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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.
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.
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 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.
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.
The quantum entangled J/ψ→Σ+Σ¯− pairs from (1.0087±0.0044)×1010 J/ψ events taken by the BESIII detector are used to study the non-leptonic two-body weak decays Σ+→nπ+ and Σ¯−→n¯π−. The CP-odd weak decay parameters of the decays Σ+→nπ+ (α+) and Σ¯−→n¯π− (α¯−) are determined to be −0.0565±0.0047stat±0.0022syst and 0.0481±0.0031stat±0.0019syst, respectively. The decay parameter α¯− is measured for the first time, and the accuracy of α+ is improved by a factor of four 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=(α++α¯−)/(α+−α¯−) = −0.080±0.052stat±0.028syst. Assuming CP conservation, the average decay parameter is determined as ⟨α+⟩=(α+−α¯−)/2 = −0.0506±0.0026stat±0.0019syst, while the ratios α+/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 Σ+→pπ0 and Σ¯−→p¯π0, respectively.
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.
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 is performed 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¯ and K∗2(1430)0K¯ to be measured. The Born cross sections for e+e−→K0SK0Lπ0 are consistent with previous measurements by BaBar and SND, but with substantially improved precision. The Born cross section lineshape of the process e+e−→K∗(892)0K¯ is consistent with a vector meson state around 2.2 GeV with a statistical significance of 3.2σ. A Breit-Wigner fit determines its mass as MY=(2164.1±9.6±3.1) MeV/c2 and its width as ΓY=(32.4±21.1±1.5) MeV, where the first uncertainties are statistical and the second ones are systematic, respectively.
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 is performed 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−→K0SK0Lπ0 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 significance of 3.2σ. A Breit-Wigner fit 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.
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.
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, which is predicted by the ΔI=1/2 rule, with a statistical significance of more than 5σ. We test for CP violation in Ξ−→Λπ− and in Λ→nπ0 with the best precision to date.
Based on 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 experimental studies of the doubly Cabibbo-suppressed decays 𝐷+𝑠→𝐾+𝐾+𝜋− and 𝐷+𝑠→𝐾+𝐾+𝜋−𝜋0 are reported. We determine the absolute branching fraction of 𝐷+𝑠→𝐾+𝐾+𝜋− to be (1.24+0.28−0.26(stat)±0.06(syst))×10−4. No significant signal of 𝐷+𝑠→𝐾+𝐾+𝜋−𝜋0 is observed and the upper limit on its decay branching fraction at 90% confidence level is set to be 1.7×10−4.
Based on 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 experimental studies of the doubly Cabibbo-suppressed decays D+s→K+K+π− and D+s→K+K+π−π0 are reported. We determine the absolute branching fraction of D+s→K+K+π− to be (1.23+0.28−0.25(stat)±0.06(syst)) ×10−4. No significant signal of D+s→K+K+π−π0 is observed and the upper limit on its decay branching fraction at 90\% confidence level is set to be 1.7×10−4.
Using a sample of 4.3×105 η′→ηπ0π0 events selected from the ten billion J/ψ event dataset collected with the BESIII detector, we study the decay η′→ηπ0π0 within the framework of nonrelativistic effective field theory. Evidence for a structure at π+π− mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the ππ scattering length combination a0−a2 is determined to be 0.226±0.060stat±0.013syst, which is in good agreement with theoretical calculation of 0.2644±0.0051.
Using a sample of 4.3×105 η′→ηπ0π0 events selected from the 10 billion J/ψ event data set collected with the BESIII detector, we study the decay η′→ηπ0π0 within the framework of non-relativistic effective field theory. Evidence for a structure at π+π− mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, which is consistent with the cusp effect as predicted by the non-relativistic effective field theory. After introducing the amplitude for describing the cusp effect, the ππ scattering length combination a0−a2 is determined to be 0.226±0.060stat.±0.012syst., which is in good agreement with theoretical calculation of 0.2644±0.0051.
Using a sample of 4.3×105 η′→ηπ0π0 events selected from the ten billion J/ψ event dataset collected with the BESIII detector, we study the decay η′→ηπ0π0 within the framework of nonrelativistic effective field theory. Evidence for a structure at π+π− mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the ππ scattering length combination a0−a2 is determined to be 0.226±0.060stat±0.013syst, which is in good agreement with theoretical calculation of 0.2644±0.0051.
Using 𝑒+𝑒− collision data with an integrated luminosity of 7.33 fb−1 collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector operating at the BEPCII collider, the branching fraction of the leptonic decay 𝐷+ 𝑠→𝜇+𝜈𝜇 is measured to be (0.5294±0.0108stat±0.0085syst)%. Based on this, the product of the 𝐷+ 𝑠 decay constant 𝑓𝐷+ 𝑠 and the magnitude of the 𝑐→𝑠 quark mixing matrix element |𝑉𝑐𝑠| is determined to be 𝑓𝐷+ 𝑠|𝑉𝑐𝑠| = 241.8±2.5stat±2.2syst MeV. Using the value of |𝑉𝑐𝑠| given by the global standard model fit, 𝑓𝐷+ 𝑠 is found to be 248.4±2.5stat±2.2syst MeV. Alternatively, using the value of 𝑓𝐷+ 𝑠 from a recent lattice quantum chromodynamics calculation, |𝑉𝑐𝑠| is determined to be 0.968±0.010stat±0.009syst.
By analyzing e+e− annihilation da ta corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with the \text{BESIII} detector, the first observation of the semileptonic decays D0→K0Sπ−π0e+νe and D+→K0Sπ+π−e+νe is reported. With a dominant hadronic contribution from K1(1270), the branching fractions are measured to be B(D0→K1(1270)−(→K0Sπ−π0)e+νe) = (1.69+0.53−0.46±0.15)×10−4 and B(D+→K¯1(1270)0(→K0Sπ+π−)e+νe) = (1.47+0.45−0.40±0.20)×10−4 with statistical significance of 5.4σ and 5.6σ, respectively. When combined with measurements of the K1(1270)→K+π−π decays, the absolute branching fractions are determined to be B(D0→K1(1270)−e+νe) = (1.05+0.33−0.28±0.12±0.12)×10−3 and B(D+→K¯1(1270)0e+νe) = (1.29+0.40−0.35±0.18±0.15)×10−3. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainties originate from the assumed branching fractions of the K1(1270)→Kππ decays.
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.
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.