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- Physik (335)
We present measurements of the Born cross sections for the processes e+e−→ωχc1 and ωχc2 at center-of-mass energies s√ from 4.308 to 4.951 GeV. The measurements are performed with data samples corresponding to an integrated luminosity of 11.0 fb−1 collected with the BESIII detector operating at the BEPCII storage ring. Assuming the e+e−→ωχc2 signals come from a single resonance, the mass and width are determined to be M=(4413.6±9.0±0.8) MeV/c2 and Γ=(110.5±15.0±2.9) MeV, respectively, which is consistent with the parameters of the well-established resonance ψ(4415). In addition, we also use one single resonance to describe the e+e−→ωχc1 lineshape, and determine the mass and width to be M=(4544.2±18.7±1.7) MeV/c2 and Γ=(116.1±33.5±1.7) MeV, respectively. The structure of this lineshape, observed for the first time, requires further understanding.
Based on 4.5 fb−1 of e+e− collision data accumulated at center-of-mass energies between 4.600GeV and 4.699GeV with the BESIII detector, we measure the absolute branching fraction of the Cabibbo-favored decay Λ+c→nK0Sπ+ with the precision improved by a factor of 2.8 and report the first evidence for the singly-Cabibbo-suppressed decay Λ+c→nK0SK+. The branching fractions for Λ+c→nK0Sπ+ and Λ+c→nK0SK+ are determined to be (1.86±0.08±0.04)×10−2 and (4.3+1.9−1.5±0.3)×10−4, respectively, where the first uncertainties are statistical and the second ones are systematic.
We present a study of the process e+e−→ηϕ using data samples collected with the BESIII detector corresponding to an integrated luminosity of 15.03 fb−1 at 23 center-of-mass energies from 3.773 to 4.600 GeV. The Born cross sections are measured at each energy and a coherent fit to cross-section lineshape is performed using a Breit-Wigner parametrization to search for charmonium-like vector states. No significant signals of the Y(4230) and Y(4360) resonances are observed.
We perform a study of the X(3872) lineshape using the data samples of e+e−→γX(3872), X(3872)→D0D¯0π0 and π+π−J/ψ collected with the BESIII detector. The effects of the coupled-channels and the off-shell D∗0 are included in the parameterization of the lineshape. The lineshape mass parameter is obtained to be MX=(3871.63±0.13+0.06−0.05) MeV. Two poles are found on the first and second Riemann sheets corresponding to the D∗0D¯0 branch cut. The pole location on the first sheet is much closer to the D∗0D¯0 threshold than the other, and is determined to be 7.04±0.15+0.07−0.08 MeV above the D0D¯0π0 threshold with an imaginary part −0.19±0.08+0.14−0.19 MeV.
The Born cross sections and effective form factors of the process 𝑒+𝑒−→Λ¯Σ0+c.c. are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of (478.5±4.8) pb−1 collected with the BESIII detector. A nonzero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BABAR Collaboration. The Born cross-section line shape is described better by a shape considering the strong-interaction effects than by a pQCD motivated functional form.
Based on (2712.4±14.3)×106 events recorded at the 𝜓(3686) nominal mass collected with the BESIII detector operating at the BEPCII collider, the 𝜓(3686)→Σ+¯Σ−𝜔 and Σ+¯Σ−𝜙 decays are observed for the first time with statistical significances of 13.8𝜎 and 7.6𝜎, respectively. The corresponding branching fractions are measured to be ℬ(𝜓(3686)→Σ+¯Σ−𝜔)=(1.89±0.18±0.21)×10−5 and ℬ(𝜓(3686)→Σ+¯Σ−𝜙)=(2.96±0.54±0.41)×10−6, where the first uncertainties are statistical and the second systematic.
Using a sample of (27.12±0.14)×108 ψ(3686) events collected with the BESIII detector, the decay ψ(3686)→ΛΛ¯η′ with η′ subsequently decaying into γπ+π− and ηπ+π− is observed for the first time. The branching fraction of ψ(3686)→ΛΛ¯η′ is measured to be (7.34±0.94(stat.)±0.43(sys.))×10−6. No resonant structures are evident in the Λη′, Λ¯η′ and ΛΛ¯ mass spectra.
This paper reports the study of D+s→τ+ν via τ+→π+ν¯τ using a boosted decision tree method, with 7.33 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.128 and 4.226~GeV. The branching fraction of D+s→τ+ντ is determined to be (5.44±0.17stat±0.13syst)%. The product of the D+s decay constant fD+s and the CKM matrix element |Vcs| is fD+s|Vcs| =(248.3±3.9stat±3.1syst±1.0input) MeV. Combining with the |Vcs| value obtained from the Standard Model global fit or the fD+s from the lattice quantum chromodynamics, we determine |Vcs| = 0.993±0.015stat±0.012syst±0.004input and fD+s =(255.0±4.0stat±3.2syst±1.0input) MeV. The first uncertainty is statistical, the second one is systematic and the third one is due to the input parameters, mainly the lifetime of D+s. All results obtained in this work supersede the BESIII previous results based on 6.32 fb−1 of e+e− collision data taken at center-of-mass energies between 4.178 and 4.226~GeV.
Precise measurement of the branching fractions of of J/ψ → Λ¯π⁺Σ⁻ + c.c. and J/ψ → Λ¯π⁻Σ⁺ + c.c.
(2023)
Based on a data sample of (10087±44)×106 J/ψ events collected with the BESIII detector, the branching fraction of J/ψ→Λ¯π+Σ−+c.c. is measured to be (1.221±0.002±0.038)×10−3, and the branching fraction of its isospin partner mode J/ψ→Λ¯π−Σ++c.c. is measured to be (1.244±0.002±0.045)×10−3 with improved precision. Here the first uncertainties are statistical and the second ones systematic. The isospin symmetry of the Σ baryon in charmonium hadronic decay and the "12% rule" are tested, and no violation is found. The potential of using these channels as Σ baryon sources for nuclear physics research is studied, and the momentum and angular distributions of these sources are provided.
Using 15.6 fb−1 of e+e− collision data collected at twenty-four center-of-mass energies from 4.0 to 4.6 GeV with the BESIII detector, the helicity amplitudes of the process e+e− → π+π−ω are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5σ are presented, such as f0(500), f0(980), f2(1270), f0(1370), b1(1235)±, and ρ(1450)±. In addition, evidence of a resonance state in e+e− → π+π−ω production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/c2, which is consistent with the production of ψ(4160) or Y(4220).
The decay 𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂 is searched for through the radiative transition 𝜓(3686)→𝛾𝜂𝑐(2𝑆) using 448 million 𝜓(3686) events accumulated at the BESIII detector. The first evidence of 𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂 is found with a statistical significance of 3.5𝜎. The product of the branching fractions of 𝜓(3686)→𝛾𝜂𝑐(2𝑆) and 𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂 is measured to be Br(𝜓(3686)→𝛾𝜂𝑐(2𝑆))×Br(𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂)=(2.97±0.81±0.26)×10−6, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay 𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂 is determined to be Br(𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂)=(42.4±11.6±3.8±30.3)×10−4, where the third uncertainty is transferred from the uncertainty of the branching fraction of 𝜓(3686)→𝛾𝜂𝑐(2𝑆).
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.
Using electron-positron annihilation data samples corresponding to an integrated luminosity of 4.5 fb−1, collected by the BESIII detector in the energy region between 4600 MeV and 4699 MeV, we report the first observations of the Cabibbo-suppressed decays Λ+c→nπ+π0, Λ+c→nπ+π−π+, and the Cabibbo-favored decay Λ+c→nK−π+π+ with statistical significances of 7.9σ, 7.8σ, and >10σ, respectively. The branching fractions of these decays are measured to be B(Λ+c→nπ+π0)=(0.64±0.09±0.02)%, B(Λ+c→nπ+π−π+)=(0.45±0.07±0.03)%, and B(Λ+c→nK−π+π+)=(1.90±0.08±0.09)%, where the first uncertainties are statistical and the second are systematic. We find that the branching fraction of the decay Λ+c→nπ+π0 is about one order of magnitude higher than that of Λ+c→nπ+.
A precision measurement of the matrix elements for η→π+π−π0 and η→π0π0π0 decays is performed using a sample of (10087±44)×106 J/ψ decays collected with the BESIII detector. The decay J/ψ→γη is used to select clean samples of 631,686 η→π+π−π0 decays and 272,322 η→π0π0π0 decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The non-zero gX2Y term for the decay mode η→π+π−π0 is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the η→π+π−π0 decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the η→π0π0π0 decay, and no obvious structure around the π+π− mass threshold is observed.
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.
The singly Cabibbo-suppressed decay Λ+𝑐→Σ−𝐾+𝜋+ is observed for the first time with a statistical significance of 5.4𝜎 by 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. The absolute branching fraction of Λ+𝑐→Σ−𝐾+𝜋+ is measured to be (3.8±1.2stat±0.2syst)×10−4 in a model-independent approach. This is the first observation of a Cabibbo-suppressed Λ+𝑐 decay involving Σ− in the final state. The ratio of branching fractions between Λ+𝑐→Σ−𝐾+𝜋+ and the Cabibbo-favored decay Λ+𝑐→Σ−𝜋+𝜋+ is observed to be (0.4±0.1)𝑠2𝑐, where 𝑠𝑐≡sin𝜃𝑐=0.2248 with 𝜃𝑐 the Cabibbo mixing angle.
We study the process e+e−→Λ+cΛ¯−c at twelve center-of-mass energies from 4.6119 to 4.9509 GeV using data samples collected by the BESIII detector at the BEPCII collider. The Born cross sections and effective form factors (|Geff|) are determined with unprecedented precision after combining the single and double-tag methods based on the decay process Λ+c→pK−π+. Flat cross sections around 4.63 GeV are obtained and no indication of the resonant structure Y(4630), as reported by Belle, is found. In addition, no oscillatory behavior is discerned in the |Geff| energy-dependence of Λ+c, in contrast to what is seen for the proton and neutron cases. Analyzing the cross section together with the polar-angle distribution of the Λ+c baryon at each energy point, the moduli of electric and magnetic form factors (|GE| and |GM|) are extracted and separated. For the first time, the energy-dependence of the form factor ratio |GE/GM| is observed, which can be well described by an oscillatory function.
Production of the doubly charged Δ baryon in e⁺e⁻ annihilation at energies from 2.3094 to 2.6464 GeV
(2023)
The processes e+e−→Δ++Δ¯−− and e+e−→Δ++p¯π−+c.c. are studied for the first time with 179 pb−1 of e+e− annihilation data collected with the BESIII detector at center-of-mass energies from 2.3094 GeV to 2.6464 GeV. No significant signal for the e+e−→Δ++Δ¯−− process is observed and the upper limit of the Born cross section is estimated at each energy point. For the process e+e−→Δ++p¯π−+c.c., a significant signal is observed at center-of-mass energies near 2.6454 GeV and the corresponding Born cross section is reported.
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.
Based on a data set of (27.12±0.10)×108 ψ(3686) events collected at the BESIII experiment, the absolute branching fractions of the three dominant Ω− decays are measured to be BΩ−→Ξ0π−=(25.03±0.44±0.53)%, BΩ−→Ξ−π0=(8.43±0.52±0.28)%, and BΩ−→ΛK−=(66.3±0.8±2.0)%, where the first and second uncertainties are statistical and systematic, respectively. The ratio between BΩ−→Ξ0π− and BΩ−→Ξ−π0 is determined to be 2.97±0.19±0.11, which is in good agreement with the PDG value of 2.74±0.15, but greater by more than four standard deviations than the theoretical prediction of 2 obtained from the ΔI=1/2 rule.