Measurements of the charge-dependent two-particle angular correlation function in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of
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A bstract = 8$$ \sqrt{s_{\textrm{NN}}} $$ . 16 TeV and lead-lead (PbPb) collisions at = 5$$ \sqrt{s_{\textrm{NN}}} $$ . 02 TeV are reported. The pPb and PbPb data sets correspond to integrated luminosities of 186 nb− 1and 0.607 nb− 1, respectively, and were collected using the CMS detector at the CERN LHC. The charge-dependent correlations are characterized by balance functions of same- and opposite-sign particle pairs. The balance functions, which contain information about the creation time of charged particle pairs and the development of collectivity, are studied as functions of relative pseudorapidity (∆η ) and relative azimuthal angle (∆ϕ ), for various multiplicity and transverse momentum (p T) intervals. A multiplicity dependence of the balance function is observed in ∆η and ∆ϕ for both systems. The width of the balance functions decreases towards high-multiplicity collisions in the momentum region< 2 GeV, for pPb and PbPb results. Integrals of the balance functions are presented in both systems, and a mild dependence of the charge-balancing fractions on multiplicity is observed. No multiplicity dependence is observed at higher transverse momentum. The data are compared withhydjet ,hijing , andampt generator predictions, none of which capture completely the multiplicity dependence seen in the data. The comparison of results with different center-of-mass energies suggests that the balance functions become narrower at higher energies, which is consistent with the idea of delayed hadronization and the effect of radial flow.Free, publicly-accessible full text available August 1, 2025 -
A search for beyond the standard model spin-0 bosons,, that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with aorgauge boson, or a top quark-antiquark pair, and uses events with three or four charged leptons, including hadronically decaying tau leptons. The proton-proton collision data set used in the analysis was collected at the LHC from 2016 to 2018 at a center-of-mass energy of 13 TeV, and corresponds to an integrated luminosity of. The observations are consistent with the predictions from standard model processes. Upper limits are placed on the product of cross sections and branching fractions of such new particles over the mass range of 15 to 350 GeV with scalar, pseudoscalar, or Higgs-boson-like couplings, as well as on the product of coupling parameters and branching fractions. Several model-dependent exclusion limits are also presented. For a Higgs-boson-likemodel, limits are set on the mixing angle of the Higgs boson with theboson. For the associated production of aboson with a top quark-antiquark pair, limits are set on the coupling to top quarks. Finally, limits are set for the first time on a fermiophilic dilaton-like model with scalar couplings and a fermiophilic axion-like model with pseudoscalar couplings.
© 2024 CERN, for the CMS Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
The production ofandmesons in lead-lead (Pb-Pb) and proton-proton () collisions is studied in their dimuon decay channel using the CMS detector at the LHC. Themeson is observed for the first time in Pb-Pb collisions, with a significance above 5 standard deviations. The ratios of yields measured in Pb-Pb andcollisions are reported for both theandmesons, as functions of transverse momentum and Pb-Pb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression ofyields in Pb-Pb collisions. This suppression increases from peripheral to central Pb-Pb collisions. Furthermore, the suppression is stronger formesons compared tomesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the,,, andmesons.
© 2024 CERN, for the CMS Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
A search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions atin events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity ofcollected in 2016–2018 with the central CMS detector and the CMS and TOTEM precision proton spectrometer (PPS). Events that have two photons with high transverse momenta (), back-to-back in azimuth, and with a large diphoton invariant mass () are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parametersand, using an effective field theory. Additionally, upper limits are placed on the production of axionlike particles with coupling strength to photonsthat varies fromtoover the mass range from 500 to 2000 GeV.
© 2024 CERN, for the CMS and TOTEMs Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
A bstract A search is presented for the decay of the 125 GeV Higgs boson (H) to a pair of new light pseudoscalar bosons (a), followed by the prompt decay of each a boson to a bottom quark-antiquark pair,
. The analysis is performed using a data sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$$ \textrm{H}\to \textrm{aa}\to \textrm{b}\overline{\textrm{b}}\textrm{b}\overline{\textrm{b}} $$ − 1. To reduce the background from standard model processes, the search requires the Higgs boson to be produced in association with a leptonically decaying W or Z boson. The analysis probes the production of new light bosons in a 15 <m a< 60 GeV mass range. Assuming the standard model predictions for the Higgs boson production cross sections for pp → WH and ZH, model independent upper limits at 95% confidence level are derived for the branching fraction . The combined WH and ZH observed upper limit on the branching fraction ranges from 1.10 for$$ \mathcal{B}\left(\textrm{H}\to \textrm{aa}\to \textrm{b}\overline{\textrm{b}}\textrm{b}\overline{\textrm{b}}\right) $$ m a= 20 GeV to 0.36 form a= 60 GeV, complementing other measurements in theμμττ ,ττττ and bbℓℓ (ℓ =μ ,τ ) channels.Free, publicly-accessible full text available June 1, 2025 -
A bstract A search for the central exclusive production of top quark-antiquark pairs (
) is performed for the first time using proton-tagged events in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 29.4 fb$$ \textrm{t}\overline{\textrm{t}} $$ − 1. The decay products are reconstructed using the central CMS detector, while forward protons are measured in the CMS-TOTEM precision proton spectrometer. An observed (expected) upper bound on the production cross section of 0.59 (1.14) pb is set at 95% confidence level, for collisions of protons with fractional momentum losses between 2 and 20%.$$ \textrm{t}\overline{\textrm{t}} $$ Free, publicly-accessible full text available June 1, 2025 -
Differential cross sections are measured for the standard model Higgs boson produced in association with vector bosons (,) and decaying to a pair ofquarks. Measurements are performed within the framework of the simplified template cross sections. The analysis relies on the leptonic decays of theandbosons, resulting in final states with 0, 1, or 2 electrons or muons. The Higgs boson candidates are either reconstructed from pairs of resolved-tagged jets, or from single large-radius jets containing the particles arising from twoquarks. Proton-proton collision data at, collected by the CMS experiment in 2016–2018 and corresponding to a total integrated luminosity of, are analyzed. The inclusive signal strength, defined as the product of the observed production cross section and branching fraction relative to the standard model expectation, combining all analysis categories, is found to be. This corresponds to an observed (expected) significance of 6.3 (5.6) standard deviations.
© 2024 CERN, for the CMS Collaboration 2024 CERN Free, publicly-accessible full text available May 1, 2025 -
A bstract A search for a new boson X is presented using CERN LHC proton-proton collision data collected by the CMS experiment at
= 13 TeV in 2016–2018, and corresponding to an integrated luminosity of 138 fb$$ \sqrt{s} $$ − 1. The resonance X decays into either a pair of Higgs bosons HH of mass 125 GeV or an H and a new spin-0 boson Y. One H subsequently decays to a pair of photons, and the second H or Y, to a pair of bottom quarks. The explored mass ranges of X are 260–1000 GeV and 300–1000 GeV, for decays to HH and to HY, respectively, with the Y mass range being 90–800 GeV. For a spin-0 X hypothesis, the 95% confidence level upper limit on the product of its production cross section and decay branching fraction is observed to be within 0.90–0.04 fb, depending on the masses of X and Y. The largest deviation from the background-only hypothesis with a local (global) significance of 3.8 (below 2.8) standard deviations is observed for X and Y masses of 650 and 90 GeV, respectively. The limits are interpreted using several models of new physics.Free, publicly-accessible full text available May 1, 2025 -
Two-particle Bose-Einstein correlations and their Lévy parameters in PbPb collisions at sNN=5.02 TeVFree, publicly-accessible full text available February 1, 2025
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A bstract 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 = 5$$ \sqrt{s_{\textrm{NN}}} $$ . 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, withv 2{2}> v 2{4} ≳v 2{6} ≳v 2{8} ≳v 2{10}. Based on these results, centrality-dependent moments for the fluctuation-driven event-by-eventv 2distribution 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.Free, publicly-accessible full text available February 1, 2025