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A new technique is developed to identify dielectrons ( $e^{+}{e}^{-}$ ) with Lorentz boost ${\gamma }_{\mathrm{L}}>20$ that produce one single merged cluster in the electromagnetic calorimeter of the CMS detector. The identification uses two multivariate models: one for the case where both electron tracks are reconstructed, and another where only one of the tracks is reconstructed. The efficiency is determined using proton-proton collision data collected at a center-of-mass energy of 13 TeV. Boosted $J/\psi$ mesons decaying into $e^{+}{e}^{-}$ pairs are used to estimate the efficiency of the model with two tracks, yielding an overall efficiency of 80%. The $Z\to {\mu }^{+}{\mu }^{-}\gamma$ events, where the photon converts into a collimated dielectron, are used for the model with a single track, yielding an efficiency of about 60%. A dedicated energy correction for dielectron candidates is also developed using $B^{\pm }\to J/\psi K^{\pm }\to e^{+}{e}^{-}{K}^{\pm }$ data. 

A search for Higgs boson ( $H$ ) production in association with two vector bosons ( $V=W$ , $Z$ ) via vector-boson scattering (VBS) is presented using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ by the CMS experiment, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . Events containing two forward jets consistent with VBS, a large-radius jet from the decay of a boosted $H$ to a pair of $b$ quarks, and zero, one, or two charged leptons coming from $V$ decays are selected. The process is excluded at 95% confidence level for observed (expected) values of the $VVHH$ coupling modifier ${\kappa }_{2V}$ outside the interval $0.40<{\kappa }_{2V}<1.60$ ( $0.34<{\kappa }_{2V}<1.66$ ), assuming standard model values for all other couplings, thus establishing a novel probe of the $VVHH$ interaction. Constraints are also set on the individual ${\kappa }_{2W}$ and ${\kappa }_{2Z}$ coupling modifiers and on the allowed region in the ${\kappa }_{2W}\text{−}{\kappa }_{2Z}$ plane. 

Evidence of the production of two $Z$ bosons and a photon in proton-proton collisions is reported for the first time in CMS. The analysis uses data collected by the CMS experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . Evidence for the process $pp\to ZZ\gamma \to 4\ell \gamma$ ( $\ell =e$ , $\mu$ ), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by $p_{\mathrm{T}}^{\gamma }>20\mathrm{GeV}$ , $\left|{\eta }^{\gamma }\right|<2.4$ , $\mathrm{\Delta }R(\ell ,\gamma )>0.5$ , $m_Z$ between 60 and 120 GeV, and the invariant mass of either of the two $Z$ bosons combined with the photon ( $m_{Z_{\gamma }}$ ) larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is ${60}_{-22}^{+27}\mathrm{ab}$ ( $47.56\pm 0.04\mathrm{ab}$ ). Additionally, the inclusive production of $pp\to 4\ell \gamma$ is studied by removing the $m_{Z_{\gamma }}$ requirement to include final state radiation where one $Z$ boson decays to $2\ell \gamma$ , yielding an observed (expected) significance of 5.0 (4.2) standard deviations and a measured (predicted) fiducial cross section of ${156}_{-35}^{+39}\mathrm{ab}$ ( $99.97\pm 0.09\mathrm{ab}$ ). 

The existence of a new spin-zero particle with a mass below the electroweak scale is predicted by several theoretical models. Searches for resonant production of photon pairs at the LHC are able to probe these models. We present a search for a narrow resonance produced through gluon fusion that decays into a pair of photons with an invariant mass between 10 and 70 GeV, using a proton-proton collision dataset from the CMS experiment. This dataset, corresponding to an integrated luminosity of $54.4{\mathrm{fb}}^{-1}$ , was recorded in 2018 at a center-of-mass energy of 13 TeV using a newly introduced diphoton trigger that enabled exploration of the low-mass diphoton spectrum. No significant excess above the expected background is observed. Upper limits are set on the product of the gluon fusion production cross section and the branching fraction of the diphoton decay of a narrow resonance. An interpretation of these limits within an effective field theory framework for axionlike particles is also provided. 

A search is performed for a new resonance $X$ decaying into a Higgs boson and a new scalar boson $Y$ ( $HY$ ) including the case where $Y$ is assumed to be a second Higgs boson ( $HH$ ), using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . This study performs a comprehensive exploitation of the $bbZZ$ events, encompassing the following decay topologies. One $H$ candidate is identified through its decay into a bottom quark-antiquark pair, while the other $H$ or the $Y$ candidate is selected through its decay into a pair of $Z$ bosons. One $Z$ boson is required to decay leptonically and the other, to decay into a pair of quarks or neutrinos. Events of interest are categorized based on the Lorentz boosts of the hadronically decaying $H$ and $Z$ bosons. Machine-learning-based discriminants, together with the reconstructed resonance mass, are employed across the different categories to separate signal from backgrounds, and their corresponding distributions are included in a simultaneous fit. No significant deviations from the standard model predictions are observed. Upper limits at the 95% confidence level are set on the $HY$ and $HH$ production cross sections. For $HY$ production, the upper limit on the cross section of the process $pp\to X\to HY\to bbZZ$ ranges from 500 to 5 fb, with the most stringent constraints achieved for high-mass $X$ resonances and $Y$ masses near the threshold for decay into a pair of massive vector bosons. This is comparable to the sensitivity achieved in other analyses, which focus on $H$ decays to $\gamma \gamma$ or $\tau \tau$ and $Y$ decays into a pair of bottom quarks or massive vector bosons. For resonant $HH$ production, the upper limit on the cross section of $pp\to X\to HH$ production is 1 pb for a high-mass resonance. 

A<sc>bstract</sc> A search for Higgs boson (H) production at high transverse momentum (p_T) in the WW decay channel is presented. The analysis uses proton-proton collisions at$$ \sqrt{s}=13 $$ $\sqrt{s}=13$ TeV recorded by the CMS experiment in 2016–2018, corresponding to an integrated luminosity of 138 fb⁻¹. The visible decay products of the Higgs boson are reconstructed as a single large-radius jet with one isolated lepton or none (1ℓand 0ℓ, respectively;ℓ= e,μ). The H-candidate jets are identified using an advanced transformer-based algorithm and are calibrated with the Lund jet plane reweighting technique. The 1ℓchannel is further split into gluon fusion, vector boson fusion, and associated production with hadronically decaying vector boson categories, while the 0ℓchannel considers all production processes inclusively. The measured cross section times the H→WW branching fraction relative to the standard model expectation is$$ \mu =-{0.19}_{-0.46}^{+0.48} $$ $\mu =-{0.19}_{-0.46}^{+0.48}$ , indicating no evidence of a signal above the background. This measurement represents the first dedicated study of highly Lorentz-boosted H→WW decays, complementing earlier searches for high-p_THiggs boson in other decay channels. 

We present a novel approach for assessing the muon content of air showers with large zenith angles on a combined analysis of their radio emission and particle footprint. We use the radiation energy reconstructed by the Auger engineering radio array (AERA) as an energy estimator and determine the muon number independently with the water-Cherenkov detector array of the Pierre Auger Observatory, deployed on a 1500 m grid. We focus our analysis on air showers with primary energy above 4 EeV to ensure full detection efficiency. Over approximately ten years of accumulated data, we identify a set of 40 high-quality events that are used in the analysis. The estimated muon contents in data are compatible with those for iron primaries as predicted by current-generation hadronic interaction models. This result can be interpreted as a deficit of muons in simulations as a lighter mass composition has been established from $X_{\max }$ measurements. This muon deficit was already observed in previous analyses of the Auger Collaboration and is confirmed using hybrid events that include radio measurements for the first time. 

The energy spectrum of cosmic rays above 2.5 EeV has been measured across the declination range −90° ≤ δ ≤ þ44.8° using ∼310 000 events accrued at the Pierre Auger Observatory from an exposure of ð104 900 3 100Þ km2 sr yr. No significant variations of energy spectra with declination are observed, after allowing or not for nonuniformities across the sky arising from the well-established dipolar anisotropies in the arrival directions of ultrahigh-energy cosmic rays. The instep feature in the spectrum at ≃10 EeV reported previously is now established at a significance above 5σ. Within the statistics, the energy spectra are indistinguishable across declinations so disfavoring an origin for the instep from a few distinctive sources. 

Abstract Deflections in the propagation of charged ultra-high-energy cosmic rays (UHECRs) caused by magnetic fields make the identification of their sources challenging. On the other hand, the arrival directions at Earth of neutrons point directly to their origin. The emission of UHECRs from a source is expected to be accompanied by the production of neutrons in its vicinity through interactions with ambient matter and radiation. Since free neutrons travel a mean distanced kpc⁻¹ = 9.2 (E EeV⁻¹) before decaying, a neutron flux in the EeV range could be detected on Earth from sources of UHECRs in our Galaxy. Using cosmic-ray data from Phase I of the Surface Detector of the Pierre Auger Observatory, we search for neutron fluxes from Galactic candidate sources. We select more than 1000 objects of astrophysical interest, stacking them into target sets. The targets all have decl. within the exposure of the Observatory, ranging from −90° up to +45° for energies above 1 EeV (and up to +20° for energies down to 0.1 EeV). Given that a neutron air shower is indistinguishable from a proton one, there is a significant background due to cosmic rays. A neutron flux from the direction of a candidate source would be identified by a celestial density of events that significantly exceeds the expected density of cosmic rays for that direction. No significant excess is found at any tested target direction, and an upper limit on the neutron flux is calculated for each candidate source.