139 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

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

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

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

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

Using proton–proton collision data corresponding to an integrated luminosity of $$140\hbox { fb}^{-1}$$ collected by the CMS experiment at $$\sqrt{s}= 13\,\text {Te}\hspace{-.08em}\text {V} $$, the $${{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{\text {J}/\uppsi }} {{{\Xi }} ^{{-}}} {{\text {K}} ^{{+}}} $$ decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the $${{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{{\uppsi }} ({2\textrm{S}})} {{\Lambda }} $$ decay, is measured to be $$\mathcal {B}({{{\Lambda }} _{\text {b}}^{{0}}} \rightarrow {{\text {J}/\uppsi }} {{{\Xi }} ^{{-}}} {{\text {K}} ^{{+}}} )/\mathcal {B}({{{\Lambda }} _{\text {b}}^{{0}}} \rightarrowmore » {{{\uppsi }} ({2\textrm{S}})} {{\Lambda }} ) = [3.38\pm 1.02\pm 0.61\pm 0.03]\%$$, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in $$\mathcal {B}({{{\uppsi }} ({2\textrm{S}})} \rightarrow {{\text {J}/\uppsi }} {{{\uppi }} ^{{+}}} {{{\uppi }} ^{{-}}} )$$ and $$\mathcal {B}({{{\Xi }} ^{{-}}} \rightarrow {{\Lambda }} {{{\uppi }} ^{{-}}} )$$.« 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