A first measurement is presented of the cross section for the scattering of same-sign W boson pairs via the detection of a $\tau$ lepton. The data from proton-proton collisions at the center-of-mass energy of 13 TeV were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 138 fb$^{-1}$. Events were selected that contain two jets with large pseudorapidity and large invariant mass, one $\tau$ lepton, one light lepton (e or $\mu$), and significant missing transverse momentum. The measured cross section for electroweak same-sign WW scattering is 1.44$^{+0.63}_{-0.56}$ times the standard model prediction. In addition, a search is presented for the indirect effects of processes beyond the standard model via the effective field theory framework, in terms of dimension-6 and dimension-8 operators.
Measured signal strength for electroweak (EW) same-sign WW scattering in events with one tau lepton and one light lepton (electron or muon), as well as two jets with large pseudorapidity separation and large dijet invariant mass. The signal strength is defined as the ratio of the observed yield to the Standard Model prediction.
Measured signal strength for combined electroweak (EW) and QCD same-sign WW scattering in events with one tau lepton and one light lepton (electron or muon), as well as two jets with large pseudorapidity separation and large dijet invariant mass. The signal strength is defined as the ratio of the observed yield to the Standard Model prediction.
Observed and expected 68% and 95% confidence intervals on the Wilson coefficients associated with the EFT dimension-6 operators.
This paper reports a search for a light CP-odd scalar resonance with a mass of 20 GeV to 90 GeV in 13 TeV proton-proton collision data with an integrated luminosity of 140 fb$^{-1}$ collected with the ATLAS detector at the Large Hadron Collider. The analysis assumes the resonance is produced via gluon-gluon fusion and decays into a $\tau^{+}\tau^{-}$ pair which subsequently decays into a fully leptonic $\mu^{+}\nu_{\mu} \bar{\nu}_{\tau} e^{-} \bar{\nu}_{e} \nu_{\tau}$ or $e^{+}\nu_{e}\bar{\nu}_{\tau} \mu^-\bar{\nu}_{\mu}\nu_{\tau}$ final state. No significant excess of events above the predicted Standard Model background is observed. The results are interpreted within a flavour-aligned two-Higgs-doublet model, and a model-independent cross-section interpretation is also given. Upper limits at 95$%$ confidence level between 3.0 pb and 68 pb are set on the cross-section for producing a CP-odd Higgs boson that decays into a $\tau^+\tau^-$ pair.
Post-fit $m_\mathrm{MMC}$ distribution in the low-mass SR for the $m_A = 20\,\mathrm{GeV}$ signal mass hypothesis. $m_\mathrm{MMC}$ is the mass reconstructed by the Missing Mass Calculator. Processes contributing to the background Others are $Z/\gamma^* \rightarrow ee/\mu\mu$ and SM Higgs. The subscript on the $A\to\tau\tau$ process indicates the mass of the $A$ boson. Total includes all backgrounds and the signal process. The low-mass Signal Region is defined as: - 1 electron and 1 muon with opposite charge - $p_\mathrm{T}$ requirements of the leptons are a combination of the following: - $p_\mathrm{T}^e > 18\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 15\,\mathrm{GeV}$ - $p_\mathrm{T}^e > 10\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 25\,\mathrm{GeV}$ - $p_\mathrm{T}^e > 27\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 10\,\mathrm{GeV}$ - $\vert \eta_e \vert < 2.47$, excluding $1.37 < \vert \eta_e \vert < 1.52$ - $\vert \eta_\mu \vert < 2.7$ - no jets with $b$-quarks - $\Delta R_{\ell\ell} < 0.7$ - $E_\mathrm{T}^\mathrm{miss} > 50\,\mathrm{GeV}$ - $m_\mathrm{T}^\mathrm{tot} = \sqrt{\left(p_\mathrm{T}^e+p_\mathrm{T}^\mu+E_\mathrm{T}^\mathrm{miss}\right)^2-\left(\vec{p}_\mathrm{T}^{\,e}+\vec{p}_\mathrm{T}^{\,\mu}+\vec{E}_\mathrm{T}^{\,\mathrm{miss}}\right)^2} < 45\,\mathrm{GeV}$ - $m_\mathrm{MMC} > 0\,\mathrm{GeV}$
Post-fit $m_\mathrm{MMC}$ distribution in the high-mass SR for the $m_A = 90\,\mathrm{GeV}$ signal mass hypothesis. $m_\mathrm{MMC}$ is the mass reconstructed by the Missing Mass Calculator. Processes contributing to the background Others are $Z/\gamma^* \rightarrow ee/\mu\mu$ and SM Higgs. The subscript on the $A\to\tau\tau$ process indicates the mass of the $A$ boson. otal includes all backgrounds and the signal process. The high-mass Signal Region is defined as: - 1 electron and 1 muon with opposite charge - $p_\mathrm{T}$ requirements of the leptons are a combination of the following: - $p_\mathrm{T}^e > 18\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 15\,\mathrm{GeV}$ or - $p_\mathrm{T}^e > 10\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 25\,\mathrm{GeV}$ or - $p_\mathrm{T}^e > 27\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 10\,\mathrm{GeV}$ - $\vert \eta_e \vert < 2.47$, excluding $1.37 < \vert \eta_e \vert < 1.52$ - $\vert \eta_\mu \vert < 2.7$ - no jets with $b$-quarks - $\Delta R_{\ell\ell} < 1.0$ - $E_\mathrm{T}^\mathrm{miss} > 30\,\mathrm{GeV}$ - $m_\mathrm{T}^\mathrm{tot} = \sqrt{\left(p_\mathrm{T}^e+p_\mathrm{T}^\mu+E_\mathrm{T}^\mathrm{miss}\right)^2-\left(\vec{p}_\mathrm{T}^{\,e}+\vec{p}_\mathrm{T}^{\,\mu}+\vec{E}_\mathrm{T}^{\,\mathrm{miss}}\right)^2} < 65\,\mathrm{GeV}$ - $35\,\mathrm{GeV} < m_\mathrm{MMC} < 130\,\mathrm{GeV}$
Expected and observed $95\%$ CL limits on the production cross-section for $gg\rightarrow A$ times the branching ratio for $A$ decaying into two $\tau$-leptons for $A$ boson masses ranging from $20$ to $90\,\mathrm{GeV}$.
This paper presents a search for supersymmetric particles in models with highly compressed mass spectra, in events consistent with being produced through vector boson fusion. The search uses 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. Events containing at least two jets with a large gap in pseudorapidity, large missing transverse momentum, and no reconstructed leptons are selected. A boosted decision tree is used to separate events consistent with the production of supersymmetric particles from those due to Standard Model backgrounds. The data are found to be consistent with Standard Model predictions. The results are interpreted using simplified models of $R$-parity-conserving supersymmetry in which the lightest supersymmetric partner is a bino-like neutralino with a mass similar to that of the lightest chargino and second-to-lightest neutralino, both of which are wino-like. Lower limits at 95% confidence level on the masses of next-to-lightest supersymmetric partners in this simplified model are established between 117 and 120 GeV when the lightest supersymmetric partners are within 1 GeV in mass.
Observed and predicted background distributions of the BDT score in $\text{SR}_\text{2j}$ after the exclusion fit. The nominal, pre-fit prediction of an example benchmark signal with $(m(\widetilde{\chi}_{2}^{0}/\widetilde{\chi}_{1}^{\pm}), \widetilde{\chi}_{1}^{0}) = (100, 99)$ GeV is shown in red. The 'Other' category contains rare backgrounds from diboson, triboson and top-quark production processes. The hatched band represents the post-fit experimental, theoretical, and statistical uncertainties in the total background. The bottom panel of each plot shows the ratio between the data and the post-fit background prediction.
Observed and predicted background distributions of the BDT score in $\text{SR}_{\geq3\text{j}}$ after the exclusion fit. The nominal, pre-fit prediction of an example benchmark signal with $(m(\widetilde{\chi}_{2}^{0}/\widetilde{\chi}_{1}^{\pm}), \widetilde{\chi}_{1}^{0}) = (100, 99)$ GeV is shown in red. The 'Other' category contains rare backgrounds from diboson, triboson and top-quark production processes. The hatched band represents the post-fit experimental, theoretical, and statistical uncertainties in the total background. The bottom panel of each plot shows the ratio between the data and the post-fit background prediction.
Expected (dashed black line) and observed (solid red line) 95% CL exclusion limits on the compressed SUSY simplified model with a bino-like LSP and wino-like NLSPs being considered. These are shown with $\pm1\sigma_\text{exp}$ (yellow band) from experimental systematic and statistical uncertainties, and with $\pm1\sigma^{\text{SUSY}}_{\text{theory}}$ (red dotted lines) from signal cross-section uncertainties, respectively. The limits set by the ATLAS searches using the soft lepton signature is illustrated by the blue region while the limit imposed by the LEP experiments is shown in grey.
An analysis is presented based on models of the intrinsic transverse momentum (intrinsic $k_\mathrm{T}$) of partons in nucleons by studying the dilepton transverse momentum in Drell-Yan events. Using parameter tuning in event generators and existing data from fixed-target experiments and from hadron colliders, our investigation spans three orders of magnitude in center-of-mass energy and two orders of magnitude in dilepton invariant mass. The results show an energy-scaling behavior of the intrinsic $k_\mathrm{T}$ parameters, independent of the dilepton invariant mass at a given center-of-mass energy.
Tuned intrinsic kT parameters BeamRemnants:PrimordialkThard in Pythia with the underlying-event tune CP5 at nucleon-nucleon center-of-mass energy from 38.8 GeV to 13 TeV.
Tuned intrinsic kT parameters BeamRemnants:PrimordialkThard in Pythia with the underlying-event tune CP4 at nucleon-nucleon center-of-mass energy from 38.8 GeV to 13 TeV.
Tuned intrinsic kT parameters BeamRemnants:PrimordialkThard in Pythia with the underlying-event tune CP3 at nucleon-nucleon center-of-mass energy from 38.8 GeV to 13 TeV.
A search for the production of top-quark pairs with the same electric charge ($tt$ or $\bar{t}\bar{t}$) is presented. The analysis uses proton-proton collision data at $\sqrt{s}=13$ TeV, recorded by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb$^{-1}$. Events with two same-charge leptons and at least two $b$-tagged jets are selected. Neural networks are employed to define two selections sensitive to additional couplings beyond the Standard Model that would enhance the production rate of same-sign top-quark pairs. No significant signal is observed, leading to an upper limit on the total production cross-section of same-sign top-quark pairs of 1.6 fb at 95$\%$ confidence level. Corresponding limits on the three Wilson coefficients associated with the ${\cal O}_{tu}^{(1)}$, ${\cal O}_{Qu}^{(1)}$, and ${\cal O}_{Qu}^{(8)}$ operators in the Standard Model Effective Field Theory framework are derived.
Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{ctu ++}$ signal region. The post-fit background expectations are shown as filled histograms, the combined pre-fit background expectations are shown as dashed lines. The signal distribution using the Wilson coefficient values $c_{tu}^{(1)}=0.04$, $c_{Qu}^{(1)}=0.1$, $c_{Qu}^{(8)}=0.1$ is shown with a dotted line, normalized to the same number of events as the background.
Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{ctu --}$ signal region. The post-fit background expectations are shown as filled histograms, the combined pre-fit background expectations are shown as dashed lines. The signal distribution using the Wilson coefficient values $c_{tu}^{(1)}=0.04$, $c_{Qu}^{(1)}=0.1$, $c_{Qu}^{(8)}=0.1$ is shown with a dotted line, normalized to the same number of events as the background.
Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{cQu ++}$ signal region. The post-fit background expectations are shown as filled histograms, the combined pre-fit background expectations are shown as dashed lines. The signal distribution using the Wilson coefficient values $c_{tu}^{(1)}=0.04$, $c_{Qu}^{(1)}=0.1$, $c_{Qu}^{(8)}=0.1$ is shown with a dotted line, normalized to the same number of events as the background.
A measurement of the Higgs boson mass and width via its decay to two Z bosons is presented. Proton-proton collision data collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb$^{-1}$ at a center-of-mass energy of 13 TeV is used. The invariant mass distribution of four leptons in the on-shell Higgs boson decay is used to measure its mass and contrain its width. This yields the most precise single measurement of the Higgs boson mass to date, 125.04 $\pm$ 0.12 GeV, and an upper limit on the width $\Gamma_\mathrm{H}$$\lt$ 330 MeV at 95% confidence level. A combination of the on- and off-shell Higgs boson production decaying to four leptons is used to determine the Higgs boson width, assuming that no new virtual particles affect the production, a premise that is tested by adding new heavy particles in the gluon fusion loop model. This result is combined with a previous CMS analysis of the off-shell Higgs boson production with decay to two leptons and two neutrinos, giving a measured Higgs boson width of 3.0$^{+2.0}_{-1.5}$ MeV, in agreement with the standard model prediction of 4.1 MeV. The strength of the off-shell Higgs boson production is also reported. The scenario of no off-shell Higgs boson production is excluded at a confidence level corresponding to 3.8 standard deviations.
Observed profile likelihood projection on mH, for different flavor categories combined, using the N-2D′ VXBS approach. Both statistical and systematic uncertainties have been considered.
Observed profile likelihood projection on mH, for the 4mu final state, using the N-2D′ VXBS approach. Both statistical and systematic uncertainties have been considered.
Observed profile likelihood projection on mH, for the 4e final state, using the N-2D′ VXBS approach. Both statistical and systematic uncertainties have been considered.
Inclusive cross-sections for top-quark pair production in association with charm quarks are measured with proton-proton collision data at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb$^{-1}$, collected with the ATLAS experiment at the LHC between 2015 and 2018. The measurements are performed by requiring one or two charged leptons (electrons and muons), two $b$-tagged jets, and at least one additional jet in the final state. A custom flavor-tagging algorithm is employed for the simultaneous identification of $b$-jets and $c$-jets. In a fiducial phase space that replicates the acceptance of the ATLAS detector, the cross-sections for $t\bar{t}+ {\geq} 2c$ and $t\bar{t}+1c$ production are measured to be $1.28^{+0.27}_{-0.24}\;\text{pb}$ and $6.4^{+1.0}_{-0.9}\;\text{pb}$, respectively. The measurements are primarily limited by uncertainties in the modeling of inclusive $t\bar{t}$ and $t\bar{t}+b\bar{b}$ production, in the calibration of the flavor-tagging algorithm, and by data statistics. Cross-section predictions from various $t\bar{t}$ simulations are largely consistent with the measured cross-section values, though all underpredict the observed values by 0.5 to 2.0 standard deviations. In a phase-space volume without requirements on the $t\bar{t}$ decay products and the jet multiplicity, the cross-section ratios of $t\bar{t}+ {\geq} 2c$ and $t\bar{t}+1c$ to total $t\bar{t}+\text{jets}$ production are determined to be $(1.23 \pm 0.25) \%$ and $(8.8 \pm 1.3) \%$.
Measured cross-section values in the fiducial phase space and inclusive volume for the various $t\bar{t}+jets$ categories.
Post-fit agreement between data and MC prediction for $SR_{\mathrm{loose}}^{1\ell5j}$ signal region, which uses the invariant mass of the two geometrically closest c-tagged jets, $m_{\mathit{cc}}^{\mathrm{min}\Delta R}$, as an observable. The hatched uncertainty bands include all uncertainties and their correlations. The last bins contain overflow events. "Other Top" includes single-top-quark production and associated production of $t\bar{t}$ and single top quarks with bosons. "Non-Top" includes W+jets, Z+jets, and diboson processes.
Post-fit agreement between data and MC prediction for the $SR_{\mathrm{tight}}^{1\ell5j}$ signal region, which uses the invariant mass of the two geometrically closest jets tagged with c@11%, $m_{\mathit{cc}}^{\mathrm{min}\Delta R}$, as an observable. The hatched uncertainty bands include all uncertainties and their correlations. The last bins contain overflow events. "Other Top" includes single-top-quark production and associated production of $t\bar{t}$ and single top quarks with bosons. "Non-Top" includes W+jets, Z+jets, and diboson processes.
Measurements of the polarization and spin correlation in top quark pairs ($\mathrm{t\bar{t}}$) are presented using events with a single electron or muon and jets in the final state. The measurements are based on proton-proton collision data from the LHC at $\sqrt{s}$ = 13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb$^{-1}$. All coefficients of the polarization vectors and the spin correlation matrix are extracted simultaneously by performing a binned likelihood fit to the data. The measurement is performed inclusively and in bins of additional observables, such as the mass of the $\mathrm{t\bar{t}}$ system and the top quark scattering angle in the $\mathrm{t\bar{t}}$ rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the $\mathrm{t\bar{t}}$ spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for $\mathrm{t\bar{t}}$ states at the production threshold and at high masses of the $\mathrm{t\bar{t}}$ system. Entanglement is observed for the first time in events at high $\mathrm{t\bar{t}}$ mass, where a large fraction of the $\mathrm{t\bar{t}}$ decays are space-like separated, with an expected and observed significance of above 5 standard deviations.
Results for full matrix measurement inclusive from $m(t\bar{t})$
Covariance for full matrix measurement inclusive from $m(t\bar{t})$
Results for full matrix measurement all bins from $m(t\bar{t})$ fit
In ultra-relativistic heavy ion collisions at the LHC, each nucleus acts a sources of high-energy real photons that can scatter off the opposing nucleus in ultra-peripheral photonuclear ($\gamma+A$) collisions. Hard scattering processes initiated by the photons in such collisions provide a novel method for probing nuclear parton distributions in a kinematic region not easily accessible to other measurements. ATLAS has measured production of dijet and multi-jet final states in ultra-peripheral Pb+Pb collisions at $\sqrt{s_{\text{NN}}} = 5.02$ TeV using a data set recorded in 2018 with an integrated luminosity of 1.72 $\text{nb}^{-1}$. Photonuclear final states are selected by requiring a rapidity gap in the photon direction; this selects events where one of the outgoing nuclei remains intact. Jets are reconstructed using the anti-$k_\text{t}$ algorithm with radius parameter, $R = 0.4$. Triple-differential cross-sections, unfolded for detector response, are measured and presented using two sets of kinematic variables. The first set consists of the total transverse momentum ($H_\text{T}$),rapidity, and mass of the jet system. The second set uses $H_\text{T}$ and particle-level nuclear and photon parton momentum fractions, $x_\text{A}$ and $z_{\gamma}$, respectively. The results are compared with leading-order (LO) perturbative QCD calculations of photonuclear jet production cross-sections, where all LO predictions using existing fits fall below the data in the shadowing region. More detailed theoretical comparisons will allow these results to strongly constrain nuclear parton distributions, and these data provide results from the LHC directly comparable to early physics results at the planned Electron-Ion Collider.
The fraction of photonuclear jet events passing the fiducial requirements in which the photon-emitting nucleus does not break up as a function of \zg. The systematic uncertainties are not symmetrized, and correlations in uncertainties are neglected for both the total systematic uncertainty and statistical uncertainty.
Fully unfolded triple-differential cross-sections as a function of $H_\text{T}$, $y_\text{jets}$, and $m_\text{jets}$. Systematic uncertainties are decomposed into symmetrized nuisance parameters, where parameters labelled "Corr" are fully correlated bin-to-bin, while parameters labelled "Uncorr" should be treated as un-correlated bin-to-bin. These cross-sections are not corrected for the effects of additional nuclear break-up. Values for the total fiducial cross-section in each bin are reported with full statistical and systematic uncertainties. Fractions of the total bin volume occupied by the fiducial region, fractions of the total cross-section in that bin satisfying fiducial requirements, and mean bin values for each axis variable are derived from Pythia 8 Monte Carlo and reported as well. For more details on these quantities, see Appendix B.
Fully unfolded triple-differential cross-sections as a function of $H_\text{T}$, $x_\text{A}$, and $z_{\gamma}$. Systematic uncertainties are decomposed into symmetrized nuisance parameters, where parameters labelled "Corr" are fully correlated bin-to-bin, while parameters labelled "Uncorr" should be treated as un-correlated bin-to-bin. These cross-sections are not corrected for the effects of additional nuclear break-up. Values for the total fiducial cross-section in each bin are reported with full statistical and systematic uncertainties. Fractions of the total bin volume occupied by the fiducial region, fractions of the total cross-section in that bin satisfying fiducial requirements, and mean bin values for each axis variable are derived from Pythia 8 Monte Carlo and reported as well. For more details on these quantities, see Appendix B.
A search for light long-lived particles decaying to displaced jets is presented, using a data sample of proton-proton collisions at a center-of-mass energy of 13.6 TeV, corresponding to an integrated luminosity of 34.7 fb$^{-1}$, collected with the CMS detector at the CERN LHC in 2022. Novel trigger, reconstruction, and machine-learning techniques were developed for and employed in this search. After all selections, the observations are consistent with the background predictions. Limits are presented on the branching fraction of the Higgs boson to long-lived particles that subsequently decay to quark pairs or tau lepton pairs. An improvement by up to a factor of 10 is achieved over previous limits for models with long-lived particle masses smaller than 60 GeV and proper decay lengths smaller than 1 m. The first constraints are placed on the fraternal twin Higgs and folded supersymmetry models, where the lower bounds on the top quark partner mass reach up to 350 GeV for the fraternal twin Higgs model and 250 GeV for the folded supersymmetry model.
The predicted background yields and the number of observed events for the data with $g_{\mathrm{prompt-veto}}>0.985$, shown for different bins of the displacd-dijet GNN score $g_{\mathrm{displaced}}$. Expected signal yields for the $\mathrm{H \to SS}$, $\mathrm{S \to b\overline{b}}$ signature are also shown for models with $m_{\mathrm{S}}=40~\mathrm{GeV}$, and $c \tau_{0}=1$, $10$ or $100\mathrm{mm}$, assuming a branching fraction of $1\%$ for the $\mathrm{H \to SS}$ decay.
The 95% CL upper limits on the branching fraction $\mathcal{B}(\mathrm{H \to SS})$ with $\mathrm{S \to b\overline{b}}$ deacy, for different LLP masses $m_{\mathrm{S}}$ and proper decay lengths $c\tau_{0}$.
The 95% CL upper limits on the branching fraction $\mathcal{B}(\mathrm{H \to SS})$ with $\mathrm{S \to d\overline{d}}$ decay, for different LLP masses $m_{\mathrm{S}}$ and proper decay lengths $c\tau_{0}$.
Forum