79 Search Results

Two-particle correlations are presented for $$K^0_S$$, $$Λ$$, and $$\overline{Λ}$$ strange hadrons as a function of relative momentum in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The dataset corresponds to an integrated luminosity of 0.607 nb^-1 and was collected using the CMS detector at the CERN LHC. These correlations are sensitive to quantum statistics and to final-state interactions between the particles. The source size extracted from the $$K^0_S$$$$K^0_S$$ correlations is found to decrease from 4.6 to 1.6 fm in going from central to peripheral collisions. Strong interaction scattering parameters (i.e., scattering length and effective range) are determined frommore » the $$ΛK^0_S$$ and $ΛΛ$ (including their charge conjugates) correlations using the Lednický–Lyuboshitz model and are compared to theoretical and other experimental results.« less

A search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ in events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity of $103{\mathrm{fb}}^{-1}$ collected 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 ( $p_{\mathrm{T}}^{\gamma }>100more »$     GeV ), back-to-back in azimuth, and with a large diphoton invariant mass ( $m_{\gamma \gamma }>350\mathrm{GeV}$ ) 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 parameters $\left|{\zeta }_1\right|<0.073{\mathrm{TeV}}^{-4}$ and $\left|{\zeta }_2\right|<0.15{\mathrm{TeV}}^{-4}$ , using an effective field theory. Additionally, upper limits are placed on the production of axionlike particles with coupling strength to photons $f^{-1}$ that varies from $0.03{\mathrm{TeV}}^{-1}$ to $1{\mathrm{TeV}}^{-1}$ over the mass range from 500 to 2000 GeV. © 2024 CERN, for the CMS and TOTEMs Collaboration 2024 CERN« less

The production of $\mathrm{\Upsilon }\left(2S\right)$ and $\mathrm{\Upsilon }\left(3S\right)$ mesons in lead-lead (Pb-Pb) and proton-proton ( $pp$ ) collisions is studied in their dimuon decay channel using the CMS detector at the LHC. The $\mathrm{\Upsilon }\left(3S\right)$ meson 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 and $pp$ collisions are reported for both the $more »$ ϒ ( 2 S ) and $\mathrm{\Upsilon }\left(3S\right)$ mesons, as functions of transverse momentum and Pb-Pb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression of $\mathrm{\Upsilon }$ yields in Pb-Pb collisions. This suppression increases from peripheral to central Pb-Pb collisions. Furthermore, the suppression is stronger for $\mathrm{\Upsilon }\left(3S\right)$ mesons compared to $\mathrm{\Upsilon }\left(2S\right)$ mesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the $J/\psi$ , $\psi \left(2S\right)$ , $\mathrm{\Upsilon }\left(1S\right)$ , and $\mathrm{\Upsilon }\left(2S\right)$ mesons. © 2024 CERN, for the CMS Collaboration 2024 CERN« less

Differential cross sections are measured for the standard model Higgs boson produced in association with vector bosons ( $W$ , $Z$ ) and decaying to a pair of $b$ quarks. Measurements are performed within the framework of the simplified template cross sections. The analysis relies on the leptonic decays of the $W$ and $Z$ bosons, resulting in final states with 0, 1, or 2 electrons or muons. The Higgs boson candidates are either reconstructed from pairs of resolved $b$ -tagged jets, or from single large-radius jets containing themore » particles arising from two $b$ quarks. Proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ , collected by the CMS experiment in 2016–2018 and corresponding to a total integrated luminosity of $138{\mathrm{fb}}^{-1}$ , 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 $\mu =1.15_{-0.20}^{+0.22}$ . This corresponds to an observed (expected) significance of 6.3 (5.6) standard deviations. © 2024 CERN, for the CMS Collaboration 2024 CERN« less

The azimuthal anisotropy of Image 1 mesons in high-multiplicity proton-lead collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 8.16 TeV. The Image 1 mesons are reconstructed using their dimuon decay channel. The anisotropy is characterized by the second Fourier harmonic coefficients, found using a two-particle correlation technique, in which the Image 1 mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. Nonflow contamination from the dijet background is removed using a low-multiplicity subtraction method, and the results are presented as a function of Image 1more » transverse momentum. The azimuthal anisotropies are smaller than those found for charmonia in proton-lead collisions at the same collision energy, but are consistent with values found for Image 1 mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV.« less

Two-particle Bose–Einstein momentum correlation functions are studied for charged-hadron pairs in lead-lead collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ . The data sample, containing $4.27\times {10}^9$ minimum bias events corresponding to an integrated luminosity of 0.607  ${\text{nb}}^{-1}$ , was collected by the CMS experiment in 2018. The experimental results are discussed in terms of a Lévy-type source distribution. The parameters of this distribution are extracted as functionsmore » of particle pair average transverse mass and collision centrality. These parameters include the Lévy index or shape parameter $\alpha$ , the Lévy scale parameter $R$ , and the correlation strength parameter $\lambda$ . The source shape, characterized by $\alpha$ , is found to be neither Cauchy nor Gaussian, implying the need for a full Lévy analysis. Similarly to what was previously found for systems characterized by Gaussian source radii, a hydrodynamical scaling is observed for the Lévy $R$ parameter. The $\lambda$ parameter is studied in terms of the core-halo model. ©2024 CERN, for the CMS Collaboration 2024 CERN« less

Measurements of the elliptic ($$v$$₂) and triangular ($$v$$₃) azimuthal anisotropy coefficients are presented for D⁰ mesons produced in b hadron decays (nonprompt D⁰ mesons) in lead-lead collisions at $$\sqrt{s_{NN}}$$ = 5.02 TeV. The results are compared with previously published charm meson anisotropies measured using prompt D⁰ mesons. The data were collected with the CMS detector in 2018 with an integrated luminosity of 0.58 nb^–1. Azimuthal anisotropy is sensitive to the interactions of quarks with the hot and dense medium created in heavy ion collisions. Comparing results for prompt and nonprompt D⁰ mesons can assist in understanding the mass dependence ofmore » these interactions. The nonprompt results show lower magnitudes of $$v$$₂ and $$v$$₃ and weaker dependences on the meson transverse momentum and collision centrality than those found for prompt D⁰ mesons. The results are in agreement with theoretical predictions that include a mass dependence in the interactions of quarks with the medium« less

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$$\,\text {Te}\hspace{-.08em}\text {V}$$. The analysis uses a data sample corresponding to a total integrated luminosity of 138$$\,\text {fb}^{-1}$$ 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 $$\hbox {W}+\hbox {c}$$ production crossmore » section and the cross section ratio $$R_\textrm{c}^{\pm }= \sigma ({\hbox {W}}^{+}+\bar{\text {c}})/\sigma (\hbox {W}^{-}+{\textrm{c}})$$ 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 $$R_\textrm{c}^{\pm }= 0.950 \pm 0.005\,\text {(stat)} \pm 0.010 \,\text {(syst)} $$. The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics.« less

For the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both proton and lead dissociation processes are presented. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy per nucleon pair of $$\sqrt{s_{NN}}$$ = 8.16 TeV , almost 300 times higher than in previous measurements of diffractive production in proton-nucleus collisions. For lead dissociation processes, which correspond to the pomeron-lead event topology, the EPOS-LHC generator predictions are a factor of 2 below the data, but the model gives a reasonable description of the rapidity gap spectrum shape. For the pomeron-proton topology,more » the EPOS-LHC, QGSJET II, and HIJING predictions are all at least a factor of 5 lower than the data. The latter effect might be explained by a significant contribution of ultraperipheral photoproduction events mimicking the signature of diffractive processes. These data may be of significant help in understanding the high energy limit of quantum chromodynamics and for modeling cosmic ray air showers.« less

The mass of the top quark is measured in 36.3 fb^-1 of LHC proton–proton collision data collected with the CMS detector at $$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V}$$. 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 171.77more » ± 0.37 GeV. This approach significantly improves the precision over previous measurements.« less