A measurement of the top-quark pole mass $m_{t}^\text{pole}$ is presented in $t\bar{t}$ events with an additional jet, $t\bar{t}+1\text{-jet}$, produced in $pp$ collisions at $\sqrt{s}=13$ TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of $140~\text{fb}^{-1}$. Events with one electron and one muon of opposite electric charge in the final state are selected to measure the $t\bar{t}+1\text{-jet}$ differential cross-section as a function of the inverse of the invariant mass of the $t\bar{t}+1\text{-jet}$ system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process $pp \to t\bar{t}j$ ($2 \rightarrow 3$), where top quarks are taken as stable particles, and the process $pp \to b\bar{b}l^+νl^- \barν j$ ($2 \to 7$), which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using a $χ^2$ fit of the unfolded normalized differential cross-section distribution. The results obtained with the $2 \to 3$ and $2 \to 7$ calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the $2 \to 3 $ measurement: $m_{t}^\text{pole}=170.7\pm0.3~(\text{stat.})\pm1.4~(\text{syst.})~\pm 0.3~(\text{scale})~\pm 0.2~(\text{PDF}\oplusα_\text{S})~\text{GeV},$ which is in good agreement with other top-quark mass results.
Unfolded number of events in the 2-to-3measurement (not normalized). The parton level is defined with two stable top-quarks and a jet with $p_{T}>50$ GeV and $|\eta|<2.5$.
Covariance matrix for statistical effects of the measured number of events after unfolding, for the 2-to-3 measurement (not normalized)
Covariance matrix for statistical and systematic effects of the measured number of events after unfolding, for the 2-to-3 measurement (not normalized)
A study on the Bose-Einstein correlations for triplets of same-sign pions is presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 7 TeV, recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb$^{-1}$. For the first time, the results are interpreted in the core-halo model. The parameters of the model are determined in regions of charged-particle multiplicity. This measurement provides insight into the nature of hadronisation in terms of coherence, showing a coherent emission of pions.
Results of the fit to the three-particle double ratio ($r_{d_{3}}$) for same-sign pion triplets, VELO track multiplicity for pp collision: 5-10.
Results of the fit to the three-particle double ratio ($r_{d_{3}}$) for same-sign pion triplets, VELO track multiplicity for pp collision: 11-20.
Results of the fit to the three-particle double ratio ($r_{d_{3}}$) for same-sign pion triplets, VELO track multiplicity for pp collision: 21-60.
Measurements of $W^+W^-\rightarrow e^\pm νμ^\mp ν$ production cross-sections are presented, providing a test of the predictions of perturbative quantum chromodynamics and the electroweak theory. The measurements are based on data from $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the Large Hadron Collider in 2015-2018, corresponding to an integrated luminosity of 140 fb$^{-1}$. The number of events due to top-quark pair production, the largest background, is reduced by rejecting events containing jets with $b$-hadron decays. An improved methodology for estimating the remaining top-quark background enables a precise measurement of $W^+W^-$ cross-sections with no additional requirements on jets. The fiducial $W^+W^-$ cross-section is determined in a maximum-likelihood fit with an uncertainty of 3.1%. The measurement is extrapolated to the full phase space, resulting in a total $W^+W^-$ cross-section of $127\pm4$ pb. Differential cross-sections are measured as a function of twelve observables that comprehensively describe the kinematics of $W^+W^-$ events. The measurements are compared with state-of-the-art theory calculations and excellent agreement with predictions is observed. A charge asymmetry in the lepton rapidity is observed as a function of the dilepton invariant mass, in agreement with the Standard Model expectation. A CP-odd observable is measured to be consistent with no CP violation. Limits on Standard Model effective field theory Wilson coefficients in the Warsaw basis are obtained from the differential cross-sections.
Measured fiducial cross-section compared with theoretical predictions from MiNNLO+Pythia8, Geneva+Pythia8, Sherpa2.2.12, and MATRIX2.1. The predictions are based on the NNPDF3.0 (red squares) and NNPDF3.1 luxQED (blue dots) PDF sets. The nNNLO predictions include photon-induced contributions (always using NNPDF3.1 luxQED) and NLO QCD corrections to the gluon-gluon initial state. The $q\bar{q}\rightarrow WW$ predictions from MiNNLO, Geneva, and Sherpa2.2.12 are combined with a Sherpa2.2.2 prediction of gluon-induced production, scaled by an inclusive NLO K-factor of 1.7. Inner (outer) error bars on the theory predictions correspond to PDF (the combination of scale and PDF) uncertainties. The MATRIX nNNLO QCD $\otimes$ NLO EW prediction using NNPDF3.1 luxQED, the best available prediction of the integrated fiducial cross-section, is in good agreement with the measurement.
Fiducial differential cross-sections as a function of $p_{\mathrm{T}}^{\mathrm{lead.\,lep.}}$. The measured cross-section values are shown as points with error bars giving the statistical uncertainty and solid bands indicating the size of the total uncertainty. The right-hand-side axis indicates the integrated cross-section of the rightmost bin. The results are compared to fixed-order nNNLO QCD + NLO EW predictions of Matrix 2.1, with the NNLO + PS predictions from Powheg MiNNLO + Pythia8 and Geneva + Pythia8, as well as Sherpa2.2.12 NLO + PS predictions. The last three predictions are combined with Sherpa 2.2.2 for the $gg$ initial state and Sherpa 2.2.12 for electroweak $WWjj$ production. These contributions are modelled at LO but a NLO QCD $k$-factor of 1.7 is applied for gluon induced production. Theoretical predictions are indicated as markers with vertical lines denoting PDF, scale and parton shower uncertainties. Markers are staggered for better visibility.
Correlation matrix of the statistical uncertainties in the measured fiducial cross section for the observable $p_{\mathrm{T}}^{\mathrm{lead.\,lep.}}$.
The polarization of Lambda, Anti-Lambda, Xi, and Anti-Xi hyperons along the angular momentum of the system has been measured in isobar collisions of Ru+Ru and Zr+Zr at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector at RHIC. The polarization dependence on collision centrality is explored and found to show an increasing trend in more peripheral collisions. Dependencies on transverse momentum and pseudorapidity are investigated for Lambda and Anti-Lambda hyperons, but no significant dependence has been observed. The polarization measurements for Lambda and Anti-Lambda are consistent with each other, indicating little contribution of the spin-magnetic coupling in the observed polarization. The results for Lambda hyperons measurements are qualitatively consistent with hydrodynamic calculations incorporating effects from shear-induced polarization and thermal vorticity, and show no obvious system size dependence in comparison with previous results in Au+Au collisions. For the first time, the dependence of the polarization on the hyperon's emission azimuthal angle with respect to the second harmonic event plane is extracted and shows stronger polarization for the in-plane emitted hyperons at the level of 2.4$\sigma$ significance in 20-50% centrality. The measurements of Xi hyperons polarization via the polarization transfer analysis exhibit a finite positive polarization, 2.9$\sigma$ significance in 20-50% centrality, slightly enhanced compared to the inclusive Lambda polarization.
Resolutions of the first-order event plane from the ZDC-SMDs as a function of collision centrality in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Resolutions of the second-order event plane from the TPC as a function of collision centrality in Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Global polarization of $\Lambda$ and $\bar\Lambda$ and their difference as a function of centrality in combined Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV.
A search is presented for hadronic signatures of beyond the Standard Model (BSM) physics, with an emphasis on signatures of a strongly-coupled hidden dark sector accessed via resonant production of a $Z'$ mediator. The ATLAS experiment dataset collected at the Large Hadron Collider from 2015 to 2018 is used, consisting of proton-proton collisions at $\sqrt{s}$ = 13 TeV and corresponding to an integrated luminosity of 140 fb$^{-1}$. The $Z'$ mediator is considered to decay to two dark quarks, which each hadronize and decay to showers containing both dark and Standard Model particles, producing a topology of interacting and non-interacting particles within a jet known as ``semi-visible". Machine learning methods are used to select these dark showers and reject the dominant background of mismeasured multijet events, including an anomaly detection approach to preserve broad sensitivity to a variety of BSM topologies. A resonance search is performed by fitting the transverse mass spectrum based on a functional form background estimation. No significant excess over the expected background is observed. Results are presented as limits on the production cross section of semi-visible jet signals, parameterized by the fraction of invisible particles in the decay and the $Z'$ mass, and by quantifying the significance of any generic Gaussian-shaped mass peak in the anomaly region.
Acceptance times efficiency weighted yields across the signal grid.
The 95% CL limits on the cross-section $\sigma(pp \rightarrow Z' \rightarrow \chi \chi$) times branching ratio B in fb with all statistical and systematic uncertainties, for the $R_{\text{inv}}=$0.2 signal points.
The 95% CL limits on the cross-section $\sigma(pp \rightarrow Z' \rightarrow \chi \chi$) times branching ratio B in fb with all statistical and systematic uncertainties, for the $R_{\text{inv}}=$0.4 signal points.
Higgs boson production cross-sections via gluon-gluon fusion and vector-boson fusion in proton-proton collisions are measured in the $H\rightarrow WW^\ast \rightarrow \ellν\ellν$ decay channel. The Large Hadron Collider delivered proton-proton collisions at a centre-of-mass energy of $13\,\textrm{TeV}$ between 2015 and 2018, which were recorded by the ATLAS detector, corresponding to an integrated luminosity of $140\,\textrm{fb}^{-1}$. The total cross-sections for Higgs boson production by gluon-gluon fusion and vector-boson fusion times the $H\rightarrow WW^\ast$ branching ratio are measured to be $12.4^{+1.3}_{-1.2}\,\textrm{pb}$ and $0.79^{+0.18}_{-0.16}\,\textrm{pb}$, respectively, in agreement with the Standard Model predictions. Higgs boson production is further characterised through measurements of Simplified Template Cross-Sections in a total of fifteen kinematic fiducial regions. A new scheme of kinematic fiducial regions has been introduced to enhance the sensitivity to CP-violating effects in Higgs boson interactions. Both schemes are used to constrain CP-even and CP-odd dimension-six operators in the Standard Model effective field theory.
Expected values and uncertainties for the $H \to WW^{\ast}$ cross-sections measured in each of the STXS categories, normalised to the corresponding SM predictions.
Best-fit values and uncertainties for the $H \to WW^{\ast}$ cross-sections measured in each of the STXS categories, normalised to the corresponding SM predictions.
Expected correlations between the production cross-sections multiplied by the $H \to WW^{\ast}$ branching ratio for each of the STXS categories.
The formation of light (anti)nuclei with mass number A of a few units (e.g., d, $^3$He, and $^4$He) in high-energy hadronic collisions presents a longstanding mystery in nuclear physics [1,2]. It is not clear how nuclei bound by a few MeV can emerge in environments characterized by temperatures above 100 MeV [3-5], about 100,000 times hotter than the center of the Sun. Despite extensive studies, this question remained unanswered. The ALICE Collaboration now addresses it with a novel approach using deuteron-pion momentum correlations in proton-proton (pp) collisions at the Large Hadron Collider (LHC). Our results provide model-independent evidence that about 80% of the observed (anti)deuterons are produced in nuclear fusion reactions [6] following the decay of short-lived resonances, such as the $\Delta (1232)$. These findings resolve a crucial gap in our understanding of nucleosynthesis in hadronic collisions. Beyond answering the fundamental question on how nuclei are formed in hadronic collisions, the results can be employed in the modeling of the production of light and heavy nuclei in cosmic rays [7] and dark matter decays [8,9].
Measured $\pi^{+}$–d$\oplus\pi^{-}$–$\overline{\mathrm{d}}$ (left panel) correlation function.
Measured $\pi^{-}$–d$\oplus\pi^{+}$–$\overline{\mathrm{d}}$ (right panel) correlation function.
The extracted kinetic decoupling temperature is derived from $\pi^{+}$–d correlation functions.
A search for pair-production of vector-like leptons is presented, considering their decays into a third-generation Standard Model (SM) quark and a vector leptoquark ($U_1$) as predicted by an ultraviolet-complete extension of the SM, referred to as the '4321' model. Given the assumed decay of $U_1$ into third-generation SM fermions, the final state can contain multiple $τ$-leptons and $b$-quarks. This search is based on a dataset of $pp$ collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of up to 140 fb$^{-1}$. No significant excess above the SM background prediction is observed, and 95% confidence level limits on the cross-section times branching ratio are derived as a function of the vector-like lepton mass. A lower observed (expected) limit of 910 GeV (970 GeV) is set on the vector-like lepton mass. Additionally, the results are interpreted for a supersymmetric model with an $R$-parity violating coupling to the third-generation quarks and leptons. Lower observed (expected) limits are obtained on the higgsino mass at 880 GeV (940 GeV) and on the wino mass at 1170 GeV (1170 GeV).
Observed (solid line with markers) and expected (dashed line) 95% CL upper limits on the VLL pair production cross-section (σ<sub>VLL</sub>) times branching ratio (BR) to third generation quarks and leptons as a function of m<sub>VLL</sub>. The limits presented in black lines are obtained after combining all five signal regions. The inner green (outer yellow) band corresponds to the ±1 σ (±2 σ) uncertainty around the combined expected limit. The 95% CL expected upper limits in the three individual channels (1τ<sub>had</sub> ≥3b MST, 1τ<sub>had</sub> ≥3b BJET and ≥2τ<sub>had</sub> ≥3b MSDT) are shown for comparison. The solid red line represents the theory prediction of the VLL pair production cross-section at NLO in QCD.
Observed (solid line with markers) and expected (dashed line) 95% CL upper limits on the higgsino pair production cross-section (σ<sub>higgsino</sub>) times branching ratio (BR) to third generation quarks and leptons as a function of m<sub>higgsino</sub>. The limits presented in black lines are obtained after combining all five signal regions. The inner green (outer yellow) band corresponds to the ±1 σ (±2 σ) uncertainty around the combined expected limit. The 95% CL expected upper limits in the three individual channels (1τ<sub>had</sub> ≥3b MST, 1τ<sub>had</sub> ≥3b BJET and ≥2τ<sub>had</sub> ≥3b MSDT) are shown for comparison. The solid red line represents the theory prediction of the higgsino pair production cross-section at NLO in QCD.
Observed (solid line with markers) and expected (dashed line) 95% CL upper limits on the wino pair production cross-section (σ<sub>wino</sub>) times branching ratio (BR) to third generation quarks and leptons as a function of m<sub>wino</sub>. The limits presented in black lines are obtained after combining all five signal regions. The surrounding inner green (outer yellow) band corresponds to the ±1 σ (±2 σ) uncertainty around the combined expected limit. The 95% CL expected upper limits in the three individual channels (1τ<sub>had</sub> ≥3b MST, 1τ<sub>had</sub> ≥3b BJET and ≥2τ<sub>had</sub> ≥3b MSDT) are shown for comparison. The solid red line represents the theory prediction of the wino pair production cross-section at NLO in QCD.
A measurement of the WZ$γ$ triboson production cross section is presented. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis focuses on the final state with three charged leptons, $\ell^\pmν\ell^+\ell^-$, where $\ell$ = e or $μ$, accompanied by an additional photon. The observed (expected) significance of the WZ$γ$ signal is 5.4 (3.8) standard deviations. The cross section is measured in a fiducial region, where events with an $\ell$ originating from a tau lepton decay are excluded, to be 5.48 $\pm$ 1.11 fb, which is compatible with the prediction of 3.69 $\pm$ 0.24 fb at next-to-leading order in quantum chromodynamics. Exclusion limits are set on anomalous quartic gauge couplings and on the production cross sections of massive axion-like particles.
The distributions of the variables used in the simultaneous fit for the nonprompt $l$ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
The distributions of the variables used in the simultaneous fit for the nonprompt $\gamma$ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
The distributions of the variables used in the simultaneous fit for the ZZ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axion-like particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photo-phobic axion-like particle model considered, this search produces the strongest limits to date for proper decay lengths greater than $\mathcal{O}(10)$ cm.
Summary of the one-DV limits for the H/ϕ arrow ss model. Comparison between observed and expected 95% CL limits on (σ/σggH)×B for an SM-like Higgs boson portal mediator and ms=35 GeV. The observed limits are consistent with the expected ones within the uncertainties.
Observed 95% CL limits on (σ/σggH)×B for all Higgs boson portal mediator samples where the cross-section is normalized to the SM Higgs boson gluon–gluon fusion production cross-section, σggH = 48.61 pb [97]. The observed limits are consistent with the expected ones within the uncertainties.
Observed 95% CL limits on σ×B for mϕ≠ 125 GeV. The observed limits are consistent with the expected ones within the uncertainties.
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