0.07(stat)±0.04(syst) were obtained for σ(Λc+)/σ(CC) and BR(Λc+→3p), respectively.
[show abstract][hide abstract] ABSTRACT: The tritium imaging plate technique was applied to determine surface tritium distributions on graphite tiles used as the first wall and W-shaped divertor in JT-60U, in which tritium produced by the D–D nuclear reaction in the plasma was implanted and/or deposited depending on the incident energy. Measured samples were isotropic graphite (IG-430U) and CFC graphite (CX-2002U), used as divertor tiles and/or baffle plates just outside the divertor. Tritium areal distributions on graphite divertor tiles, dome units and baffle plates of JT-60U were successfully measured for the first time. Tritium distributions observed in JT-60U tiles can be explained by homogeneous implantation of high energy tritium which is influenced by redeposited layers and redistributed by the temperature increase due to the plasma heat load. The tritium retention in graphite heated above 800 K was significantly small.
Journal of Nuclear Materials - J NUCL MATER. 01/2002; 307:1441-1445.