We examine the electromagnetic Dalitz decay J/ψ → e+e-η and search for di-electron decays of a dark gauge boson (γ') in J/ψ → γ'η with the two η decay modes η → γγ and η → $\pi$+$\pi$-$\pi$0 using ...(1310.6 ± 7.0) × 106 J/ψ events collected with the BESIII detector. The branching fraction of J/ψ → e+e-η is measured to be (1.43 ± 0.04(stat) ± 0.06(syst)) × 10-5, 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 Λ = 2.84 ± 0.11(stat) ± 0.08(syst) GeV/c2. We find no evidence of γ' production and set 90% confidence level upper limits on the product branching fraction $\mathcal{B(J/ψ → γ'η)× B(γ' → e^+e^-)}$ as well as the kinetic mixing strength between the Standard Model photon and γ' in the mass range of 0.01 ≤ mγ' ≤ 2.4 GeV/c2.
Using a data sample of (1310.6±7.0)×106 J/ψ events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light ...vector meson (V=ω, ϕ) via J/ψ→Vη decays. The decay of η→π+π−π0 is utilized to tag the V meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90% confidence level are determined to be B(ω→invisible)B(ω→π+π−π0)<8.1×10−5 and B(ϕ→invisible)B(ϕ→K+K−)<3.4×10−4. By using the world average values of B(ω→π+π−π0) and B(ϕ→K+K−), the upper limits on the decay branching fractions at the 90% confidence level are set as B(ω→invisible)<7.3×10−5 and B(ϕ→invisible)<1.7×10−4, respectively.
We search for J / ψ radiative decays into a weakly interacting neutral particle, namely an invisible particle, using the J / ψ produced through the process ψ ( 3686 ) → π + π − J / ψ in a data sample ...of ( 448.1 ± 2.9 ) × 10 6 ψ ( 3686 ) decays collected by the BESIII detector at BEPCII. No significant signal is observed. Using a modified frequentist method, upper limits on the branching fractions are set under different assumptions of invisible particle masses up to 1.2 GeV / c 2 . The upper limit corresponding to an invisible particle with zero mass is 7.0 × 10 −7 at the 90% confidence level.
Using a data sample of e+e− collision data with an integrated luminosity of 2.93 fb−1 taken at the center-of-mass energy s=3.773 GeV with the BESIII detector operating at the BEPCII storage rings, we ...measure the absolute branching fractions of the two-body hadronic decays D+→π+π0, K+π0, π+η, K+η, π+η′, K+η′, KS0π+, KS0K+, and D0→π+π−, K+K−, K∓π±, KS0π0, KS0η, KS0η′. Our results are consistent with previous measurements within uncertainties. Among them, the branching fractions for D+→π+π0, K+π0, π+η, π+η′, KS0π+, KS0K+ and D0→KS0π0, KS0η, KS0η′ are determined with improved precision compared to the world average values.
Observation of the Dalitz decay η ′ → γ e + e Achasov, M. N.; Amoroso, A.; An, F. F. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
7/2015, Letnik:
92, Številka:
1
Journal Article
•Coercivity enhancement of thicker sintered NdFeB magnets by grain boundary diffusion can be obtained.•Tb55Ce20Cu25 alloys infiltrate into deeper interior of the magnets, and the optimized ...microstructure after GBD result in coercivity enhancement.•10-mm-thick magnets diffused with Tb55Ce20Cu25 optimizes coercivity enhancement of 7.4 kOe as well as improves the thermal stability.
Coercivity enhancement of thicker sintered NdFeB magnets with 5–10 mm in thickness by grain boundary diffusion (GBD) with low-melting Tb75−xCexCu25 alloy powders (x = 0–45) is demonstrated. For 5-mm-thick magnets, after GBD with Tb75−xCexCu25 alloys (x = 0–45), a significant iHc increment (ΔiHc) of 8.2–11.5 kOe with a slight decrease in Br is found. Although the magnet GBD treated with Tb75Cu25 exhibits the highest ΔiHc of 11.5 kOe, the coercivity enhancement per wt% Tb usage (ΔiHc/wt.% Tb) could be increased by about 2-folds with increasing x from 0 to 45. As for the 10-mm-thick magnets, large ΔiHc of 8.4 kOe and 7.4 kOe can also be attained by GBD with Tb75Cu25 and Tb55Ce20Cu25 powders, respectively. The optimized microstructure and the effective distribution of Tb and Ce at grain boundary after GBD with Tb75−xCexCu25 are the main factors for the coercivity enhancement. As a result, the magnetic properties, as well as the thermal stability of the sintered NdFeB magnets with 5–10 mm in thickness, are improved considerably. This work provides a cost-effective way to enhance the coercivity of the thicker sintered NdFeB magnets.
The cross section of the process e+e−→η′J/ψ is measured at center-of-mass (c.m.) energies from s=4.178 to 4.600 GeV using data samples corresponding to a total integrated luminosity of 11 fb−1 ...collected with the BESIII detector operating at the BEPCII storage ring. The dependence of the cross section on s shows an enhancement around 4.2 GeV. While the shape of the cross section cannot be fully explained with a single ψ(4160) or ψ(4260) state, a coherent sum of the two states does provide a reasonable description of the data.
By analyzing 2.93 fb−1 of e+e− annihilation data taken at the center-of-mass energy √s = 3.773 GeV with the BESIII detector, we determine the branching fractions of the inclusive decays D+ → ϕX and ...D0 → ϕX to be (1.135±0.034±0.031)% and (1.091±0.027±0.035)%, respectively, where X denotes any possible particle combination. The first uncertainties are statistical, and the second are systematic. We also determine the branching fractions of the decays D → ϕX and their charge conjugate modes D¯ → ϕX¯ separately for the first time, and no significant CP asymmetry is observed.
Using a data sample collected with the BESIII detector operating at the BEPCII storage ring at a centerof- mass energy of √s = 4.600 GeV, we search for the production of e+e- → φχc0,1,2. A search is ...also performed for the charmonium-like state X(4140) in the radiative transition e+e- → γX(4140) with X(4140) subsequently decaying into φJ/ψ. The processes e+e- → φχc1 and φχc2 are observed for the first time, each with a statistical significance ofmore than 10σ, and the Born cross sections are measured to be (4.2+1.7 -1.0±0.3) pb and (6.7+3.4 -1.7 ± 0.5) pb, respectively, where the first uncertainties are statistical and the second systematic. No significant signals are observed for e+e- → φχc0 and e+e- → γX(4140) and upper limits on the Born cross sections at 90% confidence level are provided at √s = 4.600 GeV.
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