Ryu Sawada

The University of Tokyo | Todai · International Center for Elementary Particle Physics

The fidelity of certain gates on noisy quantum computers may be improved when they are implemented using more than two levels of the involved transmons. The main impediments to achieving this potential are the dynamic gate phase errors that cannot be corrected via calibration. The standard tool for countering such phase errors in two-level qubits i...

After the next planned upgrades to the LHC, the luminosity it delivers will more than double, substantially increasing the already large demand on computing resources. Therefore an efficient way to reconstruct physical objects is required. Recent studies show that one of the quantum computing techniques, quantum annealing (QA), can be used to perfo...

Super-resolution is a machine-learning technique in image processing which generates high-resolution images from low-resolution images. Inspired by this approach, we perform a numerical experiment of quantum machine learning, which takes low-resolution (low plane-wave energy cutoff) one-particle molecular wavefunctions in plane-wave basis as input...

There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivity, and coherence times, a quantum circuit optimization is essential to make the best use of near-term quantum devices. We introduce a new circuit optimizer called AQCEL, which aims to remove redundant controlled operations from control...

There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivity, and coherence times, a quantum circuit optimization is essential to make the best use of near-term quantum devices. We introduce a new circuit optimizer called AQCEL, which aims to remove redundant controlled operations from control...

We present studies of quantum algorithms exploiting machine learning to classify events of interest from background events, one of the most representative machine learning applications in high-energy physics. We focus on variational quantum approach to learn the properties of input data and evaluate the performance of the event classification using...

Quantum error correction is a crucial step beyond the current noisy-intermediate-scale quantum device towards fault-tolerant quantum computing. However, most of the error corrections ever demonstrated rely on post-selection of events or post-correction of states, based on measurement results repeatedly recorded during circuit execution. On the othe...

The usefulness and value of Multi-step Machine Learning (ML), where a task is organized into connected sub-tasks with known intermediate inference goals, as opposed to a single large model learned end-to-end without intermediate sub-tasks, is presented. Pre-optimized ML models are connected and better performance is obtained by re-optimizing the co...

There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivities, and coherence times, circuit optimization is essential to make the best use of near-term quantum devices. We introduce two separate ideas for circuit optimization and combine them in a multi-tiered quantum circuit optimization pro...

Connecting multiple machine learning models into a pipeline is effective for handling complex problems. By breaking down the problem into steps, each tackled by a specific component model of the pipeline, the overall solution can be made accurate and explainable. This paper describes an enhancement of object detection based on this multi-step conce...

The usefulness and value of Multi-step Machine Learning (ML), where a task is organized into connected sub-tasks with known intermediate inference goals, as opposed to a single large model learned end-to-end without intermediate sub-tasks, is presented. Pre-optimized ML models are connected and better performance is obtained by re-optimizing the co...

There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivities, and coherence times, circuit optimization is essential to make the best use of quantum devices produced over a next decade. We introduce two separate ideas for circuit optimization and combine them in a multi-tiered quantum circui...

We present studies of quantum algorithms exploiting machine learning to classify events of interest from background events, one of the most representative machine learning applications in high-energy physics. We focus on variational quantum approach to learn the properties of input data and evaluate the performance of the event classification using...

A Grid computing site is composed of various services including Grid middleware, such as Computing Element and Storage Element. Text logs produced by the services provide useful information for understanding the status of the services. However, it is a time-consuming task for site administrators to monitor and analyze the service logs every day. Th...

The High-Luminosity Large Hadron Collider (HL-LHC) starts from 2027 to extend the physics discovery potential at the energy frontier. The HL-LHC produces experimental data with a much higher luminosity, requiring a large amount of computing resources mainly due to the complexity of a track pattern recognition algorithm. Quantum annealing might be a...

Within the theory of supersymmetry, the lightest neutralino is a dark matter candidate and is often assumed to be the lightest supersymmetric particle (LSP) as well. If the neutral wino or higgsino is dark matter, the upper limit of the LSP mass is determined by the observed relic density of dark matter. If the LSP is a nearly-pure neutral state of...

A bstract We discuss prospects of studying supersymmetric model at future pp circular collider (FCC) with its centre-of-mass energy of ∼ 100 TeV. We pay particular attention to the model in which Wino is lighter than other supersymmetric particles and all the gauginos are within the kinematical reach of the FCC, which is the case in a large class o...

A large-area Multi-Pixel Photon Counter (MPPC) sensitive to vacuum ultra violet (VUV) light has been developed for the liquid xenon (LXe) scintillation detector of the MEG II experiment. The LXe detector is designed to detect the 52.8MeV photon from the lepton flavour violating decay μ ⁺ →e ⁺ γ and is based on 900ℓ LXe with a highly granular scinti...

We discuss prospects of studying supersymmetric model at future $pp$ circular collider (FCC) with its centre-of-mass energy of $\sim 100\ {\rm TeV}$. We pay particular attention to the model in which Wino is lighter than other supersymmetric particles and all the gauginos are within the kinematical reach of the FCC, which is the case in a large cla...

Within the theory of supersymmetry, the lightest neutralino is a dark matter candidate and is often assumed to be the lightest supersymmetric particle (LSP) as well. If the neutral wino or higgsino is dark matter, the upper limit of the LSP mass is determined by the observed relic density of dark matter. If the LSP is a pure neutral state of the wi...

A large-area Multi-Pixel Photon Counter (MPPC) sensitive to vacuum ultra violet (VUV) light has been developed for the liquid xenon (LXe) scintillation detector of the MEG II experiment. The LXe detector is designed to detect the $52.8\,\mathrm{MeV}$ photon from the lepton flavour violating decay $\mu^+ \to \mathrm{e}^+ \gamma$ and is based on $900...

The Radiative Decay Counter (RDC) is a key ingredient in the MEG II experiment. The sensitivity of the \(\mu ^{+} \rightarrow e^{+}\gamma \) branching ratio will be improved by 16\(\%\) by identifying a photon from a radiative muon decay, which is the dominant background source of the search.

A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH→ℓ+ℓ−cc¯ is studied. A data set with an integrated luminosity of 36.1 fb−1 of pp collisions at s=13TeV recorded by the ATLAS experiment at the LHC is used. The H→cc¯ signature is id...

A search is presented for photonic signatures, motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of proton-proton collision data at s=13 TeV corresponding to an integrated luminosity of 36.1 fb−1 recorded by the ATLAS detector at the LHC, and it explores models dominated by both strong and electroweak p...

A search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→Bs0π±, Bs0→J/ψϕ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb−1 of pp collisions at 7 TeV and 19.5 fb−1 at 8 TeV. No significant signal was found. Upper limits on the number...

The MEG experiment, designed to search for the \({\mu ^+ \rightarrow \hbox {e}^+ \gamma }\) decay, completed data-taking in 2013 reaching a sensitivity level of \({5.3\times 10^{-13}}\) for the branching ratio. In order to increase the sensitivity reach of the experiment by an order of magnitude to the level of \(6\times 10^{-14}\), a total upgrade...

A search for the standard model Higgs boson produced in association with a top-quark pair, tt¯H, is presented. The analysis uses 36.1 fb−1 of pp collision data at s=13 TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H→bb¯ decay mode. The selected events contain either one or two electrons...

A search for high-mass resonances decaying to τν using proton-proton collisions at s=13 TeV produced by the Large Hadron Collider is presented. Only τ-lepton decays with hadrons in the final state are considered. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb−1. No statistically significant exce...

A search for the associated production of the Higgs boson with a top quark pair (tt¯H) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1 fb−1 of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy s=13 TeV at the Large Hadron Colli...

A search for electroweak production of supersymmetric particles in scenarios with compressed mass spectra in final states with two low-momentum leptons and missing transverse momentum is presented. This search uses proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015–2016, corresponding to 36.1 fb−1 of in...

A measurement of the production of three isolated photons in proton–proton collisions at a centre-of-mass energy s=8 TeV is reported. The results are based on an integrated luminosity of 20.2 fb −1 collected with the ATLAS detector at the LHC. The differential cross sections are measured as functions of the transverse energy of each photon, the dif...

The MEG experiment, designed to search for the mu+->e+ gamma decay at a 10^-13 sensitivity level, completed data taking in 2013. In order to increase the sensitivity reach of the experiment by an order of magnitude to the level of 6 x 10-14 for the branching ratio, a total upgrade, involving substantial changes to the experiment, has been undertake...

The final results of the search for the lepton flavour violating decay \(\mathrm {\mu }^+ \rightarrow \mathrm {e}^+ \mathrm {\gamma }\) based on the full dataset collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013 and totalling \(7.5\times 10^{14}\) stopped muons on target are presented. No significant excess of ev...

The final results of the search for the lepton flavour violating decay $\mu \rightarrow {\rm e^{+}} \gamma$ based on the full dataset collected by the MEG experiment at the Paul Scherrer Institut in the period 2009--2013 and totalling $7.5\times 10^{14}$ stopped muons on target are presented. No significant excess of events is observed in the datas...

We studied the radiative muon decay \({\upmu }^{+} \rightarrow \mathrm {e}^{+} {\upnu }\bar{{\upnu }}{\upgamma }\) by using for the first time an almost fully polarized muon source. We identified a large sample (\(\sim \)13,000) of these decays in a total sample of \(1.8\times 10^{14}\) positive muon decays collected in the MEG experiment in the ye...

The MEG experiment makes use of one of the world's most intense low energy muon beams, in order to search for the lepton flavour violating process $\mu^{+} \rightarrow {\rm e}^{+} \gamma$. We determined the residual beam polarization at the thin stopping target, by measuring the asymmetry of the angular distribution of Michel decay positrons as a f...

The liquid xenon (LXe) gamma-ray detector for the MEG II experiment is based on a highly granular scintillation readout with Multi Pixel Photon Counters (MPPCs). Here we report on the development of a large area MPPC sensitive to LXe scintillation light in deep -UV range for the MEG II LXe detector. A prototype model of the deep -UV MPPC with an ac...

A muon decay accompanied by a photon through the inner Bremmstrahlung process (μ→eνν-γ, radiative muon decay) produces a time-correlated pair of positron and photon which becomes one of the main backgrounds in the search for μ→. eγ decay. This channel is also an important probe of timing calibration and cross-check of whole the experiment. We ident...

We studied the radiative muon decay $\mu^+ \to e^+\nu\nu\gamma$ by using for the first time an almost fully polarized muon beam. We identified a large sample (~13000) of these decays in a total sample of 1.8x10^14 positive muon decays collected in the MEG experiment and measured the branching ratio B($\mu^+ \to e^+\nu\nu\gamma$) = (6.03+-0.14(stat....

The analysis of a combined data set, totaling 3.6×10^{14} stopped muons on target, in the search for the lepton flavor violating decay μ^{+}→e^{+}γ is presented. The data collected by the MEG experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and yield a new upper limit on the branching ratio of th...

The MEG (Mu to Electron Gamma) experiment has been running at the Paul Scherrer Institut (PSI), Switzerland since 2008 to search for the decay μ +→e+γ by using one of the most intense continuous μ + beams in the world. This paper presents the MEG components: the positron spectrometer, including a thin target, a superconducting magnet, a set of drif...

The MEG (Mu to Electron Gamma) experiment has been running at the Paul Scherrer Institut (PSI), Switzerland since 2008 to search for the decay \meg\ by using one of the most intense continuous $\mu^+$ beams in the world. This paper presents the MEG components: the positron spectrometer, including a thin target, a superconducting magnet, a set of dr...

The analysis of a combined data set, totaling 3.6 \times 10^14 stopped muons on target, in the search for the lepton flavour violating decay mu^+ -> e^+ gamma is presented. The data collected by the MEG experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and yield a new upper limit on the branching...

In the standard model of elementary particle physics, the lepton flavor violation in the charged sector (cLFV) is forbidden and cLFV have not been observed experimentally, while neutrino oscillations have been observed in many experiments. In well-motivated new theories beyond the standard model, cLFV is naturally introduced and the branching fract...

We propose the continuation of the MEG experiment to search for the charged lepton flavour violating decay (cLFV) \mu \to e \gamma, based on an upgrade of the experiment, which aims for a sensitivity enhancement of one order of magnitude compared to the final MEG result, down to the $6 \times 10^{-14}$ level. The key features of this new MEG upgrad...

MEG experiment searches for new physics like SUSY-GUT/SUSY-seesaw through the lepton flavor violating μ → eγ decay. The current MEG experiment utilizes 846 2 inch PMTs in order to detect scintillation light in 900 ℓ liquid xenon gamma-ray calorimeter. R&D of Pixelated Photon Detector (PPD) have been actively performed in many different fields as a...

We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton-flavor-violating decay μ(+)e(+)γ. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8×10(14) muon decays, gives a 90% C.L. upper limit of 2.4×10(-12) on t...

MEG ( \( \mu^{+}_{}\) \( \rightarrow\) e +\( \gamma\) is an experiment dedicated to the search for the \( \mu^{+}_{}\) \( \rightarrow\) e +\( \gamma\) decay that is strongly suppressed in the Standard Model, but allowed in many alternative models and therefore very sensitive to new physics. The offline software is based on two frameworks. The first...

MEG (Mu to Electron Gamma) is an experiment dedicated to search for the μ⁺ → e⁺γ decay that is strongly suppressed in the Standard Model. MEG is a small-size experiment (≈ 50-60 physicists at any time) with a life span of about 10 years. The limited human resource available, in particular in the core offline group, emphasized...

MEG experiment searches for a rare muon decay (μ+→e+γ) at PSI in Switzerland. A physics run to take large amount of data was started at the end of summer in 2008. MEG will have a sensitivity around predicted branching ratio by new theories beyond the standard model. In order to discriminate signal events from backgrounds, precise measurement of ene...

The MEG experiment started a search for a lepton violating (LFV) muon decay,μ+ → e+γ, at Paul Scherrer Institut(PSI) in Switzerland. The LFV muon decay does not occur in the standard model, while new theories, such as super symmetric grand unified theory and seesaw model of neutrinos, predict observable branching ratio just below the current upper...

The MEG experiment started a search for a lepton violating (LFV) muon decay, μ+-->e+γ, at Paul Scherrer Institut(PSI) in Switzerland. The LFV muon decay does not occur in the standard model, while new theories, such as super symmetric grand unified theory and seesaw model of neutrinos, predict observable branching ratio just below the current upper...

A search for the decay μ+→e+γ, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(μ+→e+γ)⩽2.8×10−11 (90% C.L.). This corresponds to the measurement of positrons and photons from ∼1014 stopped μ+-decays by means of a superconducting positron spectrom...

We have developed a new type of photon detector for an experiment aimed at searching for the lepton flavor violating decay μ+→e+γ. In this experiment, a total of 900L of liquid xenon is used in order for the scintillation detector to detect γ-rays with an extremely high sensitivity, where the liquid xenon is viewed by an array of 846 photomultiplie...

The MEG experiment started a search for a lepton violating (LFV) muon decay, mu(+) -> e(+)gamma, at Paul Scherrer Institut(PSI) in Switzerland. The LFV muon decay does not occur in the standard model, while new theories, such as super symmetric grand unified theory and seesaw model of neutrinos, predict observable branching ratio just below the cur...

The μ-particle rare decay physics experiment, the MU-E-GAMMA (MEG) experiment, will soon be operational at the Paul Scherrer Institute in Zurich. To achieve the extremely high sensitivity required to detect gamma rays, 800 L of liquid xenon is used as the medium in the calorimeter, viewed by 830 photomultiplier tubes (PMT) immersed in it. The requi...

The MEG experiment searches for the rare muon decay μ+→e+γ, which is forbidden in the standard model. The detection of this muon decay is a probe for new physics beyond the standard model. In order to improve the sensitivity of the experiment, a liquid xenon detector is used for measuring energy, position and time of gamma rays. The detector consis...

The optical properties of liquid xenon (LXe) in the vacuum ultra violet (VUV), determining the performance of a scintillation calorimeter, are discussed in detail. The available data, measured in a wider spectral region from visible to UV light, and in a large range of Xe densities, from gas to liquid, are examined. It is shown that this informatio...

A high‐power coaxial pulse tube cryocooler, originally developed in KEK and technology‐transferred to Iwatani Industrial Gases Corp (IIGC), has been installed in a large liquid xenon calorimeter to evaluate liquid nitrogen‐free (LN2‐free) operation of the rare μ‐particle decay experiment (MEG). Features of this pulse tube cryocooler include the co...

An 800 l liquid xenon scintillation γ-ray detector is being developed for the MEG experiment which will search for μ+→e+γ decay at the Paul Scherrer Institut. Absorption of scintillation light of xenon by impurities might possibly limit the performance of such a detector. We used a 100 l prototype with an active volume of to study the scintillation...

We are developing a new type of photon detector for an experiment to search for muons decaying into a positron and a gamma ray. In this experiment, the photon detector will utilize liquid xenon (Xe) as the scintillation material. Good transparency of the liquid Xe is required in order to gain the highest performance out of the detector. Impurities...

We are developing a liquid xenon calorimeter for the MEG experiment. This experiment, to be performed at the Paul Scherrer Institut (PSI) in Villigen (CH), was designed by an Italian-Japanese-Russian-Swiss collaboration to search for the μ⁺→e⁺γ decay, forbidden in the standard model of electroweak and strong interactions. The...

An international project to search μ→eγ decay includes the use of a liquid xenon gamma ray detector. So, a liquid level meter working at a low temperature with low outgassing is needed and the prototype is constructed. The meter shows the liquid level by measuring the capacitance between electrodes with small intervals immersed in the liquid. The o...

We are developing a new type of photon detector in preparation of an experiment to search for muons decaying into positrons and gamma rays. In the experiment, the photon detector will utilize liquid xenon (Xe) as the scintillation material because of its fast response, large light yield, and high density. The scintillation light emitted in liquid X...

We are developing a new type of photon detector for an experiment to search for muons decaying into a positron and gamma ray. Our sensitivity on the branching ratio is expected to reach 10^-14 by use of the world's most intense continuous muon beam at Paul Scherrer Institut (PSI). In this experiment, the photon detector will utilize liqui...

The "intrinsic energy resolution" in a NaI(Tl) crystal for gamma-rays in the MeV region is explained based on the non-proportionality of the scintillation yield for secondary electrons produced in the crystal. From the non-proportionality of the scintillation yield in liquid xenon, which was experimentally obtained, the "intrinsic energy resolution...

We are developing a new type of photon detector for an experiment searching for muon decays to positron+gamma with a sensitivity of 10^-14 branching ratio by using the world most intense continuous muon beam provided at PSI. In this experiment the photon detector utilizes liquid xenon as a scintillation material because of its fast respon...

The MEG experiment started a search for a lepton violating (LFV) muon decay, mu+-->e+gamma, at Paul Scherrer Institut(PSI) in Switzerland. The LFV muon decay does not occur in the standard model, while new theories, such as super symmetric grand unified theory and seesaw model of neutrinos, predict observable branching ratio just below the current...