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Aoki, T.

Publications and source records attributed to Aoki, T..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Search for third-generation vector-like leptons in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for vector-like leptons in multilepton (two, three, or four-or-more electrons plus muons) final states with zero or more hadronic $τ$-lepton decays is presented. The search is performed using a dataset corresponding to an integrated luminosity of 139 fb -1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. To maximize the separation of signal and background, a machine-learning classifier is used. No excess of events is observed beyond the Standard Model expectation. Using a doublet vector-like lepton model, vector-like leptons coupling to third-generation Standard Model leptons are excluded in the mass range from 130 GeV to 900 GeV at the 95% confidence level, while the highest excluded mass is expected to be 970 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for a new $Z$' gauge boson in 4$μ$ events with the ATLAS experiment

This paper presents a search for a new Z' vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 139 fb -1 . The new gauge boson Z' is predicted by Lμ - Lτ models to address observed phenomena that cannot be explained by the Standard Model. The search examines the four-muon (4μ) final state, using a deep learning neural network classifier to separate the Z' signal from the Standard Model background events. The di-muon invariant masses in the 4μ events are used to extract the Z' resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z' production cross-section times the decay branching fraction of pp → Z'μμ → 4μ are set from 0.31 to 4.3 fb for the Z' mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, g Z' , of the Z' boson to the second and third generation leptons above 0.003 – 0.2 have been excluded.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Inclusive-photon production and its dependence on photon isolation in $pp$ collisions at $\sqrt{s}$ = 13 TeV using 139 fb -1 of ATLAS data

Measurements of differential cross sections are presented for inclusive isolated-photon production in $pp$ collisions at a centre-of-mass energy of 13 TeV provided by the LHC and using 139 -1 fb of data recorded by the ATLAS experiment. The cross sections are measured as functions of the photon transverse energy in different regions of photon pseudorapidity. The photons are required to be isolated by means of a fixed-cone method with two different cone radii. The dependence of the inclusive-photon production on the photon isolation is investigated by measuring the fiducial cross sections as functions of the isolation-cone radius and the ratios of the differential cross sections with different radii in different regions of photon pseudorapidity. The results presented in this paper constitute an improvement with respect to those published by ATLAS earlier: the measurements are provided for different isolation radii and with a more granular segmentation in photon pseudorapidity that can be exploited in improving the determination of the proton parton distribution functions. These improvements provide a more in-depth test of the theoretical predictions. Next-to-leading-order QCD predictions from JETPHOX and SHERPA and next-to-next-to-leading-order QCD predictions from NNLOJET are compared to the measurements, using several parameterisations of the proton parton distribution functions. The measured cross sections are well described by the fixed-order QCD predictions within the experimental and theoretical uncertainties in most of the investigated phase-space region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurements of Zγ +jets differential cross sections in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Differential cross-section measurements of $Zγ$ production in association with hadronic jets are presented, using the full 139 fb -1 dataset of $\sqrt{s}$ = 13 TeV proton–proton collisions collected by the ATLAS detector during Run 2 of the LHC. Distributions are measured using events in which the $Z$ boson decays leptonically and the photon is usually radiated from an initial-state quark. Measurements are made in both one and two observables, including those sensitive to the hard scattering in the event and others which probe additional soft and collinear radiation. Different Standard Model predictions, from both parton-shower Monte Carlo simulation and fixed-order QCD calculations, are compared with the measurements. In general, good agreement is observed between data and predictions from MATRIX and MiNNLO PS , as well as next-to-leading-order predictions from MADGRAPH5_AMC@NLO and SHERPA.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for leptonic charge asymmetry in $t\overline{t}W$ production in final states with three leptons at $\sqrt{s}$ = 13 TeV

A search for the leptonic charge asymmetry (${A}_{c}^{\ell}$) of top-quark-antiquark pair production in association with a $W$ boson ($t\overline{t}W$) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on $\sqrt{s}$= 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN during the years 2015–2018, corresponding to an integrated luminosity of 139 fb –1 . A profile-likelihood fit to the event yields in multiple regions corresponding to positive and negative differences between the pseudorapidities of the charged leptons from top-quark and top-antiquark decays is used to extract the charge asymmetry. At reconstruction level, the asymmetry is found to be –0.12 ± 0.14 (stat.) ± 0.05 (syst.). An unfolding procedure is applied to convert the result at reconstruction level into a charge-asymmetry value in a fiducial volume at particle level with the result of –0.11 ± 0.17 (stat.) ± 0.05 (syst.). The Standard Model expectations for these two observables are calculated using Monte Carlo simulations with next-to-leading-order plus parton shower precision in quantum chromodynamics and including next-to-leading-order electroweak corrections. They are ${–0.084}_{–0.003}^{+0.005}$ (scale) ± 0.006 (MC stat.) and ${–0.063}_{–0.004}^{+0.007}$ (scale) ± 0.004 (MC stat.) respectively, and in agreement with the measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for excited $τ$-leptons and leptoquarks in the final state with $τ$-leptons and jets in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search is reported for excited $τ$-leptons and leptoquarks in events with two hadronically decaying $τ$-leptons and two or more jets. The search uses proton-proton ($pp$) collision data at $\sqrt{s}$ = 13 TeV recorded by the ATLAS experiment during the Run 2 of the Large Hadron Collider in 2015–2018. The total integrated luminosity is 139 fb -1 . The excited $τ$-lepton is assumed to be produced and to decay via a four-fermion contact interaction into an ordinary $τ$-lepton and a quark-antiquark pair. The leptoquarks are assumed to be produced in pairs via the strong interaction, and each leptoquark is assumed to couple to a charm or lighter quark and a $τ$-lepton. No excess over the background prediction is observed. Excited $τ$-leptons with masses below 2.8 TeV are excluded at 95% CL in scenarios with the contact interaction scale Λ set to 10 TeV. At the extreme limit of model validity where Λ is set equal to the excited $τ$-lepton mass, excited $τ$-leptons with masses below 4.6 TeV are excluded. Leptoquarks with masses below 1.3 TeV are excluded at 95% CL if their branching ratio to a charm quark and a $τ$-lepton equals 1. The analysis does not exploit flavour-tagging in the signal region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for long-lived, massive particles in events with displaced vertices and multiple jets in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb –1 of $pp$ collision data collected at $\sqrt{s}$ = 13 TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to longlived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small $R$-parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $m$($\tilde{g}$) = 2.4 TeV gluinos, electroweakinos with $m$($\tilde{χ}_{1}^{0}$) = 1.5 TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of single top-quark production in the s-channel in proton–proton collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A measurement of single top-quark production in the s-channel is performed in proton–proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The dataset corresponds to an integrated luminosity of 139 fb –1 . The analysis is performed on events with an electron or muon, missing transverse momentum and exactly two $b$-tagged jets in the final state. A discriminant based on matrix element calculations is used to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and $W$-boson production in association with jets. The observed (expected) signal significance over the background-only hypothesis is 3.3 (3.9) standard deviations, and the measured cross-section is $σ$ = ${8.2}_{-2.9}^{+3.5}$ pb, consistent with the Standard Model prediction of $σ^{SM}$ = ${10.32}_{–0.36}^{+0.40}$ pb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the $t\overline{t}$ production cross-section in pp collisions at √s = 5.02 TeV with the ATLAS detector

The inclusive top-quark pair tt production cross-section σ tt is measured in proton–proton collisions at a centre-of-mass energy $\sqrt{s}$ = 5.02 TeV, using 257 pb -1 of data collected in 2017 by the ATLAS experiment at the LHC. The $t\overline{t}$ cross-section is measured in both the dilepton and single-lepton final states of the $t\overline{t}$ system and then combined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of electroweak $Z\left(\nu \overline{\nu}\right)\gamma jj$ production and limits on anomalous quartic gauge couplings in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

The electroweak production of $Z\left(\nu \overline{\nu}\right)\gamma jj$ in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton–proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb –1 collected by the ATLAS detector during the 2015–2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial $Z\left(\nu \overline{\nu}\right)\gamma jj$ cross section for electroweak production is measured to be ${0.77}_{-0.30}^{+0.34}$ fb and is consistent with the Standard Model prediction. Evidence of electroweak $Z\left(\nu \overline{\nu}\right)\gamma jj$ production is found with an observed significance of 3.2σ for the background-only hypothesis, compared with an expected significance of 3.7σ. The combination of this result with the previously published ATLAS observation of electroweak $Z\left(\nu \overline{\nu}\right)\gamma jj$ production yields an observed (expected) signal significance of 6.3σ (6.6σ). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

A search for new resonances in multiple final states with a high transverse momentum Z boson in $\sqrt{s} $ = 13 TeV pp collisions with the ATLAS detector

A generic search for resonances is performed with events containing a Z boson with transverse momentum greater than 100 GeV, decaying into e + e – or μ + μ – . The analysed data collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider correspond to an integrated luminosity of 139 fb –1 . Two invariant mass distributions are examined for a localised excess relative to the expected Standard Model background in six independent event categories (and their inclusive sum) to increase the sensitivity. No significant excess is observed. Exclusion limits at 95% confidence level are derived for two cases: a model-independent interpretation of Gaussian-shaped resonances with the mass width between 3% and 10% of the resonance mass, and a specific heavy vector triplet model with the decay mode W' → ZW → ℓℓqq.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for heavy resonances decaying into a Z or W boson and a Higgs boson in final states with leptons and b -jets in 139 fb –1 of pp collisions at $ \sqrt{s} $ = 13 TeV with the ATLAS detector

This article presents a search for new resonances decaying into a Z or W boson and a 125 GeV Higgs boson h, and it targets the $ν\bar{ν}b\bar{b}, l^{+} l^{-} b\bar{b}$, or $ll^{±} νb\bar{b}$ final states, where $\ell$ = e or µ, in proton-proton collisions at $\sqrt{s}$ = 13 TeV. The data used correspond to a total integrated luminosity of 139 fb –1 collected by the ATLAS detector during Run 2 of the LHC at CERN. The search is conducted by examining the reconstructed invariant or transverse mass distributions of Zh or W h candidates for evidence of a localised excess in the mass range from 220 GeV to 5 TeV. No significant excess is observed and 95% confidence-level upper limits between 1.3 pb and 0.3 fb are placed on the production cross section times branching fraction of neutral and charged spin-1 resonances and CP-odd scalar bosons. These limits are converted into constraints on the parameter space of the Heavy Vector Triplet model and the two-Higgs-doublet model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the total and differential Higgs boson production cross-sections at $ \sqrt{s} $ = 13 TeV with the ATLAS detector by combining the H → ZZ* → 4ℓ and H → γγ decay channels

The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H → ZZ* → 4ℓ and H → γγ decay channels. The results are based on a dataset of 139 fb –1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is $55.5$$^{+4.0}_{–3.8}$ pb, consistent with the Standard Model prediction of 55.6 ± 2.5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H → bb¯ and cc¯ decay channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1994

Characteristics of the persistent emission of SGR 1806-20

Earlier, using the X-ray satellite ASCA, we had identified the soft gamma-ray burst repeater (SGR) 1806-20 with a persistent X-ray source, AX 1805.7-2025 which is located close to the center of the radio supernova remnant G10.0-0.3. A burst seen by Burst and Transient Source Experiment (BATSE) was shown to be centered on G10.0-0.3. Here we report detailed temporal and spectral analysis of the persistent source. We find that AX 1805.7-2025 is a very compact source, size less than 30 sec in diameter, with a power-law spectrum. The count rate from AX 1805.7-2025 is steady on timescales of minutes, days, and 1 week. Most supernova remnants have extended X-ray emission ascribed to shocked gas. We set an upper limit to an extended X-ray emission both in continuum and line emission. We conclude that an isolated neutron star, most likely a pulsar, powers the radio remnant G10.0-0.3. Finally, we note that the persistent spectrum appears to be less absorbed than the burst spectrum.

Sonobe, T.↗
NASA NTRS1994

Joint IAMAS/IAHS Symposium J1 on Global Monitoring and Advanced Observing Techniques in the Atmosphere and Hydrosphere

Seventy papers were presented at the two-and-a-half-day Symposium on Global Monitoring and Advanced Observing Techniques in the Atmosphere and Hydrosphere. The symposium was jointly organized by the International Association of Meteorology and Atmospheric Sciences (IAMAS) and the International Association of Hydrological Sciences (IAHS). Global observing systems are receiving increased attention in connection with such problems as monitoring global climate change. The symposium included papers on observational requirements; measurement methodologies; descriptions of available datasets; results of analysis of observational data; plans for future observing systems, including the Global Climate Observing System (GCOS) and the Global Ocean Observing System (GOOS); and the programs and plans of the space agencies.

Ohring, G.↗
NASA NTRS1992

Mosaic CCD method: A new technique for observing dynamics of cometary magnetospheres

On April 29, 1990, the plasma tail of Comet Austin was observed with a CCD camera on the 105-cm Schmidt telescope at the Kiso Observatory of the University of Tokyo. The area of the CCD used in this observation is only about 1 sq cm. When this CCD is used on the 105-cm Schmidt telescope at the Kiso Observatory, the area corresponds to a narrow square view of 12 ft x 12 ft. By comparison with the photograph of Comet Austin taken by Numazawa (personal communication) on the same night, we see that only a small part of the plasma tail can be photographed at one time with the CCD. However, by shifting the view on the CCD after each exposure, we succeeded in imaging the entire length of the cometary magnetosphere of 1.6 x 10(exp 6) km. This new technique is called 'the mosaic CCD method'. In order to study the dynamics of cometary plasma tails, seven frames of the comet from the head to the tail region were twice imaged with the mosaic CCD method and two sets of images were obtained. Six microstructures, including arcade structures, were identified in both the images. Sketches of the plasma tail including microstructures are included.

Saito, T.↗
NASA NTRS1985

A new ultra high energy gamma ray telescope at Ohya mine

The search for ultra high energy gamma rays coming from point sources is one of the main experimental aims. A fast air shower timing system was constructed at ICRR for the study of the angular resolution of the system and operated approximately half a year. The characteristics of the surface array of Ohya air shower telescope is described.

Aoki, T.↗