A measurement of the inclusive jet production in proton-proton collisions at the LHC at $\sqrt{s}$ = 13 TeV is presented. The double-differential cross sections are measured as a function of the jet transverse momentum $p_\mathrm{T}$ and the absolute jet rapidity $\lvert y \rvert$. The anti-$k_\mathrm{T}$ clustering algorithm is used with distance parameter of 0.4 (0.7) in a phase space region with jet $p_\mathrm{T}$ from 97 GeV up to 3.1 TeV and $\lvert y \rvert\lt$ 2.0. Data collected with the CMS detector are used, corresponding to an integrated luminosity of 36.3 fb$^{-1}$ (33.5 fb$^{-1}$). The measurement is used in a comprehensive QCD analysis at next-to-next-to-leading order, which results in significant improvement in the accuracy of the parton distributions in the proton. Simultaneously, the value of the strong coupling constant at the Z boson mass is extracted as $\alpha_\mathrm{S}$(Z) = 0.1170 $\pm$ 0.0019. For the first time, these data are used in a standard model effective field theory analysis at next-to-leading order, where parton distributions and the QCD parameters are extracted simultaneously with imposed constraints on the Wilson coefficient $c_1$ of 4-quark contact interactions. Note added: in the Addendum to this paper, available as Appendix B in this document, an improved value of $\alpha_\mathrm{S}$(Z) = 0.1166 $\pm$ 0.0017 has been extracted. This result supersedes the number in the above abstract of the original publication.

A measurement of the dijet production cross section is reported based on proton-proton collision data collected in 2016 at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of up to 36.3 fb$^{-1}$. Jets are reconstructed with the anti-$k_\mathrm{T}$ algorithm for distance parameters of $R$ = 0.4 and 0.8. Cross sections are measured double-differentially (2D) as a function of the largest absolute rapidity $\lvert y_\text{max}\rvert$ of the two jets with the highest transverse momenta $p_\mathrm{T}$ and their invariant mass $m_{1,2}$, and triple-differentially (3D) as a function of the rapidity separation $y^*$, the total boost $y_\mathrm{b}$, and either $m_{1,2}$ or the average $p_\mathrm{T}$ of the two jets. The cross sections are unfolded to correct for detector effects and are compared with fixed-order calculations derived at next-to-next-to-leading order in perturbative quantum chromodynamics. The impact of the measurements on the parton distribution functions and the strong coupling constant at the mass of the Z boson is investigated, yielding a value of $\alpha_\mathrm{S}(m_\mathrm{Z})$ = 0.1179 $\pm$ 0.0019.

A measurement of the angular structure of jets containing a prompt D$^0$ meson and of inclusive jets in proton-proton collisions at the LHC at a center-of-mass energy of 5.02 TeV is presented. The data corresponding to an integrated luminosity of 301 pb$^{-1}$ were collected by the CMS experiment in 2017. Two jet grooming algorithms, late-$k_\mathrm{T}$ and soft drop, are used to study the intrajet radiation pattern using iterative Cambridge$-$Aachen declustering. The splitting-angle distributions of jets with transverse momentum ($p_\mathrm{T}$) of around 100 GeV, obtained with these two algorithms, show that there is a shift of the distribution for jets containing a prompt D$^0$ meson with respect to inclusive jets. The shift observed in the late-$k_\mathrm{T}$ grooming approach is consistent with the dead-cone effect, whereas the shift for splittings selected with the soft-drop algorithm appears to be dominated by gluon splitting to charm quark-antiquark pairs. The measured distributions are corrected to the particle level and can be used to constrain model predictions for the substructure of high-$p_\mathrm{T}$ charm quark jets.

A measurement of the substructure of bottom quark jets (b jets) in proton-proton (pp) collisions is presented. The measurement uses data collected in pp collisions at $\sqrt{s}$ = 5.02 TeV recorded by the CMS experiment in 2017, corresponding to an integrated luminosity of 301$^{-1}$. An algorithm to identify and cluster the charged decay daughters of b hadrons is developed for this analysis, which facilitates the exposure of the gluon radiation pattern of b jets using iterative Cambridge-Aachen declustering. The soft-drop-groomed jet radius, $R_\mathrm{g}$, and momentum balance, $z_\mathrm{g}$, of b quark jets are presented. These observables can be used to test perturbative quantum chromodynamics predictions that account for mass effects. Because the b hadron is partially reconstructed from its charged decay daughters, only charged particles are used for the jet substructure studies. In addition, a jet fragmentation function, $z_\text{b,ch}$, is measured, which is defined as the distribution of the ratio of the transverse momentum ($p_\mathrm{T}$) of the partially reconstructed b hadron with respect to the charged-particle component of the jet $p_\mathrm{T}$. The substructure variable distributions are unfolded to the charged-particle level. The b jet substructure is compared to the substructure of jets in an inclusive jet sample that is dominated by light-quark and gluon jets in order to assess the role of the b quark mass. A strong suppression of emissions at small $R_\mathrm{g}$ values is observed for b jets when compared to inclusive jets, consistent with the dead-cone effect. The measurement is also compared with theoretical predictions from Monte Carlo event generators. This is the first substructure measurement of b jets that clusters together the b hadron decay daughters.

This paper presents a measurement of the production cross-section of a $Z$ boson in association with $b$- or $c$-jets, in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 140 fb$^{-1}$. Inclusive and differential cross-sections are measured for events containing a $Z$ boson decaying into electrons or muons and produced in association with at least one $b$-jet, at least one $c$-jet, or at least two $b$-jets with transverse momentum $p_\textrm{T} > 20$ GeV and rapidity $|y| < 2.5$. Predictions from several Monte Carlo generators based on next-to-leading-order matrix elements interfaced with a parton-shower simulation, with different choices of flavour schemes for initial-state partons, are compared with the measured cross-sections. The results are also compared with novel predictions, based on infrared and collinear safe jet flavour dressing algorithms. Selected $Z + \ge 1 c$-jet observables, optimized for sensitivity to intrinsic-charm, are compared with benchmark models with different intrinsic-charm fractions.

This paper reports cross-section measurements of $ZZ$ production in $pp$ collisions at $\sqrt{s}=13.6$ TeV at the Large Hadron Collider. The data were collected by the ATLAS detector in 2022, and correspond to an integrated luminosity of 29 fb$^-1$. Events in the $ZZ\rightarrow4\ell$ ($\ell = e$, $\mu$) final states are selected and used to measure the inclusive and differential cross-sections in a fiducial region defined close to the analysis selections. The inclusive cross-section is further extrapolated to the total phase space with a requirement of 66 $< m_Z <$ 116 GeV for both $Z$ bosons, yielding $16.8 \pm 1.1$ pb. The results are well described by the Standard Model predictions.

A measurement of off-shell Higgs boson production in the $H^*\to ZZ\to 4\ell$ decay channel is presented. The measurement uses 140 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider and supersedes the previous result in this decay channel using the same dataset. The data analysis is performed using a neural simulation-based inference method, which builds per-event likelihood ratios using neural networks. The observed (expected) off-shell Higgs boson production signal strength in the $ZZ\to 4\ell$ decay channel at 68% CL is $0.87^{+0.75}_{-0.54}$ ($1.00^{+1.04}_{-0.95}$). The evidence for off-shell Higgs boson production using the $ZZ\to 4\ell$ decay channel has an observed (expected) significance of $2.5\sigma$ ($1.3\sigma$). The expected result represents a significant improvement relative to that of the previous analysis of the same dataset, which obtained an expected significance of $0.5\sigma$. When combined with the most recent ATLAS measurement in the $ZZ\to 2\ell 2\nu$ decay channel, the evidence for off-shell Higgs boson production has an observed (expected) significance of $3.7\sigma$ ($2.4\sigma$). The off-shell measurements are combined with the measurement of on-shell Higgs boson production to obtain constraints on the Higgs boson total width. The observed (expected) value of the Higgs boson width at 68% CL is $4.3^{+2.7}_{-1.9}$ ($4.1^{+3.5}_{-3.4}$) MeV.

Measurements of inclusive, differential cross-sections for the production of events with missing transverse momentum in association with jets in proton-proton collisions at $\sqrt{s}=13~$TeV are presented. The measurements are made with the ATLAS detector using an integrated luminosity of $140~$fb$^{-1}$ and include measurements of dijet distributions in a region in which vector-boson fusion processes are enhanced. They are unfolded to correct for detector resolution and efficiency within the fiducial acceptance, and are designed to allow robust comparisons with a wide range of theoretical predictions. A measurement of differential cross sections for the $Z~\to \nu\nu$ process is made. The measurements are generally well-described by Standard Model predictions except for the dijet invariant mass distribution. Auxiliary measurements of the hadronic system recoiling against isolated leptons, and photons, are also made in the same phase space. Ratios between the measured distributions are then derived, to take advantage of cancellations in modelling effects and some of the major systematic uncertainties. These measurements are sensitive to new phenomena, and provide a mechanism to easily set constraints on phenomenological models. To illustrate the robustness of the approach, these ratios are compared with two common Dark Matter models, where the constraints derived from the measurement are comparable to those set by dedicated detector-level searches.

A set of measurements for the production of a $W$-boson in association with high-transverse-momentum jets is presented using 140 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV collected by the ATLAS detector at the LHC. The measurements are performed in final states in which the $W$-boson decays into an electron or muon plus a neutrino and is produced in association with jets with $p_{\text{T}}>30$ GeV, where the leading jet has $p_{\text{T}}>500$ GeV. The angular separation between the lepton and the closest jet with $p_{\text{T}}>100$ GeV is measured and used to define a collinear phase space, wherein measurements of kinematic properties of the $W$-boson and the associated jet are performed. The collinear phase space is populated by dijet events radiating a $W$-boson and events with a $W$-boson produced in association with several jets and it serves as an excellent data sample to probe higher-order theoretical predictions. Measured differential distributions are compared with predictions from state-of-the-art next-to-leading order multi-leg merged Monte Carlo event generators and a fixed-order calculation of the $W$+1-jet process computed at next-to-next-to-leading order in the strong coupling constant.

A measurement of inclusive and differential fiducial cross-sections for the production of the Higgs boson decaying into two photons is performed using $139~\text{fb}^{-1}$ of proton--proton collision data recorded at $\sqrt{s} = 13$ TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio, in a fiducial region closely matching the experimental selection, is measured to be $67\pm 6$ fb, which is in agreement with the state-of-the-art Standard Model prediction of $64\pm 4$ fb. Extrapolating this result to the full phase space and correcting for the branching ratio, the total cross-section for Higgs boson production is estimated to be $58\pm 6$ pb. In addition, the cross-sections in four fiducial regions sensitive to various Higgs boson production modes and differential cross-sections as a function of either one or two of several observables are measured. All the measurements are found to be in agreement with the Standard Model predictions. The measured transverse momentum distribution of the Higgs boson is used as an indirect probe of the Yukawa coupling of the Higgs boson to the bottom and charm quarks. In addition, five differential cross-section measurements are used to constrain anomalous Higgs boson couplings to vector bosons in the Standard Model effective field theory framework.