We present a search for magnetic monopoles and high-electric-charge objects using LHC Run 2 $\sqrt{s} =$13 TeV proton$-$proton collisions recorded by the ATLAS detector. A total integrated luminosity of 138 fb$^{-1}$ was collected by a specialized trigger. No highly ionizing particle candidate was observed. Considering the Drell-Yan and photon-fusion pair production mechanisms as benchmark models, cross-section upper limits are presented for spin-0 and spin-$\frac{1}{2}$ magnetic monopoles of magnetic charge $1g_\textrm{D}$ and $2g_\textrm{D}$ and for high-electric-charge objects of electric charge $20 \leq |z| \leq 100$, for masses between 200 GeV and 4000 GeV. The search improves by approximately a factor of three the previous cross-section limits on the Drell-Yan production of magnetic monopoles and high-electric charge objects. Also, the first ATLAS limits on the photon-fusion pair production mechanism of magnetic monopoles and high-electric-charge objects have been obtained.
Observed 95% CL upper limits on the cross section for all masses and charges of Drell-Yan spin-0 monopoles production as a function of mass for magnetic charges $|g|=1g_D$ and $|g|=2g_D$.
Observed 95% CL upper limits on the cross section for all masses and charges of Drell-Yan spin-1/2 monopoles production as a function of mass for magnetic charges $|g|=1g_D$ and $|g|=2g_D$.
Observed 95% CL upper limits on the cross section for all masses and charges of photon-fusion pair-produced spin-0 monopoles as a function of mass for magnetic charges $|g|=1g_D$ and $|g|=2g_D$.
This letter reports the observation of $W(\ell\nu)\gamma\gamma$ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of $\sqrt{s} = 13$ TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb$^{-1}$. Events with a leptonically-decaying $W$ boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of $5.6$ standard deviations. The inclusive fiducial production cross section of $W(e\nu)\gamma\gamma$ and $W(\mu\nu)\gamma\gamma$ events is measured to be $\sigma_{\mathrm{fid}} = 13.8 \pm 1.1 (\mathrm{stat}) \substack{+2.1 \\ -2.0} (\mathrm{syst}) \pm 0.1 (\mathrm{lumi})$ fb, in agreement with the Standard Model prediction.
The measured fiducial $W(\rightarrow e\nu / \mu\nu)\gamma\gamma$ integrated cross section compared with both the signal event generator predictions.
A measurement of the Higgs boson (H) production via vector boson fusion (VBF) and its decay into a bottom quark-antiquark pair ($\mathrm{b\bar{b}}$) is presented using proton-proton collision data recorded by the CMS experiment at $\sqrt{s}$ = 13 TeV and corresponding to an integrated luminosity of 90.8 fb$^{-1}$. Treating the gluon-gluon fusion process as a background and constraining its rate to the value expected in the standard model (SM) within uncertainties, the signal strength of the VBF process, defined as the ratio of the observed signal rate to that predicted by the SM, is measured to be $\mu^\text{qqH}_\mathrm{Hb\bar{b}}$ = 1.01 $^{+0.55}_{-0.46}$. The VBF signal is observed with a significance of 2.4 standard deviations relative to the background prediction, while the expected significance is 2.7 standard deviations. Considering inclusive Higgs boson production and decay into bottom quarks, the signal strength is measured to be $\mu^\text{incl.}_\mathrm{Hb\bar{b}}$ = 0.99 $^{+0.48}_{-0.41}$, corresponding to an observed (expected) significance of 2.6 (2.9) standard deviations.
The mbb distribution after weighted combination of all categories in the analysis weighted with S/(S + B). where S is the total Hbb signal yield (both VBF and ggH) and B is the total background yield including QCD multijet and Z+jets
The best fit values of the signal strength modifier for the different processes. 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.
The best fit values of the signal strength modifier for the different processes by floating the VBF and ggH production rates independently. 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.
A search for new physics in final states consisting of at least one photon, multiple jets, and large missing transverse momentum is presented, using proton-proton collision events at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 137 fb$^{-1}$, recorded by the CMS experiment at the CERN LHC from 2016 to 2018. The events are divided into mutually exclusive bins characterized by the missing transverse momentum, the number of jets, the number of b-tagged jets, and jets consistent with the presence of hadronically decaying W, Z, or Higgs bosons. The observed data are found to be consistent with the prediction from standard model processes. The results are interpreted in the context of simplified models of pair production of supersymmetric particles via strong and electroweak interactions. Depending on the details of the signal models, gluinos and squarks of masses up to 2.35 and 1.43 TeV, respectively, and electroweakinos of masses up to 1.23 TeV are excluded at 95% confidence level.
SM background predictions, data observations and signal yields in the signal region.
The 95% CL observed upper limits on the production cross sections for $m_{\tilde{g}}$ in T5bbbbZg.
Gluino - neutralino mass points lying on the observed exclusion contour of T5bbbbZg model.
A search for new physics in top quark production with additional final-state leptons is performed using data collected by the CMS experiment in proton-proton collisions at $\sqrt{s}$ = 13 TeV at the LHC during 2016-2018. The data set corresponds to an integrated luminosity of 138 fb$^{-1}$. Using the framework of effective field theory (EFT), potential new physics effects are parametrized in terms of 26 dimension-six EFT operators. The impacts of EFT operators are incorporated through the event-level reweighting of Monte Carlo simulations, which allows for detector-level predictions. The events are divided into several categories based on lepton multiplicity, total lepton charge, jet multiplicity, and b-tagged jet multiplicity. Kinematic variables corresponding to the transverse momentum ($p_\mathrm{T}$) of the leading pair of leptons and/or jets as well as the $p_\mathrm{T}$ of on-shell Z bosons are used to extract the 95% confidence intervals of the 26 Wilson coefficients corresponding to these EFT operators. No significant deviation with respect to the standard model prediction is found.
The 1$\sigma$ and 2$\sigma$ uncertainty intervals extracted from the likelihood fits described in Section 7. The intervals are shown for the case where the other WCs are profiled, and the case where the other WCs are fixed to their SM values of zero.
Observed $2 \Delta NLL$ of a 2D scan for $c_{tW}$ and $c_{tZ}$ with the other WCs profiled.
Observed $2 \Delta NLL$ of a 2D scan for $c_{tW}$ and $c_{tZ}$ with the other WCs fixed to their SM values.
New particles with large masses that decay into hadronically interacting particles are predicted by many models of physics beyond the Standard Model. A search for a massive resonance that decays into pairs of dijet resonances is performed using 140 fb$^{-1}$ of proton$-$proton collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Resonances are searched for in the invariant mass of the tetrajet system, and in the average invariant mass of the pair of dijet systems. A data-driven background estimate is obtained by fitting the tetrajet and dijet invariant mass distributions with a four-parameter dijet function and a search for local excesses from resonant production of dijet pairs is performed. No significant excess of events beyond the Standard Model expectation is observed, and upper limits are set on the production cross-sections of new physics scenarios.
The average tetrajet invariant mass distributions in data, along with the fitted background estimates for 0.10 < $\alpha$ < 0.12.
The average tetrajet invariant mass distributions in data, along with the fitted background estimates for 0.12 < $\alpha$ < 0.14.
The average tetrajet invariant mass distributions in data, along with the fitted background estimates for 0.14 < $\alpha$ < 0.16.
A search for quantum black holes in electron+jet and muon+jet invariant mass spectra is performed with 140 fb$^{-1}$ of data collected by the ATLAS detector in proton-proton collisions at $\sqrt{s}$ = 13 TeV at the Large Hadron Collider. The observed invariant mass spectrum of lepton+jet pairs is consistent with Standard Model expectations. Upper limits are set at 95% confidence level on the production cross-sections times branching fractions for quantum black holes decaying into a lepton and a quark in a search region with invariant mass above 2.0 TeV. The resulting quantum black hole lower mass threshold limit is 9.2 TeV in the Arkani-Hamed-Dimopoulos-Dvali model, and 6.8 TeV in the Randall-Sundrum model.
The 95% CL model-independent upper limits on $\sigma \times Br$ for the non-SM signal production with decay into the lepton+jet. The limits take into account statistical and systematic uncertainties. Circles along the solid red line indicate the lower border of the SR (threshold of SR, Th$_\mathrm{SR}$), above which the observed limit is computed. The expected limits are shown by the dashed line. The $\pm 1\sigma$ and $\pm 2\sigma$ bands of expected limits are shown in green and yellow, respectively. The limits are obtained with pseudo-experiments.
The combined 95% CL upper limits on $\sigma \times Br$ as a function of threshold mass, $M_\mathrm{th}$, for QBH production with decay into lepton+jet for ADD-model (extra dimensions n = 6). The limits take into account statistical and systematic uncertainties. Circles along the solid red line indicate the mass $M_\mathrm{th}$ of the signal where the observed limit is computed. The expected limits are shown by the dashed line. The $\pm 1\sigma$ and $\pm 2\sigma$ bands are shown in green and yellow, respectively. The theoretically predicted $\sigma \times Br$ for the QBH production and decay is shown as the solid blue curve with squares.
The combined 95% CL upper limits on $\sigma \times Br$ as a function of threshold mass, $M_\mathrm{th}$, for QBH production with decay into lepton+jet for RS1-model (extra dimensions n = 1). The limits take into account statistical and systematic uncertainties. Circles along the solid red line indicate the mass $M_\mathrm{th}$ of the signal where the observed limit is computed. The expected limits are shown by the dashed line. The $\pm 1\sigma$ and $\pm 2\sigma$ bands are shown in green and yellow, respectively. The theoretically predicted $\sigma \times Br$ for the QBH production and decay is shown as the solid blue curve with squares.
Angular distributions of charged particles relative to jet axes are studied in $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV Au+Au collisions as a function of the jet orientation with respect to the event plane. This differential study tests the expected path-length dependence of energy loss experienced by a hard-scattered parton as it traverses the hot and dense medium formed in heavy-ion collisions. A second-order event plane is used in the analysis as an experimental estimate of the reaction plane formed by the collision impact parameter and the beam direction. Charged-particle jets with $15 < p_{\rm T, jet} <$ 20 and $20 < p_{\rm T, jet} <$ 40 GeV/$c$ were reconstructed with the anti-$k_{\rm T}$ algorithm with radius parameter setting of (R=0.4) in the 20-50% centrality bin to maximize the initial-state eccentricity of the interaction region. The reaction plane fit method is implemented to remove the flow-modulated background with better precision than prior methods. Yields and widths of jet-associated charged-hadron distributions are extracted in three angular bins between the jet axis and the event plane. The event-plane (EP) dependence is further quantified by ratios of the associated yields in different EP bins. No dependence on orientation of the jet axis with respect to the event plane is seen within the uncertainties in the kinematic regime studied. This finding is consistent with a similar experimental observation by ALICE in $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV Pb+Pb collision data.
Event-plane resolution, second-order harmonic relative to the event plane, $R_{2}(\Psi_{2})$, respectively.
Event-plane resolution, second-order harmonic relative to the event plane, $R_{4}(\Psi_{2})$, respectively.
$p_{T, jet}$ resolution for $15 < p_{T, jet}^{GEN} < 20$ GeV/c $R=0.4$ full jets. Jets are measured from all angles relative to the event plane in the 20-50% most central events.
A search for a new heavy scalar particle $X$ decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle $S$ is presented. The search uses a proton-proton ($pp$) collision data sample with an integrated luminosity of 140 fb$^{-1}$ recorded at a centre-of-mass energy of $\sqrt{s} = 13$ TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in $X$ mass ranging from 500 to 1500 GeV, with the corresponding $S$ mass in the range 200-500 GeV. The search selects events with two hadronically decaying $\tau$-lepton candidates from $H\to \tau^+\tau^-$ decays and one or two light leptons ($\ell=e,\,\mu$) from $S\to VV$ ($V = W,\,Z$) decays while the remaining $V$ boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section $\sigma(pp\to X\to SH)$ assuming the same SM-Higgs boson-like decay branching ratios for the $S\to VV$ decay. Upper limits on the visible cross-sections $\sigma(pp\to X\to SH \to WW\tau\tau)$ and $\sigma(pp\to X\to SH \to ZZ\tau\tau)$ are also set in the ranges 3-26 fb and 6-33 fb, respectively.
Observed and expected 95% CL upper limits are shown for $\sigma(pp\to X\to SH)$ obtained from $WW1\ell2\tau_{\mathrm{had}}$, $WW2\ell2\tau_{\mathrm{had}}$, $ZZ2\ell2\tau_{\mathrm{had}}$, and their combination, as a function of combined $m_{S}$ and $m_{X}$ masses ($m_{S}$+$m_{X}/25$) in GeV.
Observed and expected 95% CL upper limits are shown for $\sigma(pp\to X\to SH\to WW\tau\tau)$ obtained from the combination of $WW1\ell2\tau_{\mathrm{had}}$ and $WW2\ell2\tau_{\mathrm{had}}$ channels, as a function of combined $m_{S}$ and $m_{X}$ masses ($m_{S}$+$m_{X}/25$) in GeV. The NMSSM scans of the allowed cross-sections for $\sigma(pp\to X\to SH\to WW\tau\tau)$ are also compared.
Observed and expected 95% CL upper limits are shown for $\sigma(pp\to X\to SH\to ZZ\tau\tau)$ obtained from $ZZ2\ell2\tau_{\mathrm{had}}$ channel, as a function of combined $m_{S}$ and $m_{X}$ masses ($m_{S}$+$m_{X}/25$) in GeV. The NMSSM scans of the allowed cross-sections for $\sigma(pp\to X\to SH\to ZZ\tau\tau)$ are also compared.
Measurements of the charge-dependent two-particle angular correlation function in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV and lead-lead (PbPb) collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV are reported. The pPb and PbPb data sets correspond to integrated luminosities of 186 nb$^{-1}$ and 0.607 nb$^{-1}$, respectively, and were collected using the CMS detector at the CERN LHC. The charge-dependent correlations are characterized by balance functions of same- and opposite-sign particle pairs. The balance functions, which contain information about the creation time of charged particle pairs and the development of collectivity, are studied as functions of relative pseudorapidity ($\Delta \eta$) and relative azimuthal angle ($\Delta \phi$), for various multiplicity and transverse momentum ($p_\mathrm{T}$) intervals. A multiplicity dependence of the balance function is observed in $\Delta \eta$ and $\Delta \phi$ for both systems. The width of the balance functions decreases toward high-multiplicity collisions in the momentum region $\lt$ 2 GeV, for pPb and PbPb results. Integrals of the balance functions are presented in both systems, and a mild dependence of the charge-balancing fractions on multiplicity is observed. No multiplicity dependence is observed at higher transverse momentum. The data are compared with HYDJET, HIJING and AMPT generator predictions, none of which capture completely the multiplicity dependence seen in the data. The comparison of results with different center-of-mass energies suggest that the balance functions become narrower at higher energies, which is consistent with the idea of delayed hadronization and the effect of radial flow.
$\Delta\eta$ projection of balance function in low $p_{T}$ in 0-10% centrality
$\Delta\eta$ projection of balance function in low $p_{T}$ in 30-40% centrality
$\Delta\eta$ projection of balance function in low $p_{T}$ in 70-80% centrality
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