7 Search Results

Using a sample of ( 2712.4 ± 14.3 ) × 10 6     ψ ( 3686 ) events collected with the BESIII detector, we perform a search for the isospin-violating decays χ c J → Λ Σ ¯   0 + c . c . ( J = 0 , 1 , 2 ) and η c → Λ Σ ¯   0 + c . c . No significant signal for χ c J or η c is observed in the Λ Σ ¯   0 invariant mass distribution. The upper limits on the branching fractions at the 90% confidencemore » level are set to be B ( χ c 0 → Λ Σ ¯   0 + c . c . ) < 1.5 × 10 − 6 , B ( χ c 1 → Λ Σ ¯   0 + c . c . ) < 1.6 × 10 − 6 , B ( χ c 2 → Λ Σ ¯   0 + c . c . ) < 1.7 × 10 − 6 , and B ( η c → Λ Σ ¯   0 + c . c . ) < 6.2 × 10 − 5 for the first time.« less

The first direct measurement of the relative phase between the strong and electromagnetic amplitudes for a J/ψ decaying into a vector-pseudoscalar final state is performed using 26 energy points of e⁺e⁻ annihilation data between 3.00 GeV and 3.12 GeV. The data sets were collected by the BESIII detector with a total integrated luminosity of 452 pb⁻¹. By investigating the interference pattern in the cross section lineshape of e⁺e⁻ → ϕη, the relative phase between the strong and electromagnetic amplitudes of J/ψ decay is determined to be within [133°, 228°] at 68% confidence level.

The singly Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{K}^{+}{\pi }^{+}$ is observed for the first time with a statistical significance of $5.4\sigma$ by using $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. The absolute branching fraction of ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}more »$ K + π + is measured to be $(3.8\pm {1.2}_{\mathrm{stat}}\pm {0.2}_{\mathrm{syst}})\times {10}^{-4}$ in a model-independent approach. This is the first observation of a Cabibbo-suppressed ${\mathrm{\Lambda }}_c^{+}$ decay involving ${\mathrm{\Sigma }}^{-}$ in the final state. The ratio of branching fractions between ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{K}^{+}{\pi }^{+}$ and the Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{\pi }^{+}{\pi }^{+}$ is observed to be $(0.4\pm 0.1)s_c^2$ , where $s_c\equiv \sin {\theta }_c=0.2248$ with ${\theta }_c$ the Cabibbo mixing angle. Published by the American Physical Society 2024« less

Using $e^{+}{e}^{-}$ collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2595{)}^{-}+\mathrm{c}.\mathrm{c}.$ and ${emore »}^{}$ + e − → Λ c + Λ ¯ c ( 2625 ) − + c . c . are measured for the first time at center-of-mass energies of $\sqrt{s}=4918.0$ and 4950.9 MeV. Nonzero cross sections are observed very close to the production threshold. The measured Born cross sections of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ are about 2–3 times greater than those of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2595{)}^{-}+\mathrm{c}.\mathrm{c}.$ , providing the similar behavior as semileptonic decays of ${\mathrm{\Lambda }}_b^0$ , but different behavior from that in the hadronic decays of ${\mathrm{\Lambda }}_b^0$ . The Born cross sections are $15.6\pm 3.1\pm 0.9\mathrm{pb}$ and $29.4\pm 3.7\pm 2.7\mathrm{pb}$ for $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2595{)}^{-}+\mathrm{c}.\mathrm{c}.$ , and are $43.4\pm 4.0\pm 4.1\mathrm{pb}$ and $76.8\pm 6.5\pm 4.2\mathrm{pb}$ for $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ at $\sqrt{s}=4918.0$ and 4950.9 MeV, respectively. Based on the polar angle distributions of the ${\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}$ and ${\mathrm{\Lambda }}_c(2625{)}^{+}$ , the form-factor ratios $\sqrt{|G_E{|}^2+3|G_M{|}^2}/\left|G_C\right|$ are determined for $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c(2625{)}^{-}+\mathrm{c}.\mathrm{c}.$ for the first time, which are $5.95\pm 4.07\pm 0.15$ and $0.94\pm 0.32\pm 0.02$ at $\sqrt{s}=4918.0$ and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic. Published by the American Physical Society 2024« less

The Cabbibo-favored decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Xi }}^0{K}^{+}{\pi }^0$ is studied for the first time using $6.1{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data at center-of-mass energies between 4.600 and 4.840 GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Xi }}^{more »}$ 0 K + π 0 is measured to be $(7.79\pm 1.46\pm 0.95)\times {10}^{-3}$ , where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Xi }(1530{)}^0{K}^{+}$ is $(5.99\pm 1.04\pm 0.32)\times {10}^{-3}$ , which is consistent with the previous result of $(5.02\pm 0.99\pm 0.31)\times {10}^{-3}$ . In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to n{K}^{+}{\pi }^0$ is $7.1\times {10}^{-4}$ at the 90% confidence level. The upper limits on the branching fractions of ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}^{+}{\pi }^0$ and $\mathrm{\Lambda }{K}^{+}{\pi }^0$ are also determined to be $1.8\times {10}^{-3}$ and $2.0\times {10}^{-3}$ , respectively. Published by the American Physical Society 2024« less

Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H → ZZ, W W , γγ, ττ, bb, and μμ. All results are reported assuming a value of 125.09 GeV for the Higgs boson mass, the result of the combined measurement by themore » ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb$$^{−1}$$ at $$ \sqrt{s}=7 $$ TeV and 20 fb$$^{−1}$$ at $$ \sqrt{s}=8 $$ TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 ± 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H → ττ decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered.« less