The transverse momentum spectra of charged particles have been measured in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV by the CMS experiment at the LHC. In the transverse momentum range pt = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 5 compared to the pp yield scaled by the number of incoherent nucleon-nucleon collisions. At higher pt, this suppression is significantly reduced, approaching roughly a factor of 2 for particles with pt in the range pt=40-100 GeV/c.

Isolated photon production is measured in proton-proton and lead-lead collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80 GeV with the CMS detector at the LHC. The measured ET spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon ET-differential yields, scaled by the number of incoherent nucleon-nucleon collisions, is consistent with unity for all PbPb reaction centralities.

The anisotropy of the azimuthal distributions of charged particles produced in PbPb collisions with a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, two- and four-particle cumulants, and Lee--Yang zeros. The anisotropy is presented as a function of transverse momentum (pt), pseudorapidity (eta) over a broad kinematic range: 0.3 < pt < 20 GeV, abs(eta) < 2.4, and in 12 classes of collision centrality from 0 to 80%. The results are compared to those obtained at lower center-of-mass energies, and various scaling behaviors are examined. When scaled by the geometric eccentricity of the collision zone, the elliptic anisotropy is found to obey a universal scaling with the transverse particle density for different collision systems and center-of-mass energies.

The collective behavior of K$^0_\mathrm{S}$ and $\Lambda/\bar{\Lambda}$ strange hadrons is studied by measuring the elliptic azimuthal anisotropy ($v_2$) using the scalar-product and multiparticle correlation methods. Proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV and lead-lead (PbPb) collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV collected by the CMS experiment at the LHC are investigated. Nonflow effects in the pPb collisions are studied by using a subevent cumulant analysis and by excluding events where a jet with transverse momentum greater than 20\GeV is present. The strange hadron $v_2$ values extracted in \pPb collisions via the four- and six-particle correlation method are found to be nearly identical, suggesting the collective behavior. Comparisons of the pPb and PbPb results for both strange hadrons and charged particles illustrate how event-by-event flow fluctuations depend on the system size.

Results on two-particle angular correlations for charged particles produced in pp collisions at a center-of-mass energy of 13 TeV are presented. The data were taken with the CMS detector at the LHC and correspond to an integrated luminosity of about 270 inverse nanobarns. The correlations are studied over a broad range of pseudorapidity (abs(eta) < 2.4) and over the full azimuth (phi) as a function of charged particle multiplicity and transverse momentum (pt). In high-multiplicity events, a long-range (abs(Delta eta) > 2.0), near-side (Delta phi approximately 0) structure emerges in the two-particle Delta eta-Delta phi correlation functions. The magnitude of the correlation exhibits a pronounced maximum in the range 1.0 < pt < 2.0 GeV/c and an approximately linear increase with the charged particle multiplicity, with an overall correlation strength similar to that found in earlier pp data at sqrt(s) = 7 TeV. The present measurement extends the study of near-side long-range correlations up to charged particle multiplicities of N[ch] approximately 180, a region so far unexplored in pp collisions. The observed long-range correlations are compared to those seen in pp, pPb, and PbPb collisions at lower collision energies.

The path-length dependent parton energy loss within the dense partonic medium created in lead-lead collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV is studied by determining the azimuthal anisotropies for dijets with high transverse momentum. The data were collected by the CMS experiment in 2018 and correspond to an integrated luminosity of 1.69 nb$^{-1}$. For events containing back-to-back jets, correlations in relative azimuthal angle and pseudorapidity ($\eta$) between jets and hadrons, and between two hadrons, are constructed. The anisotropies are expressed as the Fourier expansion coefficients $v_n$, $n = $ 2-4 of these azimuthal distributions. The dijet $v_n$ values are extracted from long-range (1.5 $\lt$$\vert\Delta\eta\vert$$\lt$ 2.5) components of these correlations, which suppresses the background contributions from jet fragmentation processes. Positive dijet $v_2$ values are observed which increase from central to more peripheral events, while the $v_3$ and $v_4$ values are consistent with zero within experimental uncertainties.

A systematic study of the factorization of long-range azimuthal two-particle correlations into a product of single-particle anisotropies is presented as a function of pt and eta of both particles, and as a function of the particle multiplicity in PbPb and pPb collisions. The data were taken with the CMS detector for PbPb collisions at sqrt(s[NN]) = 2.76 TeV and pPb collisions at sqrt(s[NN]) = 5.02 TeV, covering a very wide range of multiplicity. Factorization is observed to be broken as a function of both particle pt and eta. When measured with particles of different pt, the magnitude of the factorization breakdown for the second Fourier harmonic reaches 20% for very central PbPb collisions but decreases rapidly as the multiplicity decreases. The data are consistent with viscous hydrodynamic predictions, which suggest that the effect of factorization breaking is mainly sensitive to the initial-state conditions rather than to the transport properties (e.g., shear viscosity) of the medium. The factorization breakdown is also computed with particles of different eta. The effect is found to be weakest for mid-central PbPb events but becomes larger for more central or peripheral PbPb collisions, and also for very high-multiplicity pPb collisions. The eta-dependent factorization data provide new insights to the longitudinal evolution of the medium formed in heavy ion collisions.

The hydrodynamic flow-like behavior of charged hadrons in high-energy lead-lead collisions is studied through multiparticle correlations. The elliptic anisotropy values based on different orders of multiparticle cumulants, $v_{2}\{2k\}$, are measured up to the tenth order ($k$ = 5) as functions of the collision centrality at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV. The data were recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 0.607 nb$^{-1}$. A hierarchy is observed between the coefficients, with $v_{2}\{2\} > v_{2}\{4\} \gtrsim v_{2}\{6\} \gtrsim v_{2}\{8\} \gtrsim v_{2}\{10\}$. Based on these results, centrality-dependent moments for the fluctuation-driven event-by-event $v_{2}$ distribution are determined, including the skewness, kurtosis and, for the first time, superskewness. Assuming a hydrodynamic expansion of the produced medium, these moments directly probe the initial-state geometry in high-energy nucleus-nucleus collisions.

The $B_\mathrm{c}^+$ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the $B_\mathrm{c}^+$ meson in lead-lead (PbPb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} =$ 5.02 TeV, via the $B_\mathrm{c}^+ \to (J/\psi\to\mu^+\mu^-)\mu^+\nu_\mu$ decay. The $B_\mathrm{c}^+$ nuclear modification factor, derived from the PbPb-to-pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the PbPb collision centrality. The B$_\mathrm{c}^+$ meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.

Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt(sNN) = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and laboratory rapidity abs(y) < 1 are identified via their energy loss in the silicon tracker. The average pt increases with particle mass and the charged multiplicity of the event. The increase of the average pt with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that EPOS LHC, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike HIJING and AMPT. The pt spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity.