arXiv subjects

K. Fujii

Publications and source records attributed to K. Fujii.

At least 37 records · Page 2Linked to original sources

arXiv2016

Top physics at high-energy lepton colliders

A summary is presented of the workshop "top physics at linear colliders" that was held at IFIC Valencia from the 30th of June to the 3rd July 2015. We present an up-to-date status report of studies into the potential for top quark physics of lepton colliders with an energy reach that exceeds the top quark pair production threshold, with a focus on the linear collider projects ILC and CLIC. This summary shows that such projects can offer very competitive determinations of top quark properties (mass, width) and its interactions with other Standard Model particles, in particular electroweak gauge bosons and the Higgs boson. In both areas the prospects exceed the LHC potential significantly - often by an order of magnitude.

hep-ex↗

arXiv2016

The two molecular clouds in RCW 38; evidence for formation of the youngest super star cluster in the Milky Way triggered by cloud-cloud collision

We present distributions of two molecular clouds having velocities of 2 km s$^{-1}$ and 14 km s$^{-1}$ toward RCW 38, the youngest super star cluster in the Milky Way, in the $^{12}$CO ($J=$1--0 and 3--2) and $^{13}$CO ($J=$1--0) transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the $J$=3--2 emission to the $J$=1--0 emission, the bridging feature connecting the two clouds in velocity and their morphological correspondence with the infrared dust emission. The total mass of the clouds and the cluster is too small to gravitationally bind the velocity difference. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the $\sim$20 candidate O stars which are localized within $\sim$0.3 pc of the cluster center in the 2 km s$^{-1}$ cloud. We suggest that the collision is currently continuing toward part of the 2 km s$^{-1}$ cloud where the bridging feature is localized. This is the third super star cluster alongside of Westerlund2 and NGC3603 where cloud-cloud collision triggered the cluster formation. RCW38 is the most remarkable and youngest cluster, holding a possible sign of on-going O star formation, and is the most promising site where we may be able to witness the moment of O-star formation.

astro-ph.SR↗

arXiv2016

Model independence of the measurement of the e+e- -> ZH cross section using Z->μ+μ- and Z->e+e- at the ILC

The model independent measurement of the absolute ZH cross section of the Higgsstrahlung process e+e- -> ZH is an unique measurement at the ILC indispensable for measuring the Higgs couplings and their deviations from the Standard Model in order to identify new physics models. The performance in measuring the ZH cross section using events in which the Higgs boson recoils against a Z boson which decays into a pair of muons or electrons has been demonstrated based on full simulation of the ILD detector for three center of mass energies 250, 350, and 500 GeV, and two beam polarizations (Pe-,Pe+) =(-80%, +30%) and (+80%, -30%). This paper demonstrates in detail that the analysis which achieved these results are model independent to the sub-percent level. Data selection methods are designed to optimize the precisions of the ZH cross section and at the same time minimize the bias on the measured due to discrepancy in signal efficiencies among Higgs decay modes. Under conservative assumptions which take into account unknown Higgs decay modes, the relative bias on the ZH cross section is shown to be smaller than 0.2% for all center-of-mass energies, which is five times below even the smallest ZH cross section statistical uncertainties expected from the leptonic recoil measurements in a full 20 years ILC physics program.

hep-ph↗

arXiv2015

500 GeV ILC Operating Scenarios

The ILC Technical Design Report documents the design of a 500 GeV linear collider, but does not specify the center-of-mass energy steps of operation for the collider. The ILC Parameters Joint Working Group has studied possible running scenarios, including a realistic estimate of the real time accumulation of integrated luminosity based on ramp-up and upgrade processes, and considered the evolution of the physics outcomes. These physics goals include Higgs precision measurements, top quark measurements and searches for new physics. We present an "optimized" operating scenario and the anticipated evolution of the precision of the ILC measurements.

hep-ex↗

arXiv2015

Physics at the e+ e- Linear Collider

A comprehensive review of physics at an e+e- Linear Collider in the energy range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC results, experiments from low energy as well as astroparticle physics.The report focuses in particular on Higgs boson, Top quark and electroweak precision physics, but also discusses several models of beyond the Standard Model physics such as Supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analyzed as well.

hep-ph↗

arXiv2015

ILC Operating Scenarios

The ILC Technical Design Report documents the design for the construction of a linear collider which can be operated at energies up to 500 GeV. This report summarizes the outcome of a study of possible running scenarios, including a realistic estimate of the real time accumulation of integrated luminosity based on ramp-up and upgrade processes. The evolution of the physics outcomes is emphasized, including running initially at 500 GeV, then at 350 GeV and 250 GeV. The running scenarios have been chosen to optimize the Higgs precision measurements and top physics while searching for evidence for signals beyond the standard model, including dark matter. In addition to the certain precision physics on the Higgs and top that is the main focus of this study, there are scientific motivations that indicate the possibility for discoveries of new particles in the upcoming operations of the LHC or the early operation of the ILC. Follow-up studies of such discoveries could alter the plan for the centre-of-mass collision energy of the ILC and expand the scientific impact of the ILC physics program. It is envisioned that a decision on a possible energy upgrade would be taken near the end of the twenty year period considered in this report.

hep-ex↗

arXiv2015

Revealing the Large-Scale Structures of Interstellar Gas Associated with the Magellanic SNR N132D

We report preliminary results of large-scale distribution toward the Magellanic supernova remnant N132D using Mopra and Chandra archival datasets. We identified a cavity-like CO structure along the X-ray shell toward the southern half of it. The total mass of associating molecular gas is $\sim10^4 M_\odot$, which is smaller than the previous study by an order of magnitude. Further observations using ALMA, ASTE, and Mopra will reveal the detailed spatial structures and its physical conditions.

astro-ph.GA↗

arXiv2014

Measurement and analysis of the Am-243 neutron capture cross section at the n_TOF facility at CERN

Background:The design of new nuclear reactors and transmutation devices requires to reduce the present neutron cross section uncertainties of minor actinides. Purpose: Reduce the $^{243}$Am(n,$γ$) cross section uncertainty. Method: The $^{243}$Am(n,$γ$) cross section has been measured at the n_TOF facility at CERN with a BaF$_{2}$ Total Absorption Calorimeter, in the energy range between 0.7 eV and 2.5 keV. Results: The $^{243}$Am(n,$γ$) cross section has been successfully measured in the mentioned energy range. The resolved resonance region has been extended from 250 eV up to 400 eV. In the unresolved resonance region our results are compatible with one of the two incompatible capture data sets available below 2.5 keV. The data available in EXFOR and in the literature has been used to perform a simple analysis above 2.5 keV. Conclusions: The results of this measurement contribute to reduce the $^{243}$Am(n,$γ$) cross section uncertainty and suggest that this cross section is underestimated up to 25% in the neutron energy range between 50 eV and a few keV in the present evaluated data libraries.

nucl-ex↗

arXiv2014

Search for bosonic superweakly interacting massive dark matter particles with the XMASS-I detector

Bosonic superweakly interacting massive particles (super-WIMPs) are a candidate for warm dark matter. With the absorption of such a boson by a xenon atom these dark matter candidates would deposit an energy equivalent to their rest mass in the detector. This is the first direct detection experiment exploring the vector super-WIMPs in the mass range between 40 and 120 keV. Using 165.9 days of data no significant excess above background was observed in the fiducial mass of 41 kg. The present limit for the vector super-WIMPs excludes the possibility that such particles constitute all of dark matter. The absence of a signal also provides the most stringent direct constraint on the coupling constant of pseudoscalar super-WIMPs to electrons. The unprecedented sensitivity was achieved exploiting the low background at a level $10^{-4}$ kg$^{-1}$keV$_{ee}^{-1}$day$^{-1}$ in the detector.

astro-ph.CO↗

arXiv2014

Search for inelastic WIMP nucleus scattering on $^{129}$Xe in data from the XMASS-I experiment

A search for inelastic scattering of Weakly Interacting Massive Particles (WIMPs) on the isotope $^{129}$Xe was done in data taken with the single phase liquid xenon detector XMASS at the Kamioka Observatory. Using a restricted volume containing 41 kg of LXe at the very center of our detector we observed no significant excess of events in 165.9 days of data. Our background reduction allowed us to derive our limits without explicitly subtracting the remaining events which are compatible with background expectations and derive for e.g. a 50 GeV WIMP an upper limit for its inelastic cross section on $^{129}$Xe nuclei of 3.2 pb at the 90% confidence level.

astro-ph.CO↗

arXiv2014

Cosmic ray tests of a GEM-based TPC prototype operated in Ar-CF4-isobutane gas mixtures: II

The spatial resolution along the pad-row direction was measured with a GEM-based TPC prototype for the future linear collider experiment in order to understand its performance for tracks with finite projected angles with respect to the pad-row normal. The degradation of the resolution due to the angular pad effect was confirmed to be consistent with the prediction of a simple calculation taking into account the cluster-size distribution and the avalanche fluctuation.

physics.ins-det↗

arXiv2014

Activity report of ILD-TPC Asia group

The purpose of ILD-TPC Asia group is realization of high precision Time Projection Chamber (TPC) with Gas Electron Multiplier (GEM) as a central tracker in International Linear Collider (ILC). We have been studying the many R&D items to build the real detector as a member of LCTPC collaboration. This paper describes the our efforts for realization of the ILD-TPC, the result of test beam using large prototype TPC, local field distortion, positive ion effects and gate devices, and cooling electronics which are key items to build ILD-TPC.

physics.ins-det↗

arXiv2014

Higgs Working Group Report of the Snowmass 2013 Community Planning Study

This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $CP$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Our report includes projections of measurement capabilities from detailed studies of the Compact Linear Collider (CLIC), a Gamma-Gamma Collider, the International Linear Collider (ILC), the Large Hadron Collider High-Luminosity Upgrade (HL-LHC), Very Large Hadron Colliders up to 100 TeV (VLHC), a Muon Collider, and a Triple-Large Electron Positron Collider (TLEP).

hep-ex↗

arXiv2013

Search for solar axions in XMASS, a large liquid-xenon detector

XMASS, a low-background, large liquid-xenon detector, was used to search for solar axions that would be produced by bremsstrahlung and Compton effects in the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent limit on the coupling for mass $\ll$ 1keV is $|g_{aee}|< 5.4\times 10^{-11}$ (90% C.L.), which is a factor of two stronger than the existing experimental limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are 1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced the most stringent limit, which is better than that previously derived from astrophysical arguments regarding the Sun to date.

astro-ph.CO↗

arXiv2013

Light WIMP search in XMASS

A search for light dark matter using low-threshold data from the single phase liquid xenon scintillation detector XMASS, has been conducted. Using the entire 835 kg inner volume as target, the analysis threshold can be lowered to 0.3 keVee (electron-equivalent) to search for light dark matter. With low-threshold data corresponding to a 5591.4 kg$\cdot$day exposure of the detector and without discriminating between nuclear-recoil and electronic events, XMASS excludes part of the parameter space favored by other experiments.

astro-ph.CO↗

arXiv2013

XMASS detector

The XMASS project aims to detect dark matter, pp and $^{7}$Be solar neutrinos, and neutrinoless double beta decay using ultra pure liquid xenon. The first phase of the XMASS experiment searches for dark matter. In this paper, we describe the XMASS detector in detail, including its configuration, data acquisition equipment and calibration system.

physics.ins-det↗

arXiv2011

Scintillation-only Based Pulse Shape Discrimination for Nuclear and Electron Recoils in Liquid Xenon

In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7\pm1.1(stat)\pm1.2 0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee and to 7.7\pm2.8(stat)\pm2.5 2.8(sys)\times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4\pm0.2(stat)\pm0.3 0.2(sys)\times10-1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.

physics.ins-det↗

arXiv2010

An accurate determination of the Avogadro constant by counting the atoms in a 28Si crystal

The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by "counting" the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, 6.02214084(18) x 10^23 mol^-1, is the most accurate input datum for a new definition of the kilogram.

physics.atom-ph↗