Engineering topics

Aoki, T. (ORCID:0000000266185170)

Publications and source records attributed to Aoki, T. (ORCID:0000000266185170).

86 records · Page 5

DOE OSTI2023

Measurement of exclusive pion pair production in proton–proton collisions at $\sqrt{s}={7}\,\text {TeV}$ with the ATLAS detector

The exclusive production of pion pairs in the process $pp$ → $pp π$ + $π$ - has been measured at $\sqrt{s}={7}\,\text {TeV}$ with the ATLAS detector at the LHC, using $80 µb$ -1 of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This rep resents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the pro ton momenta, the pion rapidities and transverse momenta, and the pion–pion invariant mass. Cross-section values of $4.8 ± 1.0$ ${(stat)}^{+0.3}_{-0.2}$ $(syst) µ b$ and $9 ± 6$ ${(stat)}^{+2}_{-2}$ $(syst) µ b$ are obtained in the two regions; they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for supersymmetry in final states with missing transverse momentum and three or more b-jets in 139 fb$^{-1}$ of proton–proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

A search for supersymmetry involving the pair production of gluinos decaying via off-shell third-generation squarks into the lightest neutralino ($\tilde {χ}_{1}^{0}$) is reported. It exploits LHC proton–proton collision data at a centre-of mass energy $\sqrt{s} = 13$ TeV with an integrated luminosity of 139 fb -1 collected with the ATLAS detector from 2015 to 2018. The search uses events containing large missing transverse momentum, up to one electron or muon, and several energetic jets, at least three of which must be identified as containing b-hadrons. Both a simple kinematic event selection and an event selection based upon a deep neural network are used. No significant excess above the predicted background is found. In simplified models involving the pair production of gluinos that decay via off-shell top (bottom) squarks, gluino masses less than 2.44 TeV (2.35 TeV) are excluded at 95% CL for a massless $\tilde {χ}_{1}^{0}$. Limits are also set on the gluino mass in models with variable branching ratios for gluino decays to $b$$\overline{b}$$\tilde {χ}_{1}^{0}$, $t$$\overline{t}$$\tilde {χ}_{1}^{0}$ and $t$$\overline{b}$$\tilde {χ}_{1}^{-}$ / $t$$\overline{b}$$\tilde {χ}_{1}^{+}$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of the CP properties of Higgs boson interactions with $\tau$-leptons with the ATLAS detector

A study of the charge conjugation and parity ($CP$) properties of the interaction between the Higgs boson and $\tau$-leptons is presented. The study is based on a measurement of $CP$-sensitive angular observables defined by the visible decay products of $\tau$-leptons produced in Higgs boson decays. The analysis uses 139 fb -1 of proton–proton collision data recorded at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider. Contributions from $\tau$-violating interactions between the Higgs boson and $\tau$-leptons are described by a single mixing angle parameter Φ $\tau$ in the generalised Yukawa interaction. Without constraining the $H$ $\rightarrow$ $\tau$$\tau$ signal strength to its expected value under the Standard Model hypothesis, the mixing angle Φ $\tau$ is measured to be 9° ± 16°, with an expected value of 0° ± 28° at the 68% confidence level. The pure $CP$-odd hypothesis is disfavoured at a level of 3.4 standard deviations. The results are compatible with the predictions for the Higgs boson in the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of $Z\gamma \gamma$ production in pp collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

Cross-sections for the production of a $Z$ boson in association with two photons are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb -1 recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the $Z$ boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated $Z$($\rightarrow$ $\ell$$\ell$)$\gamma \gamma$ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $Z\gamma \gamma$ system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment

A measurement of the charge asymmetry in top-quark pair ($t\bar{t}$) production in association with a photon is presented. The measurement is performed in the single-lepton $t\bar{t}$ decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb –1 . The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be A C =–0.003 ± 0.029 in agreement with the Standard Model expectation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for Higgs boson pair production in association with a vector boson in pp collisions at $\sqrt{s}=13\,\text {TeV}$ with the ATLAS detector

This paper reports a search for Higgs boson pair (hh) production in association with a vector boson ($W\; {\text {o}r}\; Z$) using 139 fb –1 of proton–proton collision data at $\sqrt{s}=13\,\text {TeV}$ recorded with the ATLAS detector at the Large Hadron Collider. The search is performed in final states in which the vector boson decays leptonically ($W\rightarrow \ell \nu ,\, Z\rightarrow \ell \ell ,\nu \nu$ with $\ell =e, \mu$) and the Higgs bosons each decay into a pair of b-quarks. It targets Vhh signals from both non-resonant hh production, present in the Standard Model (SM), and resonant hh production, as predicted in some SM extensions. A 95% confidence-level upper limit of 183 (87) times the SM cross-section is observed (expected) for non-resonant Vhh production when assuming the kinematics are as expected in the SM. Constraints are also placed on Higgs boson coupling modifiers. For the resonant search, upper limits on the production cross-sections are derived for two specific models: one is the production of a vector boson along with a neutral heavy scalar resonance H, in the mass range 260–1000 GeV, that decays into hh, and the other is the production of a heavier neutral pseudoscalar resonance A that decays into a Z boson and H boson, where the A boson mass is 360–800 GeV and the H boson mass is 260–400 GeV. Constraints are also derived in the parameter space of two-Higgs-doublet models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of the Higgs boson mass in the H → ZZ*→ 4ℓ decay channel using 139 fb –1 of s = 13 TeV pp collisions recorded by the ATLAS detector at the LHC

The mass of the Higgs boson is measured in the H→ZZ * →4ℓ decay channel. The analysis uses proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb –1 . The measured value of the Higgs boson mass is 124.99 ± 0.18(stat.) ± 0.04(syst.) GeV. In final states with muons, this measurement benefits from an improved momentum-scale calibration relative to that adopted in previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass of 124.94 ± 0.17(stat.) ± 0.03(syst.) GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Observation of four-top-quark production in the multilepton final state with the ATLAS detector

This paper presents the observation of four-top-quark ($t$$\overline{t}$$t$$\overline{t}$) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 fb -1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured $t$$\overline{t}$$t$$\overline{t}$ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The $t$$\overline{t}$$t$$\overline{t}$ production cross section is measured to be ${22.5}^{+6.6}_{-5.5}$, consistent with the SM prediction of 12.0 ± 2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect $t$$\overline{t}$$t$$\overline{t}$ production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using $pp$ collisions at $\sqrt{s}$ = 13 TeV

Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the $b\overline{b}$$b\overline{b}$, $b\overline{b}$$τ^+$$τ^–$ and $b\overline{b}$$γγ$ decay channels with single-Higgs boson analyses targeting the $γγ$, $\overline{Z}$$\overline{Z}$$^*$, $WW^*$, $τ^+$$τ^–$ and $b\overline{b}$ decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at $\sqrt{s}$ = 13 TeV and correspond to an integrated luminosity of 126–139 fb –1 . The combination of the double-Higgs analyses sets an upper limit of $μ_{HH}$ < 2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling ($λ_{HHH}$), values outside the interval –0.4 < $κ_λ$ = ($λ_{HHH}$/${λ}_{HHH}^{SM}$) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and doubleHiggs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes –1.4 < $κ_λ$ < 6.1 at 95% CL.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Observation of gauge boson joint-polarisation states in W ± Z production from pp collisions at s = 13 TeV with the ATLAS detector

Measurements of joint-polarisation states of W and Z gauge bosons in W ± Z production are presented. The data set used corresponds 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 CERN Large Hadron Collider. The W ± Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The simultaneous pair-production of longitudinally polarised vector bosons is measured for the first time with a significance of 7.1 standard deviations. The measured joint helicity fractions integrated over the fiducial region are $f$ 00 = 0.067 ± 0.010, $f$ 0T = 0.110 ± 0.029, $f$ T0 = 0.179 ± 0.023 and $f$ TT = 0.644 ± 0.032, in agreement with the next-to-leading-order Standard Model predictions. Individual helicity fractions of the W and Z bosons are also measured and found to be consistent with joint helicity fractions within the expected amounts of correlation. Both the joint and individual helicity fractions are also measured separately in W + Z and W - Z events. Inclusive and differential cross sections for several kinematic observables sensitive to polarisation are presented.

43 PARTICLE ACCELERATORS↗

DOE OSTI2023

Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at $\sqrt{s}$ = $13$ TeV with the ATLAS experiment

A measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of $\sqrt{s}$ = $13$ TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb -1 . The measurement is performed selecting $t$$\overline{t}$ events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos$⁡θ$* variable, where $θ$* is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos⁡θ* angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be $f$ 0 = 0.684 ± 0.005 (stat.) ± 0.014 (syst.), $f$ L = 0.318 ± 0.003 (stat.) ± 0.008 (syst.) and $f$ R = -0.002 ± 0.002 (stat.) ± 0.014 (syst.), in agreement with the Standard Model prediction.

43 PARTICLE ACCELERATORS↗

DOE OSTI2023

Measurement of the total cross section and $\rho$-parameter from elastic scattering in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

In a special run of the LHC with β* = 2.5 km, proton–proton elastic-scattering events were recorded at $\sqrt{s}=13$ TeV with an integrated luminosity of $340$ μb -1 using the ALFA subdetector of ATLAS in 2016. The elastic cross section was measured differentially in the Mandelstam t variable in the range from - t = 2.5 · 10 -4 GeV 2 to - t = 0.46 GeV 2 using 6.9 million elastic-scattering candidates. This paper presents measurements of the total cross section σ tot , parameters of the nuclear slope, and the p -parameter defined as the ratio of the real part to the imaginary part of the elastic-scattering amplitude in the limit t → 0. These parameters are determined from a fit to the differential elastic cross section using the optical theorem and different parameterizations of the t-dependence. The results for σ tot and p are σ tot (pp → X) = 104.7 ± 1.1 mb, p = 0.098 ± 0.011. The uncertainty in σ tot is dominated by the luminosity measurement, and in p by imperfect knowledge of the detector alignment and by modelling of the nuclear amplitude.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Combination of searches for invisible decays of the Higgs boson using 139 fb –1 of proton-proton collision data at $\sqrt{s}$ TeV collected with the ATLAS experiment

Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for $H$ → invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb –1 of proton–proton collisions at a centre–of–mass energy of $\sqrt{s}$ = 13 TeV at the LHC. In combination with the results at $\sqrt{s}$ = 13 TeV and 8 TeV, an upper limit on the $H$ → invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of substructure-dependent jet suppression in Pb + Pb collisions at 5.02 TeV with the ATLAS detector

The ATLAS detector at the Large Hadron Collider has been used to measure jet substructure modification and suppression in Pb + Pb collisions at a nucleon–nucleon center-of-mass energy $\sqrt{{^S}_{NN}}$ = 5.02 TeV in comparison with proton–proton (pp) collisions at $\sqrt{{^S}}$ = 5.02 TeV. The Pb + Pb data, collected in 2018, have an integrated luminosity of 1.72 nb -1 , while the pp data, collected in 2017, have an integrated luminosity of 260 pb -1 . Jets used in this analysis are clustered using the anti- k t algorithm with a radius parameter R = 0.4. The jet constituents, defined by both tracking and calorimeter information, are used to determine the angular scale r g of the first hard splitting inside the jet by reclustering them using the Cambridge–Aachen algorithm and employing the soft-drop grooming technique. The nuclear modification factor, R AA , used to characterize jet suppression in Pb + Pb collisions, is presented differentially in r g , jet transverse momentum, and in intervals of collision centrality. The R AA value is observed to depend significantly on jet r g . Jets produced with the largest measured r g are found to be twice as suppressed as those with the smallest r g in central Pb + Pb collisions. The R AA values do not exhibit a strong variation with jet p T in any of the r g intervals. The r g and p T dependence of jet R AA is qualitatively consistent with a picture of jet quenching arising from coherence and provides the most direct evidence in support of this approach.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗