K. Maruyama

Bio: K. Maruyama is an academic researcher from University of Tokyo. The author has contributed to research in topics: Annihilation & Photon energy. The author has an hindex of 14, co-authored 45 publications receiving 585 citations. Previous affiliations of K. Maruyama include Tokyo Institute of Technology.

Search for Top Quark in e+e- Collisions at sqrt[s]=52 GeV

Abstract: We searched for possible signatures of top-quark production in 508 e/sup +/e/sup -/ hadronic annihilation events collected at ..sqrt..s = 52 GeV by the TOPAZ detector at the KEK e/sup +/e/sup -/ collider TRISTAN. The observed total hadronic cross section and shape of hadronic events are consistent with the standard-model predictions without top quarks. A lower limit (95% confidence level) on the mass of the lightest top meson is set at 25.8 GeV.

Evidence for two pseudoscalar resonances of eta pi + pi - system in the D(1285) and E/ iota regions.

Abstract: High-statistics data on the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}n$ at 8.06 GeV/c were obtained. An isobarmodel partial-wave analysis was performed for the $\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ system. The $\ensuremath{\eta}(1275)$ meson was confirmed as a narrow $I{J}^{\mathrm{PC}}={00}^{\ensuremath{-}+}$ resonance. It decays through both $\ensuremath{\delta}\ensuremath{\pi}$ and $\ensuremath{\epsilon}\ensuremath{\eta}$. A narrow state with $I{J}^{\mathrm{PC}}={00}^{\ensuremath{-}+}$ was found in an $\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ decay channel at 1.42 GeV. It has a prominent peak in a $\ensuremath{\delta}\ensuremath{\pi}$ decay mode. No significant $E(1420)$ signal with $I{J}^{\mathrm{PC}}={01}^{++}$ was found near the mass region of 1.42 GeV.

Intestinal blood-flow velocity in uncomplicated preterm infants during the early neonatal period.

Abstract: Background. Intestinal blood-flow changes after birth. Objective. To elucidate the factors influencing intestinal blood-flow velocity in preterm infants during the early neonatal period. Materials and methods. We measured blood-flow velocity in the superior mesenteric artery by pulsed Doppler US in 44 uncomplicated infants with a gestational age of less than 34 weeks and from 1 to 6 days of age. Results. Time-averaged mean blood-flow velocity significantly increased with age from 1 to 6 days old. There was a significant correlation of time-averaged mean blood-flow velocity with birth weight at 1, 2, 4, 5 and 6 days of age and with the amount of enteral feeding from 4 to 6 days of age. Multivariate analysis showed that partial correlation of time-averaged mean blood-flow velocity with birth weight at 2 days of age and that with the amount of enteral feeding at 5 days of age were significant. End-diastolic blood-flow velocity was significantly lower at 1 day of age in infants with patent ductus arteriosus than those without it. Conclusions. Age, birth weight, the amount of enteral feeding and patent ductus arteriosus are included in the determinants of intestinal blood-flow velocity in preterm infants.

Trigger system for the TOPAZ detector at TRISTAN, KEK

Abstract: A trigger system for the TOPAZ detector at the TRISTAN e + e − collider has been developed The system consists of an energy trigger and a track trigger The track trigger uses track information from the inner drift chamber, the time-of-flight counters and the time projection chamber A three-dimensional track reconstruction is performed with high-speed logic arrays The design and the performance are described

Chiral symmetry restoration and dileptons in relativistic heavy ion collisions

Abstract: The current theoretical status in the analysis and interpretation of low-mass dilepton measurements in (ultra-) relativistic heavy-ion experiments is reviewed. Special emphasis is put on potential signals of (partial) restoration of dynamically broken chiral symmetry in a hot and dense hadronic medium. It follows from chiral symmetry alone that parity partners of hadronic correlation functions must become identical when the symmetry is restored. The assessment of medium effects in the vector channel, which governs the dilepton production, thus necessitates a simultaneous treatment of the vector and axialvector degrees of freedom. While significant progress in this respect has been made some open questions remain in establishing a rigorous link in the mass region below 1 GeV. From the present calculations a suggestive 'quark-hadron duality' emerges near the phase boundary. It implies substantial medium effects in the dilepton signal from the hadronic phase which smoothly matches a perturbative description within the plasma phase.