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.
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© 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 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 -
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 -
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. -
Abstract The strange quark content of the proton is probed through the measurement of the production cross section for a W boson and a charm (c) quark in proton–proton collisions at a center-of-mass energy of 13
. The analysis uses a data sample corresponding to a total integrated luminosity of 138$$\,\text {Te}\hspace{-.08em}\text {V}$$ collected with the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are tagged using the presence of a muon or a secondary vertex inside the jet. The$$\,\text {fb}^{-1}$$ production cross section and the cross section ratio$$\hbox {W}+\hbox {c}$$ are measured inclusively and differentially as functions of the transverse momentum and the pseudorapidity of the lepton originating from the W boson decay. The precision of the measurements is improved with respect to previous studies, reaching 1% in$$R_\textrm{c}^{\pm }= \sigma ({\hbox {W}}^{+}+\bar{\text {c}})/\sigma (\hbox {W}^{-}+{\textrm{c}})$$ . The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics.$$R_\textrm{c}^{\pm }= 0.950 \pm 0.005\,\text {(stat)} \pm 0.010 \,\text {(syst)} $$ -
Abstract The mass of the top quark is measured in 36.3
of LHC proton–proton collision data collected with the CMS detector at$$\,\text {fb}^{-1}$$ . The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to four observables per event to extract the top quark mass. The top quark mass is measured to be$$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$ . This approach significantly improves the precision over previous measurements.$$171.77\pm 0.37\,\text {Ge}\hspace{-.08em}\text {V} $$ -
A bstract The second-order (
v 2) and third-order (v 3) 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 = 5$$ \sqrt{s_{\textrm{NN}}} $$ . 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. Thev 2andv 3coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measuredv 2values for prompt J/ ψ mesons are found to be larger than those for nonprompt J/ ψ mesons. The prompt J/ ψv 2values 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 mesonv 3and prompt ψ(2S)v 2andv 3values 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.