A search for Higgs boson pair production via vector-boson fusion is performed in the Lorentz-boosted regime, where a Higgs boson candidate is reconstructed as a single large-radius jet, using 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. Only Higgs boson decays into bottom quark pairs are considered. The search is particularly sensitive to the quartic coupling between two vector bosons and two Higgs bosons relative to its Standard Model prediction, $\kappa_{2V}$. This study constrains $\kappa_{2V}$ to $0.55 < \kappa_{2V} < 1.49$ at 95% confidence level. The value $\kappa_{2V} = 0$ is excluded with a significance of 3.8 standard deviations with other Higgs boson couplings fixed to their Standard Model values. A search for new heavy spin-0 resonances that would mediate Higgs boson pair production via vector-boson fusion is carried out in the mass range of 1-5 TeV for the first time under several model and decay-width assumptions. No significant deviation from the Standard Model hypothesis is observed and exclusion limits at 95% confidence level are derived.

A search for decays of the Higgs boson into a $Z$ boson and a light resonance, with a mass of 0.5-3.5 GeV, is performed using the full 140 fb$^{-1}$ dataset of 13 TeV proton-proton collisions recorded by the ATLAS detector during Run~2 of the LHC. Leptonic decays of the $Z$ boson and hadronic decays of the light resonance are considered. The resonance can be interpreted as a $J/ψ$ or $η_c$ meson, an axion-like particle, or a light pseudoscalar in two-Higgs-doublet models. Due to its low mass, it would be produced with high boost and reconstructed as a single small-radius jet of hadrons. A neural network is used to correct the Monte Carlo simulation of the background in a data-driven way. Two additional neural networks are used to distinguish signal from background. A binned profile-likelihood fit is performed on the final-state invariant mass distribution. No significant excess of events relative to the expected background is observed, and upper limits at 95% confidence level are set on the Higgs boson's branching fraction to a $Z$ boson and a light resonance. The exclusion limit is 10% for the lower masses, and increases for higher masses. Upper limits on the effective coupling $C^\text{eff}_{ZH}/Λ$ of an axion-like particle to a Higgs boson and $Z$ boson are also set at 95% confidence level, and range from 0.9 to 2 TeV$^{-1}$.

A search for resonances in top quark pair ($\text{t}\bar{\text{t}}$) production in final states with two charged leptons and multiple jets is presented, based on proton-proton collision data collected by the CMS experiment at the CERN LHC at $\sqrt{s}$ = 13 TeV, corresponding to 138 fb$^{-1}$. The analysis explores the invariant mass of the \ttbar system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic $\text{t}\bar{\text{t}}$ threshold compared to the nonresonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar ($^1$S$^{[1]}_0$) quasi-bound toponium state, as predicted by nonrelativistic quantum chromodynamics. Using a simplified model for $^1$S$^{[1]}_0$ toponium, the cross section of the excess above the pQCD prediction is measured to be 8.8$^{+1.2}_{-1.4}$ pb.

A search for the violation of the charge-parity ($CP$) symmetry in the production of top quarks in association with Z bosons is presented, using events with at least three charged leptons and additional jets. The search is performed in a sample of proton-proton collision data collected by the CMS experiment at the CERN LHC in 2016-2018 at a center-of-mass energy of 13 TeV and in 2022 at 13.6 TeV, corresponding to a total integrated luminosity of 173 fb$^{-1}$. For the first time in this final state, observables that are odd under the $CP$ transformation are employed. Also for the first time, physics-informed machine-learning techniques are used to construct these observables. While for standard model (SM) processes the distributions of these observables are predicted to be symmetric around zero, $CP$-violating modifications of the SM would introduce asymmetries. Two $CP$-odd operators $\mathcal{O}_\text{tW}^\text{I}$ and $\mathcal{O}_\text{tZ}^\text{I}$ in the SM effective field theory are considered that may modify the interactions between top quarks and electroweak bosons. The obtained results are consistent with the SM prediction within two standard deviations, and exclusion limits on the associated Wilson coefficients of $-$2.7 $\lt$$c_\text{tW}^\text{I}$$\lt$ 2.5 and $-$0.2 $\lt$$c_\text{tZ}^\text{I}$$\lt$ 2.0 are set at 95% confidence level. The largest discrepancy is observed in $c_\text{tZ}^\text{I}$ where data is consistent with positive values, with an observed local significance with respect to the SM hypothesis of 2.5 standard deviations, when only linear terms are considered.

A measurement is presented of the cross section in proton-proton collisions for the production of two W bosons and one Z boson. It is based on data recorded by the CMS experiment at the CERN LHC at center-of-mass energies $\sqrt{s}$ = 13 and 13.6 TeV, corresponding to an integrated luminosity of 200 fb$^{-1}$. Events with four charged leptons (electrons or muons) in the final state are selected. Both nonresonant WWZ production and ZH production, with the Higgs boson decaying into two W bosons, are reported. For the first time, the two processes are measured separately in a simultaneous fit. Combining the two modes, signal strengths relative to the standard model (SM) predictions of 0.75$^{+0.34}_{-0.29}$ and 1.74$^{+0.71}_{-0.60}$ are measured for $\sqrt{s}$ = 13 and 13.6 TeV, respectively. The observed (expected) significance for the triboson signal is 3.8 (2.5) standard deviations for $\sqrt{s}$ = 13.6 TeV, thus providing the first evidence for triboson production at this center-of-mass energy. Combining the two modes and the two center-of-mass energies, the inclusive signal strength relative to the SM prediction is measured to be 1.03$^{+0.31}_{-0.28}$, with an observed (expected) significance of 4.5 (5.0) standard deviations.

The traditional quark model accounts for the existence of baryons, such as protons and neutrons, which consist of three quarks, as well as mesons, composed of a quark-antiquark pair. Only recently has substantial evidence started to accumulate for exotic states composed of four or five quarks and antiquarks. The exact nature of their internal structure remains uncertain. This paper reports the first measurement of quantum numbers of the recently discovered family of three all-charm tetraquarks, using data collected by the CMS experiment at the Large Hadron Collider from 2016 to 2018. The angular analysis techniques developed for the discovery and characterization of the Higgs boson have been applied to the new exotic states. The quantum numbers for parity $P$ and charge conjugation $C$ symmetries are found to be +1. The spin $J$ of these exotic states is consistent with 2$\hbar$, while 0$\hbar$ and 1$\hbar$ are excluded at 95% and 99% confidence level, respectively. The $J^{PC}=2^{++}$ assignment implies particular configurations of constituent spins and orbital angular momenta, which constrain the possible internal structure of these tetraquarks.

The production cross sections of B$^0_\mathrm{s}$ and B$^+$ mesons are reported in proton-proton (pp) collisions recorded by the CMS experiment at the CERN LHC with a center-of-mass energy of 5.02 TeV. The data sample corresponds to an integrated luminosity of 302 pb$^{-1}$. The cross sections are based on measurements of the B$^0_\mathrm{s}$$\to$ J/$\psi(\mu^+\mu^-)\phi$(1020)(K$^+$K$^-$) and B$^+$$\to$ J/$\psi(\mu^+\mu^-)$K$^+$ decay channels. Results are presented in the transverse momentum ($p_\mathrm{T}$) range 7-50 GeV/$c$ and the rapidity interval $\lvert y \rvert$$\lt$ 2.4 for the B mesons. The measured $p_\mathrm{T}$-differential cross sections of B$^+$ and B$^0_\mathrm{s}$ in pp collisions are well described by fixed-order plus next-to-leading logarithm perturbative quantum chromodynamics calculations. Using previous PbPb collision measurements at the same nucleon-nucleon center-of-mass energy, the nuclear modification factors, $R_\mathrm{AA}$, of the B mesons are determined. For $p_\mathrm{T}$$\lt$ 10 GeV/$c$, both mesons are found to be suppressed in PbPb collisions (with $R_\mathrm{AA}$ values significantly below unity), with less suppression observed for the B$^0_\mathrm{s}$ mesons. In this $p_\mathrm{T}$ range, the $R_\mathrm{AA}$ values for the B$^+$ mesons are consistent with those for inclusive charged hadrons and D$^0$ mesons. Below 10 GeV/$c$, both B$^+$ and B$^0_\mathrm{s}$s are found to be less suppressed than either inclusive charged hadrons or D$^0$ mesons, with the B$^0_\mathrm{s}$$R_\mathrm{AA}$ value consistent with unity. The $R_\mathrm{AA}$ values found for the B$^+$ and B$^0_\mathrm{s}$ are compared to theoretical calculations, providing constraints on the mechanism of bottom quark energy loss and hadronization in the quark-gluon plasma, the hot and dense matter created in ultrarelativistic heavy ion collisions.

The discovery of the Higgs boson has led to new possible signatures for heavy resonance searches at the LHC. Since then, search channels including at least one Higgs boson plus another particle have formed an important part of the program of new physics searches. In this report, the status of these searches by the CMS Collaboration is reviewed. Searches are discussed for resonances decaying to two Higgs bosons, a Higgs and a vector boson, or a Higgs boson and another new resonance. All analyses use proton-proton collision data collected at $\sqrt{s}$ = 13 TeV in the years 2016-2018. A combination of the results of these searches is presented together with constraints on different beyond-the-standard model scenarios, including scenarios with extended Higgs sectors, heavy vector bosons and extra dimensions. Studies are shown for the first time by CMS on the validity of the narrow-width approximation in searches for the resonant production of a pair of Higgs bosons. The potential for a discovery at the High Luminosity LHC is also discussed.

A search is presented for an extended Higgs sector with two new particles, X and $\phi$, in the process $X \to\phi\phi\to(\gamma\gamma)(\gamma\gamma)$. Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb$^{-1}$. No evidence of such resonances is seen. Upper limits are set on the production cross section for $m_X$ between 300 and 3000 GeV and $m_\phi / m_X$ between 0.5 and 2.5%, representing the most sensitive search in this channel.

The first measurement of the inclusive and normalised differential cross sections of single top quark production in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13.6 TeV is presented. The data were recorded with the CMS detector at the LHC in 2022, and correspond to an integrated luminosity of 34.7 fb$^{-1}$. The analysed events contain one muon and one electron in the final state. For the inclusive measurement, multivariate discriminants exploiting the kinematic properties of the events are used to separate the signal from the dominant top quark-antiquark production background. A cross section of 82.3 $\pm$ 2.1 (stat) ${}^{+9.9}_{-9.7}$ (syst) $\pm$ 3.3 (lumi) pb is obtained, consistent with the predictions of the standard model. A fiducial region is defined according to the detector acceptance to perform the differential measurements. The resulting differential distributions are unfolded to particle level and show good agreement with the predictions at next-to-leading order in perturbative quantum chromodynamics.