283 Search Results

In the standard model of particle physics, the masses of the W and Z bosons, the carriers of the weak interaction, are uniquely related. A precise determination of their masses is important because quantum loops of heavy, undiscovered particles could modify this relationship. Although the Z mass is known to the remarkable precision of 22 parts per million (2.0 MeV), the W mass is known much less precisely. A global fit to measured electroweak observables predicts the W mass with 6 MeV uncertainty [1$$-$$3]. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model,more » made even more urgent by a recent challenge to the global fit prediction by a measurement from the CDF Collaboration at the Fermilab Tevatron collider [4]. Here we report the measurement of the W mass by the CMS Collaboration at the CERN LHC, based on a large data sample of $$W \to \mu \nu$$ events collected in 2016 at the proton-proton collision energy of 13 TeV. The measurement exploits a high-granularity maximum likelihood fit to the kinematic properties of muons produced in W decays. By combining an accurate determination of experimental effects with marked in situ constraints of theoretical inputs, we reach a precise measurement of the W mass, of 80 360.2 $$\pm$$ 9.9 MeV, in agreement with the standard model prediction.« less

A novel method to reconstruct the energy of hadronic showersin the CMS High Granularity Calorimeter (HGCAL) is presented. TheHGCAL is a sampling calorimeter with very fine transverse andlongitudinal granularity. The active media are silicon sensors andscintillator tiles readout by SiPMs and the absorbers are acombination of lead and Cu/CuW in the electromagnetic section, andsteel in the hadronic section. The shower reconstruction method isbased on graph neural networks and it makes use of a dynamicreduction network architecture. It is shown that the algorithm isable to capture and mitigate the main effects that normally hinderthe reconstruction of hadronic showers using classicalreconstruction methods,more » by compensating for fluctuations in themultiplicity, energy, and spatial distributions of the shower'sconstituents. The performance of the algorithm is evaluated usingtest beam data collected in 2018 prototype of the CMS HGCALaccompanied by a section of the CALICE AHCAL prototype. Thecapability of the method to mitigate the impact of energy leakagefrom the calorimeter is also demonstrated.« less

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

A search for beyond the standard model spin-0 bosons, $\varphi$ , that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with a $W$ or $Z$ gauge 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 $138{\mathrm{fb}}^{-1}more »$ . 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-like $\varphi$ model, limits are set on the mixing angle of the Higgs boson with the $\varphi$ boson. For the associated production of a $\varphi$ boson 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.« 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