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Institute
- Physik (371)
Using (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector, we perform the first search for the weak baryonic decay ψ(3686)→Λ+cΣ¯−+c.c.. The analysis procedure is optimized using a blinded method. No significant signal is observed, and the upper limit on the branching fraction (B) of ψ(3686)→Λ+cΣ¯−+c.c. is set to be 1.4×10−5 at the 90\% confidence level.
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.
By analyzing 𝑒+𝑒− annihilation data with an integrated luminosity of 2.93 fb−1 collected at the center-of-mass energy √𝑠=3.773 GeV with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic 𝐷0(+) decays involving multiple pions. The highest four branching fractions obtained are ℬ(𝐷0→𝜋+𝜋−𝜋0) = (1.343±0.013stat±0.016syst)%, ℬ(𝐷0→𝜋+𝜋−2𝜋0) = (1.002±0.019stat±0.024syst)%, ℬ(𝐷+→2𝜋+𝜋−𝜋0) = (1.165±0.021stat±0.021syst)%, and ℬ(𝐷+→2𝜋+𝜋−2𝜋0) = (1.074±0.040stat±0.030syst)%. The 𝐶𝑃 asymmetries for the six decays with highest signal yields are also determined and found to be compatible with zero.
By analyzing e+e− annihilation data with an integrated luminosity of 2.93 fb−1 collected at the center-of-mass energy s√= 3.773 GeV with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic D0(+) decays involving multiple pions. The largest four branching fractions obtained are B(D0→π+π−π0) = >(1.343±0.013stat±0.016syst)%, B(D0→π+π−2π0) = (0.998±0.019stat±0.024syst)%, B(D+→2π+π−π0)
(1.174±0.021stat±0.021syst)%, and B(D+→2π+π−2π0) = (1.074±0.040stat±0.030syst)%. The CP asymmetries for the six decays with highest event yields are also determined.
Using e+e− annihilation data sets collected with the BESIII detector, we measure the cross sections of the processes e+e−→e+e− and e+e−→μ+μ− at fifteen center-of-mass energy points in the vicinity of the J/ψ resonance. By a simultaneous fit to the measured, center-of-mass energy dependent cross sections of the two processes, the combined quantities ΓeeΓee/Γtot and ΓeeΓμμ/Γtot are determined to be (0.346±0.009) and (0.335±0.006) keV, respectively, where Γee, Γμμ, and Γtot are the electronic, muonic, and total decay widths of the J/ψ resonance, respectively. Using the resultant ΓeeΓμμ/Γtot and ΓeeΓee/Γtot, the ratio Γee/Γμμ is calculated to be 1.031±0.015, which is consistent with the expectation of lepton universality within about two standard deviations. Assuming lepton universality and using the branching fraction of the J/ψ leptonic decay measured by BESIII in 2013, Γtot and Γll are determined to be (93.0±2.1) and (5.56±0.11) keV, respectively, where Γll is the average leptonic decay width of the J/ψ resonance.
Observation of 𝜒𝑐𝐽→Λ¯Λ𝜂
(2022)
By analyzing (448.1±2.9)×106 𝜓(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of 𝜒𝑐𝐽→Λ
¯Λ𝜂 (𝐽=0, 1, and 2) are observed for the first time with statistical significances of 13.9𝜎, 6.7𝜎, and 8.2𝜎, respectively. The product branching fractions of 𝜓(3686)→𝛾𝜒𝑐𝐽 and 𝜒𝑐𝐽→Λ¯Λ𝜂 are measured. Dividing by the world averages of the branching fractions of 𝜓(3686)→𝛾𝜒𝑐𝐽, the branching fractions of 𝜒𝑐𝐽→Λ¯Λ𝜂 decays are determined to be (2.31±0.30±0.21)×10−4, (5.86±1.38±0.68)×10−5, and (1.05±0.21±0.15)×10−4 for 𝐽=0, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.
Using a sample of (448.1±2.9)×106 𝜓(3686) decays collected with the BESIII detector at BEPCII, we report an observation of Ξ− transverse polarization with a significance of 7.3𝜎 in the decay 𝜓(3686)→Ξ− ¯Ξ+ (Ξ−→Λ𝜋−, ¯Ξ+→¯Λ𝜋+, Λ→𝑝𝜋−, ¯Λ→¯𝑝𝜋+). The relative phase of the electric and magnetic form factors is determined to be ΔΦ=(0.667±0.111±0.058) rad. This is the first measurement of the relative phase for a 𝜓(3686) decay into a pair of Ξ−¯Ξ+ hyperons. The Ξ− decay parameters (𝛼Ξ−, 𝜙Ξ−) and their conjugates (𝛼¯Ξ+, 𝜙¯Ξ+), the angular-distribution parameter 𝛼𝜓, and the strong-phase difference 𝛿𝑝−𝛿𝑠 for Λ𝜋− scattering are measured to be consistent with previous BESIII results.
The radiative hyperon decay Λ→nγ is studied using (10087±44)×106 J/ψ events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay Λ→nγ is determined with a significance of 5.6σ to be [0.832±0.038(stat.)±0.054(syst.)]×10−3, which lies significantly below the current PDG value. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry αγ is reported with a value of −0.16±0.10(stat.)±0.05(syst.).
Observation of ηc(2S) → 3(π⁺π⁻) and measurements of χcJ → 3(π⁺π⁻) in ψ(3686) radiative transitions
(2022)
The hadronic decay 𝜂𝑐(2𝑆)→3(𝜋+𝜋−) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 𝜓(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of 𝜂𝑐(2𝑆) are (3643.4±2.3 (stat)±4.4 (syst)) MeV/𝑐2 and (19.8±3.9 (stat)±3.1 (syst)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction ℬ[𝜓(3686)→𝛾𝜂𝑐(2𝑆)]×ℬ[𝜂𝑐(2𝑆)→3(𝜋+𝜋−)] is measured to be (9.2±1.0 (stat)±1.2 (syst))×10−6. Using ℬ[𝜓(3686)→𝛾𝜂𝑐(2𝑆)]=(7.0+3.4−2.5)×10−4, we obtain ℬ[𝜂𝑐(2𝑆)→3(𝜋+𝜋−)]=(1.31±0.15 (stat)±0.17 (syst) (+0.64−0.47) (extr))×10−2, where the third uncertainty is from ℬ[𝜓(3686)→𝛾𝜂𝑐(2𝑆)]. We also measure the 𝜒𝑐𝐽→3(𝜋+𝜋−) (𝐽=0, 1, 2) decays via 𝜓′→𝛾𝜒𝑐𝐽 transitions. The branching fractions are ℬ[𝜒𝑐0→3(𝜋+𝜋−)]=(2.080±0.006 (stat)±0.068 (syst))×10−2, ℬ[𝜒𝑐1→3(𝜋+𝜋−)]=(1.092±0.004 (stat)±0.035 (syst))×10−2, and ℬ[𝜒𝑐2→3(𝜋+𝜋−)]=(1.565±0.005 (stat)±0.048 (syst))×10−2.
Observation of ηc(2S) → 3(π⁺π⁻) and measurements of χcJ → 3(π⁺π⁻) in ψ(3686) radiative transitions
(2022)
The hadronic decay ηc(2S)→3(π+π−) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ηc(2S) are (3643.4±2.3(stat.)±4.4(syst.)) MeV/c2 and (19.8±3.9(stat.)±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[ψ(3686)→γηc(2S)]×B[ηc(2S)→3(π+π−)] is measured to be (9.2±1.0(stat.)±0.9(syst.))×10−6. Using B[ψ(3686)→γηc(2S)]=(7.0+3.4−2.5)×10−4, we obtain B[ηc(2S)→3(π+π−)]=(1.31±0.15(stat.)±0.13(syst.)(+0.64−0.47)(extr))×10−2, where the third uncertainty is from B[ψ(3686)→γηc(2S)]. We also measure the χcJ→3(π+π−) (J=0,1,2) decays via ψ(3686)→γχcJ transitions. The branching fractions are B[χc0→3(π+π−)]=(2.080±0.006(stat.)±0.068(syst.))×10−2, B[χc1→3(π+π−)]=(1.092±0.004(stat.)±0.035(syst.))×10−2, and B[χc2→3(π+π−)]=(1.565±0.005(stat.)±0.048(syst.))×10−2.
Observation of ηc(2S) → 3(π⁺π⁻) and measurements of χcJ → 3(π⁺π⁻) in ψ(3686) radiative transitions
(2022)
The hadronic decay ηc(2S)→3(π+π−) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ηc(2S) are (3643.4±2.3(stat.)±4.4(syst.)) MeV/c2 and (19.8±3.9(stat.)±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[ψ(3686) → γηc(2S)]×B[ηc(2S)→3(π+π−)] is measured to be (9.2±1.0(stat.)±0.9(syst.))×10−6. Using B[ψ(3686)→γηc(2S)]=(7.0+3.4−2.5)×10−4, we obtain B[ηc(2S)→3(π+π−)]=(1.31±0.15(stat.)±0.13(syst.)(+0.64−0.47)(extr))×10−2, where the third uncertainty is from B[ψ(3686)→γηc(2S)]. We also measure the χcJ→3(π+π−) (J=0,1,2) decays via ψ(3686)→γχcJ transitions. The branching fractions are B[χc0→3(π+π−)]=(2.080±0.006(stat.)±0.068(syst.))×10−2, B[χc1→3(π+π−)]=(1.092±0.004(stat.)±0.035(syst.))×10−2, and B[χc2→3(π+π−)]=(1.565±0.005(stat.)±0.048(syst.))×10−2.
The decays D → K−π+π+π− and D → K−π+π 0 are studied in a sample of quantum-correlated DD¯ pairs produced through the process e+e− → ψ(3770) → DD¯, exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fb−1 . Here D indicates a quantum superposition of a D0 and a D¯ 0 meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle γ of the Unitarity Triangle in B− → DK− decays at the LHCb and Belle II experiments. The coherence factors are determined to be RK3π = 0.52+0.12−0.10 and RKππ0 = 0.78 ± 0.04, with values for the average strong-phase differences that are δ K3π D = (167+31−19)◦ and δKππ0D = (196+14−15◦ , where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the D → K−π+π+π− to yield results that will allow for a more sensitive measurement of γ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6◦.
We report new measurements of the branching fraction ℬ(𝐷+𝑠→ℓ+𝜈), where ℓ+ is either 𝜇+ or 𝜏+(→𝜋+¯𝜈𝜏), based on 6.32 fb−1 of electron-positron annihilation data collected by the BESIII experiment at six center-of-mass energy points between 4.178 and 4.226 GeV. Simultaneously floating the 𝐷+𝑠→𝜇+𝜈𝜇 and 𝐷+𝑠→𝜏+𝜈𝜏 components yields ℬ(𝐷+𝑠→𝜏+𝜈𝜏)=(5.21±0.25±0.17)×10−2, ℬ(𝐷+𝑠→𝜇+𝜈𝜇)=(5.35±0.13±0.16)×10−3, and the ratio of decay widths 𝑅=Γ(𝐷+𝑠→𝜏+𝜈𝜏)Γ(𝐷+𝑠→𝜇+𝜈𝜇)=9.73+0.61−0.58±0.36, where the first uncertainties are statistical and the second systematic. No evidence of 𝐶𝑃 asymmetry is observed in the decay rates 𝐷±𝑠→𝜇±𝜈𝜇 and 𝐷±𝑠→𝜏±𝜈𝜏: 𝐴𝐶𝑃(𝜇±𝜈)=(−1.2±2.5±1.0)% and 𝐴𝐶𝑃(𝜏±𝜈)=(+2.9±4.8±1.0)%. Constraining our measurement to the Standard Model expectation of lepton universality (𝑅=9.75), we find the more precise results ℬ(𝐷+𝑠→𝜏+𝜈𝜏)=(5.22±0.10±0.14)×10−2 and 𝐴𝐶𝑃(𝜏±𝜈𝜏)=(−0.1±1.9±1.0)%. Combining our results with inputs external to our analysis, we determine the 𝑐→¯𝑠 quark mixing matrix element, 𝐷+𝑠 decay constant, and ratio of the decay constants to be |𝑉𝑐𝑠|=0.973±0.009±0.014, 𝑓𝐷+𝑠=249.9±2.4±3.5 MeV, and 𝑓𝐷+𝑠/𝑓𝐷+=1.232±0.035, respectively.
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 6.32 fb−1 of 𝑒+𝑒− collision data collected by the BESIII detector at the center-of-mass energies between 4.178 and 4.226 GeV, an amplitude analysis of the 𝐷+𝑠→𝐾0𝑆𝐾−𝜋+𝜋+ decays is performed for the first time to determine the intermediate-resonant contributions. The dominant component is the 𝐷+𝑠→𝐾*(892)+¯𝐾*(892)0 decay with a fraction of (40.6±2.9stat±4.9sys)%. Our results of the amplitude analysis are used to obtain a more precise measurement of the branching fraction of the 𝐷+𝑠→𝐾0𝑆𝐾−𝜋+𝜋+ decay, which is determined to be (1.46±0.05stat±0.05sys)%.
he Born cross sections for the process 𝑒+𝑒−→𝜂′𝜋+𝜋− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3𝜎 and a mass and width of 𝑀=(2111±43±25) MeV/𝑐2 and Γ=(135±34±30) MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in 𝑒+𝑒−→𝜂′𝜋+𝜋− and BESIII in 𝑒+𝑒−→𝜔𝜋0 within two standard deviations.