This article presents a search for new resonances decaying into a $Z$ or $W$ boson and a 125 GeV Higgs boson $h$, and it targets the $\nu\bar{\nu}b\bar{b}$, $\ell^+\ell^-b\bar{b}$, or $\ell^{\pm}{\nu}b\bar{b}$ final states, where $\ell=e$ or $\mu$, in proton-proton collisions at $\sqrt{s}=13$ TeV. The data used correspond to a total integrated luminosity of 139 fb$^{-1}$ collected by the ATLAS detector during Run 2 of the LHC at CERN. The search is conducted by examining the reconstructed invariant or transverse mass distributions of $Zh$ or $Wh$ candidates for evidence of a localised excess in the mass range from 220 GeV to 5 TeV. No significant excess is observed and 95% confidence-level upper limits between 1.3 pb and 0.3 fb are placed on the production cross section times branching fraction of neutral and charged spin-1 resonances and CP-odd scalar bosons. These limits are converted into constraints on the parameter space of the Heavy Vector Triplet model and the two-Higgs-doublet model.
Acceptance * reconstruction efficiency for the P P --> Zprime --> Zh --> vvbb/cc signals in the 0-lepton channel.
Acceptance * reconstruction efficiency for the P P --> Zprime --> Zh --> vvbb/cc signals in the 0-lepton channel.
Acceptance * reconstruction efficiency for the P P --> Zprime --> Zh --> llbb/cc signals in the 2-lepton channel.
The Standard Model of particle physics describes the known fundamental particles and forces that make up our universe, with the exception of gravity. One of the central features of the Standard Model is a field that permeates all of space and interacts with fundamental particles. The quantum excitation of this field, known as Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin. In 2012, a particle with properties consistent with the Higgs boson of the Standard Model was observed by the ATLAS and CMS experiments at the Large Hadron Collider at CERN. Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, allowing much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and $W$ and $Z$ bosons -- the carriers of the strong, electromagnetic, and weak forces -- are studied in detail. Interactions with three third-generation matter particles (bottom ($b$) and top ($t$) quarks, and tau leptons ($\tau$)) are well measured and indications of interactions with a second-generation particle (muons, $\mu$) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the Standard Model.
Observed and predicted cross sections for different Higgs boson production processes, measured assuming SM values for the decay branching fractions. The lower panels show the ratios of the measured values to their SM predictions. The $p$-value for compatibility of the measurement and the SM prediction is 65%.
Observed and predicted branching fractions for different Higgs boson decay modes measured assuming SM values for the production cross sections. The lower panels show the ratios of the measured values to their SM predictions. The $p$-value for compatibility of the measurement and the SM prediction is 56%.
Ratio of observed rate to predicted SM event rate for different combinations of Higgs boson production and decay processes. The narrow grey bands indicate the theory uncertainties in the SM cross-section times the branching fraction predictions. The $p$-value for compatibility of the measurement and the SM prediction is 72%.
In July 2012, the ATLAS and CMS Collaborations at the CERN Large Hadron Collider announced the observation of a Higgs boson at a mass of around 125 GeV. Ten years later, and with the data corresponding to the production of 30 times larger number of Higgs bosons, we have learnt much more about the properties of the Higgs boson. The CMS experiment has observed the Higgs boson in numerous fermionic and bosonic decay channels, established its spin-parity quantum numbers, determined its mass and measured its production cross sections in various modes. Here the CMS Collaboration reports the most up-to-date combination of results on the properties of the Higgs boson, including the most stringent limit on the cross section for the production of a pair of Higgs bosons, on the basis of data from proton-proton collisions at a centre-of-mass energy of 13 TeV. Within the uncertainties, all these observations are compatible with the predictions of the standard model of elementary particle physics. Much evidence points to the fact that the standard model is a low-energy approximation of a more comprehensive theory. Several of the standard model issues originate in the sector of Higgs boson physics. An order of magnitude larger number of Higgs bosons, expected to be examined over the next fifteen years, will help deepen our understanding of this crucial sector.
Inclusive signal strength modifiers $\mu$.
Signal strength modifiers per production mode $\mu_i$.
Signal strength modifiers per decay mode $\mu^f$.
This paper presents a measurement of fiducial and differential cross-sections for $W^{+}W^{-}$ production in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb$^{-1}$. Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states. The selected events have moderate values of missing transverse momentum and the `stransverse mass' variable $m_{\textrm{T2}}$, which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen so that the acceptance is enhanced for direct $W^{+}W^{-}$ production and suppressed for production via top quarks, which is treated as a background. The fiducial cross-section and particle-level differential cross-sections for six variables are measured and compared with two theoretical SM predictions from perturbative QCD calculations.
Signal region detector-level distribution for the observable $|y_{e\mu}|$.
Signal region detector-level distribution for the observable $|\Delta \phi(e \mu)|$.
Signal region detector-level distribution for the observable $ \cos\theta^{\ast}$.
A search for light long-lived neutral particles with masses in the $O$(MeV-GeV) range is presented. The analysis targets the production of long-lived dark photons in the decay of a Higgs boson produced via gluon-gluon fusion or in association with a $W$ boson. Events that contain displaced collimated Standard Model fermions reconstructed in the calorimeter or muon spectrometer are selected in 139 fb$^{-1}$ of $\sqrt{s} = 13$ TeV $pp$ collision data collected by the ATLAS detector at the LHC. Background estimates for contributions from Standard Model processes and instrumental effects are extracted from data. The observed event yields are consistent with the expected background. Exclusion limits are reported on the production cross-section times branching fraction as a function of the mean proper decay length $c\tau$ of the dark photon, or as a function of the dark-photon mass and kinetic mixing parameter that quantifies the coupling between the Standard Model and potential hidden (dark) sectors. A Higgs boson branching fraction above 1% is excluded at 95% CL for a Higgs boson decaying into two dark photons for dark-photon mean proper decay lengths between 10 mm and 250 mm and dark photons with masses between 0.4 GeV and 2 GeV.
The reconstruction efficiency for μDPJ objects satisfying the cosmic-ray tagger selection produced in the decay of a γ<sub>d</sub> into a muon pair. The reconstruction efficiency is shown for γ<sub>d</sub> with 0<|η|<1 as a function of the transverse decay length L<sub>xy</sub>.
The reconstruction efficiency for μDPJ objects satisfying the cosmic-ray tagger selection produced in the decay of a γ<sub>d</sub> into a muon pair. The reconstruction efficiency is shown for γ<sub>d</sub> with 0<|η|<1 as a function of the γ<sub>d</sub> transverse momentum in events where the γ<sub>d</sub> L<sub>xy</sub> is below 6 m.
The reconstruction efficiency for caloDPJs produced by the decay of γ<sub>d</sub> into e<sup>+</sup>e<sup>-</sup> or qq̄. The reconstruction efficiency is shown for γ<sub>d</sub> with 0<|η|<1.1 as a function of the transverse decay length L<sub>xy</sub>. The efficiency drop at 2.5 m corresponds to the end of the first layer of the HCAL.
The results of a search for Higgs boson pair (HH) production in the WW*WW*, WW*$\tau\tau$, and $\tau\tau\tau\tau$ decay modes are presented. The search uses 138 fb$^{-1}$ of proton-proton collision data recorded by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV from 2016 to 2018. Analyzed events contain two, three, or four reconstructed leptons, including electrons, muons, and hadronically decaying tau leptons. No evidence for a signal is found in the data. Upper limits are set on the cross section for nonresonant HH production, as well as resonant production in which a new heavy particle decays to a pair of Higgs bosons. For nonresonant production, the observed (expected) upper limit on the cross section at 95% confidence level (CL) is 21.3 (19.4) times the standard model (SM) prediction. The observed (expected) ratio of the trilinear Higgs boson self-coupling to its value in the SM is constrained to be within the interval $-$6.9 to 11.1 ($-$6.9 to 11.7) at 95% CL, and limits are set on a variety of new-physics models using an effective field theory approach. The observed (expected) limits on the cross section for resonant HH production range from 0.18 to 0.90 (0.08 to 1.06) pb at 95% CL for new heavy-particle masses in the range 250-1000 GeV.
Distribution of an input to the BDT classifier in the $2\ell$(ss) category: The scalar $p_{T}$ sum, denoted as $H_{T}$, of the two reconstructed $\ell$ and all small-radius jets.
Distribution of an input to the BDT classifier in the $2\ell$(ss) category: The angular separation $\Delta R$ between the two $\ell$.
Distribution of an input to the BDT classifier in the $3\ell$ category: The angular separation between $\ell_{3}$ and the nearest small-radius jet (j). The $\ell_{3}$ in is defined as the $\ell$ that is not part of the opposite-sign $\ell\ell$ pair of lowest mass.
A search for pairs of dijet resonances with the same mass is conducted in final states with at least four jets. Results are presented separately for the case where the four jet production proceeds via an intermediate resonant state and for nonresonant production. The search uses a data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ collected by the CMS detector in proton-proton collisions at $\sqrt{s}$ = 13 TeV. Model-independent limits, at 95% confidence level, are reported on the production cross section of four-jet and dijet resonances. These first LHC limits on resonant pair production of dijet resonances via high mass intermediate states are applied to a signal model of diquarks that decay into pairs of vector-like quarks, excluding diquark masses below 7.6 TeV for a particular model scenario. There are two events in the tails of the distributions, each with a four-jet mass of 8 TeV and an average dijet mass of 2 TeV, resulting in local and global significances of 3.9 and 1.6 standard deviations, respectively, if interpreted as a signal. The nonresonant search excludes pair production of top squarks with masses between 0.50 TeV to 0.77 TeV, with the exception of a small interval between 0.52 and 0.58 TeV, for supersymmetric $R$-parity-violating decays to quark pairs, significantly extending previous limits. Here, the most significant excess above the predicted background occurs at an average dijet mass of 0.95 TeV, for which the local and global significances are 3.6 and 2.5 standard deviations, respectively.
The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for resonant production of paired dijet resonances decaying to a quark-gluon pair, with $M(X)/M(Y) = 0.11$. The corresponding expected limits and their variations at the 1 and 2 standard deviation levels are also shown. Limits are compared to predictions for a scalar diquark with couplings to pairs of up quarks, $y_{uu}$ = 0.4, and to pairs of vector-like quarks, $y_{χ}$ = 0.6.
The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for resonant production of paired dijet resonances decaying to a quark-gluon pair, with $M(X)/M(Y) = 0.13$. The corresponding expected limits and their variations at the 1 and 2 standard deviation levels are also shown. Limits are compared to predictions for a scalar diquark with couplings to pairs of up quarks, $y_{uu}$ = 0.4, and to pairs of vector-like quarks, $y_{χ}$ = 0.6.
The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for resonant production of paired dijet resonances decaying to a quark-gluon pair, with $M(X)/M(Y) = 0.15$. The corresponding expected limits and their variations at the 1 and 2 standard deviation levels are also shown. Limits are compared to predictions for a scalar diquark with couplings to pairs of up quarks, $y_{uu}$ = 0.4, and to pairs of vector-like quarks, $y_{χ}$ = 0.6.
Production cross sections of the standard model Higgs boson decaying to a pair of W bosons are measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis targets Higgs bosons produced via gluon fusion, vector boson fusion, and in association with a W or Z boson. Candidate events are required to have at least two charged leptons and moderate missing transverse momentum, targeting events with at least one leptonically decaying W boson originating from the Higgs boson. Results are presented in the form of inclusive and differential cross sections in the simplified template cross section framework, as well as couplings of the Higgs boson to vector bosons and fermions. The data set collected by the CMS detector during 2016-2018 is used, corresponding to an integrated luminosity of 138 fb$^{-1}$. The signal strength modifier $\mu$, defined as the ratio of the observed production rate in a given decay channel to the standard model expectation, is measured to be $\mu$ = 0.95 $^{+0.10}_{-0.09}$. All results are found to be compatible with the standard model within the uncertainties.
Results of likelihood scans for the signal strength modifiers corresponding to the four main SM H boson production mechanisms. The uncertainties, corresponding to one standard deviation confidence intervals, include both statistical and systematic sources. The additional breakdown of the uncertainties into their separate statistical and systematic contributions is also shown
Correlation matrix of the signal strength modifiers corresponding to the four main SM H boson production mechanisms.
Profile likelihood as a function of the overall HWW signal strength modifier, considering all uncertainties
A search for the nonresonant production of Higgs boson pairs (HH) via gluon-gluon and vector boson fusion processes in final states with two bottom quarks and two tau leptons is presented. The search uses data from 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$^{-1}$. Events in which at least one tau lepton decays hadronically are considered and multiple machine learning techniques are used to identify and extract the signal. The data are found to be consistent, within uncertainties, with the standard model (SM) predictions. Upper limits on the HH production cross section are set to constrain the parameter space for anomalous Higgs boson couplings. The observed (expected) upper limit at 95% confidence level corresponds to 3.3 (5.2) times the SM prediction for the inclusive HH cross section and to 124 (154) times the SM prediction for the vector boson fusion HH cross section. At 95% confidence level, the Higgs field self-coupling is constrained to be within -1.7 and 8.7 times the SM expectation, and the coupling of two Higgs bosons to two vector bosons is constrained to be within -0.4 and 2.6 times the SM expectation.
Exclusion limits on the product of the production cross section and the branching fraction for non resonant SM-like HH decaying to 4lbb, as a function of the klamda hypothesis. The green and yellow bands represent, respectively, the one and two standard deviation (s.d.) quantiles around the expected limit.
Upper limit on the signal strength at 95% CL for each year and for their combination. The green and yellow bands represent, respectively, the one and two standard deviation (s.d.) quantiles around the expected limit.
A precise measurement of the invisible width of the Z boson produced in proton-proton collisions at a center-of-mass energy of 13 TeV is presented using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 36.3 fb$^{-1}$. The result is obtained from a simultaneous fit to kinematic distributions for two data samples of Z boson plus jets: one dominated by Z boson decays to invisible particles and the other by Z boson decays to muon and electron pairs. The invisible width is measured to be 523 $\pm$ 3 (stat) $\pm$ 16 (syst) MeV. This result is the first precise measurement of the invisible width of the Z boson at a hadron collider, and is the single most precise direct measurement to date, competitive with the combined result of the direct measurements from the LEP experiments.
Measured Z invisible width.
Systematic uncertainties on Z invisible width.
Forum