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We search for an axion-like particle (ALP) a through the process ψ(3686)→π+π−J/ψ, J/ψ→γa, a→γγ in a data sample of (2.71±0.01)×109 ψ(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ψ→γa and the ALP-photon coupling constant gaγγ are set at 95% confidence level in the mass range of 0.165≤ma≤2.84GeV/c2. The limits on B(J/ψ→γa) range from 8.3×10−8 to 1.8×10−6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165≤ma≤1.468GeV/c2.
We search for an axion-like particle (ALP) a through the process ψ(3686)→π+π−J/ψ, J/ψ→γa, a→γγ in a data sample of (2.71±0.01)×109 ψ(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ψ→γa and the ALP-photon coupling constant gaγγ are set at 95% confidence level in the mass range of 0.165≤ma≤2.84GeV/c2. The limits on B(J/ψ→γa) range from 8.3×10−8 to 1.8×10−6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165 ≤ ma ≤ 1.468GeV/c2.
We search for the semi-leptonic decays Λ + c → Λπ+π−e+νe and Λ + c → pK0 Sπ−e+νe in a sample of 4.5 fb−1 of e+e− annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Λ+c → Λπ+π−e+νe ) < 3.9 × 10−4 and B(Λ + c → pK0Sπ−e+νe ) < 3.3 × 10−4 at the 90% confidence level, respectively.
Based on 4.5 fb−1 data taken at seven center-of-mass energies ranging from 4.600 to 4.699 GeV with the BESIII detector at the BEPCII collider, we measure the branching fractions of Λ + c → Σ + + hadrons relative to Λ + c → Σ +π +π −. Combining with the world average branching fraction of Λ + c → Σ +π +π −, their branching fractions are measured to be (0.377 ± 0.042 ± 0.020 ± 0.021)% for Λ + c → Σ +K+K−, (0.200 ± 0.023 ± 0.011 ± 0.011)% for Λ + c → Σ+K+π−, (0.414 ± 0.080 ± 0.030 ± 0.023)% for Λ + c → Σ +φ and (0.197 ± 0.036 ± 0.009 ± 0.011)% for Λ + c → Σ +K+K−(non-φ). In all the above results, the first uncertainties are statistical, the second are systematic and the third are from external input of the branching fraction of Λ + c → Σ +π +π −. Since no signal for Λ + c → Σ +K+π−π 0 is observed, the upper limit of its branching fraction is determined to be 0.13% at the 90% confidence level.
With data samples collected with the BESIII detector at seven energy points at √s = 3.68 − 3.71 GeV, corresponding to an integrated luminosity of 333 pb−1, we present a study of the Λ transverse polarization in the e+e− → ΛΛ¯ reaction. The signifcance of polarization by combining the seven energy points is found to be 2.6σ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the ΛΛ¯ helicity states. The modulus ratio and the relative phase of EM-psionic form factors combined with all energy points are measured to be RΨ = 0.71+0.10−0.10 ± 0.03 and ∆ΦΨ = 23+8.8−8.0 ± 1.6◦, where the frst uncertainties are statistical and the second systematic.
The cross sections of the 𝑒+𝑒−→𝜙𝜂′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn and decrease as the center-of-mass energy increases as 𝑠−𝑛/2 with 𝑛=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of 𝑛=3.5±0.9. In addition, the charmless decay 𝜓(3770)→𝜙𝜂′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of ℬ(𝜓(3770)→𝜙𝜂′) at the 90% confidence level is determined to be 2.3×10−5.
Using (1.0087±0.0044)×1010 𝐽/𝜓 events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays Ξ0→𝐾−𝑒+ with Δ(𝐵−𝐿)=0 and Ξ0→𝐾+𝑒− with |Δ(𝐵−𝐿)|=2, where 𝐵 (𝐿) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to ℬ(Ξ0→𝐾−𝑒+)<3.6×10−6 and ℬ(Ξ0→𝐾+𝑒−)<1.9×10−6 at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.
Using data samples with an integrated luminosity of 22.42 fb−1 collected by the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the 𝑒+𝑒−→𝜂𝐽/𝜓 process at center-of-mass energies from 3.808 to 4.951 GeV. Three structures are observed in the line shape of the measured cross sections. A maximum-likelihood fit with 𝜓(4040), two additional resonances, and a nonresonant component are performed. The mass and width of the first additional state are (4219.7±2.5±4.5) MeV/𝑐2 and (80.7±4.4±1.4) MeV, respectively, consistent with the 𝜓(4230). For the second state, the mass and width are (4386±13±17) MeV/𝑐2 and (177±32±13) MeV, respectively, consistent with the 𝜓(4360). The first uncertainties are statistical, and the second ones are systematic. The statistical significance of 𝜓(4040) is 8.0𝜎 and those for 𝜓(4230) and 𝜓(4360) are more than 10.0𝜎.
Evidence for the singly Cabibbo suppressed decay Λ+c→pπ0 is reported for the first time with a statistical significance of 3.7σ based on 6.0 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Λ+c→pπ0 is measured to be (1.56+0.72−0.58±0.20)×10−4, which distinctly exceeds the upper limit measured by Belle experiment. Combining with the branching fraction of Λ+c→nπ+, (6.6±1.3)×10−4, the ratio of the branching fractions of Λ+c→nπ+ and Λ+c→pπ0 is calculated to be 3.2+2.2−1.2. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Λ+c→pη is measured to be (1.63±0.31stat±0.11syst)×10−3, which is consistent with previous measurements.
Evidence for the singly Cabibbo suppressed decay Λ+c→pπ0 is reported for the first time with a statistical significance of 3.7σ based on 6.0 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Λ+c→pπ0 is measured to be (1.56+0.72−0.58±0.20)×10−4. Combining with the branching fraction of Λ+c→nπ+, (6.6±1.3)×10−4, the ratio of the branching fractions of Λ+c→nπ+ and Λ+c→pπ0 is calculated to be 3.2+2.2−1.2. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Λ+c→pη is measured to be (1.63±0.31stat±0.11syst)×10−3.
Precision measurements of the semileptonic decays 𝐷+𝑠→𝜂𝑒+𝜈𝑒 and 𝐷+𝑠→𝜂′𝑒+𝜈𝑒 are performed with 7.33 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector. The branching fractions obtained are ℬ(𝐷+𝑠→𝜂𝑒+𝜈𝑒) = (2.255±0.039stat±0.051syst)% and ℬ(𝐷+𝑠→𝜂′𝑒+𝜈𝑒)=(0.810±0.038stat±0.024syst)%. Combining these results with the ℬ(𝐷+→𝜂𝑒+𝜈𝑒) and ℬ(𝐷+→𝜂′𝑒+𝜈𝑒) obtained from previous BESIII measurements, the 𝜂−𝜂′ mixing angle in the quark flavor basis is determined to be 𝜙P=(40.0±2.0stat±0.6syst)°. Moreover, from the fits to the partial decay rates of 𝐷+𝑠→𝜂𝑒+𝜈𝑒 and 𝐷+𝑠→𝜂′𝑒+𝜈𝑒, the products of the hadronic transition form factors 𝑓𝜂(′)+(0) and the modulus of the 𝑐→𝑠 Cabibbo-Kobayashi-Maskawa matrix element |𝑉𝑐𝑠| are determined by using different hadronic transition form factor parametrizations. Based on the two-parameter series expansion, the products 𝑓𝜂+(0)|𝑉𝑐𝑠| = 0.4519±0.0071stat±0.0065syst and 𝑓𝜂′+(0)|𝑉𝑐𝑠| = 0.525±0.024stat±0.009syst are extracted. All results determined in this work supersede those measured in the previous BESIII analyses based on the 3.19 fb−1 subsample of data at 4.178 GeV.
Evidence for the singly Cabibbo suppressed decay Λ+c→pπ0 is reported for the first time with a statistical significance of 3.7σ based on 6.0 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Λ+c→pπ0 is measured to be (1.56+0.72−0.58±0.20)×10−4, which distinctly exceeds the upper limit measured by Belle experiment. Combining with the branching fraction of Λ+c→nπ+, (6.6±1.3)×10−4, the ratio of the branching fractions of Λ+c→nπ+ and Λ+c→pπ0 is calculated to be 3.2+2.2−1.2. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Λ+c→pη is measured to be (1.63±0.31stat±0.11syst)×10−3, which is consistent with previous measurements.
Using data samples with an integrated luminosity of 22.42 fb−1 collected by the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the $e^{+}e^{-}\rightarrow\etaJ/\psi$ process at center-of-mass energies from 3.808 to 4.951 GeV. Three structures are observed in the line shape of the measured cross sections. A maximum-likelihood fit with ψ(4040), two additional resonances, and a non-resonant component is performed. The mass and width of the first additional state are (4219.7±2.5±4.5)MeV/c2 and (80.7±4.4±1.4)MeV, respectively, consistent with the ψ(4230). For the second state, the mass and width are (4386±13±17)MeV/c2 and (177±32±13)MeV, respectively, consistent with the ψ(4360). The first uncertainties are statistical and the second ones are systematic. The statistical significance of ψ(4040) is 8.0σ and those for ψ(4230) and ψ(4360) are more than 10.0σ.
We present the first observation of the singly Cabibbo-suppressed decay Λ+c→ΛK+π0 with a significance of 5.7σ and the first evidence of Λ+c→ΛK+π+π− decay with a significance of 3.1σ, based on e+e− annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to an integrated luminosity of 6.4 fb−1, in the center-of-mass energy range from 4.600 GeV to 4.950 GeV. We determine the branching fractions of Λ+c→ΛK+π0 and Λ+c→ΛK+π+π− relative to their Cabibbo-favored counterparts to be B(Λ+c→ΛK+π0)B(Λ+c→Λπ+π0)=(2.09±0.39stat.±0.07syst.)×10−2 and B(Λ+c→ΛK+π+π−)B(Λ+c→Λπ+π+π−)=(1.13±0.41stat.±0.06syst.)×10−2, respectively. Moreover, by combining our measured result with the world average of B(Λ+c→Λπ+π0), we obtain the branching fraction B(Λ+c→ΛK+π0)=(1.49±0.27stat.±0.05syst.±0.08ref.)×10−3. This result significantly departs from theoretical predictions based on quark SU(3) flavor symmetry, which is underpinned by the presumption of meson pair S-wave amplitude dominance.
Using 2.93 fb−1 of e+e− collision data collected with the BESIII detector at the center-of-mass energy 3.773 GeV, we perform the first amplitude analysis of the decay D+ → π+π0π0 and determine the relative magnitudes and phases of different intermediate processes. The absolute branching fraction of D+ → π+π0π0 is measured to be (2.888 ± 0.058stat. ± 0.069syst.)%. The dominant intermediate processes are D+ → a1(1260)+(→ ρ+π0) and D+ → *0ρ+, with branching fractions of (8.66 ± 1.04stat. ± 1.39syst.) × 10−3 and (9.70 ± 0.81stat. ± 0.53syst.) × 10−3, respectively.
First study of reaction Ξ⁰n → Ξ⁻ p using Ξ⁰-nucleus scattering at an electron-positron collider
(2023)
Using ð1.0087 0.0044Þ × 1010 J=ψ events collected with the BESIII detector at the BEPCII storage ring, the process Ξ0n → Ξ−p is studied, where the Ξ0 baryon is produced in the process J=ψ → Ξ0Ξ¯ 0 and the neutron is a component of the 9 Be, 12C, and 197Au nuclei in the beam pipe. A clear signal is observed with a statistical significance of 7.1σ. The cross section of the reaction Ξ0 þ 9 Be → Ξ− þ p þ 8 Be is determined to be σðΞ0 þ 9 Be → Ξ− þ p þ 8 BeÞ¼ð22.1 5.3stat 4.5sysÞ mb at the Ξ0 momentum of 0.818 GeV=c, where the first uncertainty is statistical and the second is systematic. No significant H-dibaryon signal is observed in the Ξ−p final state. This is the first study of hyperon-nucleon interactions in electron-positron collisions and opens up a new direction for such research.
We present the first observation of the singly Cabibbo-suppressed decay Λ+𝑐→Λ𝐾+𝜋0 with a significance of 5.7𝜎 and the first evidence of Λ+𝑐→Λ𝐾+𝜋+𝜋− decay with a significance of 3.1𝜎, based on 𝑒+𝑒−annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to an integrated luminosity of 6.4 fb−1, in the center-of-mass energy range from 4.600 to 4.950 GeV. We determine the branching fractions of Λ+𝑐→Λ𝐾+𝜋0 and Λ+𝑐→Λ𝐾+𝜋+𝜋− relative to their Cabibbo-favored counterparts to be ℬ(Λ+𝑐→Λ𝐾+𝜋0)ℬ(Λ+𝑐→Λ𝜋+𝜋0) = (2.09±0.39stat±0.07syst)×10−2 and ℬ(Λ+𝑐→Λ𝐾+𝜋+𝜋−)ℬ(Λ+𝑐→Λ𝜋+𝜋+𝜋−) = (1.13±0.41stat±0.06syst)×10−2, respectively. Moreover, by combining our measured result with the world average of ℬ(Λ+𝑐→Λ𝜋+𝜋0), we obtain the branching fraction ℬ(Λ+𝑐→Λ𝐾+𝜋0) = (1.49±0.27stat±0.05syst±0.08ref)×10−3. This result significantly departs from theoretical predictions based on quark 𝑆𝑈(3) flavor symmetry, which is underpinned by the presumption of meson pair 𝑆-wave amplitude dominance.
Quantum-correlated 𝐷¯𝐷 pairs collected by the BESIII experiment at the 𝜓(3770) resonance corresponding to an integrated luminosity of 2.93 fb−1 are used to study the 𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0 decay mode. The 𝐶𝑃-even fraction of 𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0 decays is determined to be 0.235±0.010±0.002, where the first uncertainty is statistical and the second is systematic.
The quantum entangled J=ψ → ΣþΣ¯ − pairs from ð1.0087 0.0044Þ × 1010 J=ψ events taken by the BESIII detector are used to study the nonleptonic two-body weak decays Σþ → nπþ and Σ¯ − → n¯π−. The CP-odd weak decay parameters of the decays Σþ → nπþ (αþ) and Σ¯ − → n¯π− (α¯−) are determined to be 0.0481 0.0031stat 0.0019syst and −0.0565 0.0047stat 0.0022syst, respectively. The decay parameter α¯− is measured for the first time, and the accuracy of αþ is improved by a factor of 4 compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of ACP ¼ ðαþ þ α¯−Þ=ðαþ − α¯−Þ ¼ −0.080 0.052stat 0.028syst. Assuming CP conservation, the average decay parameter is determined as hαþi¼ðαþ − α¯−Þ=2 ¼ −0.0506 0.0026stat 0.0019syst, while the ratios αþ=α0 and α¯−=α¯ 0 are −0.0490 0.0032stat 0.0021syst and −0.0571 0.0053stat 0.0032syst, where α0 and α¯ 0 are the decay parameters of the decays Σþ → pπ0 and Σ¯ − → p¯ π0, respectively.