arXiv subjects

Keisuke Fujii

Publications and source records attributed to Keisuke Fujii.

338 records · Page 19Linked to original sources

arXiv2009

Simulation study of ZHAH mode in Littlest Higgs Model with T-Parity

We investigate a possibility to measure parameters of the Littlest Higgs model with T-parity at the ILC with sqrt(s) = 500 GeV. The model predicts new gauge bosons (AH, ZH, and WH), among which the heavy photon (AH) is a candidate for dark matter. Through Monte Carlo simulations of the process of e+ e- -> AH ZH, we show that the masses can be determined with accuracies of 16.2% for m_AH and 4.3% for m_ZH. In additionally, the vacuum expectation value can be determined with accuracies of 4.3%.

hep-ph↗

arXiv2008

Entanglement Purification with Double Selection

We investigate efficient entanglement purification through double selection process. This method works with higher noise thresholds for the communication channels and local operations, and achieves higher fidelity of purified states. Furthermore it provides a yield comparable to the usual protocol with single selection. It is shown by general considerations that the double selection is optimal to remove the first-order errors, achieving the upper bound on the fidelity of purified states in the low noise regime. The double selection is also applied to purification of multi-partite entanglement such as two-colorable graph states.

quant-ph↗

arXiv2008

A Handy Tool for History Keeping of Geant4 Tracks -- J4HistoryKeeper --

The Particle Flow Analysis (PFA) is currently under intense studies as the most promising way to achieve precision jet energy measurements required at the future linear $e^+e^-$ collider. In order to optimize detector configurations and to tune up the PFA it is crucial to identify factors that limit the PFA performance and clarify the fundamental limits on the jet energy resolution that remain even with the perfect PFA and an infinitely granular calorimeter. This necessitates a tool to connect each calorimeter hit in particle showers to its parent charged track, if any, and eventually all the way back to its corresponding primary particle, while identifying possible interactions and decays along the way. In order to realize this with a realistic memory space, we have developed a set of C++ classes that facilitates history keeping of particle tracks within the framework of Geant4. This software tool, hereafter called J4HistoryKeeper, comes in handy in particular when one needs to stop this history keeping for memory space economy at multiple geometrical boundaries beyond which a particle shower is expected to start. In this paper this software tool is described and applied to a generic detector model to demonstrate its functionality.

physics.comp-ph↗

arXiv2008

Hidden particle production at the ILC

In a class of new physics models, new physics sector is completely or partly hidden, namely, singlet under the Standard Model (SM) gauge group. Hidden fields included in such new physics models communicate with the Standard Model sector through higher dimensional operators. If a cutoff lies in the TeV range, such hidden fields can be produced at future colliders. We consider a scalar filed as an example of the hidden fields. Collider phenomenology on this hidden scalar is similar to that of the SM Higgs boson, but there are several features quite different from those of the Higgs boson. We investigate productions of the hidden scalar at the International Linear Collider (ILC) and study the feasibility of its measurements, in particular, how well the ILC distinguishes the scalar from the Higgs boson, through realistic Monte Carlo simulations.

hep-ex↗

arXiv2008

Fault-tolerant quantum computation in concatenation of verified cluster states

A novel scheme is presented for fault-tolerant quantum computation based on the cluster model. Some relevant logical cluster states are constructed in concatenation by post-selection through verification, without necessity of recovery operation, where a suitable code such as the Steane's 7-qubit code is adopted for transversal operations. This simple concatenated construction of verified cluster states achieves a high noise threshold ~1%, and restrains the divergence of resources.

quant-ph↗

arXiv2007

A Handy Tool for History Keeping of Geant4 Tracks and its Application to Studies of Fundamental Limits on PFA Performance

It is widely recognized that good jet energy resolution is one of the most important requirements to the detectors for the future linear $e^+e^-$ collider experiments. The Particle Flow Analysis (PFA) is currently under intense studies as the most promising way to achieving the best attainable resolution. In order to clarify the fundamental limits on the jet energy resolution with the PFA, we have developed a set of C++ classes that facilitates history keeping of particle tracks within the framework of Geant4. In this paper this software tool is described and applied to a generic detector model so as to identify fundamental limiting factors to the PFA performance.

physics.comp-ph↗

arXiv2006

Fault-tolerant Quantum Computation with Highly Verified Logical Cluster States

We investigate a scheme of fault-tolerant quantum computation based on the cluster model. Logical qubits are encoded by a suitable code such as the Steane's 7-qubit code. Cluster states of logical qubits are prepared by post-selection through verification at high fidelity level, where the unsuccessful ones are discarded without recovery operation. Then, gate operations are implemented by transversal measurements on the prepared logical cluster states. The noise threshold is improved significantly by making the high fidelity preparation and transversal measurement. It is estimated to be about 3% by a numerical simulation.

quant-ph↗

arXiv2005

Mass and Cross-section Measurements of Chargino at Linear Colliders in Large tan(beta) Case

The lighter chargino pair production ($e^+e^- \to \tildeχ^{+}_{1} \tildeχ^{-}_{1}$) is one of key processes for determination of supersymmetric parameters at a linear collider. If $\tanβ$ is a large value, the lighter stau ($\tildeτ^{\pm}_{1}$) might be lighter than the $\tildeχ^{\pm}_{1}$, while the other sleptons stay heavier. This case leads a cascade decay, $\tildeχ^{\pm}_{1} \to \tildeτ^{\pm}_{1} ν_τ$ followed by $\tildeτ^{\pm}_{1} \to \tildeχ^{0}_{1} τ^{\pm}$, where $\tildeχ^{0}_{1}$ is the lightest supersymmetric particle. This paper addresses to what extent this cascade decay may affect the measurements of the chargino mass and its production cross section.

hep-ph↗

arXiv2004

Higgs pair production at a linear e+e- collider in models with large extra dimensions

In this paper, we will derive the cross section formula for the Higgs pair production at a linear $e^+e^-$ collider in models with large extra dimensions and study the feasibility of its measurement through realistic Monte Carlo simulations. Since the process has essentially no Standard Model background, once produced, it will provide us with a very clean signature of physics beyond the Standard Model. Moreover, since the final state particles are spinless, the spin 2 of the intermediate virtual KK gravitons has to be conserved by the orbital angular momentum of the Higgs pair. This results in a very characteristic angular distribution of the final states. Taking into account finite detector acceptance and resolutions as well as initial state radiation and beamstrahlung, we demonstrate in this paper that, given a sufficiently high center of mass energy, the angular distribution of the Higgs pair is indeed measurable at the linear collider and will allow us to prove the spin 2 nature of the KK gravitons exchanged in the s-channel.

hep-ex↗

arXiv2003

Development of a Geant4 Solid for Stereo Mini-jet Cells in a Cylindrical Drift Chamber

Stereo mini-jet cells will be indispensable components of a future $e^+e^-$ linear collider central tracker such as JLC-CDC. There is, however, no official Geant4 solid available at present to describe such geometrical objects, which had been a major obstacle for us to develop a full Geant4-based simulator with stereo cells built in. We have thus extended Geant4 to include a new solid ({\tt TwistedTubs}), which consists of three kinds of surfaces: two end planes, inner and outer hyperboloidal surfaces, and two so-called twisted surfaces that make slant and twisted $ϕ$-boundaries. Design philosophy and its realization in the Geant4 framework are described together with algorithmic details. We have implemented stereo cells with the new solid, and tested them using geantinos and Pythia events ($e^{+}e^{-}\to ZH$ at $\sqrt{s} = 350 {\rm GeV}$). The performance was found reasonable: the stereo cells consumed only 25% more CPU time than ordinary axial cells.

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↗

arXiv1996

Confronting the Minimal Supersymmetric Standard Model with the Study of Scalar Leptons at Future Linear e+e- Colliders

Sleptons can easily be found at future linear e+e- colliders if kinematically accessible. Measurements of their masses and decay distributions would then determine MSSM parameters. This paper presents a detailed MC study of the production and decay of the lighter scalar tau lepton, stau1. We found that mstau1 and the left-right mixing angle of stau would be measured within an error of a few percent. tanbeta is determinable in some region of the parameter space through simultaneous studies of stau1-and selectron-pair production: the polarization measurement of the tau leptons from stau1 decays and the M1, mchi1 determination using selectron pair production and decay. We also point out the possibility to determine bino-selectron-e coupling through the measurement of the angular distribution of the selectron-pair production. The error on the coupling is expected to be comparable to its typical SUSY radiative correction, which is proportional to log(msquark/mslepton). The radiative correction affects M1 and tanbeta determination, necessitating the full 1-loop radiative correction to the selectron production processes. The implication of these measurements of the MSSM parameters on selecting models of the origin of supersymmetry breaking is also discussed.

hep-ph↗

arXiv1995

Precision Study of MSSM at future $e^+e^-$ linear colliders

The lighter scalar tau lepton $\sti$ may be the lightest scalar lepton and therefore would be found earlier in future collider experiments. We point out the impact of the measurement of the mass and the mixing angle of $\st$ to discriminate the models of SUSY breaking. Furthermore, the measurement of the polarization of $τ$ lepton($P_τ$) from the decaying $\sti$ helps to determine the Yukawa sector of minimal supersymmetric standard model. We present our MC study of the production and the decay of $\sti$ lepton at a future linear collider at $\sqrt{s}=500$ GeV. The mass, mixing angle of $\sti$ and $P_τ(\sti\rightarrowτχ_1^0)$ would be measured precisely at the future LC. ( talks given at Yukawa International Seminar(YIKS) '95 on some very hot and humid day in August, and also at Workshop on {\it Physics and Experiments with Linear $e^+e^-$ Colliders} Appi, Iwate Japan Sep.8-12 1995.)

hep-ph↗