242 Search Results

Despite the f₀(980) hadron having been discovered half a century ago, the question about its quark content has not been settled: it might be an ordinary quark-antiquark ($$q\bar{q}$$) meson, a tetraquark ($$q\bar{q}$$$$q\bar{q}$$) exotic state, a kaon-antikaon ($$K\bar{K}$$) molecule, or a quark-antiquark-gluon ($$q\bar{q}$$g) hybrid. This paper reports strong evidence that the f₀(980) state is an ordinary $$q\bar{q}$$ meson, inferred from the scaling of elliptic anisotropies (v₂) with the number of constituent quarks (n_q), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f₀(980) state is reconstructed via its dominant decay channel f₀(980) → π⁺π⁻, in proton-lead collisions recordedmore » by the CMS experiment at the LHC, and its v₂ is measured as a function of transverse momentum (p_T). It is found that the n_q = 2 ($$q\bar{q}$$ state) hypothesis is favored over n_q = 4 ($$q\bar{q}$$$$q\bar{q}$$ or $$K\bar{K}$$ states) by 7.7, 6.3, or 3.1 standard deviations in the p_T < 10, 8, or 6 GeV/c ranges, respectively, and over n_q = 3 ($$q\bar{q}$$g hybrid state) by 3.5 standard deviations in the p_T < 8 GeV/c range. This result represents the first determination of the quark content of the f₀(980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates.« less

A search for flavor-changing neutral current interactions of the top quark (𝑡) and the Higgs boson (𝐻) is presented. The search is based on proton-proton collision data collected in 2016–2018 at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and corresponding to an integrated luminosity of 138 fb⁻¹. Events containing a pair of leptons with the same-sign electric charge and at least one jet are considered. The results are used to constrain the branching fraction (ℬ) of the top quark decaying to a Higgs boson and an up (𝑢) or charm (𝑐) quark. No significantmore » excess above the estimated background was found. The observed (expected) upper limits at a 95% confidence level are found to be 0.072% (0.059%) for ℬ⁡(𝑡 → 𝐻⁡𝑢) and 0.043% (0.062%) for ℬ⁡(𝑡 → 𝐻⁡𝑐). These results are combined with two other searches performed by the CMS Collaboration for flavor-changing neutral current interactions of top quarks and Higgs bosons in final states where the Higgs boson decays to either a pair of photons or a pair of bottom quarks. The resulting observed (expected) upper limits at the 95% confidence level are 0.019% (0.027%) for ℬ⁡(𝑡 → 𝐻⁡𝑢) and 0.037% (0.035%) for ℬ⁡(𝑡 → 𝐻⁡𝑐).« less

Measurements of the production yields of charm baryons (Λ$$^+_c$$ ) and charm mesons (D⁰ ) in proton-lead collisions at a nucleon-nucleon center-of-mass energy of 8.16 TeV are presented. The data were collected in 2016 with the CMS experiment and correspond to an integrated luminosity of 186 nb^-1. The Λ$$^+_c$$ baryon is reconstructed from the decay channel Λ$$^+_c$$ → K$$^0_S$$p , while the D⁰ meson is reconstructed via D⁰ → K^-π⁺. The Λ$$^+_c$$ baryon and D⁰ meson yields are extracted in several charged-particle multiplicity classes. No strong multiplicity dependence of the Λ$$^+_c$$-to-D⁰ yield ratio is observed, unlike the observed strange baryonmore » to strange meson yield ratio of $$Λ/\bar{Λ}$$to K$$^0_S$$, which shows a strong multiplicity dependence. This observation indicates different mechanisms for the multiplicity evolution of hadronization processes for charm and strange quarks and provides new constraints to the understanding of heavy flavor production and collectivity in small collision systems.« less

Measurements of fiducial and total inclusive cross sections for W and Z boson production are presented in proton-proton collisions at $$ \sqrt{s} $$ = 5.02 and 13 TeV. Electron and muon decay modes (ℓ = e or μ) are studied in the data collected with the CMS detector in 2017, in dedicated runs with reduced instantaneous luminosity. The data sets correspond to integrated luminosities of 298 ± 6 pb$$^{−1}$$ at 5.02 TeV and 206 ± 5 pb$$^{−1}$$ at 13 TeV. Measured values of the products of the total inclusive cross sections and the branching fractions at 5.02 TeV are σ(ppmore » → W + X)$$ \mathcal{B} $$(W → ℓν) = 7300 ± 10 (stat) ± 60 (syst) ± 140 (lumi) pb, and σ(pp → Z+X)$$ \mathcal{B} $$(Z → ℓ$$^{+}$$ℓ$$^{−}$$) = 669 ± 2 (stat) ± 6 (syst) ± 13 (lumi) pb for the dilepton invariant mass in the range of 60–120 GeV. The corresponding results at 13 TeV are 20480 ± 10 (stat) ± 170 (syst) ± 470 (lumi) pb and 1952 ± 4 (stat) ± 18 (syst) ± 45 (lumi) pb. The measured values agree with cross section calculations at next-to-next-to-leading-order in perturbative quantum chromodynamics. Fiducial and total inclusive cross sections, ratios of cross sections of W$$^{+}$$ and W$$^{−}$$ production as well as inclusive W and Z boson production, and ratios of these measurements at 5.02 and 13 TeV are reported.« less

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

The results of a search for a standard model-like Higgs boson decaying into two photons in the mass range between 70 and 110 GeV are presented. The analysis uses the data set collected by the CMS experiment in proton-proton collisions at $$\sqrt{s} = 13$$ TeV corresponding to integrated luminosities of 36.3 fb^-1, 41.5 fb^-1 and 54.4 fb^-1 during the 2016, 2017, and 2018 LHC running periods, respectively. No significant excess over the background expectation is observed and 95% confidence level upper limits are set on the product of the cross section and branching fraction for decays of an additional Higgsmore » boson into two photons. The maximum deviation with respect to the background is seen for a mass hypothesis of 95.4 GeV with a local (global) significance of 2.9 (1.3) standard deviations. The observed upper limit ranges from 15 to 73 fb.« less

This Letter presents the first measurements of the groomed jet radius R_g and the jet girth g in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables R_g and g provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7 nb^-1 and 301 pb^-1 , respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentummore » $$p^{γ}_{T} > 100$$ GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum $$p^{jet}_{T}$$ such that $$p^{jet}_{T}/p^{γ}_{T} > 0.4$$ . The measured R_g and g distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with $$p^{jet}_{T}/p^{γ}_{T} > 0.8$$ , i.e., those that closely balance the photon $$p^{γ}_{T}$$ , are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with $$p^{jet}_{T}/p^{γ}_{T} > 0.4$$ reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements.« less

A measurement is performed of Higgs bosons produced with high transverse momentum (p$$_{T}$$) via vector boson or gluon fusion in proton-proton collisions. The result is based on a data set with a center-of-mass energy of 13 TeV collected in 2016–2018 with the CMS detector at the LHC and corresponds to an integrated luminosity of 138 fb$$^{−1}$$. The decay of a high-p$$_{T}$$ Higgs boson to a boosted bottom quark-antiquark pair is selected using large-radius jets and employing jet substructure and heavy-flavor taggers based on machine learning techniques. Independent regions targeting the vector boson and gluon fusion mechanisms are defined based onmore » the topology of two quark-initiated jets with large pseudorapidity separation. The signal strengths for both processes are extracted simultaneously by performing a maximum likelihood fit to data in the large-radius jet mass distribution. The observed signal strengths relative to the standard model expectation are $$ {4.9}_{-1.6}^{+1.9} $$ and $$ {1.6}_{-1.5}^{+1.7} $$ for the vector boson and gluon fusion mechanisms, respectively. A differential cross section measurement is also reported in the simplified template cross section framework.[graphic not available: see fulltext]« less

Diboson production in association with jets is studied in the fully leptonic final states, pp → (Z/γ$$^{*}$$)(Z/γ$$^{*}$$) + jets → 2ℓ2ℓ′ + jets, (ℓ, ℓ′ = e or μ) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb$$^{−1}$$ collected with the CMS detector at the LHC. Differential distributions and normalized differential cross sections are measured as a function of jet multiplicity, transverse momentum p$$_{T}$$, pseudorapidity η, invariant mass and ∆η of the highest-p$$_{T}$$ and second-highest-p$$_{T}$$ jets, and as a function of invariant mass of the four-lepton system formore » events with various jet multiplicities. These differential cross sections are compared with theoretical predictions that mostly agree with the experimental data. However, in a few regions we observe discrepancies between the predicted and measured values. Further improvement of the predictions is required to describe the ZZ+jets production in the whole phase space.« less