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Institute
- Physik (380)
We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative J/ψ decays, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a signal and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.7−48.5)×10−8 and (2.2−101.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
Using (10087±44)×106 J/ψ events collected with the BESIII detector, numerous Ξ− and Λ decay asymmetry parameters are simultaneously determined from the process J/ψ→Ξ−Ξ¯+→Λ(pπ−)π−Λ¯(n¯π0)π+ and its charge-conjugate channel. The precisions of α0 for Λ→nπ0 and α¯0 for Λ¯→n¯π0 compared to world averages are improved by factors of 4 and 1.7, respectively. The ratio of decay asymmetry parameters of Λ→nπ0 to that of Λ→pπ−, ⟨α0⟩/⟨αΛ−⟩, is determined to be 0.873±0.012+0.011−0.010, where the first and the second uncertainties are statistical and systematic, respectively. The ratio is smaller than unity more than 5σ, which signifies the existence of the ΔI=3/2 transition in Λ for the first time. Beside, we test for CP violation in Ξ−→Λπ− and in Λ→nπ0 with the best precision to date.
We measured the Born cross sections for the process e+e− → ωη′ at 22 center-of-mass energies from 2.000 to 3.080 GeV with the BESIII detector at the BEPCII collider. We observed a resonant structure with a statistical significance of 9.6σ. A Breit-Wigner fit determines its mass to be MR = (2153 ± 30 ± 31) MeV/c2 and its width to be ΓR = (167 ± 77 ± 7) MeV, where the first uncertainties are statistical and the second are systematic.
Based on e+e− collision data collected at center-of-mass energies from 2.000 to 3.080 GeV by the BESIII detector at the BEPCII collider, a partial wave analysis isperformed for the process e+e− → K0SK0Lπ0. The results allow the Born cross sections of the process e+e− → K0SK0Lπ0, as well as its subprocesses e+e− → K∗(892)0K¯ 0 and K∗2(1430)0K¯ 0 to be measured. The Born cross sections for e+e− → K0SK0 Lπ 0 are consistent with previous measurements by BaBar, but with substantially improved precision. The Born cross section lineshape of the process e+e − → K∗(892)0K¯ 0 is consistent with a vector meson state around 2.2 GeV with a signifcance of 3.2σ. A Breit-Wigner ft determines its mass as MY = (2164.7 ± 9.1 ± 3.1) MeV/c2 and its width as ΓY = (32.4 ± 21.0 ± 1.8) MeV.
Search for X(3872)→π⁰π⁰χc₁,₂
(2024)
Using 10.1 fb−1 of e+e− collision data collected by the BESIII detector with center-of-mass energies between 4.15 GeV and 4.30 GeV, we search for the decays X(3872)→π0π0χc1,2, where the X(3872) is produced in e+e−→γX(3872). No evidence above 3σ is found for either decay. Upper limits at the 90% C.L. on the branching fractions of X(3872)→π0π0χc1,2 normalized to the branching fraction of X(3872)→π+π−J/ψ are set to be B(X(3872)→π0π0χc1)/B(X(3872)→π+π−J/ψ)<1.1 and B(X(3872)→π0π0χc2)/B(X(3872)→π+π−J/ψ)<0.5, taking into account both statistical and systematic uncertainties.
Using data samples with an integrated luminosity of 4.67 fb−1 collected by the BESIII detector operating at the BEPCII collider, we search for the process e+e−→η′ψ(2S) at center-of-mass energies from 4.66 to 4.95 GeV. No significant signal is observed, and upper limits for the Born cross sections σB(e+e−→η′ψ(2S)) at the 90\% confidence level are determined.
Based on 4.4 fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure W-exchange decay Λ+c→Ξ0K+ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be αΞ0K+=0.01±0.16(stat.)±0.03(syst.). This result reflects the interference between the S- and P-wave amplitudes. The phase shift between S- and P-wave amplitudes is δp−δs=−1.55±0.25(stat.)±0.05(syst.) rad.
Using data samples with an integrated luminosity of 4.5 fb−1 collected by the BESIII detector at center-of-mass energies ranging from 4.66 to 4.95 GeV, we study the processes of e+e−→ωX(3872) and e+e−→γX(3872). With the e+e−→ωX(3872) process, the branching fraction ratio R≡B(X(3872)→γJ/ψ)B(X(3872)→π+π−J/ψ) is measured to be 0.38±0.20stat.±0.01syst. (R<0.83 at 90\% confidence level). In addition, we measure the ratio of the average cross section of e+e−→ωX(3872) to e+e−→ωχc1(ωχc2) to be σωX(3872)/σωχc1 (σωX(3872)/σωχc2)=5.2±1.0stat.±1.9syst. (5.5±1.1stat.±2.4syst.). Finally, we search for the process of e+e−→γX(3872), and no obvious signal is observed. The upper limit on the ratio of the average cross section of e+e−→γX(3872) to e+e−→ωX(3872) is set as σγX(3872)/σωX(3872)<0.23 at 90\% confidence level.
Using a data sample of (10087±44)×106 J/ψ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process J/ψ→e+e−η(1405) is observed via the decay η(1405)→π0f0(980), f0(980)→π+π−, with a significance of about 9.6σ. The branching fraction of this decay is measured to be B(J/ψ→e+e−π0η(1405)→e+e−π0f0(980)→e+e−π0π+π−)=(2.02±0.24(stat.)±0.09(syst.))×10−7. The branching-fraction ratio B(J/ψ→e+e−η(1405))/B(J/ψ→γη(1405)) is determined to be (1.35±0.19(stat.)±0.06(syst.))×10−2. Furthermore, an e+e− invariant-mass dependent transition form factor of J/ψ→e+e−η(1405) is presented for the first time. The obtained result provides input for different theoretical models, and is valuable for the improved understanding the intrinsic structure of the η(1405) meson.
The energy-dependent cross section for e+e−→ηψ(2S) is measured at eighteen center of mass energies from 4.288 GeV to 4.951 GeV using the BESIII detector. Using the same data samples, we also perform the first search for the reaction e+e−→ηX~(3872), but no evidence is found for the X~(3872) in the π+π−J/ψ mass distribution. At each of the eighteen center of mass energies, upper limits at the 90\% confidence level on the cross section for e+e−→ηψ(2S) and on the product of the e+e−→ηX~(3872) cross section with the branching fraction of X~(3872)→π+π−J/ψ are reported.
The process 𝑒+𝑒−→Σ+¯Σ− is studied from threshold up to 3.04 GeV/𝑐2 via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb−1, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of Σ are measured in eleven Σ+¯Σ− invariant mass intervals from threshold to 3.04 GeV/𝑐2. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays 𝐽/𝜓→Σ+¯Σ− and 𝜓(3686)→Σ+¯Σ− are determined and the obtained results are consistent with the previous results of BESIII.
The CP-even fractions (F+) of the decays D0→π+π−π0 and D0→K+K−π0 are measured with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment corresponding to an integrated luminosity of 7.93 fb−1. The results are Fπ+π−π0+=0.9406±0.0036±0.0021 and FK+K−π0+=0.631±0.014±0.011, where the first uncertainties are statistical and the second systematic. These measurements are consistent with the previous determinations, and the uncertainties for Fπ+π−π0+ and FK+K−π0+ are reduced by factors of 3.9 and 2.6, respectively. The reported results provide important inputs for the precise measurement of the angle γ of the Cabibbo-Kobayashi-Maskawa matrix and indirect CP violation in charm mixing.
We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative J/ψ decays, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a signal and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.7−48.5)×10−8 and (2.2−101.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
In the effective field theory, the massless dark photon γ′ can only couple with the Standard Model particle through operators of dimension higher than four, thereby offering a high sensitivity to the new physics energy scale. Using 7.9 fb−1 of e+e− collision data collected at s√=3.773 GeV with the BESIII detector at the BEPCII collider, we measure the effective flavor-changing neutral current coupling of cuγ′ in D0→ωγ′ and D0→γγ′ processes to search for the massless dark photon. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be 1.1×10−5 and 2.0×10−6 for D0→ωγ′ and D0→γγ′, respectively. These results provide the most stringent constraint on the new physics energy scale associated with cuγ′ coupling in the world, with the new physics energy scale related parameter |C|2+|C5|2<8.2×10−17 GeV−2 at the 90% confidence level, playing a unique role in the dark sector search with the charm sector.
Model-independent determination of the strong-phase difference between D⁰ and D̄⁰ → π⁺π⁻π⁺π⁻ decays
(2024)
Measurements of the strong-phase difference between D0 and D¯0→π+π−π+π− are performed in bins of phase space. The study exploits a sample of quantum-correlated DD¯ mesons collected by the BESIII experiment in e+e− collisions at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 2.93~fb−1. Here, D denotes a neutral charm meson in a superposition of flavor eigenstates. The reported results are valuable for measurements of the CP-violating phase γ (also denoted ϕ3) in B±→DK±, D→π+π−π+π− decays, and the binning schemes are designed to provide good statistical sensitivity to this parameter. The expected uncertainty on γ arising from the precision of the strong-phase measurements, when applied to very large samples of B-meson decays, is around 1.5∘ or 2∘, depending on the binning scheme. The binned strong-phase parameters are combined to give a value of F4π+=0.746±0.010±0.004 for the CP-even fraction of D0→π+π−π+π− decays, which is around 30\% more precise than the previous best measurement of this quantity.
Based on 4.4 fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure \textit{W}-boson-exchange decay Λ+c→Ξ0K+ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be αΞ0K+=0.01±0.16(stat.)±0.03(syst.). This result reflects the non-interference effect between the S- and P-wave amplitudes. The phase shift between S- and P-wave amplitudes has two solutions, which are δp−δs=−1.55±0.25(stat.)±0.05(syst.) rad or 1.59±0.25(stat.)±0.05(syst.) rad.
Based on 4.4 fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure \textit{W}-boson-exchange decay Λ+c→Ξ0K+ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be αΞ0K+=0.01±0.16(stat.)±0.03(syst.). This result reflects the non-interference effect between the S- and P-wave amplitudes. The phase shift between S- and P-wave amplitudes has two solutions, which are δp−δs=−1.55±0.25(stat.)±0.05(syst.) rad or 1.59±0.25(stat.)±0.05(syst.) rad.
Based on (2712.4±14.3)×106 ψ(3686) events, we investigate four hadronic decay modes of the P-wave charmonium spin-singlet state hc(1P1)→h+h−π0/η (h=π or K) via the process ψ(3686)→π0hc at BESIII. The hc→π+π−π0 decay is observed with a significance of 9.6σ after taking into account systematic uncertainties. Evidences for hc→K+K−π0 and hc→K+K−η are found with significances of 3.5σ and 3.3σ, respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be B(hc→π+π−π0)=(1.36±0.16±0.14)×10−3, B(hc→K+K−π0)=(3.26±0.84±0.36)×10−4, and B(hc→K+K−η)=(3.13±1.08±0.38)×10−4, where the first uncertainties are statistical and the second are systematic. No significant signal of hc→π+π−η is found, and the upper limit of its decay branching fraction is determined to be B(hc→π+π−η)<4.0×10−4 at 90% confidence level.
The processes hc→γP(P=η′, η, π0)) are studied with a sample of (27.12±0.14)×108 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The branching fractions of hc→γη′ and hc→γη are measured to be (1.40±0.11±0.04±0.10)×10−3 and (3.77±0.55±0.13±0.26)×10−4, respectively, where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ(3686)→π0hc. The ratio Rhc=B(hc→γη)B(hc→γη′) is calculated to be (27.0±4.4±1.0)%. The measurements are consistent with the previous results with improved precision by a factor of 2. The results are valuable for gaining a deeper understanding of η−η′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay hc→γπ0, and an upper limit is placed on its branching fraction of B(hc→γπ0)<5.0×10−5, at the 90\% confidence level.
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.