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This paper describes theCombinesoftware package used for statistical analyses by the CMS Collaboration. The package, originally designed to perform searches for a Higgs boson and the combined analysis of those searches, has evolved to become the statistical analysis tool presently used in the majority of measurements and searches performed by the CMS Collaboration. It is not specific to the CMS experiment, and this paper is intended to serve as a reference for users outside of the CMS Collaboration, providing an outline of the most salient features and capabilities. Readers are provided with the possibility to runCombineand reproduce examples provided in this paper using a publicly available container image. Since the package is constantly evolving to meet the demands of ever-increasing data sets and analysis sophistication, this paper cannot cover all details ofCombine. However, the online documentation referenced within this paper provides an up-to-date and complete user guide.

Using proton–proton collision data corresponding to an integrated luminosity of$$140\hbox { fb}^{-1}$$$140{\text{fb}}^{-1}$collected by the CMS experiment at$$\sqrt{s}= 13\,\text {Te}\hspace{-.08em}\text {V} $$$\sqrt{s}=13\text{Te}\text{V}$, the$${{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{\text {J}/\uppsi }} {{{\Xi }} ^{{-}}} {{\text {K}} ^{{+}}} $$${\Lambda }_{\text{b}}^0\to \text{J}/\psi {\Xi }^{-}{\text{K}}^{+}$decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the$${{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{{\uppsi }} ({2\textrm{S}})} {{\Lambda }} $$${\Lambda }_{\text{b}}^0\to \psi \left(2\text{S}\right)\Lambda$decay, is measured to be$$\mathcal {B}({{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{\text {J}/\uppsi }} {{{\Xi }} ^{{-}}} {{\text {K}} ^{{+}}} )/\mathcal {B}({{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{{\uppsi }} ({2\textrm{S}})} {{\Lambda }} ) = [3.38\pm 1.02\pm 0.61\pm 0.03]\%$$$B({\Lambda }_{\text{b}}^0\to \text{J}/\psi {\Xi }^{-}{\text{K}}^{+})/B({\Lambda }_{\text{b}}^0\to \psi \left(2\text{S}\right)\Lambda )=[3.38\pm 1.02\pm 0.61\pm 0.03]\%$, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in$$\mathcal {B}({{{\uppsi }} ({2\textrm{S}})} \rightarrow {{\text {J}/\uppsi }} {{{\uppi }} ^{{+}}} {{{\uppi }} ^{{-}}} )$$$B(\psi \left(2\text{S}\right)\to \text{J}/\psi {\pi }^{+}{\pi }^{-})$and$$\mathcal {B}({{{\Xi }} ^{{-}}} \rightarrow {{\Lambda }} {{{\uppi }} ^{{-}}} )$$$B({\Xi }^{-}\to \Lambda {\pi }^{-})$.

A search for collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged particles using the CMS detector at the CERN LHC. The analysis uses data collected at a center-of-mass energy of$\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of$138{\mathrm{fb}}^{-1}$. Jets are reconstructed with the anti-$k_{\mathrm{T}}$algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550 GeV and pseudorapidity$|{\eta }^{\text{jet}}|<1.6$. Two-particle correlations among the charged particles within the jets are studied as functions of the particles’ azimuthal angle and pseudorapidity separations ($\mathrm{\Delta }{\varphi }^{*}$and$\mathrm{\Delta }{\eta }^{*}$) in a jet coordinate basis, where particles’${\eta }^{*}$,${\varphi }^{*}$are defined relative to the direction of the jet. The correlation functions are studied in classes of in-jet charged-particle multiplicity up to$N_{\mathrm{ch}}^{\mathrm{j}}\approx 100$. Fourier harmonics are extracted from long-range azimuthal correlation functions to characterize azimuthal anisotropy for$|\mathrm{\Delta }{\eta }^{*}|>2$. For low-$N_{\mathrm{ch}}^{\mathrm{j}}$jets, the long-range elliptic anisotropic harmonic,$v_2^{*}$, is observed to decrease with$N_{\mathrm{ch}}^{\mathrm{j}}$. This trend is well described by Monte Carlo event generators. However, a rising trend for$v_2^{*}$emerges at$N_{\mathrm{ch}}^{\mathrm{j}}\gtrsim 80$, hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of jet evolution in the vacuum.

A measurement is presented of the primary Lund jet plane (LJP) density in inclusive jet production in proton-proton collisions. The analysis uses 138 fb⁻¹of data collected by the CMS experiment at$$ \sqrt{s} $$$\sqrt{s}$= 13 TeV. The LJP, a representation of the phase space of emissions inside jets, is constructed using iterative jet declustering. The transverse momentumk_Tand the splitting angle ∆Rof an emission relative to its emitter are measured at each step of the jet declustering process. The average density of emissions as function of ln(k_T/GeV) and ln(R/∆R) is measured for jets with distance parametersR= 0.4 or 0.8, transverse momentump_T>700 GeV, and rapidity |y|<1.7. The jet substructure is measured using the charged-particle tracks of the jet. The measured distributions, unfolded to the level of stable charged particles, are compared with theoretical predictions from simulations and with perturbative quantum chromodynamics calculations. Due to the ability of the LJP to factorize physical effects, these measurements can be used to improve different aspects of the physics modeling in event generators.

A combination of fifteen top quark mass measurements performed by the ATLAS and CMS experiments at the LHC is presented. The datasets used correspond to an integrated luminosity of up to 5 and$20{\mathrm{fb}}^{-1}$of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, respectively. The combination includes measurements in top quark pair events that exploit both the semileptonic and hadronic decays of the top quark, and a measurement using events enriched in single top quark production via the electroweak$t$channel. The combination accounts for the correlations between measurements and achieves an improvement in the total uncertainty of 31% relative to the most precise input measurement. The result is$m_t=172.52\pm 0.14(\mathrm{stat})\pm 0.30(\mathrm{syst})\mathrm{GeV}$, with a total uncertainty of 0.33 GeV.

The second-order (v₂) and third-order (v₃) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/ψ, as well as prompt ψ(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of$$ \sqrt{s_{\textrm{NN}}} $$$\sqrt{s_{\mathrm{NN}}}$= 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb⁻¹recorded with the CMS detector. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay channel. Thev₂andv₃coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measuredv₂values for prompt J/ψ mesons are found to be larger than those for nonprompt J/ψ mesons. The prompt J/ψv₂values at highp_Tare found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ψ mesonv₃and prompt ψ(2S)v₂andv₃values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.