B. Abbott’s research while affiliated with University of Oklahoma and other places

The energy and mass measurements of jets are crucial tasks for the Large Hadron Collider experiments. This paper presents a new calibration method to simultaneously calibrate these quantities for large-radius jets measured with the ATLAS detector using a deep neural network (DNN). To address the specificities of the calibration problem, special loss functions and training procedures are employed, and a complex network architecture, which includes feature annotation and residual connection layers, is used. The DNN-based calibration is compared to the standard numerical approach in an extensive series of tests. The DNN approach is found to perform significantly better in almost all of the tests and over most of the relevant kinematic phase space. In particular, it consistently improves the energy and mass resolutions, with a 30% better energy resolution obtained for transverse momenta pT>500 GeV.

A bstract A search for heavy pseudo-scalar ( A ) and scalar ( H ) Higgs bosons decaying into a top-quark pair ( $t\overline{t}$ t t ¯ ) has been performed with 140 fb − 1 of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}$ s = 13 TeV. Interference effects between the signal process and Standard Model (SM) $t\overline{t}$ t t ¯ production are taken into account. Final states with exactly one or exactly two electrons or muons are considered. No significant deviation from the SM prediction is observed. The results of the search are interpreted in the context of a two-Higgs-doublet model (2HDM) of type II in the alignment limit with mass-degenerate pseudo-scalar and scalar Higgs bosons ( m A = m H ) and the hMSSM parameterisation of the minimal supersymmetric extension of the Standard Model. Ratios of the two vacuum expectation values, tan β , smaller than 3.49 (3.16) are excluded at 95% confidence level for m A = m H = 400 GeV in the 2HDM (hMSSM). Masses up to 1240 GeV are excluded for the lowest tested tan β value of 0.4 in the 2HDM. In the hMSSM, masses up to 950 GeV are excluded for tan β = 1.0. In addition, generic exclusion limits are derived separately for single scalar and pseudo-scalar states for different choices of their mass and total width.

A search is presented for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark ( q=u,c q = u , c ) with the ATLAS detector at the Large Hadron Collider. The analysis considers leptonic decays of the top quark along with Higgs boson decays into two W W bosons, two Z Z bosons or a $\tau ^{+}\tau ^{-}$ τ + τ - pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons. The considered processes are $t\bar{t}$ t t ¯ and Ht production. For the $t\bar{t}$ t t ¯ production, one top quark decays via $t\rightarrow Hq$ t → H q . The proton–proton collision data set analysed amounts to $({140}\,{\hbox {fb}^{-1}})$ ( 140 fb - 1 ) at $(\sqrt{s}={13}\,\hbox {TeV})$ ( s = 13 TeV ) . No significant excess beyond Standard Model expectations is observed and upper limits are set on the $t\rightarrow Hq$ t → H q branching ratios at 95 % confidence level, amounting to observed (expected) limits of $\mathcal {B}(t\rightarrow Hu)<2.8\,(3.0) \times 10^{-4}$ B ( t → H u ) < 2.8 ( 3.0 ) × 10 - 4 and $\mathcal {B}(t\rightarrow Hc)<3.3\,(3.8) \times 10^{-4}$ B ( t → H c ) < 3.3 ( 3.8 ) × 10 - 4 . Combining this search with other searches for tHq tHq flavour-changing neutral-current interactions previously conducted by ATLAS, considering $H\rightarrow b\bar{b}$ H → b b ¯ and $H\rightarrow \gamma \gamma$ H → γ γ decays, as well as $H\rightarrow \tau ^{+}\tau ^{-}$ H → τ + τ - decays with one or two hadronically decaying $\tau$ τ -leptons, yields observed (expected) upper limits on the branching ratios of $\mathcal {B}(t\rightarrow Hu)<2.6\,(1.8) \times 10^{-4}$ B ( t → H u ) < 2.6 ( 1.8 ) × 10 - 4 and $\mathcal {B}(t\rightarrow Hc)<3.4\,(2.3) \times 10^{-4}$ B ( t → H c ) < 3.4 ( 2.3 ) × 10 - 4 .

Presented is the search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run 2 data set of $140\,\text {fb}^{-1}$ 140 fb - 1 of proton-proton collisions at a centre-of-mass energy of $13\,\text {TeV}$ 13 TeV recorded by the ATLAS experiment. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the $(g-2)_\mu$ ( g - 2 ) μ discrepancy. This analysis covers an ALP mass range from 100 to $62\,\text {GeV}$ 62 GeV and ALP-photon couplings in the range $10^{-7}\,\text {TeV}^{-1}<C_{a\gamma \gamma }/\Lambda <1 \,\text {TeV}^{-1}$ 10 - 7 TeV - 1 < C a γ γ / Λ < 1 TeV - 1 , and therefore includes signatures with significantly displaced vertices and highly collinear photons. No significant excess of events above the Standard Model background is observed. Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to two ALPs in the four-photon final state, and are in the range of $10^{-5}$ 10 - 5 to $3\times 10^{-2}$ 3 × 10 - 2 , depending on the hypothesized ALP mass and ALP-photon coupling strength.

A search is reported for long-lived dark photons with masses between 0.1 GeV and 15 GeV, from exotic decays of Higgs bosons produced via vector-boson-fusion. Events that contain displaced collimated Standard Model fermions reconstructed in the calorimeter or muon spectrometer are probed. This search uses the full LHC Run 2 (2015–2018) data sample collected in proton–proton collisions at $\sqrt{s}=13$ s = 13 TeV, corresponding to an integrated luminosity of 139 $fb^{-1}$ f b - 1 . Dominant backgrounds from Standard Model processes and non-collision sources are estimated using data-driven techniques. The observed event yields in the signal regions are consistent with the expected background. Upper limits on the Higgs boson to dark photon branching fraction are reported as a function of the dark photon mean proper decay length or of the dark photon mass and the coupling between the Standard Model and the potential dark sector. This search is combined with previous ATLAS searches obtained in the gluon–gluon fusion and WH production modes. A branching fraction above 10% is excluded at 95% CL for a 125 GeV Higgs boson decaying into two dark photons for dark photon mean proper decay lengths between 173 and 1296 mm and mass of 10 GeV.

Clusters of topologically connected calorimeter cells around cells with large absolute signal-to-noise ratio ( topo-clusters ) are the basis for calorimeter signal reconstruction in the ATLAS experiment. Topological cell clustering has proven performant in LHC Runs 1 and 2. It is, however, susceptible to out-of-time pile-up of signals from soft collisions outside the 25 ns proton-bunch-crossing window associated with the event’s hard collision. To reduce this effect, a calorimeter-cell timing criterion was added to the signal-to-noise ratio requirement in the clustering algorithm. Multiple versions of this criterion were tested by reconstructing hadronic signals in simulated events and Run 2 ATLAS data. The preferred version is found to reduce the out-of-time pile-up jet multiplicity by ${\sim }50\%$ ∼ 50 % for jet $p_{\textrm{T}}\sim 20$ p T ∼ 20 GeV and by ${\sim }80\%$ ∼ 80 % for jet $p_{\textrm{T}} \gtrsim 50$ p T ≳ 50 GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for $20< p_{\textrm{T}} < 30$ 20 < p T < 30 GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, $\tau$ τ -leptons), reducing the overall event size on disk by about $6\%$ 6 % in early Run 3 pile-up conditions. Offline reconstruction for Run 3 includes the timing requirement.

A bstract A search for R-parity-violating supersymmetry in final states with high jet multiplicity is presented. The search uses 140 fb − 1 of proton-proton collision data at $\sqrt{s}$ s = 13 TeV collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature prompt gluino-pair production decaying directly to three jets each or decaying to two jets and a neutralino which subsequently decays promptly to three jets. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted. Gluinos with masses up to 1800 GeV are excluded when decaying directly to three jets. In the cascade scenario, gluinos with masses up to 2340 GeV are excluded for a neutralino with mass up to 1250 GeV.

A bstract A summary of the constraints from searches performed by the ATLAS collaboration for the electroweak production of charginos and neutralinos is presented. Results from eight separate ATLAS searches are considered, each using 140 fb − 1 of proton-proton data at a centre-of-mass energy of $\sqrt{s}$ s = 13 TeV collected at the Large Hadron Collider during its second data-taking run. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, where R -parity conservation is assumed and the lightest supersymmetric particle is assumed to be the lightest neutralino. Constraints from previous electroweak, flavour and dark matter related measurements are also considered. The results are presented in terms of constraints on supersymmetric particle masses and are compared with limits from simplified models. Also shown is the impact of ATLAS searches on parameters such as the dark matter relic density and the spin-dependent and spin-independent scattering cross-sections targeted by direct dark matter detection experiments. The Higgs boson and Z boson ‘funnel regions’, where a low-mass neutralino would not oversaturate the dark matter relic abundance, are almost completely excluded by the considered constraints. Example spectra for non-excluded supersymmetric models with light charginos and neutralinos are also presented.

A bstract A search for CP violation in the decay kinematics and vector-boson fusion production of the Higgs boson is performed in the H → ZZ * → 4 ℓ ( ℓ = e, μ ) decay channel. The results are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb − 1 . Matrix element-based optimal observables are used to constrain CP-odd couplings beyond the Standard Model in the framework of Standard Model effective field theory expressed in the Warsaw and Higgs bases. Differential fiducial cross-section measurements of the optimal observables are also performed, and a new fiducial cross-section measurement for vector-boson-fusion production is provided. All measurements are in agreement with the Standard Model prediction of a CP-even Higgs boson.

A bstract Three searches for the direct production of τ -sleptons or charginos and neutralinos in final states with at least two hadronically decaying τ -leptons are presented. For chargino and neutralino production, decays via intermediate τ -sleptons or W and h bosons are considered. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb − 1 , recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed and supersymmetric particle mass limits at 95% confidence level are obtained in simplified models. For direct production of ${\overset{\sim }{\chi}}_1^{+}{\overset{\sim }{\chi}}_1^{-}$ χ ~ 1 + χ ~ 1 − , chargino masses are excluded up to 970 GeV, while ${\overset{\sim }{\chi}}_1^{\pm }$ χ ~ 1 ± and ${\overset{\sim }{\chi}}_2^0$ χ ~ 2 0 masses up to 1160 GeV (330 GeV) are excluded for ${\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_2^0/{\overset{\sim }{\chi}}_1^{+}{\overset{\sim }{\chi}}_1^{-}$ χ ~ 1 ± χ ~ 2 0 / χ ~ 1 + χ ~ 1 − production with subsequent decays via τ -sleptons ( W and h bosons). Masses of τ -sleptons up to 500 GeV are excluded for mass degenerate ${\overset{\sim }{\tau}}_{L,R}$ τ ~ L , R scenarios and up to 425 GeV for ${\overset{\sim }{\tau}}_L$ τ ~ L -only scenarios. Sensitivity to ${\overset{\sim }{\tau}}_R$ τ ~ R -only scenarios from the ATLAS experiment is presented here for the first time, with ${\overset{\sim }{\tau}}_R$ τ ~ R masses excluded up to 350 GeV.