Engineering topics

Amelung, C.

Publications and source records attributed to Amelung, C..

At least 127 records · Page 7

DOE OSTI2024

Measurement of the production cross-section of $J/\psi$ and $\psi (2{\textrm{S}})$ mesons in pp collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

Measurements of the differential production cross-sections of prompt and non-prompt J/ψ and ψ(2S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range |y| < 2 are reported. Furthermore, measurements of the non-prompt fractions of J/ψ and ψ(2S), and the prompt and non-prompt ψ(2S)-to-J/ψ pro duction ratios, are presented. The analysis is performed using 140 fb -1 of $\sqrt{s}$ = 13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

Search for resonant production of dark quarks in the dijet final state with the ATLAS detector

This paper presents a search for a new Z' resonance decaying into a pair of dark quarks which hadronise into dark hadrons before promptly decaying back as Standard Model particles. This analysis is based on proton-proton collision data recorded at $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb –1 . After selecting events containing large-radius jets with high track multiplicity, the invariant mass distribution of the two highest-transverse-momentum jets is scanned to look for an excess above a data-driven estimate of the Standard Model multijet background. No significant excess of events is observed and the results are thus used to set 95% confidence-level upper limits on the production cross-section times branching ratio of the Z' to dark quarks as a function of the Z' mass for various dark-quark scenarios.

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DOE OSTI2024

Search for pair production of squarks or gluinos decaying via sleptons or weak bosons in final states with two same-sign or three leptons with the ATLAS detector

A search for pair production of squarks or gluinos decaying via sleptons or weak bosons is reported. The search targets a final state with exactly two leptons with same-sign electric charge or at least three leptons without any charge requirement. The analysed data set corresponds to an integrated luminosity of 139 fb –1 of proton-proton collisions collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Multiple signal regions are defined, targeting several SUSY simplified models yielding the desired final states. A single control region is used to constrain the normalisation of the WZ + jets background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of several supersymmetric models featuring R-parity conservation or R-parity violation, yielding exclusion limits surpassing those from previous searches. In models considering gluino (squark) pair production, gluino (squark) masses up to 2.2 (1.7) TeV are excluded at 95% confidence level.

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DOE OSTI2024

Search for top-philic heavy resonances in pp collisions at $\sqrt{s}=13$ $\text {TeV}$ with the ATLAS detector

A search for the associated production of a heavy resonance with a top-quark or a top-antitop-quark pair, and decaying into a $\overline{tt}$ pair is presented. The search uses the data recorded by the ATLAS detector in pp collisions at $\sqrt{s}$ = 13 TeV at the Large Hadron Collider during the years 2015–2018, corresponding to an integrated luminosity of 139 fb -1 . Events containing exactly one electron or muon are selected. The two hadronically decaying top quarks from the resonance decay are reconstructed using jets clustered with a large radius parameter of R = 1. The invariant mass spectrum of the two top quark candidates is used to search for a resonance signal in the range of 1.0 TeV to 3.2 TeV. The presence of a signal is examined using an approach with minimal model dependence followed by a model-dependent interpretation. No significant excess is observed over the background expectation. Upper limits on the production cross section times branching ratio at 95% confidence level are provided for a heavy Z' boson based on a simplified model, for Z' mass between 1.0 TeV and 3.0 TeV. The observed (expected) limits range from 21 (14) fb to 119 (86) fb depending on the choice of model parameters

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DOE OSTI2024

Search for non-resonant Higgs boson pair production in the $2b+2\ell +{E}_{\textrm{T}}^{\textrm{miss}}$ final state in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for non-resonant Higgs boson pair (HH) production is presented, in which one of the Higgs bosons decays to a b-quark pair ($b\bar{b}$) and the other decays to WW * , ZZ * , or τ + τ – , with in each case a final state with ℓ + ℓ – + neutrinos (ℓ = e, μ). The analysis targets separately the gluon-gluon fusion and vector boson fusion production modes. Data recorded by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb –1 , are used in this analysis. Events are selected to have exactly two b-tagged jets and two leptons with opposite electric charge and missing transverse momentum in the final state. These events are classified using multivariate analysis algorithms to separate the HH events from other Standard Model processes. No evidence of the signal is found. The observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 9.7 (16.2) times the Standard Model prediction at 95% confidence level. The Higgs boson self-interaction coupling parameter κ λ and the quadrilinear coupling parameter κ 2V are each separately constrained by this analysis to be within the ranges [–6.2, 13.3] and [–0.17, 2.4], respectively, at 95% confidence level, when all other parameters are fixed.

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DOE OSTI2024

Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data

This paper presents the electron and photon energy calibration obtained with the ATLAS detector using 140 fb -1 of LHC proton-proton collision data recorded at $\sqrt{s}$ = 13 TeV between 2015 and 2018. Methods for the measurement of electron and photon energies are outlined, along with the current knowledge of the passive material in front of the ATLAS electromagnetic calorimeter. The energy calibration steps are discussed in detail, with emphasis on the improvements introduced in this paper. The absolute energy scale is set using a large sample of Z-boson decays into electron-positron pairs, and its residual dependence on the electron energy is used for the first time to further constrain systematic uncertainties. The achieved calibration uncertainties are typically 0.05% for electrons from resonant Z-boson decays, 0.4% at E T ~ 10 GeV, and 0.3% at E T ~ 1 TeV; for photons at E T ~ 60 GeV, they are 0.2% on average. This is more than twice as precise as the previous calibration. The new energy calibration is validated using J/ψ → ee and radiative Z-boson decays.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

Measurement of the $H \rightarrow \gamma \gamma $ and $H \rightarrow ZZ^* \rightarrow 4 \ell $ cross-sections in $pp$ collisions at $\sqrt{s}=13.6$ TeV with the ATLAS detector

The inclusive Higgs boson production crosssection is measured in the di-photon and the Z Z* → 4$\ell$ decay channels using 31.4 and 29.0 fb –1 of pp collision data respectively, collected with the ATLAS detector at a centreof-mass energy of $\sqrt{s}$ = 13.6 TeV. To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the channel’s detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are σ fid,γγ = $76^{+14}_{–13}$ fb, and $σ_{\text{fid,4}\ell}$ = 2.80 ± 0.74 fb, in agreement with the corresponding Standard Model predictions of 67.6±3.7 fb and 3.67±0.19 fb. Assuming Standard Model acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of σ (pp → H) = $67^{+12}_{–11}$ pb and 46±12 pb at 13.6 TeV from the di-photon and Z Z* → 4$\ell$ measurements respectively. The two measurements are combined into a total cross-section measurement of σ (pp → H) = 58.2±8.7 pb, to be compared with the Standard Model prediction of σ (pp → H) SM = 59.9 ± 2.6 pb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Studies of new Higgs boson interactions through nonresonant $HH$ production in the $ b\overline{b}\gamma \gamma $ final state in $pp$ collisions at $ \sqrt{s} $ = 13 TeV with the ATLAS detector

A search for nonresonant Higgs boson pair production in the $ b\overline{b}\gamma \gamma $ final state is performed using 140 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. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this final state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifier κλ but also of the quartic HHVV (V = W, Z) coupling modifier κ 2V . No significant excess above the expected background from Standard Model processes is observed. An observed upper limit μHH < 4.0 is set at 95% confidence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confidence intervals for the coupling modifiers are –1.4 < κ λ < 6.9 and –0.5 < κ 2V < 2.7, assuming all other Higgs boson couplings except the one under study are fixed to the Standard Model predictions. The results are interpreted in the Standard Model effective field theory and Higgs effective field theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Observation of W Z γ Production in p p Collisions at s = 13 TeV with the ATLAS Detector

This Letter reports the observation of W Z γ production and a measurement of its cross section using 140.1 ± 1.2 fb − 1 of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The W Z γ production cross section, with both the W and Z bosons decaying leptonically, p p → W Z γ → ℓ ′ ± ν ℓ + ℓ − γ ( ℓ ( ′ ) = e , μ ), is measured in a fiducial phase-space region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01 ± 0.30 ( stat ) ± 0.16 ( syst ) fb . The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50 ± 0.06 fb . The observed significance of the W Z γ signal is 6.3 σ , compared with an expected significance of 5.0 σ . © 2024 CERN, for the ATLAS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Differential cross-section measurements of the production of four charged leptons in association with two jets using the ATLAS detector

Differential cross-sections are measured for the production of four charged leptons in association with two jets. These measurements are sensitive to final states in which the jets are produced via the strong interaction as well as to the purely-electroweak vector boson scattering process. The analysis is performed using proton-proton collision data collected by ATLAS at $\sqrt{s}$ = 13 TeV and with an integrated luminosity of 140 fb –1 . The data are corrected for the effects of detector inefficiency and resolution and are compared to state-of-the-art Monte Carlo event generator predictions. The differential cross-sections are used to search for anomalous weak-boson self-interactions that are induced by dimension-six and dimension-eight operators in Standard Model effective field theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for flavour-changing neutral $tqH$ interactions with $H$ → γγ in $pp$ collisions at $ \sqrt{s} $ = 13 TeV using the ATLAS detector

A search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q (q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb –1 , was collected at $\sqrt{s}$ = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t → qH in $t\bar{t}$ production and the production process pp → tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t → cH and the t → uH branching ratios of 4.3 × 10 –4 and 3.8 × 10 –4 , respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7 × 10 –4 and 3.9 × 10 –4 . Combining this search with ATLAS searches in the H → τ + τ – and H → $b\bar{b}$ final states yields observed (expected) upper limits on the t → cH branching ratio of 5.8 × 10 –4 (3.0 × 10 –4 ) at the 95% confidence level. The corresponding observed (expected) upper limit on the t → uH branching ratio is 4.0 × 10 –4 (2.4 × 10 –4 ).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at $\sqrt{s} $ = 13 TeV with the ATLAS detector

Searches for electroweak production of wino-like chargino pairs, ${\overset{\sim }{\chi}}_1^{+}{\overset{\sim }{\chi}}_1^{-}$, and of wino-like chargino and next-to-lightest neutralino, ${\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_2^0$, are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, ${\overset{\sim }{\chi}}_1^{\pm}\to {W}^{\pm }{\overset{\sim }{\chi}}_1^0$. The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to ${\overset{\sim }{\chi}}_1^0$ and either a Z or a Higgs boson, ${\overset{\sim }{\chi}}_2^0\to Z{\overset{\sim }{\chi}}_1^0$ or $h{\overset{\sim }{\chi}}_1^0$. The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb –1 of $\sqrt{s}$ = 13 TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless ${\overset{\sim }{\chi}}_1^0$ in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless ${\overset{\sim }{\chi}}_1^0$ for ${\overset{\sim }{\chi}}_2^0\to Z{\overset{\sim }{\chi}}_1^0$. For decays through an on-shell Higgs boson and for mass-splitting between ${\overset{\sim }{\chi}}_1^{\pm }/{\overset{\sim }{\chi}}_2^0$ and ${\overset{\sim }{\chi}}_1^0$ as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200–260 GeV and 280–470 GeV compared to previous ATLAS constraints.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

Combined Measurement of the Higgs Boson Mass from the $H→γγ$ and $H→ZZ$*→ 4⁢ℓ Decay Channels with the ATLAS Detector Using $\sqrt{s}$ = 7, 8, and 13 TeV $pp$ Collision Data

A measurement of the mass of the Higgs boson combining the H → ZZ* → 4ℓ and H → γγ decay channels is presented. The result is based on 140 fb –1 of proton-proton collision data collected by the ATLAS detector during LHC run 2 at a centre-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, yielding a Higgs boson mass of 125.11 ± 0.09 (stat.) ± 0.06 (syst.) = 125.11 ± 0.11 GeV. This corresponds to a 0.09 % precision achieved on this fundamental parameter of the Standard Model of particle physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for heavy Majorana or Dirac neutrinos and right-handed $W$ gauge bosons in final states with charged leptons and jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for heavy right-handed Majorana or Dirac neutrinos N R and heavy right-handed gauge bosons W R is performed in events with energetic electrons or muons, with the same or opposite electric charge, and energetic jets. The search is carried out separately for topologies of clearly separated final-state products (“resolved” channel) and topologies with boosted final states with hadronic and/or leptonic products partially overlapping and reconstructed as a large-radius jet (“boosted” channel). The events are selected from pp collision data at the LHC with an integrated luminosity of 139 fb -1 collected by the ATLAS detector at $\sqrt{s}=13$ TeV. No significant deviations from the Standard Model predictions are observed. The results are interpreted within the theoretical framework of a left-right symmetric model, and lower limits are set on masses in the heavy right handed W R boson and N R plane. The excluded region extends to about m(W R ) = 6.4 TeV for both Majorana and Dirac N R neutrinos at m(N R ) < 1 TeV. N R with masses of less than 3.5 (3.6) TeV are excluded in the electron (muon) channel at m(W R ) = 4.8 TeV for the Majorana neutrinos, and lim its of m(N R ) up to 3.6 TeV for m(W R ) = 5.2 (5.0) TeV in the electron (muon) channel are set for the Dirac neutrinos. These constitute the most stringent exclusion limits to date for the model considered.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for Dark Photons in Rare $Z$ Boson Decays with the ATLAS Detector

A search for events with a dark photon produced in association with a dark Higgs boson via rare decays of the standard model Z boson is presented, using 139 fb –1 of $\sqrt{s}$ = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. The dark boson decays into a pair of dark photons, and at least two of the three dark photons must each decay into a pair of electrons or muons, resulting in at least two same-flavor opposite-charge lepton pairs in the final state. The data are found to be consistent with the background prediction, and upper limits are set on the dark photon’s coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, α D ϵ 2 , in the dark photon mass range of [5, 40] GeV except for the $Υ$ mass window [8.8, 11.1] GeV. This search explores new parameter space not previously excluded by other experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at $ \sqrt{s} $ = 13 TeV

A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 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 ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 ± 0.60 fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.

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DOE OSTI2023

Observation of $Wγγ$ triboson production in proton-proton collisions at s = 13 TeV with the ATLAS detector

This letter reports the observation of W(ℓν)γγ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of $\sqrt{s}$ = 13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb -1 . Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of W(eν)γγ and W(μν)γγ events is measured to be σ fid = 13.8 ± 1.1(stat) $^{+2.1}_{-2.0}$(syst) ± 0.1(lumi) fb, in agreement with the Standard Model prediction.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

Pursuit of paired dijet resonances in the Run 2 dataset with ATLAS

New particles with large masses that decay into hadronically interacting particles are predicted by many models of physics beyond the Standard Model. A search for a massive resonance that decays into pairs of dijet resonances is performed using 140 fb –1 of proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Resonances are searched for in the invariant mass of the tetrajet system, and in the average invariant mass of the pair of dijet systems. A data-driven background estimate is obtained by fitting the tetrajet and dijet invariant mass distributions with a four-parameter dijet function and a search for local excesses from resonant production of dijet pairs is performed. No significant excess of events beyond the Standard Model expectation is observed, and upper limits are set on the production cross sections of new physics scenarios.

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