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Using e+e− collision data collected with the BESIII detector at the BEPCII collider at center-of-mass energies between 3.510 and 4.914GeV, corresponding to an integrated luminosity of 25 fb−1, we measure the Born cross sections for the process e+e−→K−Ξ¯+Λ/Σ0 at thirty-five energy points with a partial-reconstruction strategy. By fitting the dressed cross sections of e+e−→K−Ξ¯+Λ/Σ0, evidence for ψ(4160)→K−Ξ¯+Λ is found for the first time with a significance of 4.4σ, including systematic uncertainties. No evidence for other possible resonances is found. In addition, the products of electronic partial width and branching fraction for all assumed resonances decaying into K−Ξ¯+Λ/Σ0 are determined.
Using (27.12±0.14)×108 ψ(3686) events collected with the BESIII detector, we present the first observation of the decays χcJ→ΛΛ¯ω, where J=0,1,2, with statistical significances of 11.7σ,11.2σ, and 11.8σ. The branching fractions of these decays are determined to be B(χc0→ΛΛ¯ω)=(2.37±0.22±0.23)×10−4, B(χc1→ΛΛ¯ω)=(1.01±0.10±0.11)×10−4, and B(χc2→ΛΛ¯ω)=(1.40±0.13±0.17)×10−4, where the first uncertainties are statistical and the second are systematic. We observe no clear intermediate structures.
Based on (2712.4±14.3)×106 ψ(3686) events, we investigate four hadronic decay modes of the P-wave charmonium spin-singlet state hc(1P1)→h+h−π0/η (h=π or K) via the process ψ(3686)→π0hc at BESIII. The hc→π+π−π0 decay is observed with a significance of 9.6σ after taking into account systematic uncertainties. Evidences for hc→K+K−π0 and hc→K+K−η are found with significances of 3.5σ and 3.3σ, respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be B(hc→π+π−π0)=(1.36±0.16±0.14)×10−3, B(hc→K+K−π0)=(3.26±0.84±0.36)×10−4, and B(hc→K+K−η)=(3.13±1.08±0.38)×10−4, where the first uncertainties are statistical and the second are systematic. No significant signal of hc→π+π−η is found, and the upper limit of its decay branching fraction is determined to be B(hc→π+π−η)<4.0×10−4 at 90% confidence level.
The processes hc→γP(P=η′, η, π0) are studied with a sample of (27.12±0.14)×108 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The decay hc→γη is observed for the first time with the significance of 9.0σ, and the branching fraction is determined to be (3.77±0.55±0.13±0.26)×10−4, while B(hc→γη′) is measured to be (1.40±0.11±0.04±0.10)×10−3, where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ(3686)→π0hc. The combination of these results allows for a precise determination of Rhc=B(hc→γη)B(hc→γη′), which is calculated to be (27.0±4.4±1.0)%. The results are valuable for gaining a deeper understanding of η−η′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay hc→γπ0, and an upper limit is placed on its branching fraction of B(hc→γπ0)<5.0×10−5, at the 90% confidence level.
Using e+e− annihilation data corresponding to an integrated luminosity of 6.32 fb−1 collected at center-of-mass energies between 4.178 GeV and 4.226 GeV with the BESIII detector, we perform the first amplitude analysis of the decay D+s→K0SK+π0 and determine the relative branching fractions and phases for intermediate processes. We observe the a0(1710)+, the isovector partner of the f0(1710) and f0(1770) mesons, in its decay to K0SK+ for the first time. In addition, we measure the ratio B(D+s→K¯∗(892)0K+)B(D+s→K¯0K∗(892)+) to be 2.35+0.42−0.23stat.±0.10syst.. Finally, we provide a precision measurement of the absolute branching fraction B(D+s→K0SK+π0)=(1.46±0.06stat.±0.05syst.)%.
The energy-dependent cross section for e+e−→ηψ(2S) is measured at eighteen center of mass energies from 4.288 GeV to 4.951 GeV using the BESIII detector. Using the same data samples, we also perform the first search for the reaction e+e−→ηX~(3872), but no evidence is found for the X~(3872) in the π+π−J/ψ mass distribution. At each of the eighteen center of mass energies, upper limits at the 90\% confidence level on the cross section for e+e−→ηψ(2S) and on the product of the e+e−→ηX~(3872) cross section with the branching fraction of X~(3872)→π+π−J/ψ are reported.
Using 9.0 fb−1 of e+e− collision data collected at center-of-mass energies from 4.178 to 4.278 GeV with the BESIII detector at the BEPCII collider, we perform the first search for the radiative transition χc1(3872)→γψ2(3823). No χc1(3872)→γψ2(3823) signal is observed. The upper limit on the ratio of branching fractions B(χc1(3872)→γψ2(3823), ψ2(3823)→γχc1)/B(χc1(3872)→π+π−J/ψ) is set as 0.075 at the 90\% confidence level. Our result contradicts theoretical predictions under the assumption that the χc1(3872) is the pure charmonium state χc1(2P).
The cross sections of e+e−→K+K−J/ψ at center-of-mass energies from 4.127 to 4.600~GeV are measured based on 15.6 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in the line shape of the cross sections. The mass and width of the first structure are measured to be (4225.3±2.3±21.5) MeV and (72.9±6.1±30.8)~MeV, respectively. They are consistent with those of the established Y(4230). The second structure is observed for the first time with a statistical significance greater than 8σ, denoted as Y(4500). Its mass and width are determined to be (4484.7±13.3±24.1) MeV and (111.1±30.1±15.2) MeV, respectively. The first presented uncertainties are statistical and the second ones are systematic. The product of the electronic partial width with the decay branching fraction Γ(Y(4230)→e+e−)B(Y(4230)→K+K−J/ψ) is reported.
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.
The processes hc→γP(P=η′, η, π0) are studied with a sample of (27.12±0.14)×108 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The decay hc→γη is observed for the first time with the significance of 9.0σ, and the branching fraction is determined to be (3.77±0.55±0.13±0.26)×10−4, while B(hc→γη′) is measured to be (1.40±0.11±0.04±0.10)×10−3, where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ(3686)→π0hc. The combination of these results allows for a precise determination of Rhc=B(hc→γη)B(hc→γη′), which is calculated to be (27.0±4.4±1.0)%. The results are valuable for gaining a deeper understanding of η−η′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay hc→γπ0, and an upper limit is placed on its branching fraction of B(hc→γπ0)<5.0×10−5, at the 90% confidence level.
An amplitude analysis of the 𝐾𝑆𝐾𝑆 system produced in radiative 𝐽/𝜓 decays is performed using the (1310.6±7.0)×106 𝐽/𝜓 decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parametrizing the 𝐾𝑆𝐾𝑆 invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the 𝐾𝑆𝐾𝑆 system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the 𝑓0(1710), 𝑓0(2200), and 𝑓′2(1525). The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative 𝐽/𝜓 decays to 𝐾𝑆𝐾𝑆 is measured to be (8.1±0.4)×10−4, where the uncertainty is systematic and the statistical uncertainty is negligible.
Based on an 𝑒+𝑒− collision data sample corresponding to an integrated luminosity of 567 pb−1 taken at the center-of-mass energy of √𝑠=4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive decay Λ+𝑐→Λ+𝑋 to be ℬ(Λ+𝑐→Λ+𝑋)=(38.2+2.8−2.2±0.9)% using the double-tag method, where 𝑋 refers to any possible final state particles. In addition, we search for direct 𝐶𝑃 violation in the charge asymmetry of this inclusive decay for the first time, and obtain 𝒜𝐶𝑃≡[ℬ(Λ+𝑐→Λ+𝑋)−ℬ(¯Λ−𝑐 → ¯Λ+𝑋)]/[ℬ(Λ+𝑐→Λ+𝑋)+ℬ(¯Λ−𝑐 → ¯Λ+𝑋)]=(2.1+7.0−6.6±1.6)%, a statistically limited result with no evidence of 𝐶𝑃 violation.
Based on a sample of 4.4 fb−1 of e+e− annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays Λ+c→Σ0K+ and Λ+c→Σ+K0S are studied. The ratio of the branching fraction B(Λ+c→Σ0K+) relative to B(Λ+c→Σ0π+) is measured to be 0.0361±0.0073(stat.)±0.0005(syst.), and the ratio of B(Λ+c→Σ+K0S) relative to B(Λ+c→Σ+π+π−) is measured to be 0.0106±0.0031(stat.)±0.0004(syst.). After taking the world-average branching fractions of the reference decay channels, the branching fractions B(Λ+c→Σ0K+) and B(Λ+c→Σ+K0S) are determined to be (4.7±0.9(stat.)±0.1(syst.)±0.3(ref.))×10−4 and (4.8±1.4(stat.)±0.2(syst.)±0.3(ref.))×10−4, respectively. The branching fraction of the Λ+c→Σ+K0S decay is measured for the first time.
Using data samples collected at center-of-mass energies between 2.000 and 3.080 GeV with the BESIII detector operating at the BEPCII collider, a partial-wave analysis is performed on the process e+e−→ηπ+π−. In addition to the dominant e+e−→ρη component, the e+e−→a2(1320)π process is also sizeable, contributing up to 24% of the total reaction. The measured cross sections of the process e+e−→ηπ+π− are systematically higher than those of BaBar by more than 3σ at center-of-mass energies between 2.000 and 2.300 GeV. In the cross section lineshape for e+e−→a2(1320)π, a resonant structure is observed with a significance of 5.5σ, with M=(2044±31±4) MeV/c2, Γ=(163±69±24) MeV and BR⋅ΓRe+e−=(34.6±17.1±6.0) eV or (137.1±73.3±2.1) eV. In the cross section lineshape for e+e−→ρη, an evidence of a dip structure around 2180 MeV/c2 is observed with statistical significance of 3.0σ.
First study of antihyperon-nucleon scattering Λ¯p → Λ¯p and measurement of Λp → Λp cross section
(2024)
Using (10.087±0.044)×109 J/ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λp→Λp and Λ¯p→Λ¯p are studied, where the Λ/Λ¯ baryons are produced in the process J/ψ→ΛΛ¯ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in −0.9≤cosθΛ/Λ¯≤0.9 are measured to be σ(Λp→Λp)=(12.2±1.6stat±1.1sys) mb and σ(Λ¯p→Λ¯p)=(17.5±2.1stat±1.6sys) mb at the Λ/Λ¯ momentum of 1.074 GeV/c within a range of ±0.017 GeV/c, where the θΛ/Λ¯ are the scattering angles of the Λ/Λ¯ in the Λp/Λ¯p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λp→Λp, and a strong forward peak for Λ¯p→Λ¯p. We present an approach to extract the total elastic cross sections by extrapolation. The study of Λ¯p→Λ¯p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.
We perform for the first time an amplitude analysis of the decay D+→K0Sπ+η and report the observation of the decay D+→K0Sa0(980)+ using 2.93 fb−1 of e+e− collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only W-annihilation free decay among D to a0(980)-pseudoscalar, D+→K0Sa0(980)+ is the ideal decay to extract the contributions of the external and internal W-emission amplitudes involving a0(980) and study the final-state interactions. The absolute branching fraction of D+→K0Sπ+η is measured to be (1.27±0.04stat.±0.03syst.)%. The product branching fractions of D+→K0Sa0(980)+ with a0(980)+→π+η and D+→π+K∗0(1430)0 with K∗0(1430)0→K0Sη are measured to be (1.33±0.05stat.±0.04syst.)% and (0.14±0.03stat.±0.01syst.)%, respectively.
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.
The absolute branching fraction of the decay Λc(2625)+→Λ+cπ+π− is measured for the first time to be (50.7±5.0stat.±4.9syst.)% with 368.48 pb−1 of e+e− collision data collected by the BESIII detector at the center-of-mass energies of s√=4.918 and 4.950 GeV. This result is lower than the naive prediction of 67\%, obtained from isospin symmetry, by more than 2σ, thereby indicating that the novel mechanism referred to as the \textit{threshold effect}, proposed for the strong decays of Λc(2595)+, also applies to Λc(2625)+. This measurement is necessary to obtain the coupling constants for the transitions between s-wave and p-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Λc(2595)+→Λ+cπ+π−. No significant signal is observed, and the upper limit on its branching fraction is determined to be 80.8\% at the 90\% confidence level.
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.
Based on (27.12±0.14)×108 𝜓(2𝑆) events collected by the BESIII detector, we search for the decay 𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂𝑐 via 𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆). No significant signal is observed, and the upper limit on the product branching fraction ℬ(𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆))×ℬ(𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂𝑐) is determined to be 2.21×10−5 at the 90% confidence level. In addition, the 𝜂𝑐(2𝑆)→𝜋+𝜋−𝐾0𝑆𝐾±𝜋∓ decay is studied via 𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆) and is observed with a statistical significance of 10𝜎 for the first time. The branching fraction of 𝜂𝑐(2𝑆)→𝜋+𝜋−𝐾0𝑆𝐾±𝜋∓ is determined to be (1.33±0.11±0.40±0.95)×10−2, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the quoted ℬ(𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆)).