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S. Kawabata

Publications and source records attributed to S. Kawabata.

28 records · Page 2Linked to original sources
arXiv2005

Macroscopic quantum tunneling in a d-wave high-Tc superconductor

There is a wide recognition that Josephson-junction-like structures intrinsic to the layered cuprate high temperature superconductors offer an attractive stage for exploiting possible applications to new quantum technologies. On the other hand the low energy quasiparticle excitations characteristically present in these d-wave superconductors may easily destruct the coherence required. Here we demonstrate for the first time the feasibility of macroscopic quantum tunneling in the intrinsic Josephson junctions of a high temperature superconductor, and find it to be characterized by a high classic-to-quantum crossover temperature and a relatively weak quasiparticle dissipation.

cond-mat.supr-con↗
arXiv2005

Solenoidal Coils Made from Monofilamentary and Multifilamentary MgB2 strands

Three solenoids have been wound and with MgB2 strand and tested for transport properties. One of the coils was wound with Cu-sheathed monofilamentary strand and the other two with a seven filament strand with Nb-reaction barriers, Cu stabilization, and an outer monel sheath. The wires were first S-glass insulated, then wound onto an OFHC Cu former. The coils were then heat treated at 675C/30 min (monofilamentary strand) and 700C/20 min (multifilamentary strand). Smaller (1 m) segments of representative strand were also wound into barrel-form samples and HT along with the coils. After HT the coils were epoxy impregnated. Transport Jc measurements were performed at various taps along the coil lengths. Measurements were made initially in liquid helium, and then as a function of temperature up to 30 K. Homogeneity of response along the coils was investigated and a comparison to the short sample results was made. Each coil contained more than 100 m of 0.84-1.01 mm OD strand. One of the 7 strand coils reached 222 A at 4.2 K, self field, with a Jc of 300 kA/cm2 in the SC and a winding pack Je of 23 kA/cm2. At 20 K these values were 175 kA/cm2 and 13.4 kA/cm2. Magnet bore fields of 1.5 T and 0.87 T were achieved at 4.2 K and 20 K, respectively. The other multifilamentary coil gave similar results.

cond-mat.supr-con↗
arXiv2003

QCD event generators with next-to-leading order matrix-elements and parton showers

A new method to construct event-generators based on next-to-leading order QCD matrix-elements and leading-logarithmic parton showers is proposed. Matrix elements of loop diagram as well as those of a tree level can be generated using an automatic system. A soft/collinear singularity is treated using a leading-log subtraction method. Higher order re-summation of the soft/collinear correction by the parton shower method is combined with the NLO matrix-element without any double-counting in this method. An example of the event generator for Drell-Yan process is given for demonstrating a validity of this method.

hep-ph↗
arXiv2000

Automatic Computation of Cross Sections in HEP

For the study of reactions in High Energy Physics (HEP) automatic computation systems have been developed and are widely used nowadays. GRACE is one of such systems and it has achieved much success in analyzing experimental data. Since we deal with the cross section whose value can be given by calculating hundreds of Feynman diagrams, we manage the large scale calculation, so that effective symbolic manipulation, the treat of singularity in the numerical integration are required. The talk will describe the software design of GRACE system and computational techniques in the GRACE.

hep-ph↗
arXiv1997

susy23 v2.0: an Event Generator for Supersymmetric Processes at $e^+e^-$ Colliders

\susy23 is a Monte-Carlo package for generating supersymmetric (SUSY) processes at $e^+e^-$ colliders. Twenty-three types of SUSY processes with 2 or 3 final state particles at tree level are included in version 2.0. {\susy23} addresses event simulation requirements at $e^+e^-$ colliders such as LEP. Matrix elements are generated by GRACE with the helicity amplitude method for processes involving massive fermions. The phase space integration of the matrix element gives the total and differential cross sections, then unweighted events are generated. Sparticle widths and decay branching ratios are calculated. Each final state particle may then decay according to these probabilities. Spin correlations are taken into account in the decays of sparticles. Corrections of initial state radiation (ISR) are implemented in two ways, one is based on the electron structure function formalism and the second uses the parton shower algorithm called QEDPS. Parton shower and hadronization of the final quarks are performed through an interface to JETSET.

hep-ph↗
arXiv1997

$e^+e^- \to b \bar{b} u \bar{d} μ^- \barν_μ$ with a $t\bar{t}$ production

The cross section of $e^+e^- \to b \bar{b} u \bar{d} μ^- \barν_μ$ process with a complete set of tree diagrams, 232 diagrams in the unitary gauge, was calculated at the energy range of $\sqrt{s}$ = 340 - 500 GeV by using GRACE system. A main contribution to the cross section comes from $t\bar{t}$ production, where $t$ and $\bar{t}$ decay into $bu\bar{d}$ and $\bar{b} μ^- \barν_μ$, respectively. It was found that the interference between the diagrams with $t\bar{t}$ production and those with single-$t$ through $ WW $ pair production amounts to 10% at the $t \bar{t}$ threshold energy region. In the energy region above twice of the top quark mass, more than 95% of the cross section comes from the $t\bar{t}$ diagrams.

hep-ph↗
arXiv1997

Event Generators for WW Physics

The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.

hep-ph↗
arXiv1996

grc4f v1.0: a Four-fermion Event Generator for e+e- Collisions

grc4f is a Monte-Carlo package for generating e+e- to 4-fermion processes in the standard model. All of the 76 LEP-2 allowed fermionic final state processes evaluated at tree level are included in version 1.0. grc4f addresses event simulation requirements at e+e- colliders such as LEP and up-coming linear colliders. Most of the attractive aspects of grc4f come from its link to the GRACE system: a Feynman diagram automatic computation system. The GRACE system has been used to produce the computational code for all final states, giving a higher level of confidence in the calculation correctness. Based on the helicity amplitude calculation technique, all fermion masses can be kept finite and helicity information can be propagated down to the final state particles. The phase space integration of the matrix element gives the total and differential cross sections, then unweighted events are Generated. Initial state radiation (ISR) corrections are implemented in two ways, one is based on the electron structure function formalism and the second uses the parton shower algorithm called QEDPS. The latter can also be applied for final state radiation (FSR) though the interference with the ISR is not yet taken into account. Parton shower and hadronization of the final quarks are performed through an interface to JETSET. Coulomb correction between two intermediate W's, anomalous coupling as well as gluon contributions in the hadronic processes are also included.

hep-ph↗
arXiv1994

Non-resonant diagrams in radiative four-fermion processes

The complete tree level cross section for $e^+e^- \to e^- \barν_e u \bar{d} γ$ is computed and discussed in comparison with the cross sections for $e^+e^- \to e^- \barν_e u \bar{d} $ and $e^+e^- \to \bar{u} d u \bar{d}$. Event generators based on the GRACE package for the non-radiative and radiative case are presented. Special interest is brought to the effect of the non-resonant diagrams overlooked so far in other studies. Their contribution to the total cross section is presented for the LEP II energy range and for future linear colliders ($\sqrt s$ =500 GeV). Effects, at the W pair threshold, of order 3\% ($e^- \barν_e u \bar{d}$) and 27\% ($\bar{u} d u \bar{d}$) are reported. Similar behaviour for the radiative case is shown. At $\sqrt s$ = 500 GeV, the relative contribution of the non-resonant diagrams for the radiative channel reaches 42.5\%.

hep-ph↗