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Institute
The Cabbibo-favored decay Λ+c→Ξ0K+π0 is studied for the first time using 6.1 fb−1 of e+e− collision data at center-of-mass energies between 4.600 and 4.840 GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay Λ+c→Ξ0K+π0 is measured to be (7.79±1.46±0.71)×10−3, where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay Λ+c→Ξ(1530)0K+ is (5.99±1.04±0.29)×10−3, which is consistent with the previous result of (5.02±0.99±0.31)×10−3. In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay Λ+c→nK+π0 is 7.1×10−4 at the 90% confidence level. The upper limits on the branching fractions of Λ+c→Σ0K+π0 and ΛK+π0 are also determined to be 1.8×10−3 and 2.0×10−3, 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.
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.
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±1.2±0.4)×10−4, the ratio of the branching fractions Λ+c→nπ+ and Λ+c→pπ0 is calculated to be 4.2+2.2−1.9; this is an important input for the understanding of the decay mechanisms of charmed baryons. 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 a sample of (10087±44)×106 𝐽/𝜓 events, which is about 45 times larger than that was previously analyzed, a further investigation on the 𝐽/𝜓→𝛾3(𝜋+𝜋−) decay is performed. A significant distortion at 1.84 GeV/𝑐2 in the line shape of the 3(𝜋+𝜋−) invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, 𝑋(1840) and 𝑋(1880). The new state 𝑋(1880) is observed with a statistical significance larger than 10𝜎. The mass and width of 𝑋(1880) are determined to be 1882.1±1.7±0.7 MeV/𝑐2 and 30.7±5.5±2.4 MeV, respectively, which indicates the existence of a 𝑝¯ 𝑝 bound state.
Observation of η_(c)(1S, 2S) and χ_(cJ) decays to 2(π⁺π^(−))η via ψ(3686) radiative transitions
(2024)
Based on 2.7×109 ψ(3686) decays collected with the BESIII detector, the radiative decay ψ(3686)→γ2(π+π−)η is investigated to measure properties of S- and P-wave charmonium states. The branching fraction of the decay ηc(1S)→2(π+π−)η, which is found to have a strong dependence on the interference pattern between ηc(1S) and non-ηc(1S) processes, is measured in both destructive and constructive interference scenarios for the first time. The mass and width of the ηc(1S) are measured to be M=(2984.14±0.13±0.38) MeV/c2 and Γ=(28.82±0.11±0.82) MeV, respectively. Clear signals for the decays of the χcJ(J=0,1,2) and the ηc(2S) to 2(π+π−)η are also observed for the first time, and the corresponding branching fractions are measured. The ratio of the branching fractions between the ηc(2S) and ηc(1S) decays is significantly lower than the theoretical prediction, which might suggest different dynamics in their decays.
A light scalar X0 or vector X1 particles have been introduced as a possible explanation for the (g−2)μ anomaly and dark matter phenomena.
Using (8.998±0.039)×109 $\jpsi$ events collected by the BESIII detector, we search for a light muon philic scalar X0 or vector X1 in the processes J/ψ→μ+μ−X0,1 with X0,1 invisible decays. No obvious signal is found, and the upper limits on the coupling g′0,1 between the muon and the X0,1 particles are set to be between 1.1×10−3 and 1.0×10−2 for the X0,1 mass in the range of 1<M(X0,1)<1000 MeV/c2 at 90% confidence level.
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.
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.
We report a search for a heavier partner of the recently observed Zcs(3985)− state, denoted as Z′−cs, in the process e+e−→K+D∗−sD∗0+c.c., based on e+e− collision data collected at the center-of-mass energies of s√=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Z′−cs is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate K+ recoil-mass spectra, which are probed for a potential contribution from Z′−cs→D∗−sD∗0 (c.c.). We find an excess of Z′−cs→D∗−sD∗0 (c.c.) candidates with a significance of 2.1σ, after considering systematic uncertainties, at a mass of (4123.5±0.7stat.±4.7syst.) MeV/c2. As the data set is limited in size, the upper limits are evaluated at the 90\% confidence level on the product of the Born cross sections (σBorn) and the branching fraction (B) of Z′−cs→D∗−sD∗0, under different assumptions of the Z′−cs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of σBorn⋅B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Z′−cs state and clarify its nature in the coming years.
Measurement of the absolute branching fraction of the singly Cabibbo suppressed decay Λc⁺ → pη′
(2022)
The singly Cabibbo suppressed decay Λ+c→pη′ is measured using 4.5 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for Λ+c→pη′ with a statistical significance of 3.6σ is reported with a double-tag approach. The Λ+c→pη′ absolute branching fraction is determined to be (5.62+2.46−2.04±0.26)×10−4, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of 1σ.
By analyzing (27.12±0.14)×108 ψ(3686) events accumulated with the BESIII detector, the decay ηc(2S)→K+K−η is observed for the first time with a significance of 6.2σ after considering systematic uncertainties. The product of the branching fractions of ψ(3686)→γηc(2S) and ηc(2S)→K+K−η is measured to be B(ψ(3686)→γηc(2S))×B(ηc(2S)→K+K−η)=(2.39±0.32±0.34)×10−6, where the first uncertainty is statistical, and the second one is systematic. The branching fraction of ηc(2S)→K+K−η is determined to be B(ηc(2S)→K+K−η)=(3.42±0.46±0.48±2.44)×10−3, where the third uncertainty is due to the branching fraction of ψ(3686)→γηc(2S). Using a recent BESIII measurement of B(ηc(2S)→K+K−π0), we also determine the ratio between the branching fractions of ηc(2S)→K+K−η and ηc(2S)→K+K−π0 to be 1.49±0.22±0.25, which is consistent with the previous result of BaBar at a comparable precision level.
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.
We perform the first investigation of the process e+e−→K+K−ψ(2S) and report its Born cross sections over a range of center-of-mass energies from 4.699 to 4.951~GeV. The measurements are carried out using several partial reconstruction techniques using data samples collected by the BESIII detector with a total integrated luminosity of 2.5~fb−1. We search for new tetraquark candidates Z±cs in the decays Z±cs→K±ψ(2S). No significant Z±cs signals are observed.
Observation of χcJ → 3(K⁺K⁻)
(2024)
By analyzing (27.12±0.14)×108 𝜓(3686) events collected with the BESIII detector operating at the BEPCII collider, the decay processes 𝜒𝑐𝐽→3(𝐾+𝐾−) (𝐽=0, 1, 2) are observed for the first time with statistical significances of 8.2𝜎, 8.1𝜎, and 12.4𝜎, respectively. The product branching fractions of 𝜓(3686)→𝛾𝜒𝑐𝐽, 𝜒𝑐𝐽→3(𝐾+𝐾−) are presented and the branching fractions of 𝜒𝑐𝐽→3(𝐾+𝐾−) decays are determined to be ℬ𝜒𝑐0→3(𝐾+𝐾−)=(10.7±1.8±1.1)×10−6, ℬ𝜒𝑐1→3(𝐾+𝐾−)=(4.2±0.9±0.5)×10−6, and ℬ𝜒𝑐2→3(𝐾+𝐾−)=(7.2±1.1±0.8)×10−6, where the first uncertainties are statistical and the second are systematic.
Using (2.712±0.014)×109 ψ(3686) events collected with the BESIII detector operating at the BEPCII, we find an evidence of the ηc(2S)→K+K−η′ decay with a statistical significance of 3.1σ. Its decay branching fraction is measured to be (12.24±4.60(stat.)±2.37(syst.)±4.68(extr.))×10−4, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is from the branching fraction of the ψ(3686)→γηc(2S) decay. The upper limit on the product branching fraction B[ψ(3686)→γηc(2S)]× B[ηc(2S)→K+K−η′] is set to be 1.14×10−6 at 90% confidence level. In addition, the branching fractions of χc1→K+K−η′ and χc2→K+K−η′ are updated to be (8.47±0.09(stat.)±0.47(syst.))×10−4 and (1.53±0.04(stat.)±0.08(syst.))×10−4, respectively. The precision is improved by twofold.
Using e+e− annihilation data sets corresponding to an integrated luminosity of 4.5 fb−1, collected with the BESIII detector at center-of-mass energies between 4.600 and 4.699 GeV, we report the first measurements of the absolute branching fractions B(Λ+c→pK0L)=(1.67±0.06±0.04)%, B(Λ+c→pK0Lπ+π−)=(1.69±0.10±0.05)%, and B(Λ+c→pK0Lπ0)=(2.02±0.13±0.05)%, where the first uncertainties are statistical and the second systematic. Combining with the known branching fractions of Λ+c→pK0S, Λ+c→pK0Sπ+π−, and Λ+c→pK0Sπ0, we present the first measurements of the K0S-K0L asymmetries R(Λ+c,K0S,LX)=B(Λ+c→K0SX)−B(Λ+c→K0LX)B(Λ+c→K0SX)+B(Λ+c→K0LX) in charmed baryon decays: R(Λ+c,pK0S,L)=−0.025±0.031, R(Λ+c,pK0S,Lπ+π−)=−0.027±0.048, and R(Λ+c,pK0S,Lπ0)=−0.015±0.046. No significant asymmetries within the uncertainties are observed.
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.
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.