The GlueX experiment at Jefferson Lab has observed $p\bar{p}$ and, for the first time, $Λ\barΛ$ and $p\barΛ$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$-channel exchange. Asymmetric wide-angle anti-baryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double $t$-channel exchange process where anti-baryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the $Λ\barΛ$ and $p\barΛ$ systems but general similarity to the $p\bar{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of $s\bar{s}$ quark pairs relative to $d\bar{d}$ quark pairs is similar to what has been seen in other reactions.
Measured $\frac{d\sigma}{dm_{\Lambda\bar{\Lambda}}}~[\mathrm{nb/GeV}]$ for reaction $\gamma p\to \{\Lambda \bar{\Lambda}\} p$ including data of $6.5 \leq E_{\gamma} \leq 11.5$ [GeV], splitted in 10 energy bins (each as a column in the table). The observable $m_{\Lambda\bar{\Lambda}}$ is in unit of $[\mathrm{nb/GeV}]$ and is divided into bins of width 0.05 $[\mathrm{GeV}]$ (each as a row in the table). The global systematic uncertainty is 19% (not included in the table), with contributions of 5% from kinematic fitting, 10% from data selection, 5% from flux normalization, 13% from tracking efficiency, 3% from model dependence, and 6% from run-period variations.
Measured $\frac{d\sigma}{dm_{p\bar{\Lambda}}}~[\mathrm{nb/GeV}]$ for reaction $\gamma p\to \{p \bar{\Lambda}\} \Lambda$ including data of $6.5 \leq E_{\gamma} \leq 11.5$ [GeV], splitted in 10 energy bins (each as a column in the table). The observable $m_{p\bar{\Lambda}}$ is in unit of $[\mathrm{nb/GeV}]$ and is divided into bins of width 0.1 $[\mathrm{GeV}]$ (each as a row in the table). The global systematic uncertainty is 22% (not included in the table), with contributions of 2% from kinematic fitting, 10% from data selection, 5% from flux normalization, 15% from tracking efficiency, 3% from model dependence, and 10% from run-period variations.
Measured $\frac{d\sigma}{dm_{p\bar{p}}}~[\mathrm{nb/GeV}]$ for reaction $\gamma p\to \{p \bar{p}\} p$ including data of $3.5 \leq E_{\gamma} \leq 11.5$ [GeV], splitted in 15 energy bins (each as a column in the table). The observable $m_{p\bar{p}}$ is in unit of $[\mathrm{nb/GeV}]$ and is divided into bins of width 0.044 $[\mathrm{GeV}]$ (each as a row in the table). The global systematic uncertainty is 13% (not included in the table), with contributions of 8% from kinematic fitting, 4% from data selection, 5% from flux normalization, 8% from tracking efficiency, 3% from model dependence, and 1% from run-period variations.
This article reports on a search for dijet resonances using $132$ fb$^{-1}$ of $pp$ collision data recorded at $\sqrt{s} = 13$ TeV by the ATLAS detector at the Large Hadron Collider. The search is performed solely on jets reconstructed within the ATLAS trigger to overcome bandwidth limitations imposed on conventional single-jet triggers, which would otherwise reject data from decays of sub-TeV dijet resonances. Collision events with two jets satisfying transverse momentum thresholds of $p_{\textrm{T}} \ge 85$ GeV and jet rapidity separation of $|y^{*}|<0.6$ are analysed for dijet resonances with invariant masses from $375$ to $1800$ GeV. A data-driven background estimate is used to model the dijet mass distribution from multijet processes. No significant excess above the expected background is observed. Upper limits are set at $95\%$ confidence level on coupling values for a benchmark leptophobic axial-vector $Z^{\prime}$ model and on the production cross-section for a new resonance contributing a Gaussian-distributed line-shape to the dijet mass distribution.
Observed $m_{jj}$ distribution for the J50 signal region, using variable-width bins and the analysis selections. The background estimate corresponds to the ansatz fit, integrated over each bin.
Observed $m_{jj}$ distribution for the J100 signal region, using variable-width bins and the analysis selections. The background estimate corresponds to the ansatz fit, integrated over each bin.
Observed 95% $\text{CL}_\text{S}$ upper limits on the production cross-section times acceptance times branching ratio to jets, $\sigma \cdot A \cdot \text{BR}$, of Gaussian-shaped signals of 5%, 10%, and 15% width relative to their peak mass, $m_G$. Also included are the corresponding expected upper limits predicted for the case the $m_{jj}$ distribution is observed to be identical to the background prediction in each bin and the $1\sigma$ and $2\sigma$ envelopes of outcomes expected for Poisson fluctuations around the background expectation. Limits are derived from the J50 signal region.
This paper presents a search for physics beyond the Standard Model targeting a heavy resonance visible in the invariant mass of the lepton-jet system. The analysis focuses on final states with a high-energy lepton and jet, and is optimised for the resonant production of leptoquarks-a novel production mode mediated by the lepton content of the proton originating from quantum fluctuations. Four distinct and orthogonal final states are considered: $e$+light jet, $μ$+light jet, $e$+$b$-jet, and $μ$+$b$-jet, constituting the first search at the Large Hadron Collider for resonantly produced leptoquarks with couplings to electrons and muons. Events with an additional same-flavour lepton, as expected from higher-order diagrams in the signal process, are also included in each channel. The search uses proton-proton collision data from the full Run 2, corresponding to an integrated luminosity of 140 fb$^{-1}$ at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, and from a part of Run 3 (2022-2023), corresponding to 55 fb$^{-1}$ at $\sqrt{s} = 13.6$ TeV. No significant excess over Standard Model predictions is observed. The results are interpreted as exclusion limits on scalar leptoquark ($\tilde{S}_1$) production, substantially improving upon previous ATLAS constraints from leptoquark pair production for large coupling values. The excluded $\tilde{S}_1$ mass ranges depend on the coupling strength, reaching up to 3.4 TeV for quark-lepton couplings $y_{de} = 1.0$, and up to 4.3 TeV, 3.1 TeV, and 2.8 TeV for $y_{sμ}$, $y_{be}$, and $y_{bμ}$ couplings set to 3.5, respectively.
Data (dots) and post-fit SM distribution (histograms) of m<sub>ℓj</sub> in (a, b) SR-1L-ej and (c, d) SR-2L-ej of the e+light-jet channel obtained by a CR+SR background-only fit for Run 2 and Run 3, respectively. The lower panel shows the ratio of observed data to the total post- and pre-fit SM prediction. The last bin includes the overflow. Uncertainties in the background estimates include both the statistical and systematic uncertainties, with correlations between uncertainties taken into account. The dashed lines show the predicted yields for two benchmark signal models corresponding to S̃<sub>1</sub> (m, y<sub>de</sub>) = (2.0 TeV, 1.0) and S̃<sub>1</sub> (m, y<sub>de</sub>) = (3.0 TeV, 1.0), respectively. Note: the values in the table are normalized by the width of corresponding bin
Data (dots) and post-fit SM distribution (histograms) of m<sub>ℓj</sub> in (a, b) SR-1L-ej and (c, d) SR-2L-ej of the e+light-jet channel obtained by a CR+SR background-only fit for Run 2 and Run 3, respectively. The lower panel shows the ratio of observed data to the total post- and pre-fit SM prediction. The last bin includes the overflow. Uncertainties in the background estimates include both the statistical and systematic uncertainties, with correlations between uncertainties taken into account. The dashed lines show the predicted yields for two benchmark signal models corresponding to S̃<sub>1</sub> (m, y<sub>de</sub>) = (2.0 TeV, 1.0) and S̃<sub>1</sub> (m, y<sub>de</sub>) = (3.0 TeV, 1.0), respectively. Note: the values in the table are normalized by the width of corresponding bin
Data (dots) and post-fit SM distribution (histograms) of m<sub>ℓj</sub> in (a, b) SR-1L-ej and (c, d) SR-2L-ej of the e+light-jet channel obtained by a CR+SR background-only fit for Run 2 and Run 3, respectively. The lower panel shows the ratio of observed data to the total post- and pre-fit SM prediction. The last bin includes the overflow. Uncertainties in the background estimates include both the statistical and systematic uncertainties, with correlations between uncertainties taken into account. The dashed lines show the predicted yields for two benchmark signal models corresponding to S̃<sub>1</sub> (m, y<sub>de</sub>) = (2.0 TeV, 1.0) and S̃<sub>1</sub> (m, y<sub>de</sub>) = (3.0 TeV, 1.0), respectively. Note: the values in the table are normalized by the width of corresponding bin
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 search for single production of a vector-like quark $Q$, which could be either a singlet $T$, with charge $\tfrac23$, or a $Y$ from a $(T,B,Y)$ triplet, with charge $-\tfrac43$, is performed using data from proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to the full integrated luminosity of 140 fb$^{-1}$ recorded with the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis targets $Q \to Wb$ decays where the $W$ boson decays leptonically. The data are found to be consistent with the expected Standard Model background, so upper limits are set on the cross-section times branching ratio, and on the coupling of the $Q$ to the Standard Model sector for these two benchmark models. Effects of interference with the Standard Model background are taken into account. For the singlet $T$, the 95% confidence level limit on the coupling strength $κ$ ranges between 0.22 and 0.52 for masses from 1150 to 2300 GeV. For the $(T,B,Y)$ triplet, the limits on $κ$ vary from 0.14 to 0.46 for masses from 1150 to 2600 GeV.
Distributions of the VLQ-candidate mass, m<sub>VLQ</sub>, in the (a–c) SRs, (d–f) W+jets CRs and (g–i) tt̄ CRs after the fit to the background-only hypothesis. The columns correspond from left to right to the low-, middle-, and high-p<sub>T</sub><sup>W</sup> bins in each region. Other includes remaining backgrounds from top quarks or that contain two W/Z bosons. The last bin includes overflow. Note: the 'Data' values in the table are normalized by the width of the bin to correspond to the number of events per 100 GeV
Distributions of the VLQ-candidate mass, m<sub>VLQ</sub>, in the (a–c) SRs, (d–f) W+jets CRs and (g–i) tt̄ CRs after the fit to the background-only hypothesis. The columns correspond from left to right to the low-, middle-, and high-p<sub>T</sub><sup>W</sup> bins in each region. Other includes remaining backgrounds from top quarks or that contain two W/Z bosons. The last bin includes overflow. Note: the 'Data' values in the table are normalized by the width of the bin to correspond to the number of events per 100 GeV
Distributions of the VLQ-candidate mass, m<sub>VLQ</sub>, in the (a–c) SRs, (d–f) W+jets CRs and (g–i) tt̄ CRs after the fit to the background-only hypothesis. The columns correspond from left to right to the low-, middle-, and high-p<sub>T</sub><sup>W</sup> bins in each region. Other includes remaining backgrounds from top quarks or that contain two W/Z bosons. The last bin includes overflow. Note: the 'Data' values in the table are normalized by the width of the bin to correspond to the number of events per 100 GeV
The total cross section for Compton scattering off atomic electrons, $γ+e\rightarrowγ'+e'$, was measured using photons with energies between 6.5 and 11.1 GeV incident on a $^9$Be target as part of the PrimEx-eta experiment in Hall D at Jefferson Lab. This is the first measurement of this fundamental QED process within this energy range. The total uncertainties of the cross section, combining the statistical and systematic components in quadrature, averaged to 3.4% across all energy bins. This not only demonstrates the capability of this experimental setup to perform precision cross-section measurements at forward angles but also allows us to compare with state-of-the-art QED calculations.
$\gamma +e^- \rightarrow \gamma + e^-$ total cross section in bins of photon beam energy. The first uncertainties are statistical, and the second are systematic.
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.
We measure the spin-density matrix elements (SDMEs) for the photoproduction of $ϕ(1020)$ off of the proton in its decay to $K_S^0K_L^0$, using 105 pb$^{-1}$ of data collected with a linearly polarized photon beam using the GlueX experiment. The SDMEs are measured in nine bins of the squared four-momentum transfer $t$ in the range $-t=0.15-1.0$ GeV$^2$, providing the first measurement of their $t$-dependence for photon beam energies $E_γ= 8.2-8.8$ GeV. We confirm the dominance of Pomeron exchange in this region, and put constraints on the contribution of other Regge exchanges. We also find that helicity amplitudes where the helicity of the photon and the $ϕ(1020)$ differ by two units are negligible.
Spin-density matrix elements of $\phi(1020)$ mesons produced by a linearly polarized photon beam in the helicity system. For each bin of $-t$, the limits of the bin range are given, along with the average $-\bar t$ and root-mean-square deviation $-t_\text{RMS}$ of all events that fall within the bin.
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.
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