arXiv subjects

Katsumasa Ikematsu

Publications and source records attributed to Katsumasa Ikematsu.

16 recordsLinked to original sources

arXiv2023

A novel technique for the measurement of the avalanche fluctuation of gaseous detectors

We have developed a novel technique for the measurement of the avalanche fluctuation of gaseous detectors using a UV laser. The technique is simple and requires a short data-taking time of about ten minutes. Furthermore, it is applicable for relatively low gas gains. Our experimental setup as well as the measurement principle, and the results obtained with a stack of Gas Electron Multipliers (GEMs) operated in several gas mixtures are presented.

physics.ins-det↗

arXiv2022

Double-hit separation and dE/dx resolution of a time projection chamber with GEM readout

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.

physics.ins-det↗

arXiv2016

A Time Projection Chamber with GEM-Based Readout

For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.

physics.ins-det↗

arXiv2013

Measuring Anomalous Couplings in H->WW* Decays at the International Linear Collider

Measurement of the Higgs coupling to W-bosons is an important test of our understanding of the electroweak symmetry breaking mechanism. We study the sensitivity of the International Linear Collider (ILC) to the presence of anomalous HW+W- couplings using ZH -> nu nu WW* -> nu nu 4j events. Using an effective Lagrangian approach, we calculate the differential decay rates of the Higgs boson including the effects of new dimension-5 operators. We present a Monte Carlo simulation of events at the ILC, using a full detector simulation based on geant4 and a real event reconstruction chain. Expected constraints on the anomalous couplings are given.

hep-ph↗

arXiv2012

A feasibility study of the measurement of Higgs pair creation at a Photon Linear Collider

We studied the feasibility of the measurement of Higgs pair creation at a Photon Linear Collider (PLC). From the sensitivity to the anomalous self-coupling of the Higgs boson, the optimum $γγ$ collision energy was found to be around 270 GeV for a Higgs mass of 120 GeV/$c^2$. We found that large backgrounds such as $γγ\rightarrow W^+W^-, ZZ,$ and $b\bar{b}b\bar{b}$, can be suppressed if correct assignment of tracks to parent partons is achieved and Higgs pair events can be observed with a statistical significance of $\sim 5 σ$ by operating the PLC for 5 years.

hep-ph↗

arXiv2012

Feasibility study of measurement of Higgs pair creation in a gamma gamma collider

We studied the feasibility of measurement of Higgs pair creation in a gamma gamma collider. We found the optimum collision energy is around 270 GeV from the sensitivity study with Higgs boson mass of 120 GeV/c^2. Main backgrounds are gamma gamma to WW, gamma gamma to ZZ, and gamma gamma to bbbb at the optimum collision energy. The preliminary analysis shows HH could be observed with the statistical significance of about 5 sigma when we chose correct assignment of a track by using color singlet information.

hep-ex↗

arXiv2011

Measuring the top Yukawa coupling at the ILC at sqrt(s) = 500 GeV

We report on the feasibility of the direct measurement of the top Yukawa coupling g_t at the International Linear Collider (ILC) during its first phase of operation with a center-of-mass energy of 500 GeV. The signal and background models incorporate the non-relativistic QCD corrections which enhance the production cross section near the t-tbar threshold. The e+e- -> t tbar H signal is reconstructed in the 6-jet + lepton and the 8-jet modes. The results from the two channels are combined. The background processes considered are e+e- -> t bbar W- / tbar b W+ (which includes e+e- -> t tbar), e+e- -> t tbar Z, and e+e- -> t tbar g* -> t tbar b bar. We use a realistic fast Monte-Carlo detector simulation. Signal events are selected using event shape variables, through jet clustering, and by identifying heavy flavor jets. Assuming a Higgs mass of 120 GeV, polarized electron and positron beams with (Pe-,Pe+) = (-0.8,+0.3), and an integrated luminosity of 1 ab-1, we estimate that the e+e- -> t tbar H events can be seen with a statistical significance of 5.2 sigma, corresponding to the relative top Yukawa coupling measurement accuracy of |Delta g_t / g_t| = 10%.

hep-ph↗

arXiv2010

Proceedings of the ILC Physics Working Group Meeting at KEK in the period from May 2007 to June 2009

The ILC physics working group is a mixture of experimentalists and theorists mainly working in Japan. It has its origin in the previous LC physics study group and has been reformed with the initiative of a JSPS Creative Scientific Research project: "Research and Development of a Novel Detector System for the International Linear Collider". The working group is, however, formally independent of the JSPS project and is open to everybody who is interested in ILC physics. The primary task of the working group is to reexamine the ILC physics in the context of the expected LHC outcome and to further strengthen the physics case for the ILC project. The topics covered in the working group activities range from key measurements such as those of the Higgs self-coupling and the top Yukawa coupling to uncover the secrets of the electroweak symmetry breaking to various new physics scenarios like supersymmetry, large extra dimensions, and other models of terascale physics. The working group has held ten General Meetings in the period of May 2007 to June 2009 to discuss the topics mentioned above. This report ummarizes the progress made in this period and sets a milestone for future developments in ILC physics.

hep-ph↗

arXiv2010

A study of top-quark Yukawa coupling measurement in e+e- -> t tbar H at sqrt(s) = 500 GeV

We report on the feasibility of measuring the top Yukawa coupling in the process: $e^+e^-\to t\bar{t}H$. This measurement is crucial to test the mass generation mechanism for matter particles. Since the cross section for this process attains its maximum around $\sqrt{s}=700 $GeV, most of the past studies were done assuming this energy region. It has been pointed out, however, that the QCD threshold correction enhances the cross section significantly and might enable its measurement at $\sqrt{s}=500 $GeV, which will be accessible already in the first phase of the ILC project. We have implemented this threshold enhancement into our $t\bar{t}H$ event generator and carried out Monte Carlo simulations. Our results show that $t\bar{t}H$ events can be observed with a significance of $4.1\,σ$ with no beam polarization and $5.4 σ$ with the $e^-$ and $e^+$ beam polarization combination: $(-0.8,+0.3)$.

hep-ex↗

arXiv2010

Feasibility study of Higgs pair creation in gamma gamma collider

We studied a feasibility of measuring Higgs boson pair production in a Photon Linear Collider. The optimum energy of gamma gamma collision was estimated with a realistic luminosity distribution. We also discussed simulation study for detecting the signal against W boson pair backgrounds.

hep-ph↗

arXiv2010

KEK GRID for ILC Experiments

The LCG GRID system is the indispensable infrastructure for large scale computing required for ILC experiments. It had been used extensively for ILD LOI studies and its use will be further increased in coming DBD studies. Experiences during the LOI era and plan towards DBD study in KEK are presented.

physics.ins-det↗

arXiv2010

Measurement of Higgs Anomalous Coupling with H->WW* at International Linear Collider

The measurement of the Higgs coupling to W bosons is an important program at the international linear collider (ILC) to search for the anomaly in the coupling to the gauge bosons. We study the sensitivity of ILC to the Higgs anomalous coupling to W bosons by using ZH->vvWW* events. In this article, we report the status of the study.

hep-ph↗

arXiv2010

Feasibility study of the forward-backward asymmetry of the e+e- -> t tbar process in all-hadronic decay modes at sqrt(s) = 500 GeV with the ILD detector

We have studied the measurement accuracy of the forward-backward asymmetry of the $e^+e^- \rightarrow t\bar{t}$ process in the 6-jet mode at $\sqrt{s} = 500$ GeV with the ILD detector. In the analysis the vertex charges of b-jets were used to distinguish t from $\bar{t}$ in each event. The distribution of the cosine of the reconstructed polar angle of so identified t or $\bar{t}$ showed a clear forward-backward asymmetry. After the correction for charge misidentification the forward-backward asymmetry was determined to be $A^t_{FB} = 0.334 \pm 0.0079$ for 500 fb$^{-1}$ with the beam polarization combination of $P(e^+, e^-) = (+30\%, -80\%)$, demonstrating a very good statistical accuracy ($\sim 2\%$) even in the 6-jet mode.

hep-ex↗

arXiv2009

Tau-pair Performance in ILD detectors

Tau-pair process has been analyzed in the ILD detector model as a benchmark process for LoI. Results of background rejection, forward-backward asymmetry and polarization measurements are obtained with full detector simulation. Impact of detector parameters for tau-pair analysis is also discussed in this paper.

hep-ex↗

arXiv2003

How Well Can We Reconstruct the ttbar System Near its Threshold at Future e+e- Linear Colliders?

We developed a new method for full kinematical reconstruction of the ttbar system near its threshold at future linear e+e- colliders. In the core of the method lies likelihood fitting which is designed to improve measurement accuracies of the kinematical variables that specify the final states resulting from ttbar decays. The improvement is demonstrated by applying this method to a Monte-Carlo ttbar sample generated with various experimental effects including beamstrahlung, finite acceptance and resolution of the detector system, etc. In most cases the fit brings a broad non-Gaussian distribution of a given kinematical variable to a nearly Gaussian shape, thereby justifying phenomenological analyses based on simple Gaussian smearing of parton-level momenta. The standard deviations of the resultant distributions of various kinematical variables are given in order to facilitate such phenomenological analyses. A possible application of the kinematical fitting method and its expected impact are also discussed.

hep-ph↗

arXiv2002

Kinematical Reconstruction of the ttbar System Near its Threshold at Future e+e- Linear Colliders

hep-ex↗