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1. Observation of the $J/\psi \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ decay in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevD.109.L111101  

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

   The $J/\psi \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of $33.6{\mathrm{fb}}^{-1}$. Normalizing to the $J/\psi \to {\mu }^{+}{\mu }^{-}$decay mode leads to a branching fraction of $[{10.1}_{-2.7}^{+3.3}\left(\mathrm{stat}\right)\pm 0.4\left(\mathrm{syst}\right)]\times {10}^{-7}$, a value that is consistent with the standard model prediction. © 2024 CERN, for the CMS Collaboration2024CERN 

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2. First Measurement of ${\nu }_e$ and ${\nu }_{\mu }$ Interaction Cross Sections at the LHC with FASER’s Emulsion Detector

   https://doi.org/10.1103/PhysRevLett.133.021802  

   Abraham, Roshan Mammen; Anders, John; Antel, Claire; Ariga, Akitaka; Ariga, Tomoko; Atkinson, Jeremy; Bernlochner, Florian U; Boeckh, Tobias; Boyd, Jamie; Brenner, Lydia; et al (July 2024, Physical Review Letters)

   The first results of the study of high-energy electron neutrino ( ${\nu }_e$) and muon neutrino ( ${\nu }_{\mu }$) charged-current interactions in the $\mathrm{FASER}\nu$emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the $\mathrm{FASER}\nu$volume was analyzed after exposure to $9.5{\mathrm{fb}}^{-1}$of $\sqrt{s}=13.6\mathrm{TeV}$ $pp$data. Four (eight) ${\nu }_e$( ${\nu }_{\mu }$) interaction candidate events are observed with a statistical significance of $5.2\sigma$( $5.7\sigma$). This is the first direct observation of ${\nu }_e$interactions at a particle collider and includes the highest-energy ${\nu }_e$and ${\nu }_{\mu }$ever detected from an artificial source. The interaction cross section per nucleon $\sigma /E_{\nu }$is measured over an energy range of 560–1740 GeV (520–1760 GeV) for ${\nu }_e$( ${\nu }_{\mu }$) to be $\left({1.2}_{-0.7}^{+0.8}\right)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$[ $(0.5\pm 0.2)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges. Published by the American Physical Society2024 

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3. 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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4. Search for the $Z$ Boson Decay to $\tau \tau \mu \mu$ in Proton-Proton Collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.133.161805  

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

   The first search for the $Z$boson decay to $\tau \tau \mu \mu$at the CERN LHC is presented, based on data collected by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. The data are compatible with the predicted background. For the first time, an upper limit at the 95% confidence level of 6.9 times the standard model expectation is placed on the ratio of the $Z\to \tau \tau \mu \mu$to $Z\to 4\mu$branching fractions. Limits are also placed on the six flavor-conserving four-lepton effective-field-theory operators involving two muons and two tau leptons, for the first time testing all such operators. © 2024 CERN, for the CMS Collaboration2024CERN 

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5. Photoproduction of $K^{+}{K}^{-}$ Pairs in Ultraperipheral Collisions

   https://doi.org/10.1103/PhysRevLett.132.222303  

   Acharya, S; Adamová, D; Aglieri_Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; Akindinov, A; et al (May 2024, Physical Review Letters)

   $K^{+}{K}^{-}$pairs may be produced in photonuclear collisions, either from the decays of photoproduced $\varphi \left(1020\right)$mesons or directly as nonresonant $K^{+}{K}^{-}$pairs. Measurements of $K^{+}{K}^{-}$photoproduction probe the couplings between the $\varphi \left(1020\right)$and charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction of $K^{+}{K}^{-}$pairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of direct $K^{+}{K}^{-}$production. There is significant $K^{+}{K}^{-}$production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range $1.1<M_{KK}<1.4\mathrm{GeV}/c^2$above the $\varphi \left(1020\right)$resonance, for rapidity $\left|y_{KK}\right|<0.8$and $p_{T,KK}<0.1\mathrm{GeV}/c$, the measured coherent photoproduction cross section is $\mathrm{d}\sigma /\mathrm{d}y=3.37\pm 0.61\left(\text{stat}\right)\pm 0.15\left(\mathrm{syst}\right)\mathrm{mb}$. The center-of-mass energy per nucleon of the photon-nucleus (Pb) system $W_{\gamma \mathrm{Pb},n}$ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for $\varphi \left(1020\right)$photoproduction alone. The mass spectrum is fit to a cocktail consisting of $\varphi \left(1020\right)$decays, direct $K^{+}{K}^{-}$photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct $K^{+}{K}^{-}$photoproduction are presented. © 2024 CERN, for the ALICE Collaboration2024CERN 

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