395 Search Results

A search for new physics in events featuring a single photon and missing transverse momentum is presented, using proton-proton √𝑠 =13 TeV collision data corresponding to an integrated luminosity of 101 fb⁻¹ collected by the CMS experiment at the CERN LHC between 2017 and 2018. This analysis, combined with a previous study of 36 fb⁻¹ of 2016 data (totaling 137 fb⁻¹), reveals no significant deviations from standard model expectations. The results are then used to establish 95% confidence level limits on parameters in theoretical models involving dark matter and large extra dimensions. Compared to the 2016-only analysis, this search achievesmore » up to a 14% improvement in exclusion reach for mediator masses in simplified dark matter models, along with 11% and 10% enhancements in the limits on the effective field theory suppression scale and the fundamental Planck scale, respectively. These results are the most stringent constraints on these parameters to date.« less

This Letter reports the first measurement of photonuclear 𝐷⁰ meson production in ultraperipheral heavy ion collisions. The study is performed using lead-lead collision data, with an integrated luminosity of 1.34 nb⁻¹, collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.36 TeV. Photonuclear events, where one of the colliding nuclei breaks up and the other remains intact, are selected based on breakup neutron emissions and by requiring no particle activity in a large rapidity interval in the direction of the photon-emitting nucleus. The 𝐷⁰ mesons are reconstructed via the 𝐷⁰ → 𝐾^−⁢𝜋⁺ decay channel, with the cross sectionmore » measured as a function of 𝐷⁰ meson transverse momentum and rapidity. The results are compared with next-to-leading-order perturbative QCD calculations that employ recent parametrizations of the lead nuclear parton distribution functions, as well as with predictions based on the color glass condensate framework. This measurement is the first photonuclear collision study characterizing parton distribution functions of lead nuclei for parton fractional momenta 𝑥 (relative to the nucleon) ranging approximately from a few 10⁻⁴ to 10⁻² for different hard energy scale 𝑄² selections.« less

An analysis of the flavour structure of dimension-6 effective field theory (EFT) operators in multilepton final states is presented, focusing on the interactions of quarks with Z bosons. For the first time, the flavour structure of these operators is disentangled by simultaneously probing the interactions with different quark generations. The analysis targets the associated production of a top quark pair and a Z boson, as well as diboson processes in final states with at least three leptons, which can be electrons or muons. The data were recorded by the CMS experiment in the years 2016–2018 in proton-proton collisions at amore » centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb⁻¹. Consistency with the standard model of particle physics is observed and limits are set on the selected Wilson coefficients, split into couplings to light- and heavy-quark generations.« less

A model-independent measurement of the differential production cross section of the Higgs boson decaying into a pair of W bosons, with a final state including two jets produced in association, is presented. In the analysis, events are selected in which the decay products of the two W bosons consist of an electron, a muon, and missing transverse momentum. The model independence of the measurement is maximized by employing a discriminating variable, developed through machine learning, that is agnostic to the signal hypothesis. The analysis is based on proton-proton collision data at $$\sqrt{s}=13$$ TeV collected with the CMS detector from 2016–2018,more » corresponding to an integrated luminosity of 138 fb⁻¹. The production cross section is measured as a function of the difference in azimuthal angle between the two jets. The differential cross section measurements are used to constrain Higgs boson couplings within the standard model effective field theory framework.« less

A search for nonresonant new physics phenomena in high-mass dilepton events produced in association with b-tagged jets is performed using proton-proton collision data collected in 2016–2018 by the CMS experiment at the CERN LHC, at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb⁻¹. The analysis considers two effective field theory models with dimension-six operators; involving four-fermion contact interactions between two leptons (ℓℓ, electrons or muons) and b or s quarks (bbℓℓ and bsℓℓ). Two lepton flavor combinations (ee and μμ) are required and events are classified as having 0, 1, or ≥2 b-tagged jetsmore » in the final state. No significant excess is observed over the standard model backgrounds. Upper limits are set on the production cross section of the new physics signals. These translate into lower limits on the energy scale Λ of 6.9 to 9.0 TeV in the bbℓℓ model, depending on model parameters, and on the ratio of energy scale and effective coupling, Λ/g*, of 2.0 to 2.6 TeV in the bsℓℓ model. Lepton flavor universality is also tested by comparing the dielectron (ee) and dimuon (μμ) mass spectra for different b-tagged jet multiplicities. No significant deviation from the standard model expectation of unity is observed.« less

This paper presents a search for new physics through the process where a massive particle, X, decays into a Higgs boson and a second particle, Y. The Higgs boson subsequently decays into a bottom quark–antiquark pair, which is reconstructed as a single large-radius jet. The decay products of Yare also assumed to produce a single large-radius jet. The identification of the Yparticle is enhanced by computing the anomaly score of its candidate jet using an autoencoder, which measures deviations from typical quark- or gluon-induced jets. This allows a simultaneous search for multiple Ydecay scenarios within a single analysis. In themore » main benchmark process, Yis a scalar particle that decays into a Wboson pair. Two other scalar Ydecay processes are also considered as benchmarks: decays to a light quark–antiquark pair, and decays to a top quark–antiquark pair. A fourth benchmark process considers Yas a hadronically decaying top quark, arising from the decay of a vector-like quark into a top quark and a Higgs boson. Data recorded by the CMS experiment at a center-of-mass energy of 13 TeV in 2016–2018, corresponding to an integrated luminosity of 138 fb^-1, are analyzed. The search covers Xmasses between 1.4 and 3.0 TeV and Ymasses between 90 and 400 TeV, with all simulated signals produced in the narrow-width approximation. No significant excess above the standard model background expectation is observed. The most stringent upper limits to date are placed on benchmark signal cross sections for various masses of X and Y particles« less

Using proton-proton collision data collected by the CMS experiment at √𝑠 = 13 TeV in 2016–2018, corresponding to an integrated luminosity of 140 fb⁻¹, the first full reconstruction of the three vector 𝐵 meson states, 𝐵*⁺, 𝐵*⁰, and 𝐵$$^{*0}_{𝑠}$$, is performed. The mass differences between the excited mesons and their corresponding ground states are measured to be 𝑚⁡(𝐵*⁺)−𝑚⁡(𝐵⁺) = 45.277 ± 0.039 ± 0.027 MeV, 𝑚⁡(𝐵^*0)−𝑚⁡(𝐵⁰) = 45.471 ± 0.056 ± 0.028 MeV, and 𝑚⁡(𝐵$$^{*0}_{𝑠}$$)−𝑚⁡(𝐵$$^{0}_{𝑠}$$) = 49.407 ± 0.132 ± 0.041 MeV, where the first uncertainties are statistical and the second are systematic. These results improve on the precision ofmore » previous measurements by an order of magnitude.« less

Measurements are presented of the W and Z boson production cross sections in proton-proton collisions at a center-of-mass energy of 13.6 TeV. Data collected in 2022 and corresponding to an integrated luminosity of 5.01 fb⁻¹ with one or two identified muons in the final state are analyzed. The results for the products of total inclusive cross sections and branching fractions for muonic decays of W and Z bosons are 11.93 ± 0.08 (syst) ± 0.17 (lumi) $$^{+0.07}_{−0.07}$$ (acceptance) nb for W⁺ boson production, 8.86 ± 0.06 (syst) ± 0.12 (lumi) $$^{+0.05}_{−0.06}$$ (acceptance) nb for W⁻ boson production, and 2.021 ±more » 0.009 (syst) ± 0.028 (lumi) $$^{+0.011}_{−0.013}$$ (acceptance) nb for the Z boson production in the dimuon mass range of 60–120 GeV, all with negligible statistical uncertainties. Furthermore, the corresponding fiducial cross sections, as well as cross section ratios for both fiducial and total phase space, are provided. The ratios include charge-separated results for W boson production (W⁺ and W⁻) and the sum of the two contributions (W^±), each relative to the measured Z boson production cross section. Additionally, the ratio of the measured cross sections for W⁺ and W⁻ boson production is reported. All measurements are in agreement with theoretical predictions, calculated at next-to-next-to-leading order accuracy in quantum chromodynamics.« less

A search for the standard model Higgs boson decaying to a charm quark-antiquark pair, 𝐻→$$c\bar{c}$$, produced in association with a top quark-antiquark pair ($$t\bar{t}$$𝐻) is presented. The search is performed with data from proton-proton collisions at √𝑠 =13  TeV, corresponding to an integrated luminosity of 138  fb−1. Advanced machine learning techniques are employed for jet flavor identification and event classification. The Higgs boson decay to a bottom quark-antiquark pair is measured simultaneously and the observed $$t\bar{t}$$𝐻(𝐻→$$b\bar{b}$$) event rate relative to the standard model expectation is 0.91$$^{+0.26}_{−0.22}$$. The observed (expected) upper limit on the product of production cross section and branching fraction 𝜎⁡($$t\bar{t}$$𝐻)⁢ℬ⁡(𝐻→$$c\bar{c}$$)more » is 0.11 (0.13) pb at 95% confidence level, corresponding to 7.8 (8.7) times the standard model prediction. When combined with the previous search for 𝐻 →$$c\bar{c}$$ via associated production with a 𝑊 or 𝑍 boson, the observed (expected) 95% confidence interval on the Higgs-charm Yukawa coupling modifier, 𝜅_𝑐, is |𝜅_𝑐| < 3.5 (2.7), the most stringent constraint to date.« less

Many analyses at the CERN LHC exploit the substructure of jets to identify heavy resonances produced with high momenta that decay into multiple quarks and/or gluons. This paper presents a new technique for correcting the substructure of simulated large-radius jets from multiprong decays. The technique is based on reclustering the jet constituents into several subjets such that each subjet represents a single prong, and separately correcting the radiation pattern in the Lund jet plane of each subjet using a correction derived from data. The data presented here correspond to an integrated luminosity of 138 fb⁻¹ collected by the CMS experimentmore » between 2016–2018 at a center-of-mass energy of 13 TeV. The correction procedure improves the agreement between data and simulation for several different substructure observables of multiprong jets. This technique establishes, for the first time, a robust calibration for the substructure of jets with four or more prongs, enabling future measurements and searches for new phenomena containing these signatures.« less