A measurement of the fiducial cross section of the associated production of a Z boson and a high-$p_\mathrm{T}$ photon, where the Z decays to two neutrinos, and a search for anomalous triple gauge couplings are reported. The results are based on data collected by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s}$ = 13 TeV during 2016$-$2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The fiducial Z$γ$ cross section, where a photon with a $p_\mathrm{T}$ greater than 225 GeV is produced in association with a Z, and the Z decays to a $ν\barν$ pair (Z($ν\barν$)$γ$), is measured to be 23.3$^{+1.4}_{-1.3}$ fb, in agreement, within uncertainties, with the standard model prediction. The differential cross section as a function of the photon $p_\mathrm{T}$ has been measured and compared with standard model predictions computed at next-to-leading and at next-to-next-to-leading order in perturbative quantum chromodynamics. Constraints have been placed on the presence of anomalous couplings that affect the ZZ$γ$ and Z$γγ$ vertex using the $p_\mathrm{T}$ spectrum of the photons. The observed 95% confidence level intervals for $CP$-conserving $h_3^γ$ and $h_4^γ$ are determined to be ($-$3.4, 3.5) $\times$ 10$^{-4}$ and ($-$6.8, 6.8) $\times$ 10$^{-7}$, and for $h_3^\mathrm{Z}$ and $h_4^\mathrm{Z}$ they are ($-$2.2, 2.2) $\times$ 10$^{-4}$ and ($-$4.1, 4.2) $\times$ 10$^{-7}$, respectively. These are the strictest limits to date on $h_3^γ$, $h_3^\mathrm{Z}$ and $h_4^\mathrm{Z}$.
Post-fit reconstruction-level photon transverse momentum $p_{T}^{\gamma}$ distribution in the ECAL barrel signal region. The yields correspond to the post-fit expectation from the maximum-likelihood fit used in the analysis, with uncertainties reflecting the post-fit total (stat+syst) uncertainty per bin. Data correspond to the full Run-2 dataset (138 fb$^{-1}$ at $\sqrt{s}=13$ TeV).
Post-fit reconstruction-level photon transverse momentum $p_{T}^{\gamma}$ distribution in the ECAL endcaps signal region. The yields correspond to the post-fit expectation from the maximum-likelihood fit used in the analysis, with uncertainties reflecting the post-fit total (stat+syst) uncertainty per bin. Data correspond to the full Run-2 dataset (138 fb$^{-1}$ at $\sqrt{s}=13$ TeV).
Measured and predicted fiducial cross sections (fb) in the EB, EE, and combined phase space. The fiducial phase space definition follows the analysis selection in the paper. Predictions are shown at NLO (MADGRAPH5_aMC@NLO) and NNLO (MATRIX).
A combined statistical analysis of searches for heavy vector boson resonances decaying into pairs of W, Z, or Higgs bosons, as well as into quark pairs ($\mathrm{q\bar{q}}$, $\mathrm{b\bar{b}}$, $\mathrm{t\bar{t}}$, $\mathrm{t\bar{b}}$) or lepton pairs ($\ell^+\ell^-$, $\ell\barν$), with $\ell =$ e, $μ$, $τ$, is presented. The results are based on proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$, collected by the CMS experiment from 2016 to 2018. No significant deviation from the expectations of the standard model is observed. The results are interpreted in the simplified heavy vector triplet (HVT) framework, setting 95% confidence level upper limits on the production cross sections and coupling strengths to standard model particles or the HVT bosons. The results exclude HVT resonances with masses below 5.5 TeV in a weakly coupled scenario, below 4.8 TeV in a strongly coupled scenario, and up to 2.0 TeV in the case of production via vector boson fusion. The combination provides the most stringent constraints to date on new phenomena predicted by the HVT model.
Expected and observed 95% CL upper limits on the V'boson production cross section as functions of the resonance mass mV' shown separately for the V' → quarks category. The limits are evaluated in the HVT model A scenario.
Expected and observed 95% CL upper limits on the V'boson production cross section as functions of the resonance mass mV' shown separately for the V' → leptons category. The limits are evaluated in the HVT model A scenario.
Expected and observed 95% CL upper limits on the V' boson production cross section as functions of the resonance mass mV' shown separately for the V' → bosons category. The limits are evaluated in the HVT model B scenario.
The first observation of electroweak production of a photon in association with two forward jets in proton-proton collisions is presented. The measurement uses data recorded by the CMS experiment at the LHC during 2016$-$2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis is performed in a region enriched in photon production via vector boson fusion, with a requirement on the transverse momentum of the photon to exceed 200 GeV. The cross section is measured to be 202$^{+36}_{-32}$ fb, at a significance with respect to the null hypothesis that exceeds five standard deviations. This is in agreement with the standard model prediction of 177$^{+13}_{-12}$ fb. Differential cross sections are measured as a function of various observables. Limits are set on dimension-6 effective field theory operators that contribute to the WW$γ$ interaction. The observed 95% confidence intervals for the corresponding Warsaw basis Wilson coefficients $c_\mathrm{W}$ and $c_\mathrm{HWB}$ are [$-$0.11, 0.16] and [$-$1.6, 1.5], respectively.
Summary of uncertainties affecting the measurement as extracted from the fit to data. The total uncertainty is obtained by adding individual contributions in quadrature.
The rapidity gap fraction as a function of $p_{\mathrm{T}^{veto}}$ in data and simulated samples for EW $\gamma$jj and QCD $\gamma$jj. The black points with error bars represent the data and their statistical uncertainties. The theory prediction, calculated using Madgraph5_aMC@NLO version 2.6.5 at NLO in QCD together with PYTHIA version 8.240, as well as MC statistical uncertainties are shown by the colored band.
Normalized differential cross sections, compared with the SM predictions, as a function of the absolute value of pseudorapidity of the leading jet in transverse momentum. The SM predictions are obtained using Madgraph5_aMC@NLO version 2.6.5 at NLO in QCD with PYTHIA version 8.240
A search for a new neutral gauge boson, Z', produced in association with one or two jets, including at least one b jet, and decaying into a pair of muons is presented. The analysis uses proton-proton collision data collected with the CMS detector at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. No significant deviation from background expectations is observed. Upper limits at 95% confidence level on the product of cross section, branching fraction to dimuons, acceptance, and efficiency, from 0.2 to 2 fb, are set for Z' boson masses between 125 and 350 GeV. Process-dependent products of acceptance and efficiency, and model-independent limits on the signal yield are provided. These are the only results to date in the 125$-$200 GeV mass range and the most stringent for b quark fusion production modes in the 200$-$350 GeV range, complementing inclusive Z' boson searches.
Distributions of $m_{\ell\ell}$ in the $\mathrm{SR_{b}^{mm}}$ SR. Events are divided by the bin width. Simulated signal shapes for $Z'$ boson masses of 125, 200, and 350 GeV are shown. The "Stat + syst" band shows the envelope of the fit variations with statistical uncertainties. The ratio of the nominal MC background values (dashed line) and data to the ABCD prediction is shown as a dashed line in the ratio plot. The MC background uncertainties are not shown for visual clarity.
Distributions of $m_{\ell\ell}$ in the $\mathrm{SR_{b+\textrm{j}/b}^{mm}}$ SR. Events are divided by the bin width. Simulated signal shapes for $Z'$ boson masses of 125, 200, and 350 GeV are shown. The "Stat + syst" band shows the envelope of the fit variations with statistical uncertainties. The ratio of the nominal MC background values (dashed line) and data to the ABCD prediction is shown as a dashed line in the ratio plot. The MC background uncertainties are not shown for visual clarity.
Data vs. the ABCD method background prediction for 2016 in $\mathrm{SR_{b}^{mm}}$. Events are divided by the bin width, hence fractional data counts. Error bars show statistical uncertainties of data. The blue band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The lower panels show the ratio of the observed data to the background estimation.
This paper presents a combination of searches for the nonresonant production of Higgs boson pairs (HH) in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data set was collected by the CMS experiment at the LHC from 2016 to 2018 and corresponds to a total integrated luminosity of 138 fb$^{-1}$. The observed (expected) upper limit on the inclusive HH production cross section relative to the standard model (SM) prediction is found to be 3.5 (2.5). Assuming all other Higgs boson couplings are equal to their SM values, the Higgs boson trilinear self-coupling modifier $κ_λ=λ_3/λ_{3}^\text{SM}$ is constrained in the range $-$1.35 $\leq$$κ_λ$$\leq$ 6.37 at 95% confidence level. Similarly, for the coupling modifier $κ_{2\mathrm{V}}$, which governs the interaction between two vector bosons and two Higgs bosons, we have excluded $κ_{2\mathrm{V}}$ = 0 at more than 5 standard deviations for all values of $κ_λ$. At 95% confidence level assuming other couplings are equal to their SM values, $κ_{2\mathrm{V}}$ is constrained in the range 0.64 $\leq$ $κ_{2\mathrm{V}}$ $\leq$ 1.40. This work also studies HH production in several new physics scenarios, using the Higgs effective field theory (HEFT) framework. The HEFT framework is further exploited to study various ultraviolet complete models with an extended Higgs sector and set constraints on specific parameters. An extrapolation of the results to the integrated luminosity expected after the high-luminosity upgrade of the LHC is reported as well.
Values of the effective Lagrangian couplings for the Higgs Effective field theory benchmarks proposed in Ref. [33].
Values of the effective Lagrangian couplings for the Higgs Effective field theory benchmarks proposed in Ref. [34].
Summary of results for the HH analyses included in this combination. The second column is the observed (expected) 95$\%$ CL upper limit on the inclusive signal strength $r$. The third (fourth) column is the allowed 68$\%$ CL interval for the coupling modifier $\kappa_\lambda$ ($\kappa _{2V}$). The last column indicates whether the analysis is included in the results using the HEFT parametrisation.
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.
A general search is presented for supersymmetric particles (sparticles) in scenarios featuring compressed mass spectra using proton-proton collisions at a center-of-mass energy of 13 TeV, recorded with the CMS detector at the LHC. The analyzed data sample corresponds to an integrated luminosity of 138 fb$^{-1}$. A wide range of potential sparticle signatures are targeted, including pair production of electroweakinos, sleptons, and top squarks. The search focuses on events with a high transverse momentum system from initial-state-radiation jets recoiling against a potential sparticle system with significant missing transverse momentum. Events are categorized based on their lepton multiplicity, jet multiplicity, number of b-tagged jets, and kinematic variables sensitive to the sparticle masses and mass splittings. The sensitivity extends to higher parent sparticle masses than previously probed at the LHC for production of pairs of electroweakinos, sleptons, and top squarks with mass spectra featuring small mass splittings (compressed mass spectra). The observed results demonstrate agreement with the predictions of the background-only model. Lower mass limits are set at 95% confidence level on production of pairs of electroweakinos, sleptons, and top squarks that extend to 325, 275, and 780 GeV, respectively, for the most favorable compressed mass regime cases.
Event counts observed in data, $N_{\rm{obs}}$, in each of the model-independent bins, compared with predictions from the control region fit, $N^{\rm{pred}}_{\rm{bkg}}$, their corresponding uncertainties, $\sigma(N^{\rm{pred}}_{\rm{bkg}})$, and the upper limits at 95% CL on the signal strength $(S_{UL}^{95\%})$.
Top squark pair production. Observed upper limits at 95% CL on the product of the cross section and relevant branching fractions, $\sigma (\tilde{\mathrm{t}} \tilde{\mathrm{t}}) \, \mathcal{B}^{2} ( \tilde{\mathrm{t}} \rightarrow \mathrm{t} \tilde{\chi}_1^0 )$, are shown using the color scale where the $\tilde{\mathrm{t}}$ mass is on the $x$-axis and the mass difference between the $\tilde{\mathrm{t}}$ and the LSP is on the $y$-axis
Top squark pair production. Observed upper limits at 95% CL on the product of the cross section and relevant branching fractions, $\sigma (\tilde{\mathrm{t}} \tilde{\mathrm{t}}) \, \mathcal{B}^{2} ( \tilde{\mathrm{t}} \rightarrow \mathrm{t} \tilde{\chi}_1^0 )$, are shown using the color scale where the $\tilde{\mathrm{t}}$ mass is on the $x$-axis and the mass difference between the $\tilde{\mathrm{t}}$ and the LSP is on the $y$-axis
A search for a pair of light pseudoscalar bosons (a$_1$) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a$_1$ decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a$_1$ boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb$^{-1}$. No excess above standard model (SM) expectations is observed. The study combines the 4$τ$ and 2$μ$2$τ$ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4$τ$ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a$_1$ boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a$_1$ bosons exceeding 16% are excluded at 95% CL for a$_1$ boson masses between 5 and 15 GeV and $\tanβ$ $\gt$ 2, with the exception of scenarios in which the a$_1$ boson mixes with charm or bottom quark-antiquark bound states.
The observed and expected upper limits at 95% confidence level on the product of the signal cross section and the branching fraction $\sigma (\mathrm{pp} \to \mathrm{H}+\text{X}) {\mathcal{B}} (\mathrm{H} \to \mathrm{a}_1\,\mathrm{a}_1) {\mathcal{B}}^{2} (\mathrm{a}_1 \to \tau \tau)$, relative to the inclusive Higgs boson production cross section $\sigma_\text{SM}$ predicted in the SM. The green and yellow bands indicate the regions containing 68% and 95% of the distribution of limits expected under the background-only hypothesis.
The observed and expected upper limits at 95% CLs on $\sigma (\mathrm{pp} \to \mathrm{H}+\text{X}) {\mathcal{B}} (\mathrm{H} \to \mathrm{a}_1\,\mathrm{a}_1)$, relative to $\sigma_\text{SM}$, as a function of $m_{\mathrm{a}_1}$ for Type I 2HD+S model ($\tan\beta$ independent).
The observed and expected upper limits at 95% CLs on $\sigma (\mathrm{pp} \to \mathrm{H}+\text{X}) {\mathcal{B}} (\mathrm{H} \to \mathrm{a}_1\,\mathrm{a}_1)$, relative to $\sigma_\text{SM}$, as a function of $m_{\mathrm{a}_1}$ for Type II 2HD+S model, $\tan\beta = 5$.
Several new physics models including versions of supersymmetry (SUSY) characterized by $R$-parity violation (RPV) or with additional hidden sectors predict the production of events with top quarks, low missing transverse momentum, and many additional quarks or gluons. The results of a search for top squarks decaying to two top quarks and six additional light-flavor quarks or gluons are reported. The search employs a novel machine learning method for background estimation from control samples in data using decorrelated discriminators. The search is performed using events with 0, 1, or 2 electrons or muons in conjunction with at least six jets. No requirement is placed on the magnitude of the missing transverse momentum. The result is based on a sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to 138 fb$^{-1}$ of integrated luminosity collected with the CMS detector at the LHC in 2016$-$2018. The data are used to determine upper limits on the top squark pair production cross section in the frameworks of RPV and stealth SUSY. Models with top squark masses less than 700 (930) GeV are excluded at 95% confidence level for RPV (stealth) SUSY scenarios.
Cutflows and signal efficiencies for the RPV SUSY model in the $0\ell$ channel corresponding to two values of $m_{\tilde{t}}$.
Cutflows and signal efficiencies for the Stealth SYY SUSY model in the $0\ell$ channel corresponding to two values of $m_{\tilde{t}}$.
Cutflows and signal efficiencies for the RPV SUSY model in the $1\ell$ channel corresponding to two values of $m_{\tilde{t}}$.
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 $p_{\mathrm{T}}^{\mathrm{lead.\,lep.}}$.
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