In the standard model of particle physics, the masses of the carriers of the weak interaction, the W and Z bosons, are uniquely related. Physics beyond the standard model could change this relationship through the effects of quantum loops of virtual particles, thus making it of great importance to measure these masses with the highest possible precision. Although the mass of the Z boson is known to the remarkable precision of 22 parts per million (2.0 MeV), the W boson mass is known much less precisely, given the difficulty of the measurement. A global fit to electroweak data, used to predict the W boson mass in the standard model, yields an uncertainty of 6 MeV. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model. Furthermore, a precision measurement of the W boson mass performed by the CDF Collaboration at the Fermilab Tevatron has challenged the standard model by significantly disagreeing with the prediction of the global electroweak fit and the average of other $m_\mathrm{W}$ measurements. We report the first W boson mass measurement by the CMS Collaboration at the CERN LHC, based on a data sample collected in 2016 at the proton-proton collision energy of 13 TeV. The W boson mass is measured using a large sample of W$\to\mu\nu$ events via a highly granular binned maximum likelihood fit to the kinematic properties of the muons produced in the W$^{+}$ and W$^{-}$ boson decays. The significant in situ constraints of theoretical inputs and their corresponding uncertainties, together with an accurate determination of the experimental effects, lead to a precise W boson mass measurement, $m_\mathrm{W} =$ 80$\,$360.2 $\pm$ 9.9 MeV, in agreement with the standard model prediction.

A search for a pair of light pseudoscalar bosons (a$_1$) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a$_1$ decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a$_1$ boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb$^{-1}$. No excess above standard model (SM) expectations is observed. The study combines the 4$τ$ and 2$μ$2$τ$ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4$τ$ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a$_1$ boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a$_1$ bosons exceeding 16% are excluded at 95% CL for a$_1$ boson masses between 5 and 15 GeV and $\tanβ$ $\gt$ 2, with the exception of scenarios in which the a$_1$ boson mixes with charm or bottom quark-antiquark bound states.

A search for new long-lived particles decaying to leptons using proton-proton collision data produced by the CERN LHC at $\sqrt{s}$ = 13 TeV is presented. Events are selected with two leptons (an electron and a muon, two electrons, or two muons) that both have transverse impact parameter values between 0.01 and 10 cm and are not required to form a common vertex. Data used for the analysis were collected with the CMS detector in 2016, 2017, and 2018, and correspond to an integrated luminosity of 118 (113) fb$^{-1}$ in the ee channel (e$\mu$ and $\mu\mu$ channels). The search is designed to be sensitive to a wide range of models with displaced e$\mu$, ee, and $\mu\mu$ final states. The results constrain several well-motivated models involving new long-lived particles that decay to displaced leptons. For some areas of the available phase space, these are the most stringent constraints to date.

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 search for a new massive charged gauge boson, $W'$, is performed with the ATLAS detector at the LHC. The dataset used in this analysis was collected from proton-proton collisions at a centre-of-mass energy of $\sqrt{s} =13$ TeV, and corresponds to an integrated luminosity of 139 fb$^{-1}$. The reconstructed $tb$ invariant mass is used to search for a $W'$ boson decaying into a top quark and a bottom quark. The result is interpreted in terms of a $W'$ boson with purely right-handed or left-handed chirality in a mass range of 0.5-6 TeV. Different values for the coupling of the $W'$ boson to the top and bottom quarks are considered, taking into account interference with single-top-quark production in the $s$-channel. No significant deviation from the background prediction is observed. The results are expressed as upper limits on the $W' \rightarrow tb$ production cross-section times branching ratio as a function of the $W'$-boson mass and in the plane of the coupling vs the $W'$-boson mass.

First measurements of hadron(h)$-\Lambda$ azimuthal angular correlations in p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV using the ALICE detector at the Large Hadron Collider are presented. These correlations are used to separate the production of associated $\Lambda$ baryons into three different kinematic regions, namely those produced in the direction of the trigger particle (near-side), those produced in the opposite direction (away-side), and those whose production is uncorrelated with the jet axis (underlying event). The per-trigger associated $\Lambda$ yields in these regions are extracted, along with the near- and away-side azimuthal peak widths, and the results are studied as a function of associated particle $p_{\rm T}$ and event multiplicity. Comparisons with the DPMJET event generator and previous measurements of the $\phi(1020)$ meson are also made. The final results indicate that strangeness production in the highest multiplicity p$-$Pb collisions is enhanced relative to low multiplicity collisions in both the jet-like regions and the underlying event. The production of $\Lambda$ relative to charged hadrons is also enhanced in the underlying event when compared to the jet-like regions. Additionally, the results hint that strange quark production in the away-side of the jet is modified by soft interactions with the underlying event.

We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=3$ GeV with the STAR experiment at RHIC. $K^0_S$ meson and $\Lambda$ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of $\Lambda$ and $K^0_S$ are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4$\pi$ yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.

A study of the polarisation and CP properties in $ZZ$ production is presented. The used data set corresponds to an integrated luminosity of 140 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of $13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. The $ZZ$ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised $Z$ bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be $2.45 \pm 0.60$ fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.

A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron-muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb$^{-1}$ at $\sqrt{s}=7$ TeV and about 20 fb$^{-1}$ at $\sqrt{s}=8$ TeV for each experiment. The combined cross-sections are determined to be $178.5 \pm 4.7$ pb at $\sqrt{s}=7$ TeV and $243.3^{+6.0}_{-5.9}$ pb at $\sqrt{s}=8$ TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be $R_{8/7}= 1.363\pm 0.032$. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are $m_t^\text{pole} = 173.4^{+1.8}_{-2.0}$ GeV and $\alpha_\text{s}(m_Z)= 0.1170^{+ 0.0021}_{-0.0018}$.

A combination of searches for the single production of vector-like top quarks ($T$) is presented. These analyses are based on proton$-$proton collisions at $\sqrt{s}=13$ TeV recorded in 2015$-$2018 with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. The $T$-quark decay modes considered in this combination are into a top quark and either a Standard Model Higgs boson or a $Z$ boson ($T \to Ht$ and $T \to Zt$). The individual searches used in the combination are differentiated by the number of leptons ($e$, $\mu$) in the final state. The observed data are found to be in good agreement with the Standard Model background prediction. Interpretations are provided for a range of masses and couplings of the vector-like top quark for benchmark models and generalized representations in terms of 95% confidence level limits. For a benchmark signal prediction of a vector-like top quark SU2 singlet with electroweak coupling, $\kappa$, of 0.5, masses below 2.1 TeV are excluded, resulting in the most restrictive limits to date.