Search

A new silicon-strip readout chip named "SliT" has been developed for the measurement of the muon anomalous magnetic moment and electric dipole moment at J-PARC. The SliT is designed in the Silterra 180 nm CMOS technology with mixed-signal integrated circuits. An analog circuit incorporates a conventional charge-sensitive amplifier, shaping amplifiers, and two distinct discriminators for each of 128 identical channels. A digital part includes storage memories, an event building block, a serializer, and LVDS drivers. A distinct feature of the SliT is utilization of the zero-cross architecture, which consists of a CR-RC filter followed by a CR circuit as a voltage differentiator. This architecture enables to generate hit signals with subnanosecond amplitude-independent time walk, which is the primary requirement for the experiment. The test results show the time walk of $0.38 \pm 0.16$ ns between 0.5 and 3 MIP signals. The equivalent noise charge is $1547 \pm 75 $ $e^{-}$ (rms) at $C_{\rm det} = 33$ pF as a strip-sensor capacitance. Other functionalities such as a strip-sensor readout chip have also been proven in the tests. The SliT128C satisfies all requirements of the J-PARC muon $g-2$/EDM experiment., 7 pages, 12 figures

We are developing position sensitive silicon detectors (PSDs) which have an electrode at each of four corners so that incident position of a charged particle can be obtained with signal from the electrodes. It is expected that the position resolution of the electromagnetic calorimeter (ECAL) of the ILD detector will be improved by introducing PSDs to detection layers. We have been developing the PSDs for several years. In the previous production we found that the charge separation is not optimally done due to the readout impedance. To solve the issue, we produced new PSDs with higher surface resistance with an additional resistive layer on the surface. We also implemented several techniques to decrease position distortion and increase signal-to-noise ratio which are essential for the optimal position resolution. The measurements on the prototype sensors are ongoing, including radiation source measurement and laser measurement using an ASIC for silicon pad detectors., 7 pages, 8 figures. Talk presented at the Calorimetry for the High Energy Frontier 2019 (CHEF2019), Fukuoka, Japan, 25-29 November 2019

Nuclear instruments & methods in physics research / A 950, 162969 (2020). doi:10.1016/j.nima.2019.162969, The technological prototype of the CALICE highly granular silicon–tungsten electromagnetic calorimeter (SiW-ECAL) was tested in a beam at DESY in 2017. The setup comprised seven layers of silicon sensors. Each layer comprised four sensors, with each sensor containing an array of 256 5.5×5.5 mm$^2$ silicon PIN diodes. The four sensors covered a total area of 18 × 18 cm and comprised a total of 1024 channels. The readout was split into a trigger line and a charge signal line. Key performance results for signal over noise for the two output lines are presented, together with a study of the uniformity of the detector response. Measurements of the response to electrons for the tungsten loaded version of the detector are also presented., Published by North-Holland Publ. Co., Amsterdam

International audience; Silicon sensors with high time resolution can help particle identification in the International Linear Collider (ILC). We are studying Low Gain Avalanche Diodes (LGADs) as a high timing resolution sensor. As a step to develop LGADs, we are now focusing to characterize Avalanche Photo Diode (APD)s, because the APDs has the same multiplication structure as LGADs. We studied the characteristics of APDs with particles from radioisotopes.

The muon anomalous magnetic moment $(g-2)_{\mu}$ and electric dipole moment (EDM) are sensitive to new physics beyond the Standard Model. We aim to measure $(g-2)_{\mu}$ with a precision of 0.1 parts per million and search for EDM with a sensitivity of $10^{-21}~e \cdot$cm at J-PARC. In this experiment, we use a silicon strip detector with high granularity and fast response to detect positrons from muon decay. We report on the development status of the silicon strip detector.

This paper introduces a new approach to measure the muon magnetic moment anomaly $a_{\mu} = (g-2)/2$, and the muon electric dipole moment (EDM) $d_{\mu}$ at the J-PARC muon facility. The goal of our experiment is to measure $a_{\mu}$ and $d_{\mu}$ using an independent method with a factor of 10 lower muon momentum, and a factor of 20 smaller diameter storage-ring solenoid compared with previous and ongoing muon $g-2$ experiments with unprecedented quality of the storage magnetic field. Additional significant differences from the present experimental method include a factor of 1,000 smaller transverse emittance of the muon beam (reaccelerated thermal muon beam), its efficient vertical injection into the solenoid, and tracking each decay positron from muon decay to obtain its momentum vector. The precision goal for $a_{\mu}$ is statistical uncertainty of 450 part per billion (ppb), similar to the present experimental uncertainty, and a systematic uncertainty less than 70 ppb. The goal for EDM is a sensitivity of $1.5\times 10^{-21}~e\cdot\mbox{cm}$., Comment: 24 pages, 14 figures

International Linear Collider (ILC) is a next-generation e + e − linear collider to explore Higgs, Beyond-Standard-Models, top and electroweak particles with great precision. We are optimizing our two detectors, International Large Detector (ILD) and Silicon Detector (SiD) to maximize the physics reach expected in ILC with reasonable detector cost and good reliability. The optimization study on vertex detectors, main trackers and calorimeters is underway. We aim to conclude the optimization to establish final designs in a few years, to finish detector TDR and proposal in reply to expected “green sign” of the ILC project.

EUDAQ is a generic data acquisition software developed for use in conjunction with common beam telescopes at charged particle beam lines. Providing high-precision reference tracks for performance studies of new sensors, beam telescopes are essential for the research and development towards future detectors for high-energy physics. As beam time is a highly limited resource, EUDAQ has been designed with reliability and ease-of-use in mind. It enables flexible integration of different independent devices under test via their specific data acquisition systems into a top-level framework. EUDAQ controls all components globally, handles the data flow centrally and synchronises and records the data streams. Over the past decade, EUDAQ has been deployed as part of a wide range of successful test beam campaigns and detector development applications., Comment: 32 pages, 11 figures

High precision measurements of the ground state hyperfine structure (HFS) of muonium is a stringent tool for testing bound-state quantum electrodynamics (QED) theory, determining fundamental constants of the muon magnetic moment and mass, and searches for new physics. Muonium is the most suitable system to test QED because both theoretical and experimental values can be precisely determined. Previous measurements were performed decades ago at LAMPF with uncertainties mostly dominated by statistical errors. At the J-PARC Muon Science Facility (MUSE), the MuSEUM collaboration is planning complementary measurements of muonium HFS both at zero and high magnetic field. The new high-intensity muon beam that will soon be available at H-Line will provide an opportunity to improve the precision of these measurements by one order of magnitude. An overview of the different aspects of these new muonium HFS measurements, the current status of the preparation for high-field measurements, and the latest results at zero field are presented.

A high-intensity pulsed muon beam is becoming available at the at the Japan Proton Accelerator Research Complex (J-PARC). Many experiments to study fundamental physics using this high-intensity muon beam are proposed. An experiment to measure the muon magnetic moment anomaly ($g-2$) and the muon electric dipole moment (EDM) is one of these experiments and it requires a tracking detector for positrons from muon decay. Fine segmentation is required in a detector to tolerate the high rate of positrons. The time resolution is required to be much better than the muon anomalous spin precession period while a buffer depth of a front-end electronics needs to be much longer than the accelerated muon lifetime. Requirements of this detector also meet requirements of a measurement of the muonium hyperfine structure interval at the J-PARC and another experiment to measure the proton charge radius at Tohoku University. We have developed a single-sided silicon strip sensor with a 190 $\mu$m pitch, a front-end electronics with a sampling rate of 200 MHz and a buffer memory depth of 8192, and a data acquisition system based on DAQ-Middleware for the J-PARC muon $g-2$/EDM experiment. We have fabricated detector modules consisting of this sensor and the front-end electronics. Performance of fabricated detector modules was evaluated at a laboratory and a beam test using the positron beam at Tohoku University. The detector is confirmed to satisfy all requirements of the experiments except for the time walk, which will be solved by the next version of a front-end electronics., Comment: 18 pages, 17 figures

The positron tracking detector is developed for the J-PARC muon g − 2 /EDM (E34) experiment. It uses silicon strip sensors for positron detection and signals from sensors are transferred to the front-end readout system via flexible printed circuits (FPCs) glued on the sensors. The front-end readout system consists of application specific integrated circuits (ASICs) on FPCs and the field-programmable gate array (FPGA)-based readout board. Mass production of silicon strip sensors is ongoing. Designs of the FPC on the sensor and the front-end ASIC were fixed and their mass production has been started. Development of other detector components are also ongoing. The status of these developments and fabrications are presented.

We report on the progress in flavor identification tools developed for a future $e^+e^-$ linear collider such as the International Linear Collider (ILC) and Compact Linear Collider (CLIC). Building on the work carried out by the LCFIVertex collaboration, we employ new strategies in vertex finding and jet finding, and introduce new discriminating variables for jet flavor identification. We present the performance of the new algorithms in the conditions simulated using a detector concept designed for the ILC. The algorithms have been successfully used in ILC physics simulation studies, such as those presented in the ILC Technical Design Report., Comment: 12 pages, 2 figures

The excellent jet energy resolution required for precise physics measurements at ILC is achievable using a Particle Flow Method and highly granular calorimeters. As it was shown by CALICE international R&D collaboration, the silicon-tungsten imaging electromagnetic calorimeter provides the best granularity, stability and resolution of jet energy measurement. After proving the calorimeter concept with physical prototypes in 2005–2011, an emphasis is now moved to building a technological prototype satisfying challenging requirements. All chosen technologies should be reliable and scalable for a mass production of a future detector. We report on the current status of R&D, in particular, on beam and charge injection tests of the technological prototype and on the tests of ECAL mechanical structure. We also report on our plans to build a realistic prototype detector and test it together with an existing carbon fiber-tungsten mechanical structure. A similar silicon-tungsten calorimeter technology has been recently proposed for the Phase 2 upgrade of CMS end-cap calorimeter and future high energy circular collider projects.

This paper presents results obtained with the combined CALICE Scintillator Electromagnetic Calorimeter, Analogue Hadronic Calorimeter and Tail Catcher & Muon Tracker, three high granularity scintillator-SiPM calorimeter prototypes. The response of the system to pions with momenta between 4 GeV/c and 32 GeV/c is analysed, including the energy response, resolution, and longitudinal shower profiles. The results of a software compensation technique based on weighting according to hit energy are compared to those of a standard linear energy reconstruction. The results are compared to predictions of the GEANT4 physics lists QGSP_BERT_HP and FTFP_BERT_HP., 31 pages, 41 figures

The muon anomalous magnetic moment $(g -2)_{\mu}$ and electric dipole moment (EDM) are sensitive to new physics beyond the Standard Model. We aim to measure $( g -2 ) _{\mu}$ with a precision of 0.1 parts per million and search for EDM with a sensitivity of 10-21e. cm at J-PARC. In this experiment, we use a silicon strip detector with high granularity and fast response to detect positrons from muon decay. The readout ASIC is required to tolerate a high hit rate of 1.4 MHz per strip, to be stable to the change of hit rate by a factor of 1 /150, and to have deep memory for the period of $\sim 40 \mu \mathrm{s}$ with 5 ns resolution. The prototype readout ASIC "SliT128A" has been fabricated using the Silterra $0.18- \mu \mathrm{m}$ CMOS process. We also connected the SliT128A with a silicon strip sensor and tested it with a muon beam at J-PARC. In this paper, we report the performance of the prototype ASIC itself and the prototype detector module.

Positronium is an ideal system for research on Quantum Electrodynamics (QED), especially in a bound state. A discrepancy of 3.9 standard deviations has been found between the measured hyperfine structure (Ps-HFS) and the QED predictions. This may be due to the contribution of unknown new physics or common systematic effects in previous measurements, in all of which the Zeeman effect was used. We propose a new method to directly measure the Ps-HFS using a high power gyrotron. We compare two resonators which have been developed to supply sufficient power to drive the direct transition, a Fabry-Perot resonator and a ring resonator with a diffraction grating. We plan to perform first direct measurement of Ps-HFS within the next six months.

The CALICE collaboration is preparing large scale prototypes for highly granular calorimeters for detectors to be operated at a future lepton collider. Currently a prototype of a silicon-tungsten electromagnetic calorimeter SiW-ECAL will be assembled which in terms of dimensions and layout meets already most of the requirements given by the lepton collider physics programme and hence the detector design. In particular the front end electronics will be embedded into the layer structure of the calorimeter and have to fit within alveolar layers with less than 1 cm in height. In this paper the design of the prototype and the steps towards the realisation are presented. The presented technology plays also a key role in the upgrades of the LHC Experiments CMS and ATLAS.

Calorimeters with silicon detectors have many unique features and are proposed for several world-leading experiments. We discuss the tests of the first three 18x18 cm$^2$ layers segmented into 1024 pixels of the technological prototype of the silicon-tungsten electromagnetic calorimeter for a future $e^+e^-$ collider. The tests have beem performed in November 2015 at CERN SPS beam line., Comment: Proceedings for "Instrumentation for Colliding Beam Physics" (INSTR17) conference, 27 February - 3 March 2017, Novosibirsk, Russia

Positronium is an ideal system for research on QED, especially in a bound state. A discrepancy (3.9σ) is found recently between measured HFS values and the QED prediction (including up-to O(α3 log α − 1), where α is the fine-structure constant.). It might be due to a contribution of unknown new physics or common systematic problems in all the previous measurements. A new method to measure HFS directly is performed using a high power gyrotron. The transition from ortho-positronium to para-positronium has been observed with 5 σ CL, which is the first observation of M1 transition in (sub)Terahertz region. New technologies of high power gyrotrons are developed for precision spectroscopy.

A novel final focus system design featuring the Local Chromaticity Correction scheme has beenproposed for ILC. This is to be verified at ATF2, a test facility for ILC, through focusing an e-beam down to the design vertical beam size (“σy”) of 37 nm. Shintake Beam Size Monitor (“IPBSM”),installed at the virtual interaction point of ATF2, is the only existing device capable of measuring σy below 100 nm, making it indispensable for achieving the goals of ATF2 and a strong candidate for R&D at future linear colliders. This is attributed to its ingenious technique of scanning the phase oflaser interference fringes relative to the e-beam. Beam sizes are derived from the resulting Compton signal modulation measured by a downstream detector. Having been upgraded in a variety of ways since its first debut at FFTB, Shintake Monitor is capable of measuring a wide range of σy from 25 nm to 6 μm with better than 10% resolution. This paper describes the system's design, role in beam tuning, and various hardware upgrades to further improve its performance.

Positronium is an ideal system for the research of the bound state QED. The hyperfine splitting of positronium (Ps-HFS, about 203 GHz) is an important observable but all previous measurements of Ps-HFS had been measured indirectly using Zeeman splitting. There might be the unknown systematic errors on the uniformity of magnetic field. We are trying to measure Ps-HFS directly using sub-THz radiation. We developed an optical system to accumulate high power (about 10 kW) radiation in a Fabry-Perot resonant cavity and observed the positronium hyperfine transition for the first time.

Positronium is an ideal system for the research of Quantum Electrodynamics (QED), especially for QED in bound state. The discrepancy of 3.9σ was found recently between the measured HFS values and the QED prediction of O(α3). It might be due to the contribution of unknown new physics or systematic problems in the all previous measurements. We propose a new method to measure HFS directly and precisely. A gyrotron, a novel sub-THz light source is adopted with a Fabry-Pérot cavity with high finesse and an efficient transportation system in order to obtain sufficient radiation power at 203 GHz. The present status of the optimization studies and the current design of the experiment are described.

The ground state hyperfine splitting of positronium, , is sensitive to high order corrections of QED. A new calculation up to O( ) has revealed a 3.9 discrepancy between the QED prediction and the experimental results. This discrepancy might either be due to systematic problems in the previous experiments or to contributions beyond the Standard Model. We propose an experiment to measure employing new methods designed to remedy the possible systematic errors which may have affected the previous experiments. Our experiment will provide an independent check of the discrepancy. The prototype run has been performed and a result of = 203.3804 0.0022 (stat., 11 ppm) 0.0081 (sys., 40 ppm) GHz has been obtained. Compensation magnets to obtain O(ppm) magnetic field uniformity has been developed. The final run will start soon and a measurement with a precision of O(ppm) is expected within a few years.

We developed an electron beam size monitor for nanometer scaled beam sizes. It uses a laser interference fringe for a scattering target with the electron beam. The target beam size for the monitor is 25–6000 nm to achieve and confirm the 37 nm design beam size of ATF2, a final focus test facility for the ILC. Resolution of less than 10% for the full range is shown to be realistic, with a precise fringe control system. We describe the overall design, implementation, and performance of the monitor.

We evaluate the measurement precision of the production cross section times the branching ratio of the Higgs boson decaying into tau lepton pairs at the International Linear Collider (ILC). We analyze various final states associated with the main production mechanisms of the Higgs boson, the Higgs-strahlung and WW-fusion processes. The statistical precision of the production cross section times the branching ratio is estimated to be 2.6% and 6.9% for the Higgs-strahlung andWW-fusion processes, respectively, with the nominal integrated luminosities assumed in the ILC Technical Design Report; the precision improves to 1.0% and 3.4% with the running scenario including possible luminosity upgrades. The study provides a reference performance of the ILC for future phenomenological analyses., Comment: 10 pages, 6 figures, 9 tables, revised from v2

Journal of Instrumentation 12(05), P05009 (2017). doi:10.1088/1748-0221/12/05/P05009, The high granularity of the CALICE Semi-Digital Hadronic CALorimeter (SDHCAL)provides the capability to reveal the track segments present in hadronic showers. These segmentsare then used as a tool to probe the behaviour of the active layers in situ, to better reconstructthe energy of these hadronic showers and also to distinguish them from electromagnetic ones. Inaddition, the comparison of these track segments in data and the simulation helps to discriminateamong the different shower models used in the simulation. To extract the track segments in theshowers recorded in the SDHCAL, a Hough Transform is used after being adapted to the presenceof the dense core of the hadronic showers and the SDHCAL active medium structure., Published by Inst. of Physics, London

A novel scheme for the focusing of high-energy leptons in future linear colliders was proposed in 2001 [ P. Raimondi and A. Seryi , Phys. Rev. Lett. 86 , 3779 ( 2001 ) ]. This scheme has many advantageous properties over previously studied focusing schemes, including being significantly shorter for a given energy and having a significantly better energy bandwidth. Experimental results from the ATF2 accelerator at KEK are presented that validate the operating principle of such a scheme by demonstrating the demagnification of a 1.3 GeV electron beam down to below 65 nm in height using an energy-scaled version of the compact focusing optics designed for the ILC collider.

We plan to directly measure the hyperfine structure of the ground-state positronium. The hyperfine structure between ortho-positronium and para-positronium is about 203 GHz. We develop a new optical system to accumulate about 20 kW power using a gyrotron and high finesse Fabry-Perot resonator. We report the current status of our experiment.

We plan to directly measure the hyperfine structure of the ground-state positronium. The hyperfine structure between ortho-positronium and para-positronium is about 203 GHz. We develop a new optical system to accumulate about 10 kW power using a gyrotron and a Fabry-Perot cavity, and have already observed the hyperfine transition at a frequency point of 202.9 GHz. The transition probability is measured to be A = 3.1 −1.2 +1.6×10−8 s−1, which is in good agreement with the theoretical value of 3.37×10−8 s−1. In order to measure the hyperfine structure, we have to repeat transition measurements at different frequencies around 203 GHz. We are now refining the optical system to quickly change output frequency and obtain more power.

We are preparing an experiment searching for hypothetical particles which couple very weakly to photons, such as axions and paraphotons. Using sub-THz photons, our new experiment is sensitive to different axion/paraphoton masses from existing experiments which use visible photons.

We report the first direct measurement of the hyperfine transition of the ground state positronium. The hyperfine structure between ortho-positronium and para-positronium is about 203 GHz. We develop a new optical system to accumulate about 10 kW power using a gyrotron, a mode converter, and a Fabry-P\'erot cavity. The hyperfine transition has been observed with a significance of 5.4 standard deviations. The transition probability is measured to be $A={3.1}_{\ensuremath{-}1.2}^{+1.6}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ for the first time, which is in good agreement with the theoretical value of $3.37\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$.

The direct transition from ortho-positronium to para-positronium with high-power sub-THz radiation has been observed with 5.1 σ significance. The observed transition rate is consistent with the theoretical calculation. A sub-THz gyrotron is used as the light source, and a quasi-optical Fabry-Perot cavity is utilized to accumulate the radiation. This is the first observation of the positronium hyperfine splitting (Ps-HFS), which leads to the first direct measurement of Ps-HFS with a target accuracy of 100 ppm in several years.

The direct transition from o-Ps to p-Ps was firstly observed, using a gyrotron, a mode-converter and a Fabry-Perot cavity. The Einstein's A coefficient is measured as 3.9 (+1.8 −1.7) • 10−8 s−1. It is the first step to directly examine a reported discrepancy of positronium hyperfine splitting.

The large hadron collider (LHC) is anticipated to provide signals of new physics at the TeV scale, which are likely to involve production of a WIMP dark matter candidate. The international linear collider (ILC) is to sort out these signals and lead us to some viable model of the new physics at the TeV scale. In this article, we discuss how the ILC can discriminate new physics models, taking the following three examples: the inert Higgs model, the supersymmetric model, and the littlest Higgs model with T-parity. These models predict dark matter particles with different spins, 0, 1/2, and 1, respectively, and hence comprise representative scenarios. Specifically, we focus on the pair production process, e+e- -> chi+chi- -> chi0chi0W+W-, where chi0 and chi+- are the WIMP dark matter and a new charged particle predicted in each of these models. We then evaluate how accurately the properties of these new particles can be determined at the ILC and demonstrate that the ILC is capable of identifying the spin of the new charged particle and discriminating these models., 30 pages, 9 figures, submitted to Physical Review D

Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, $\Delta_{\mathrm{HFS}}$, gives a good test of the bound state calculations and probes new physics beyond the Standard Model. A new method of QED calculations has revealed the discrepancy by 15\,ppm (3.9$\sigma$) of $\Delta_{\mathrm{HFS}}$ between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of $\Delta_{\mathrm{HFS}} = 203.395\,1 \pm 0.002\,4 (\mathrm{stat.}, 12\,\mathrm{ppm}) \pm 0.001\,9 (\mathrm{sys.}, 9.5\,\mathrm{ppm})\,\mathrm{GHz} $ has been obtained so far. A measurement with a precision of $O$(ppm) is expected within a year., Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by Hyperfine Interactions

My presentation focuses on the Shintake (Beamsize) Monitor which can measure nanometer electron beam sizes. The Shintake Monitor is installed in the Accelerator Test Facility 2 (ATF2) at KEK, Japan. ATF2 is a realistic scaled down model of the final focus system for the International Linear Collider. The final focusing scheme named the Local Chromaticity Correction will be tested for the first time in the world. The vertical design beam size at the focal point (virtual interaction point) is 37 nm. Shintake monitor has been designed to measure a beamsize down to 20 nm. It employs the interference pattern made by splitting laser beams and crossing them at the focal point of the electron beam. In their intersecting region, the electromagnetic fields of the two laser beams form a standing wave (interference fringe). The probability of the Compton scattering varies according to the phase of the standing wave where the electrons pass through. Then the total energy of photons from the Compton scattering is measured in a multi-layered ganma ray detector located downstream from the interaction point. This scheme was originally proposed by T. Shintake whose team measured a beamsize of approximately 65 nm with 10 percent resolution at FFTB, SLAC, a former test facility for the ILC. We upgraded this monitor to measure the even smaller beam sizes to be available at ATF2. The laser wavelength has been modified from 1064 nm to 532 nm using a second harmonics generator. The laser optics was newly designed and constructed by implementing a laser wire scheme to measure a larger horizontal beam size, and by enabling different crossing angles of split laser beams to measure a wide (diverse) range of vertical beam sizes. The gamma detector for Shintake monitor has also been newly developed. We evaluated the performance of Shintake monitor with a beam of several microns in size and confirmed its consistency with wire scanner measurements. The expected performance of the Shintake monitor and the current status of the electron beam at ATF, achieved a record in beam size history and near future plan for 37 nm beam size measurement will be mentioned.

A calorimetric detector for inverse-compton photons from the Shintake monitor at the ATF2 test beam facility at KEK is developed. The Shintake monitor is the precision beam size monitor based on laser interferometer, which is planned to be used at a commissioning of the ILC beam delivery system. The detector has original structure to separate the compton signal from Bremsstrahlung background using the difference in shower development. The beam test of the detector was performed at ATF in the 2007’s winter using a laser wire and a wire scanner. It was confirmed to be able to see the difference in the shower development and to separate compton photons from Bremsstrahlung photons. The beamtest plan of Shintake monitor at ATF2 on 2008’s winter is also described.

We report on the first measurement of the Breit-Wigner resonance of the transition from {\it ortho-}positronium to {\it para-}positronium. We have developed an optical system to accumulate a power of over 20 kW using a frequency-tunable gyrotron and a Fabry-P\'{e}rot cavity. This system opens a new era of millimeter-wave spectroscopy, and enables us to directly determine both the hyperfine interval and the decay width of {\it p-}Ps.

The positronium hyperfine splitting is a good target to study Quantum Electrodynamics in the bound state. There is a discrepancy between precision measurements and a theoretical calculation. We are planning to directly measure the positroinum hyperfine structure for the first time. A gyrotron oscillator is used as a novel radiation source in terahertz region. A Fabry-Perot resonator is also developed to increase photon density. We have already observed the direct transition at 202.9 GHz. The direct measurement of the order of 100 ppm will be performed within about a year.

Positronium is an ideal system for the research of the bound state QED. The hyperfine splitting of positronium (Ps-HFS: about 203 GHz) is a good tool to test QED and also sensitive to new physics beyond the Standard Model via a quantum oscillation between an ortho-Ps and a virtual photon. Previous experimental results show 3.9 σ (15 ppm) discrepancy from the QED calculation. All previous experiments used an indirect method with static magnetic field to cause Zeeman splitting (a few GHz) between triplet states of ortho-Ps, from which the HFS value was derived. One possible systematic error source of the indirect method is non-uniformity of the static magnetic field. We are developing a new direct Ps-HFS measurement system without static magnetic field. In this measurement we use a gyrotron, a novel sub-THz light source, with a high-finesse Fabry-Perot cavity to obtain enough radiation power at 203 GHz. The present status of the optimization studies and current design of the experiment are described.

Positronium is a QCD-free system and the measurement of its hyperfine splitting provides a strict test of quantum electrodynamics (QED). Recent research revealed a discrepancy of 3.9? between the QED prediction and previous experimental results. We report on the prototype run of an improved experimental set-up and the performance of its RF system.

Interference between different energy eigenstates in a quantum system results in an oscillation with a frequency which is proportional to the difference in energy between the states. Such an oscillation is observable in polarized positronium when it is placed in a magnetic field. In order to measure the hyperfine splitting of positronium, we perform the precise measurement of this oscillation using a high quality superconducting magnet and fast photon-detectors. A result of $203.324 \pm 0.039\rm{~(stat.)} \pm 0.015\rm{(~sys.)}$~GHz is obtained which is consistent with both theoretical calculations and previous precise measurements., Comment: 4 figures accepted by Phys. Lett. B

The ground state hyperfine splitting of positronium, ΔHFS, is sensitive to high order corrections of QED. A new calculation up to O(α3) has revealed a 3.9 σ discrepancy between the QED prediction and the experimental results. This discrepancy might either be due to systematic problems in the previous experiments or to contributions beyond the Standard Model. We propose an experiment to measure ΔHFS employing new methods designed to remedy the systematic errors which may have affected the previous experiments. Our experiment will provide an independent check of the discrepancy. The measurement is in progress and a result of ΔHFS = 203.385 ± 0.011 GHz (58ppm) has been obtained from the prototype run. A measurement with a precision of O(ppm) is expected within a few years.