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A search is performed for dark matter particles produced in association with a resonantly produced pair of b-quarks with 30 < mbb < 150 GeV using 140 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. This signature is expected in extensions of the standard model predicting the production of dark matter particles, in particular those containing a dark Higgs boson s that decays into bb¯. The highly boosted s → bb¯ topology is reconstructed using jet reclustering and a new identification algorithm. This search places stringent constraints across regions of the dark Higgs model parameter space that satisfy the observed relic density, excluding dark Higgs bosons with masses between 30 and 150 GeV in benchmark scenarios with Z0 mediator masses up to 4.8 TeV at 95% confidence level. 

A combination of searches for singly and doubly charged Higgs bosons, 𝐻± and 𝐻±±, produced via vector-boson fusion is performed using 140 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during Run 2 of the Large Hadron Collider. Searches targeting decays to massive vector bosons in leptonic final states (electrons or muons) are considered. New constraints are reported on the production cross section times branching fraction for charged Higgs boson masses between 200 GeV and 3000 GeV. The results are interpreted in the context of the Georgi-Machacek model for which the most stringent constraints to date are set for the masses considered in the combination. 

This paper presents a search for exotic decays of the Higgs boson into a pair of new pseudoscalar particles, H → aa, where one pseudoscalar decays into a b-quark pair and the other decays into a τ-lepton pair, in the mass range 12 ≤ ma ≤ 60 GeV. The analysis uses pp collision data at \sqrt{s} = 13 TeV collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb−1. No significant excess above the Standard Model (SM) prediction is observed. Assuming the SM Higgs boson production cross section, the search sets upper limits at 95% confidence level on the branching ratio of Higgs bosons decaying into BR (H → aa → bb\tau\tau), between 2.2% and 3.9% depending on the pseudoscalar mass. 

A search for the nonresonant production of Higgs boson pairs in the $HH\to b\overline{b}{\tau }^{+}{\tau }^{-}$channel is performed using $140{\mathrm{fb}}^{-1}$of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The analysis strategy is optimized to probe anomalous values of the Higgs boson self-coupling modifier ${\kappa }_{\lambda }$and of the quartic $HHVV$( $V=W,Z$) coupling modifier ${\kappa }_{2V}$. No significant excess above the expected background from Standard Model processes is observed. An observed (expected) upper limit ${\mu }_{HH}<5.9\left(3.3\right)$is set at 95% confidence-level on the Higgs boson pair production cross section normalized to its Standard Model prediction. The coupling modifiers are constrained to an observed (expected) 95% confidence interval of $-3.1<{\kappa }_{\lambda }<9.0$( $-2.5<{\kappa }_{\lambda }<9.3$) and $-0.5<{\kappa }_{2V}<2.7$( $-0.2<{\kappa }_{2V}<2.4$), assuming all other Higgs boson couplings are fixed to the Standard Model prediction. The results are also interpreted in the context of effective field theories via constraints on anomalous Higgs boson couplings and Higgs boson pair production cross sections assuming different kinematic benchmark scenarios. © 2024 CERN, for the ATLAS Collaboration2024CERN 

Several processes studied by the ATLAS experiment at the Large Hadron Collider produce low momentum b-flavored hadrons in the final state. This paper describes the calibration of a dedicated tagging algorithm that identifies b-flavored hadrons outside of hadronic jets by reconstructing the soft secondary vertices originating from their decays. The calibration is based on a proton-proton collision dataset at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb−1. Scale factors used to correct the algorithm’s performance in simulated events are extracted for the b-tagging efficiency and the mistag rate of the algorithm using a data sample enriched in t¯t events. Several orthogonal measurement regions are defined, binned as a function of the multiplicities of soft secondary vertices and jets containing a b-flavored hadron in the event. The mistag rate scale factors are estimated separately for events with low and high average numbers of interactions per bunch crossing. The results, which are derived from events with low missing transverse momentum, are successfully validated in a phase space characterized by high missing transverse momentum and therefore are applicable to new physics searches carried out in either phase space regime. 

The production of $\mathrm{\Upsilon }\left(2S\right)$and $\mathrm{\Upsilon }\left(3S\right)$mesons in lead-lead (Pb-Pb) and proton-proton ( $pp$) collisions is studied in their dimuon decay channel using the CMS detector at the LHC. The $\mathrm{\Upsilon }\left(3S\right)$meson is observed for the first time in Pb-Pb collisions, with a significance above 5 standard deviations. The ratios of yields measured in Pb-Pb and $pp$collisions are reported for both the $\mathrm{\Upsilon }\left(2S\right)$and $\mathrm{\Upsilon }\left(3S\right)$mesons, as functions of transverse momentum and Pb-Pb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression of $\mathrm{\Upsilon }$yields in Pb-Pb collisions. This suppression increases from peripheral to central Pb-Pb collisions. Furthermore, the suppression is stronger for $\mathrm{\Upsilon }\left(3S\right)$mesons compared to $\mathrm{\Upsilon }\left(2S\right)$mesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the $J/\psi$, $\psi \left(2S\right)$, $\mathrm{\Upsilon }\left(1S\right)$, and $\mathrm{\Upsilon }\left(2S\right)$mesons. © 2024 CERN, for the CMS Collaboration2024CERN 

A search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$in events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity of $103{\mathrm{fb}}^{-1}$collected in 2016–2018 with the central CMS detector and the CMS and TOTEM precision proton spectrometer (PPS). Events that have two photons with high transverse momenta ( $p_{\mathrm{T}}^{\gamma }>100\mathrm{GeV}$), back-to-back in azimuth, and with a large diphoton invariant mass ( $m_{\gamma \gamma }>350\mathrm{GeV}$) are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parameters $\left|{\zeta }_1\right|<0.073{\mathrm{TeV}}^{-4}$and $\left|{\zeta }_2\right|<0.15{\mathrm{TeV}}^{-4}$, using an effective field theory. Additionally, upper limits are placed on the production of axionlike particles with coupling strength to photons $f^{-1}$that varies from $0.03{\mathrm{TeV}}^{-1}$to $1{\mathrm{TeV}}^{-1}$over the mass range from 500 to 2000 GeV. © 2024 CERN, for the CMS and TOTEMs Collaboration2024CERN 

A<sc>bstract</sc> A search for the central exclusive production of top quark-antiquark pairs ($$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$) is performed for the first time using proton-tagged events in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 29.4 fb⁻¹. The$$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$decay products are reconstructed using the central CMS detector, while forward protons are measured in the CMS-TOTEM precision proton spectrometer. An observed (expected) upper bound on the production cross section of 0.59 (1.14) pb is set at 95% confidence level, for collisions of protons with fractional momentum losses between 2 and 20%.