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Institute
We present cross sections for the reaction e+e−→K0SK0L at center-of-mass energies ranging from 3.51 GeV to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb−1. The ratio of neutral-to-charged kaon form factors at large momentum transfers (12 GeV2<Q2<25 GeV2) is determined to be 0.21±0.01, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and consequently excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction |F(π±)|/|F(K±)|=f2π/f2K, where F(π±) and F(K±) are the form factors, and fπ and fK are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay ψ(3770)→K0SK0L for the first time. Within a 1σ contour of the likelihood value, the the branching fraction for ψ(3770)→K0SK0L is determined to be B=(2.63+1.40−1.59)×10−5, and the relative phase between the continuum and ψ(3770) amplitudes is ϕ=(−0.39+0.05−0.10)π. The branching fraction is in good agreement with the S- and D-wave charmonia mixing scheme proposed in the interpretation of the "ρπ puzzle" between J/ψ and ψ(3686) decays.
Using 4.7fb−1 of e+e− collision data at center-of-mass energies from 4.661 to 4.951 GeV collected by the BESIII detector at the BEPCII collider, we observe the X(3872) production process e+e−→ωX(3872) for the first time. The significance is 7.5σ, including both the statistical and systematic uncertainties. The e+e−→ωX(3872) Born cross section and the corresponding upper limit at 90\% confidence level at each energy point are reported. The line shape of the cross section indicates that the ωX(3872) signals may be from the decays of some non-trivial structures.
Cross sections for the process e+e−→K0SK0SJ/ψ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb−1 collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230) state is observed in the energy dependence of the e+e−→K0SK0SJ/ψ cross section for the first time with a statistical significance of 26.0σ. In addition, an enhancement around 4.710 GeV, called the Y(4710), is seen with a statistical significance of 4.2σ. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230) state to be 4226.9±6.6±21.9 MeV/c2 and 71.7±16.2±31.4 MeV, respectively, and the mass and width of the Y(4710) state to be 4704.0±52.3±69.5 MeV/c2 and 183.2±114.0±90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+e−→K0SK0SJ/ψ to e+e−→K+K−J/ψ is measured to be 0.388+0.035−0.028±0.016, or 0.426+0.038−0.031±0.018 if three-body phase space is considered.
Using a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider, we search for a scalar partner of the X(3872), denoted as X(3700), via ψ(3770)→γηη′ and γπ+π−J/ψ processes. No significant signals are observed and the upper limits of the product branching fractions B(ψ(3770)→γX(3700))⋅B(X(3700)→ηη′) and B(ψ(3770)→γX(3700))⋅B(X(3700)→π+π−J/ψ) are determined at the 90\% confidence level, for the narrow X(3700) with a mass ranging from 3710 to 3740 MeV/c2, which are from 0.8 to 1.8 (×10−5) and 0.9 to 3.4 (×10−5), respectively.
Using a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider, we search for a scalar partner of the X(3872), denoted as X(3700), via ψ(3770)→γηη′ and γπ+π−J/ψ processes. No significant signals are observed and the upper limits of the product branching fractions B(ψ(3770)→γX(3700))⋅B(X(3700)→ηη′) and B(ψ(3770)→γX(3700))⋅B(X(3700)→π+π−J/ψ) are determined at the 90\% confidence level, for the narrow X(3700) with a mass ranging from 3710 to 3740 MeV/c2, which are from 0.8 to 1.8 (×10−5) and 0.9 to 3.4 (×10−5), respectively.
Using e+e− collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of e+e−→Λ+cΛ¯c(2595)−+c.c. and e+e−→Λ+cΛ¯c(2625)−+c.c. are measured for the first time at center-of-mass energies of s√=4918.0 and 4950.9 MeV. Non-zero cross sections are observed very close to the production threshold. The measured Born cross sections of e+e−→Λ+cΛ¯c(2625)−+c.c. are about 2∼3 times greater than those of e+e−→Λ+cΛ¯c(2595)−+c.c., thereby indicating that the exotic structure potentially exists in the excited charmed baryons. The Born cross sections are 15.6±3.1±0.9 pb and 29.4±3.7±2.7 pb for e+e−→Λ+cΛ¯c(2595)−+c.c., and are 43.4±4.0±4.1 pb and 76.8±6.5±4.2 pb for e+e−→Λ+cΛ¯c(2625)−+c.c. at s√=4918.0 and 4950.9 MeV, respectively. Based on the polar angle distributions of the Λ¯c(2625)− and Λc(2625)+, the form-factor ratios |GE|2+3|GM|2−−−−−−−−−−−−√/|GC| are determined for e+e−→Λ+cΛ¯c(2625)−+c.c. for the first time, which are 5.95±4.07±0.15 and 0.94±0.32±0.02 at s√=4918.0 and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic.
With a data sample corresponding to an integrated luminosity of 11.5~fb−1 collected with the BESIII detector operating at the BEPCII storage ring, for the first time the light hadron decay χc1(3872)→π+π−η is searched for. While no significant signal is observed, the upper limits at the 90\% confidence level for σ[e+e−→γχc1(3872)]B[χc1(3872)→π+π−η] at center-of-mass energies from 4.13 to 4.34 GeV are determined. By normalizing to the χc1(3872)→π+π−J/ψ decay channel, a 90\% confidence level upper limit for the branching fraction ratio R=B[χc1(3872)→π+π−η]/B[χc1(3872)→π+π−J/ψ]<0.12 is given. These measurements provide important inputs for understanding the internal structure of the χc1(3872) resonance.
Cross sections for the process e+e−→K0SK0SJ/ψ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb−1 collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230) state is observed in the energy dependence of the e+e−→K0SK0SJ/ψ cross section for the first time with a statistical significance of 26.0σ. In addition, an enhancement around 4.710 GeV, called the Y(4710), is seen with a statistical significance of 4.2σ. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230) state to be 4226.9±6.6±21.9 MeV/c2 and 71.7±16.2±31.4 MeV, respectively, and the mass and width of the Y(4710) state to be 4704.0±52.3±69.5 MeV/c2 and 183.2±114.0±90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+e−→K0SK0SJ/ψ to e+e−→K+K−J/ψ is measured to be 0.388+0.035−0.028±0.016, or 0.426+0.038−0.031±0.018 if three-body phase space is considered.
Based on data samples collected with the BESIII detector at the BEPCII collider, the process e+e−→Σ+Σ¯− is studied at center-of-mass energies s√ = 2.3960, 2.6454, and 2.9000~GeV. Using a fully differential angular description of the final state particles, the complete information of the Σ+ electromagnetic form factors in the time-like region is extracted. The relative phase between the electric and magnetic form factors is determined to be sinΔΦ = -0.67~±~0.29~(stat.)~±~0.18~(syst.) at s√ = 2.3960~GeV, ΔΦ = 55∘~±~19∘~(stat.) ±~14∘~(syst.) at s√ = 2.6454~GeV, and 78∘~±~22∘~(stat.) ±~9∘~(syst.) at s√ = 2.9000~GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.
Based on 7.33 fb−1 of e+e− collision data taken at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we measure the branching fraction of D∗+s→D+sπ0 relative to that of D∗+s→D+sγ to be (6.16±0.43±0.19)%. The first uncertainty is statistical and the second one is systematic. By using the world average value of the branching fraction of D∗+s→D+se+e−, we determine the branching fractions of D∗+s→D+sγ and D∗+s→D+sπ0 to be (93.57±0.44±0.19)% and (5.76±0.44±0.19)%, respectively.