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論文

The Belle II SVD data readout system

Thalmeier, R.*; 谷田 聖; 他97名*

Nuclear Instruments and Methods in Physics Research A, 845, p.633 - 638, 2017/02

 被引用回数:5 パーセンタイル:31.96(Instruments & Instrumentation)

The Belle II Experiment at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, will explore the asymmetry between matter and antimatter and search for new physics beyond the standard model. 172 double-sided silicon strip detectors are arranged cylindrically in four layers around the collision point to be part of a system which measures the tracks of the collision products of electrons and positrons. A total of 1748 radiation-hard APV25 chips read out 128 silicon strips each and send the analog signals by time-division multiplexing out of the radiation zone to 48 Flash Analog Digital Converter Modules (FADC). Each of them applies processing to the data; for example, it uses a digital finite impulse response filter to compensate line signal distortions, and it extracts the peak timing and amplitude from a set of several data points for each hit, using a neural network. We present an overview of the SVD data readout system, along with front-end electronics, cabling, power supplies and data processing.

論文

EMC studies for the vertex detector of the Belle II experiment

Thalmeier, R.*; 谷田 聖; 他102名*

Journal of Instrumentation (Internet), 11(1), p.C01044_1 - C01044_10, 2016/01

 被引用回数:2 パーセンタイル:82.27(Instruments & Instrumentation)

The upgrade of the Belle II experiment plans to use a vertex detector based on two different technologies, DEPFET pixel (PXD) technology and double side silicon microstrip (SVD) technology. The vertex electronics are characterized by the topology of SVD bias that forces to design a sophisticated grounding because of the floating power scheme. The complex topology of the PXD power cable bundle may introduce some noise inside the vertex area. This paper presents a general overview of the EMC issues present in the vertex system, based on EMC tests on an SVD prototype and a study of noise propagation in the PXD cable bundle based on Multi-conductor transmission line theory.

論文

Correlation effects on antiferromagnetism in Fe pnictides

久保 勝規; Thalmeier, P.*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA121_1 - SA121_3, 2011/07

 被引用回数:7 パーセンタイル:48.39(Physics, Multidisciplinary)

We investigate the magnetism and orbital state of the ground state of a two-orbital model proposed for Fe pnictides which includes $$d_{zx}$$ and $$d_{yz}$$ orbitals of Fe ions. We apply a Hartree-Fock approximation and a variational Monte Carlo method to this model. First, we apply the Hartree-Fock approximation. The antiferromagnetic order with ordering vector $$(pi,0)$$is stabilized by the nesting between hole and electron pockets. This antiferromagnetic state accompanies ferro-orbital order, that is, the occupancies of $$d_{zx}$$ and $$d_{yz}$$ orbitals become different. Under such ferro-orbital order, the lattice should be distorted from a tetragonal to orthorhombic structure through an electron-lattice interaction. We also apply the variational Monte Carlo method to the model. We find that correlation effects reduce the ordered moment. Even for a large value of the Coulomb interaction comparable to the band width, the ordered moment can be small.

口頭

鉄系超伝導体の強軌道秩序と磁性

久保 勝規; Thalmeier, P.*

no journal, , 

鉄系超伝導体に対して提唱されている2軌道モデルの磁性をハートリー・フォック近似及び変分モンテカルロ法を用いて調べた。本研究では、通常の磁気秩序に加えて、軌道秩序の可能性も考慮に入れた。まずハートリー・フォック近似を用いて、波数$$(pi,0)$$の磁気秩序が、電子面とホール面のネスティングによって引き起こされることがわかった。この磁気秩序状態では、$$x$$方向と$$y$$方向の等価性が破れるために、必然的に$$d_{zx}$$$$d_{yz}$$軌道の電子数は等しくなくなる。つまり、強的軌道秩序が引き起こされる。そのため、この秩序状態では、電子-格子相互作用によって正方晶から直方晶に格子が歪むはずである。さらに、相関効果を調べるために、変分モンテカルロ法を適用した。その結果、相関効果により秩序状態の磁気モーメントは縮み、クーロン相互作用がバンド幅程度の大きさでも、小さくなり得ることがわかった。

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