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Institute
- Physik (942) (remove)
We study the electromagnetic Dalitz decay ๐ฝ/๐โ๐+โข๐โโข๐ and search for dielectron decays of a dark gauge boson (๐พโฒ) in ๐ฝ/๐โ๐พโฒโข๐ with the two ๐ decay modes ๐โ๐พโข๐พ and ๐โ๐+โข๐โโข๐0 using (1310.6ยฑ7.0)ร106โโ๐ฝ/๐ events collected with the BESIII detector. The branching fraction of ๐ฝ/๐โ๐+โข๐โโข๐ is measured to be (1.43ยฑ0.04โข(stat)ยฑ0.06โข(syst))ร10โ5, with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be ฮ=2.84ยฑ0.11โข(stat)ยฑ0.08โข(syst)โโGeV/๐2. We find no evidence of ๐พโฒ production and set 90% confidence level upper limits on the product branching fraction โฌโก(๐ฝ/๐โ๐พโฒโข๐)รโฌโก(๐พโฒโ๐+โข๐โ) as well as the kinetic mixing strength between the standard model photon and ๐พโฒ in the mass range of 0.01โค๐๐พโฒโค2.4โโGeV/๐2.
Search for heavy Majorana neutrino in lepton number violating decays of DโโโKฯeโบeโบ
(2019)
Using a data sample with an integrated luminosity of 2.93โโfbโ1 taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino (๐๐) in the lepton number violating decays ๐ทโ๐พโข๐โข๐+โข๐+. No significant signal is observed, and the upper limits on the branching fraction at the 90% confidence level are set to be โฌโก(๐ท0โ๐พโโข๐โโข๐+โข๐+)<2.8ร10โ6, โฌโก(๐ท+โ๐พ0๐โข๐โโข๐+โข๐+)<3.3ร10โ6 and โฌโก(๐ท+โ๐พโโข๐0โข๐+โข๐+)<8.5ร10โ6. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0โโGeV/๐2 in the decays ๐ท0โ๐พโโข๐+โข๐๐,๐๐โ๐โโข๐+ and ๐ท+โ๐พ0๐โข๐+โข๐๐,๐๐โ๐โโข๐+, and the upper limits on the branching fraction at the 90% confidence level are at the level of 10โ7โผ10โ6, depending on the mass of the Majorana neutrino. The constraints on the mixing matrix element |๐๐โข๐๐|2 are also evaluated.
We extract the e+eโ โฯ+ฯโ cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fbโ1 taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor |Fฯ|2 as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (gโ2)ฮผ. We find this value to be aฯฯ,LO ฮผ (600โ900 MeV) = (368.2 ยฑ2.5statยฑ3.3sys) ยท10โ10, which is between the corresponding values using the BaBar or KLOE data.
The decays of ฯc2โK+Kโฯ0, KSKยฑฯโ and ฯ+ฯโฯ0 are studied with the ฯ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of ฯc2โKโKยฏยฏยฏยฏยฏ, ฯc2โaยฑ2(1320)ฯโ/a02(1320)ฯ0 and ฯc2โฯ(770)ยฑฯโ are measured. Here KโKยฏยฏยฏยฏยฏ denotes both KโยฑKโ and Kโ0Kยฏยฏยฏยฏยฏ0+c.c., and Kโ denotes the resonances Kโ(892), Kโ2(1430) and Kโ3(1780). The observations indicate a strong violation of the helicity selection rule in ฯc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of ฯc2โKโ(892)Kยฏยฏยฏยฏยฏ are more than 20 times larger than that of ฯc2โฯ(770)ยฑฯโ, which implies the effects are largely due to U-spin symmetry breaking, rather than just isospin symmetry breaking in charmonium decays.
The decays of ฯc2โK+Kโฯ0, KSKยฑฯโ and ฯ+ฯโฯ0 are studied with the ฯ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of ฯc2โKโKยฏยฏยฏยฏยฏ, ฯc2โaยฑ2(1320)ฯโ/a02(1320)ฯ0 and ฯc2โฯ(770)ยฑฯโ are measured. Here KโKยฏยฏยฏยฏยฏ denotes both KโยฑKโ and Kโ0Kยฏยฏยฏยฏยฏ0+c.c., and Kโ denotes the resonances Kโ(892), Kโ2(1430) and Kโ3(1780). The observations indicate a strong violation of the helicity selection rule in ฯc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of ฯc2โKโ(892)Kยฏยฏยฏยฏยฏ are more than 10 times larger than the upper limit of ฯc2โฯ(770)ยฑฯโ, which is so far the first direct observation of a significant U-spin symmetry breaking effect in charmonium decays.
The decays of ฯc2โK+Kโฯ0, KSKยฑฯโ and ฯ+ฯโฯ0 are studied with the ฯ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of ฯc2โKโKยฏยฏยฏยฏยฏ, ฯc2โaยฑ2(1320)ฯโ/a02(1320)ฯ0 and ฯc2โฯ(770)ยฑฯโ are measured. Here KโKยฏยฏยฏยฏยฏ denotes both KโยฑKโ and Kโ0Kยฏยฏยฏยฏยฏ0+c.c., and Kโ denotes the resonances Kโ(892), Kโ2(1430) and Kโ3(1780). The observations indicate a strong violation of the helicity selection rule in ฯc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of ฯc2โKโ(892)Kยฏยฏยฏยฏยฏ are more than 20 times larger than that of ฯc2โฯ(770)ยฑฯโ, which implies the effects are largely due to U-spin symmetry breaking, rather than just isospin symmetry breaking in charmonium decays.
Using a sample of 4.48ร108 ฯ(3686) events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons ฯ0, ฮท, ฮทโฒ, ฮท(1405), ฮท(1475), ฮท(1760), and X(1835) in J/ฯ radiative decays using ฯ(3686)โฯ+ฯโJ/ฯ events. The ฯ0, ฮท and ฮทโฒ mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be B(J/ฯโฮณฯ0โ3ฮณ)=(3.57ยฑ0.12ยฑ0.16)ร10โ5, B(J/ฯโฮณฮทโ3ฮณ)=(4.42ยฑ0.04ยฑ0.18)ร10โ4, and B(J/ฯโฮณฮทโฒโ3ฮณ)=(1.26ยฑ0.02ยฑ0.05)ร10โ4, where the first errors are statistical and the second systematic. No clear signal for ฮท(1405), ฮท(1475), ฮท(1760) or X(1835) is observed in the two-photon mass spectra, and upper limits at the 90% confidence level on the product branching fractions are obtained.
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process ๐+โข๐โโ๐๐โข๐โข๐+โข๐โ. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The ๐๐ meson is reconstructed in 16 exclusive decay modes. No signal is observed in the ๐๐ mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.
An amplitude analysis of the ๐พ๐โข๐พ๐ system produced in radiative ๐ฝ/๐ decays is performed using the (1310.6ยฑ7.0)ร106โโ๐ฝ/๐ decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parametrizing the ๐พ๐โข๐พ๐ invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the ๐พ๐โข๐พ๐ system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the ๐0โก(1710), ๐0โก(2200), and ๐โฒ2โก(1525). The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative ๐ฝ/๐ decays to ๐พ๐โข๐พ๐ is measured to be (8.1ยฑ0.4)ร10โ4, where the uncertainty is systematic and the statistical uncertainty is negligible.