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Institute
- Physik (261)
Using 448 million ψ(2S) events, the spin-singlet P-wave charmonium state hc(11P1) is studied via the ψ(2S)→π0hc decay followed by the hc→γηc transition. The branching fractions are measured to be BInc(ψ(2S)→π0hc)×BTag(hc→γηc)=(4.22+0.27−0.26±0.19)×10−4 , BInc(ψ(2S)→π0hc)=(7.32±0.34±0.41)×10−4, and BTag(hc→γηc)=(57.66+3.62−3.50±0.58)%, where the uncertainties are statistical and systematic, respectively. The hc(11P1) mass and width are determined to be M=(3525.32±0.06±0.15) MeV/c2 and Γ=(0.78+0.27−0.24±0.12) MeV. Using the center of gravity mass of the three χcJ(13PJ) mesons (M(c.o.g.)), the 1P hyperfine mass splitting is estimated to be Δhyp=M(hc)−M(c.o.g.)=(0.03±0.06±0.15) MeV/c2, which is consistent with the expectation that the 1P hyperfine splitting is zero at the lowest-order.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− are observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data was collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− is observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− are observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
Analyzing (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the ψ(3686)→ωK0SK0S decay is observed for the first time. The branching fraction for this decay is determined to be Bψ(3686)→ωK0SK0S=(7.04±0.39±0.36)×10−5, where the first uncertainty is statistical and the second is systematic.
Based on an e+e− collision data sample corresponding to an integrated luminosity of 2.93 fb−1 collected with the BESIII detector at √s=3.773 GeV, the first amplitude analysis of the singly Cabibbo-suppressed decay D+→K+K0Sπ0 is performed. From the amplitude analysis, the K∗(892)+K0S component is found to be dominant with a fraction of (57.1±2.6±4.2)%, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction B(D+→K+K0Sπ0) measured by BESIII, we obtain B(D+→K∗(892)+K0S)=(8.69±0.40±0.64±0.51)×10−3, where the third uncertainty is due to the branching fraction B(D+→K+K0Sπ0). The precision of this result is significantly improved compared to the previous measurement. This result also differs from most of theoretical predictions by about 4σ, which may help to improve the understanding of the dynamics behind.
The integrated luminosities of the data samples collected in the BESIII experiment in 2016--2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of the old data sets collected in 2010--2014 are updated by considering correction related to the detector performance, offsettting the effect of newly discovered readout errors in the electromagnetic calorimeter that happen haphazardly.
Using a sample of about 1010 𝐽/𝜓 events collected at a center-of-mass energy √𝑠=3.097 GeV with the BESIII detector, the electromagnetic Dalitz decays 𝐽/𝜓→𝑒+𝑒−𝜋+𝜋−𝜂′, with 𝜂′→𝛾𝜋+𝜋− and 𝜂′→𝜋+𝜋−𝜂, have been studied. The decay 𝐽/𝜓→𝑒+𝑒−𝑋(1835) is observed with a significance of 15𝜎, and also an 𝑒+𝑒− invariant-mass dependent transition form factor of 𝐽/𝜓→𝑒+𝑒−𝑋(1835) is presented for the first time. The intermediate states 𝑋(2120) and 𝑋(2370) are also observed in the 𝜋+𝜋−𝜂′ invariant-mass spectrum with significances of 5.3𝜎 and 7.3𝜎. The corresponding product branching fractions for 𝐽/𝜓→𝑒+𝑒−𝑋, 𝑋→𝜋+𝜋−𝜂′ [𝑋=𝑋(1835), 𝑋(2120), and 𝑋(2370)] are reported.
Using 2.93 fb−1 of e+e− collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0→K1(1270)−e+νe semileptonic decay is presented. The statistical significance of the decay D0→K1(1270)−e+νe is greater than 10σ. The branching fraction of D0→K1(1270)−e+νe is measured to be (1.09±0.13+0.09−0.13±0.12)×10−3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)−→K−π+π−.
Using 2.93 fb−1 of e+e− collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0→K1(1270)−e+νe semileptonic decay is presented. The statistical significance of the decay D0→K1(1270)−e+νe is greater than 10σ. The branching fraction of D0→K1(1270)−e+νe is measured to be (1.09±0.13+0.09−0.16±0.12)×10−3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)−→K−π+π−. The fraction of longitudinal polarization in D0→K1(1270)−e+νe is determined for the first time to be 0.50±0.19stat±0.08syst.
Using e+e− collision data at ten center-of-mass energies between 2.644 and 3.080 GeV collected with the BESIII detector at BEPCII and corresponding to an integrated luminosity of about 500 pb−1, we measure the cross sections and effective form factors for the process e+e−→Ξ0Ξ¯0 utilizing a single-tag method. A fit to the cross section of e+e−→Ξ0Ξ¯0 with a pQCD-driven power function is performed, from which no significant resonance or threshold enhancement is observed. In addition, the ratio of cross sections for the processes e+e−→Ξ−Ξ¯+ and Ξ0Ξ¯0 is calculated using recent BESIII measurement and is found to be compatible with expectation from isospin symmetry.
Using e+e− collision data at ten center-of-mass energies between 2.644 and 3.080 GeV collected with the BESIII detector at BEPCII and corresponding to an integrated luminosity of 500.0 pb−1, we measure the cross sections and effective form factors for the process e+e−→Ξ0Ξ¯0 utilizing a single-tag method. A fit to the cross section of e+e−→Ξ0Ξ¯0 with a pQCD-driven power function is performed, from which no significant resonance or threshold enhancement is observed. In addition, the ratio of cross sections for the processes e+e−→Ξ−Ξ¯+ and Ξ0Ξ¯0 is calculated using recent BESIII measurement and is found to be compatible with expectation from isospin symmetry.
Search for the lepton number violating decay Σ⁻ → pe⁻e⁻ and the rare inclusive decay Σ⁻ → Σ⁺X
(2021)
Using a data sample of (1310.6±7.0)×106 𝐽/𝜓 events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay Σ−→𝑝𝑒−𝑒− and the rare inclusive decay Σ−→Σ+𝑋, where 𝑋 denotes any possible particle combination. The Σ− candidates are tagged in 𝐽/𝜓→¯Σ(1385)+Σ− decays. No signal candidates are found, and the upper limits on the branching fractions at the 90% confidence level are determined to be ℬ(Σ−→𝑝𝑒−𝑒−)<6.7×10−5 and ℬ(Σ−→Σ+𝑋)<1.2×10−4.
Using e+e− collision data at ten center-of-mass energies between 2.644 and 3.080 GeV collected with the BESIII detector at BEPCII and corresponding to an integrated luminosity of about 500 pb−1, we measure the cross sections and effective form factors for the process e+e−→Ξ0Ξ¯0 utilizing a single-tag method. A fit to the cross section of e+e−→Ξ0Ξ¯0 with a pQCD-driven power function is performed, from which no significant resonance or threshold enhancement is observed. In addition, the ratio of cross sections for the processes e+e−→Ξ−Ξ¯+ and Ξ0Ξ¯0 is calculated using recent BESIII measurement and is found to be compatible with expectation from isospin symmetry.
By analyzing an e+e− annihilation 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, we measure the branching fraction of the D0→ρ−μ+νμ decay for the first time. We obtain BD0→ρ−μ+νμ=(1.35±0.09stat±0.09syst)×10−3. Using the world average of BD0→ρ−e+νe, we find a branching fraction ratio of BD0→ρ−μ+νμ/BD0→ρ−e+νe=0.90±0.11, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. Combining the world average of BD+→ρ0μ+νμ and the lifetimes of D0(+), we obtain a partial decay width ratio of ΓD0→ρ−μ+νμ/(2ΓD+→ρ0μ+νμ)=0.71±0.14, which is consistent with the isospin symmetry expectation of one within 2.1σ. For the reported values of BD0→ρ−μ+νμ/BD0→ρ−e+νe and ΓD0→ρ−μ+νμ/2ΓD+→ρ0μ+νμ, the uncertainty is the quadratic sum of the statistical and systematic uncertainties.
We measure the inclusive semielectronic decay branching fraction of the D+s meson. A double-tag technique is applied to e+e− annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range 4.178–4.230 GeV. We select positrons fromD+s→Xe+νe with momenta greater than 200 MeV/c and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the D+s semielectronic branching fraction to be(6.30±0.13(stat.)±0.09(syst.)±0.04(ext.))%, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the D+s and D0 semielectronic widths, Γ(D+s→Xe+νe)Γ(D0→Xe+νe)=0.790±0.016(stat.)±0.011(syst.)±0.016(ext.). Our results are consistent with and more precise than previous measurements.
The electromagnetic process is studied with the initial-state-radiation technique using 7.5 fb−1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/ using the invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process eþe− → π0Xð3872Þγ and search for Zcð4020Þ0 → Xð3872Þγ. We find no significant signal and set upper limits on σðeþe− → π0Xð3872ÞγÞ · BðXð3872Þ → πþπ−J=ψÞ and σðeþe− → π0Zcð4020Þ0Þ · BðZcð4020Þ0 → Xð3872ÞγÞ · BðXð3872Þ → πþπ−J=ψÞ for each energy point at 90% confidence level, which is of the order of several tenths pb.
The process e+e−→ϕη is studied at 22 center-of-mass energy points (√s) between 2.00 and 3.08 GeV using 715 pb−1 of data collected with the BESIII detector. The measured Born cross section of e+e−→ϕη is found to be consistent with BABAR measurements, but with improved precision. A resonant structure around 2.175 GeV is observed with a significance of 6.9σ with mass (2163.5±6.2±3.0) MeV/c2 and width (31.1+21.1−11.6±1.1) MeV, where the first uncertainties are statistical and the second are systematic.
By analyzing 6.32 fb − 1 of e+ e− annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay D + s → τ + ντ, with τ+ → π + π0¯ντ, to be B D + s → τ + ν τ = (5.29 ± 0.25 stat ± 0.20 syst) %. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element |Vcs|and the D + s decay constant f D + s to be f D + s|Vcs| = (244.8 ± 5.8 stat ± 4.8syst) MeV, using the known values of the τ + and D + s masses as well as the D + s lifetime, together with our branching fraction measurement. Combining the value of |Vcs| obtained from a global fit in the standard model and f D + s from lattice quantum chromodynamics, we obtain f D + s = (251.6 ± 5.9 stat ± 4.9syst) MeV and |Vcs| = 0.980 ± 0.023 stat ± 0.019 syst. Using the branching fraction of B D + s → μ + νμ = (5.35±0.21)×10−3, we obtain the ratio of the branching fractions B D + s → τ + ντ/B D +s → μ+νμ = 9.89±0.71, which is consistent with the standard model prediction of lepton flavor universality.