Y. Ikedo

Probing Electron Transfer in DNA – New Life Science with Muons

Using the method of labelled electrons with muons which was first applied to conducting polymers and recently extended to representative electron-transfer proteins, electron transfer phenomena in DNA were successfully studied, for the first time microscopically. The characteristic dependence of muon spin relaxation on inverse magnetic field between 80 and 4000 G strongly suggests an existence of topological one-dimensional (1D) electron transfer along the DNA strands in both A- and B-forms. The low-field behavior, on the other hand, showed remarkable dependence on the molecular conformations.

Measurement of Muonium Hyperfine Splitting at J-PARC

J-PARC K. S. Tanaka1,3, M. Aoki4, H. Iinuma2, Y. Ikedo2, K. Ishida3, M. Iwasaki3, K. Ueno2, Y. Ueno1, T. Okubo2, T. Ogitsu2, R. Kadono2, O. Kamigaito3, N. Kawamura2, D. Kawall8, S. Kanda2,6, K. Kubo7, A. Koda2, K. M. Kojima2, N. Saito2, N. Sakamoto3, K. Sasaki2, K. Shimomura2, M. Sugano2, M. Tajima1, D. Tomono9, A. Toyoda2, H. A. Torii1, E. Torikai5, K. Nagamine2, K. Nishiyama2, P. Strasser2, Y. Higashi1, T. Higuchi1, Y. Fukao2, Y. Fujiwara6, Y. Matsuda1, T. Mibe2, Y. Miyake2, T. Mizutani1, M. Yoshida2, and A. Yamamoto2

The gradient distribution of Ni ions in cation-disordered Li[Ni1/2Mn3/2]O4 clarified by muon-spin rotation and relaxation (μSR)

Cation-ordered Li[Ni1/2Mn3/2]O4 with a P4332 space group (CO-LNMO) and “cation-disordered” (CDO) LNMO are thought to be the state-of-the-art materials for lithium-ion batteries. However, in contrast to CO-LNMO, the crystal structure and electrochemical reaction scheme of CDO-LNMO are not fully understood. We have measured the muon-spin rotation and relaxation (μSR) spectra for samples of both CO-LNMO and CDO-LNMO, in particular at their magnetic transition temperatures (TC) below 130 K. The weak transverse field (wTF) μSR measurements reveal that the range of TC for the CDO-LNMO sample is very large (ΔTC ∼ 55 K) compared with that for the CO-LNMO sample (ΔTC < 5 K). This suggests an inhomogeneous cation distribution in the CDO-LNMO sample, because the sample consists of multiple phases with different TC. Based on the wTF-μSR result for stoichiometric LiMn2O4, we have proposed that CDO-LNMO is a mixture of Li[Ni1/2−ωMn3/2+ω]O4 and LiMn2O4.

Conceptual Design of a Superconducting Solenoid System for the Super Omega Muon Beam Line at J-PARC

A 3-GeV (333 μA, 1.0 MW) proton beam from the J-PARC Rapid Cycle Synchrotron passes through a graphite target producing muons in the Materials and Life Science Facility. Muons of various momenta of up to 50 MeV/c and of both electric charges are captured and transported to an experimental area by using an axial magnetic field in the bore of solenoid magnets. This beam line, named Super Omega, is composed of a normal conducting MIC (Mineral Insulation Cable) magnet for capture, a curved superconducting solenoid system for transportation, and an axial focusing magnet system. Once in the experimental area, the muon beam is focused onto an experimental target for various purposes. The superconducting solenoid system is composed of one 6-m long straight section and two 45-degree segmented curved sections at both ends of the straight section. A magnetic field of about 2 T is applied in the transportation channel of 300 mm in diameter. The conceptual design of this solenoid system is reported.

The Next Generation Muon Source at J‐PARC/MLF

The Materials and Life Science Facility (MLF) is currently under construction at J‐PARC in Tokai, Japan. The muon section of the facility will house the muon production target and four secondary beam lines used to transport the muons into two experimental halls. Currently, one of the four beam lines (the Decay beam line) has been completed and is operational. The beam line currently under construction is the large acceptance beam line (the so called Super‐Omega beam line) which, when completed, will produce the highest intensity pulsed muon beam in the world. The expected rate of surface muons for this beam line is 4×108 μ+/s, and a cloud muon rate of 107 μ−/s. The beam line consists of the normal‐conducting capture solenoids, the superconducting curved transport solenoids, and an axial focusing magnet. The capture solenoids have been fabricated and installed on the beam line, while the transport solenoids are under design, with initial prototype coils under fabrication.

Precise Measurement of Muonium HFS at J-PARC MUSE

Hiroyuki A. Torii1 on behalf of MuSEUM Collaboration∗. H. A. Torii1, M. Aoki2, Y. Fukao3, Y. Higashi1, T. Higuchi1, H. Iinuma3, Y. Ikedo3, K. Ishida4, M. Iwasaki4, R. Kadono3, O. Kamigaito4, S. Kanda5, D. Kawall6, N. Kawamura3, A. Koda3, K. M. Kojima3, K. Kubo7, Y. Matsuda1, T. Mibe3, Y. Miyake3, T. Mizutani1, K. Nagamine4, K. Nishiyama3, T. Ogitsu3, R. Okubo3, N. Saito3, K. Sasaki3, K. Shimomura3, P. Strasser3, M. Sugano3, M. Tajima1, K. S. Tanaka1,4 D. Tomono4†, E. Torikai8, A. Toyoda3, K. Ueno3, Y. Ueno1, A. Yamamoto3, and M. Yoshida3. 1Graduate School of Arts and Sciences, University of Tokyo; 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan 2Osaka University; Toyonaka, Osaka 560-0043, Japan 3KEK; 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 4RIKEN; 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 5Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 6University of Massachusetts Amherst; MA 01003-9337, USA 7International Christian University (ICU); Mitaka, Tokyo 181-8585, Japan 8University of Yamanashi; Kofu, Yamanashi 400-8511, Japan †Current affiliation: Kyoto University; Kyoto 606-8501, Japan ∗The collaboration name MuSEUM stands for “Muonium Spectroscopy Experiment Using Microwave.” E-mail: torii@radphys4.c.u-tokyo.ac.jp

Precision Measurement of Muonium Hyperfine Splitting at J-PARC and Integrated Detector System for High-Intensity Pulsed Muon Beam Experiment

Muonium is the bound state of a positive muon and an electron. In the standard model of particle physics, muonium is considered as the two-body system of structureless leptons. At J-PARC, we plan to measure muonium’s hyperfine splitting precisely. Our experiment has three major objectives: test of QED with the highest accuracy, precision measurement of the ratio of muon’s magnetic moment to proton’s magnetic moment, and search for CPT violation via the oscillation with sidereal variations. The experimental methodology is microwave spectroscopy of muonium. Figure 1 shows the conceptual overview of the experiment. Spectroscopy of the energy states can be performed by measurement of positron decay asymmetry. The uncertainty of the most recent experimental result[1] was mostly statistical (more than 90% of total uncertainty). Hence, improved statistics is essential for higher precision of the measurement. Our goal is to improve accuracy by an order of magnitude compared to the most recent experiment. For the improvement of precision, we use the J-PARC’s highestintensity pulsed muon beam and highly segmented positron detector with SiPM (Silicon PhotoMultiplier). After the improvement of statistical precision, reduction of systematic uncertainty becomes more important to reduce systematic uncertainty. Thus, we reduce the systematic uncertainty by using a longer cavity, a high-precision superconducting magnet, and an online/offline beam profile monitor. The detector system consists of several layers of hodoscopes and fast readout circuits with custom ASIC and FPGA-based multi hit TDC. Important requirements of the positron detector are high event rate capability and high detection efficiency. The designed muon beam intensity at J-PARC MUSE H-Line is 1 × 108 μ/s. To establish the optimal design of the positron detector, we developed GEANT4-based Monte-Carlo simulation tools. Figure 2 shows a simulated muon stopping distribution in the target gas chamber. Under realistic conditions, the highest instantaneous event rate is about 3 MHz/cm. The resonance lineshape was calculated numerically, and the systematic uncertainty of the resonance frequency due to the detector specification was evaluated as a function of the detector performance. Based on the results of the simulation study, a new prototype of the detector is under development

Construction of Ultra Slow Muon Beam Line at J-PARC

T. Nagatomo1, Y. Ikedo1, P. Strasser1, S. Makimura1, J. Nakamura1, K. Nishiyama1, K. Shimomura1, N. Kawamura1, A. Koda1, H. Fujimori1, Y. Kobayashi1, T.U. Ito2, W. Higemoto2, A.D. Pant3, R. Kadono1, E. Torikai3 and Y. Miyake1 1Muon Science Laboratory, High Energy Accelerator Research Organization (KEK), Ibaraki 319-1106, Japan 2Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1184, Japan 3Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi 400-0016, Japan

Development of High-Rate Positron Tracker for the Muonium Production Experiment at J-PARC

1 Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan 2 Institute of Materials Structure Science, KEK, 1-1 Oho, Tsukuba, Ibaraki, Japan 3 Institute of Particle and Nuclear Studies, KEK, 1-1 Oho, Tsukuba, Ibaraki, Japan 4 Advanced Meson Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama, Japan 5 Department of Physics, Korea University, 145, Aman-ro, Seongbuk-gu, Seoul, 137-713, Korea 6 Department of Physics, Tokyo University of Science, 1-3, Kagurazaka, Sinjuku-ku, Tokyo, Japan

Optimal crossed overlap of coherent vacuum ultraviolet radiation and thermal muonium emission for μSR with the Ultra Slow Muon

For μSR with ultra slow muon, we are constructing U line in materials and life science facility (MLF), J-PARC at present. Generation of ultra slow muon requires thermal muonium generation and laser resonant ionization process with vacuum ultraviolet radiation (1S→2P) and 355-nm radiation (2P→unbound). For laser resonant ionization, the coherent radiations and the thermal muonium emission must be coincident in time and space. The radiations can be steered in a chamber for reasonable overlap in space, and they can be easily overlapped in time because they are generated from one laser source. The trigger signal of the accelerator is useful for stable overlap in time.