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1. Determination of the Relative Sign of the Higgs Boson Couplings to $W$ and $Z$ Bosons Using $WH$ Production via Vector-Boson Fusion with the ATLAS Detector

   https://doi.org/10.1103/PhysRevLett.133.141801  

   Aad, G; Abbott, B; Abeling, K; Abicht, N J; Abidi, S H; Aboulhorma, A; Abramowicz, H; Abreu, H; Abulaiti, Y; Acharya, B S; et al (October 2024, Physical Review Letters)

   The associated production of Higgs and $W$bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to $W$and $Z$bosons. In this Letter, two searches for this process are presented, using $140{\mathrm{fb}}^{-1}$of proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$recorded by the ATLAS detector at the LHC. The first search targets scenarios with opposite-sign couplings of the $W$and $Z$bosons to the Higgs boson, while the second targets standard model-like scenarios with same-sign couplings. Both analyses consider Higgs boson decays into a pair of $b$quarks and $W$boson decays with an electron or muon. The data exclude the opposite-sign coupling hypothesis with a significance beyond $5\sigma$, and the observed (expected) upper limit set on the cross section for vector-boson fusion $WH$production is 9.0 (8.7) times the standard model value at 95% confidence level. © 2024 CERN, for the ATLAS Collaboration2024CERN 

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2. Search for the nonresonant production of Higgs boson pairs via gluon fusion and vector-boson fusion in the $b\overline{b}{\tau }^{+}{\tau }^{-}$ final state in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ with the ATLAS detector

   https://doi.org/10.1103/PhysRevD.110.032012  

   Aad, G; Aakvaag, E; Abbott, B; Abeling, K; Abicht, N J; Abidi, S H; Aboelela, M; Aboulhorma, A; Abramowicz, H; Abreu, H; et al (August 2024, Physical Review D)

   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 

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3. Combination of Searches for Higgs Boson Pair Production in $pp$ Collisions at $\sqrt{s}=13\mathrm{TeV}$ with the ATLAS Detector

   https://doi.org/10.1103/PhysRevLett.133.101801  

   Aad, G; Aakvaag, E; Abbott, B; Abdelhameed, S; Abeling, K; Abicht, N J; Abidi, S H; Aboelela, M; Aboulhorma, A; Abramowicz, H; et al (September 2024, Physical Review Letters)

   This Letter presents results from a combination of searches for Higgs boson pair production using $126–140{\mathrm{fb}}^{-1}$of proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$recorded with the ATLAS detector. At 95% confidence level (CL), the upper limit on the production rate is 2.9 times the standard model (SM) prediction, with an expected limit of 2.4 assuming no Higgs boson pair production. Constraints on the Higgs boson self-coupling modifier ${\kappa }_{\lambda }={\lambda }_{HHH}/{\lambda }_{HHH}^{\mathrm{SM}}$, and the quartic $HHVV$coupling modifier ${\kappa }_{2V}=g_{HHVV}/g_{HHVV}^{\mathrm{SM}}$, are derived individually, fixing the other parameter to its SM value. The observed 95% CL intervals are $-1.2<{\kappa }_{\lambda }<7.2$and $0.6<{\kappa }_{2V}<1.5$, respectively, while the expected intervals are $-1.6<{\kappa }_{\lambda }<7.2$and $0.4<{\kappa }_{2V}<1.6$in the SM case. Constraints obtained for several interaction parameters within Higgs effective field theory are the strongest to date, offering insights into potential deviations from SM predictions. © 2024 CERN, for the ATLAS Collaboration2024CERN 

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4. Building the case for forward muon detection at a muon collider

   https://doi.org/10.1103/PhysRevD.111.053010  

   Ruhdorfer, Maximilian; Salvioni, Ennio; Wulzer, Andrea (March 2025, Physical Review D)

   We survey the opportunities offered by the detection of the forward muons that accompany the creation of neutral effective vector bosons at a muon collider, in different kinematic regimes. Vectors with relatively low energy produce the Higgs boson and the extended muon angular coverage enables studies of the Higgs properties, such as the measurement of the inclusive production cross section and the branching ratio to invisible final states. New heavy particles could be produced by vectors of higher energy, through Higgs portal interactions. If the new particles are invisible, the detection of the forward muons is essential in order to search for this scenario. The angular correlations of the forward muons are sensitive to the quantum interference between the vector-boson helicity amplitudes and can be exploited for the characterization of vector-boson scattering and fusion processes. This is illustrated by analyzing the $CP$properties of the Higgs coupling to the $Z$boson. Our findings provide a physics case and a set of benchmarks for the design of a dedicated forward muon detector. Published by the American Physical Society2025 

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5. Search for long-lived particles decaying in the CMS muon detectors in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevD.110.032007  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; Jeitler, M; et al (August 2024, Physical Review D)

   A search for long-lived particles (LLPs) decaying in the CMS muon detectors is presented. A data sample of proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$, recorded at the LHC in 2016–2018, is used. The decays of LLPs are reconstructed as high multiplicity clusters of hits in the muon detectors. In the context of twin Higgs models, the search is sensitive to LLP masses from 0.4 to 55 GeV and a broad range of LLP decay modes, including decays to hadrons, $\tau$leptons, electrons, or photons. No excess of events above the standard model background is observed. The most stringent limits to date from LHC data are set on the branching fraction of the Higgs boson decay to a pair of LLPs with masses below 10 GeV. This search also provides the best limits for various intervals of LLP proper decay length and mass. Finally, this search sets the first limits at the LHC on a dark quantum chromodynamic sector whose particles couple to the Higgs boson through gluon, Higgs boson, photon, vector, and dark-photon portals, and is sensitive to branching fractions of the Higgs boson to dark quarks as low as $2\times {10}^{-3}$. © 2024 CERN, for the CMS Collaboration2024CERN 

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