113 Search Results

A search is presented for fractionally charged particles with charges below 1⁢𝑒, using their small energy loss in the tracking detector as a key variable to observe a signal. The analyzed dataset corresponds to an integrated luminosity of 138 fb⁻¹ of proton-proton collisions collected at $$\sqrt{𝑠}$$ = 13 TeV in 2016–2018 at the CERN LHC. This is the first search at the LHC for new particles with a charge between 𝑒/3 and 0.9⁢𝑒, including an extension of previous results at a charge of 2⁢𝑒/3. Masses up to 640 GeV and charges as low as 𝑒/3 are excluded at 95% confidencemore » level. These are the most stringent limits to date for the considered Drell-Yan-like production mode.« less

A search is performed for charged-lepton flavor violating processes in top quark (𝑡) production and decay. The data were collected by the CMS experiment from proton-proton collisions at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb⁻¹. The selected events are required to contain one opposite-sign electron-muon pair, a third charged lepton (electron or muon), and at least one jet of which no more than one is associated with a bottom quark. Boosted decision trees are used to distinguish signal from background, exploiting differences in the kinematics of the final states particles. The datamore » are consistent with the standard model expectation. Upper limits at 95% confidence level are placed in the context of effective field theory on the Wilson coefficients, which range between 0.024–0.424 TeV⁻² depending on the flavor of the associated light quark and the Lorentz structure of the interaction. These limits are converted to upper limits on branching fractions involving up (charm) quarks, 𝑡 → 𝑒⁢𝜇⁢𝑢 (𝑡 → 𝑒⁢𝜇⁢𝑐), of 0.032⁢(0.498) × 10⁻⁶, 0.022⁢(0.369) × 10⁻⁶, and 0.012⁢(0.216) × 10⁻⁶ for tensorlike, vectorlike, and scalarlike interactions, respectively.« less

A measurement of the dijet production cross section is reported based on proton–proton collision data collected in 2016 at $$\sqrt{s}$$ = 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of up to 36.3 fb^–1. Jets are reconstructed with the anti-$$k$$_T algorithm for distance parameters of R = 0.4 and 0.8. Cross sections are measured double-differentially (2D) as a function of the largest absolute rapidity |y|_max of the two jets with the highest transverse momenta $$p$$_T and their invariant mass $$m$$_1,2, and triple-differentially (3D) as a function of the rapidity separation $$y$$*, the totalmore » boost $$y$$_b, and either $$m$$_1,2 or the average $$p$$_T of the two jets. The cross sections are unfolded to correct for detector effects and are compared with fixed-order calculations derived at next-to-next-to-leading order in perturbative quantum chromodynamics. The impact of the measurements on the parton distribution functions and the strong coupling constant at the mass of the Z boson is investigated, yielding a value of $$α$$_S($$m$$_Z) = 0.1179 ± 0.0019.« less

A search for Higgs boson pair (HH) production in association with a vector boson V (W or Z boson) is presented. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. Both hadronic and leptonic decays of V bosons are used. The leptons considered are electrons, muons, and neutrinos. The HH production is searched for in the $$ \textrm{b}\overline{\textrm{b}}\textrm{b}\overline{\textrm{b}} $$ decay channel. An observed (expected) upper limit at 95% confidence level of VHH production cross section is set atmore » 294 (124) times the standard model prediction. Constraints are also set on the modifiers of the Higgs boson trilinear self-coupling, k$$_{λ}$$, assuming k$$_{2V}$$ = 1, and vice versa on the coupling of two Higgs bosons with two vector bosons, k$$_{2V}$$. The observed (expected) 95% confidence intervals of these coupling modifiers are −37.7 < k$$_{λ}$$ < 37.2 (−30.1 < k$$_{λ}$$ < 28.9) and −12.2 < k$$_{2V}$$ < 13.5 (−7.2 < k$$_{2V}$$ < 8.9), respectively.[graphic not available: see fulltext]« less

The operation and performance of the Compact Muon Solenoid(CMS) electromagnetic calorimeter (ECAL) are presented, based ondata collected in pp collisions at√$$_{s}$$ =13 TeV at the CERN LHC, in the years from 2015 to 2018(LHC Run 2), corresponding to an integrated luminosity of151 fb$$^{-1}$$. The CMS ECAL is a scintillating lead-tungstatecrystal calorimeter, with a silicon strip preshower detector in theforward region that provides precise measurements of the energy andthe time-of-arrival of electrons and photons. The successfuloperation of the ECAL is crucial for a broad range of physics goals,ranging from observing the Higgs boson and measuring its properties,to other standard model measurements andmore » searches for newphenomena. Precise calibration, alignment, and monitoring of theECAL response are important ingredients to achieve these goals. Toface the challenges posed by the higher luminosity, whichcharacterized the operation of the LHC in Run 2, the proceduresestablished during the 2011–2012 run of the LHC have been revisitedand new methods have been developed for the energy measurement andfor the ECAL calibration. The energy resolution of the calorimeter,for electrons from Z boson decays reaching theECAL without significant loss of energy by bremsstrahlung, wasbetter than 1.8%, 3.0%, and 4.5% in the |η| intervals[0.0,0.8], [0.8,1.5], [1.5, 2.5], respectively. This resultingperformance is similar to that achieved during Run 1 in 2011–2012,in spite of the more severe running conditions.« 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

The results of a search for stealth supersymmetry in final states with two photons and jets, targeting a phase space region with low missing transverse momentum ( $p_{\mathrm{T}}^{\mathrm{miss}}$ ), are reported. The study is based on a sample of proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ collected by the CMS experiment, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . As LHC results continue to constrain the parameter spacemore » of the minimal supersymmetric standard model, the low $p_{\mathrm{T}}^{\mathrm{miss}}$ regime is increasingly valuable to explore. To estimate the backgrounds due to standard model processes in such events, we apply corrections derived from simulation to an estimate based on a control selection in data. The results are interpreted in the context of simplified stealth supersymmetry models with gluino and squark pair production. The observed data are consistent with the standard model predictions, and gluino (squark) masses of up to 2150 (1850) GeV are excluded at the 95% confidence level.« less