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A measurement of the CP-even fraction of the decay D0→π+π−π+π− is performed with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93 fb−1. Using a combination of CP eigenstates, D→π+π−π0 and D→K0S,Lπ+π− as tagging modes, the CP-even fraction is measured to be F4π+=0.735±0.015±0.005, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the CKM angle γ with B±→DK± decays, and for time-dependent studies of CP violation and mixing in the D0-D¯0 system.
Using a data set corresponding to an integrated luminosity of 6.32 fb−1 recorded by the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, an amplitude analysis of the decay D+s → π+π0π0 is performed, and the relative fractions and phases of different intermediate processes are determined. The absolute branching fraction of the decay D+s → π+π0π0 is measured to be (0.50 ± 0.04stat ± 0.02syst)%. Theabsolute branching fraction of the intermediate process D+s → f0(980)π+, f0(980) → π0π0 is determined to be (0.28 ± 0.04stat ± 0.04syst)%.
Using 4.5fb−1 of e+e− annihilation data samples collected at center-of-mass energies ranging from 4.600 to 4.698 GeV with the BESIII detector at the BEPCII collider, we measured the absolute branching fraction for the inclusive semileptonic decay Λ+c→Xe+νe, where X refers to any possible particle system. The branching fraction of the decay is determined to be B(Λ+c→Xe+νe)=(4.06±0.10stat.±0.09syst.)%. Our result improves the precision of previous measurement of B(Λ+c→Xe+νe) by more than threefold. Using the known Λ+c lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons, we measure the ratio of inclusive semileptonic decay widths Γ(Λ+c→Xe+νe)/Γ¯(D→Xe+νe)=1.28±0.05, where statistical and systematic uncertainties are combined.
Observation of resonance structures in e⁺e⁻ → π⁺π⁻ψ₂(3823) and mass measurement of ψ₂(3823)
(2022)
Using a data sample corresponding to an integrated luminosity of 11.3 fb−1 collected at center-of-mass energies from 4.23 to 4.70 GeV with the BESIII detector, we measure the product of the 𝑒+𝑒−→𝜋+𝜋−𝜓2(3823) cross section and the branching fraction ℬ[𝜓2(3823)→𝛾𝜒𝑐1]. For the first time, resonance structure is observed in the cross section line shape of 𝑒+𝑒−→𝜋+𝜋−𝜓2(3823) with significances exceeding 5𝜎. A fit to data with two coherent Breit-Wigner resonances modeling the √𝑠-dependent cross section yields 𝑀(𝑅1)=4406.9±17.2±4.5 MeV/𝑐2, Γ(𝑅1)=128.1±37.2±2.3 MeV, and 𝑀(𝑅2)=4647.9±8.6±0.8 MeV/𝑐2, Γ(𝑅2)=33.1±18.6±4.1 MeV. Though weakly disfavored by the data, a single resonance with 𝑀(𝑅)=4417.5±26.2±3.5 MeV/𝑐2, Γ(𝑅)=245±48±13 MeV is also possible to interpret data. This observation deepens our understanding of the nature of the vector charmoniumlike states. The mass of the 𝜓2(3823) state is measured as (3823.12±0.43±0.13) MeV/𝑐2, which is the most precise measurement to date.
The integrated luminosities of data samples collected in the BESIII experiment in 2016–2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010–2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur.
The integrated luminosities of the data samples collected in the BESIII experiment in 2016--2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of the old data sets collected in 2010--2014 are updated by considering correction related to the detector performance, offsettting the effect of newly discovered readout errors in the electromagnetic calorimeter that happen haphazardly.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, the cross section of the inclusive process e+e−→η+X, normalized by the total cross section of e+e−→hadrons, is measured at eight center-of-mass energy points from 2.0000 GeV to 3.6710 GeV. These are the first measurements with momentum dependence in this energy region. Our measurement shows a significant discrepancy from calculations with the existing fragmentation functions. To address this discrepancy, a new QCD analysis is performed at the next-to-next-to-leading order with hadron mass corrections and higher twist effects, which can explain both the established high-energy data and our measurements reasonably well.
Based on electron positron collision data collected with the BESIII detector operating at the BEPCII storage rings, the differential cross sections of inclusive π0 and K0S production as a function of hadron momentum, normalized by the total cross section of the e+e−→ hadrons process, are measured at six center-of-mass energies from 2.2324 to 3.6710 GeV. Our results with a relative hadron energy coverage from 0.1 to 0.9 significantly deviate from several theoretical calculations based on existing fragmentation functions, especially at lower energies.
Based on electron positron collision data collected with the BESIII detector operating at the BEPCII storage rings, the differential cross sections of inclusive π0 and K0S production as a function of hadron momentum, normalized by the total cross section of the e+e−→ hadrons process, are measured at six center-of-mass energies from 2.2324 to 3.6710 GeV. Our results with a relative hadron energy coverage from 0.1 to 0.9 significantly deviate from several theoretical calculations based on existing fragmentation functions, especially at lower energies.
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).
The decay $\eta_c(2S)\to\pipieta$ 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 $\eta_c(2S)\to\pipieta$ is measured to be $Br(\psi(3686)\to\gamma\eta_c(2S))\times Br(\eta_c(2S)\to\pipieta)=(2.97\pm0.81\pm0.26)\times10^{-6}$, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay $\eta_c(2S)\to\pipieta$ is determined to be $Br(\eta_c(2S)\to\pipieta)=(42.4\pm11.6\pm3.8\pm30.3)\times10^{-4}$, where the third uncertainty is transferred from the uncertainty of the branching fraction of ψ(3686)→γηc(2S).
The decay $\eta_c(2S)\to\pipieta$ 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 $\eta_c(2S)\to\pipieta$ is measured to be $Br(\psi(3686)\to\gamma\eta_c(2S))\times Br(\eta_c(2S)\to\pipieta)=(2.97\pm0.81\pm0.26)\times10^{-6}$, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay $\eta_c(2S)\to\pipieta$ is determined to be $Br(\eta_c(2S)\to\pipieta)=(42.4\pm11.6\pm3.8\pm30.3)\times10^{-4}$, 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 2.9σ, after considering systematic uncertainties, at a mass of (4123.5±0.7stat.±1.1syst.)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 section and the branching fraction of Z′−cs→D∗−sD∗0, σBorn⋅B at the three energy points, under different assumptions of the Z′−cs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV. Under various mass and width assumptions, the upper limits of σBorn⋅B are found to lie in the range of 2∼6, 3∼7 and 3∼6 pb at s√=4.661, 4.682 and 4.699 GeV, respectively. The larger data samples that will be collected in the coming years will allow a clearer picture to emerge concerning the existence and nature of the Z′−cs state.
We report a measurement of the cross section for the process e+e−→π+π−J/ψ around the X(3872) mass in search for the direct formation of e+e−→X(3872) through the two-photon fusion process. No enhancement of the cross section is observed at the X(3872) peak and an upper limit on the product of electronic width and branching fraction of X(3872)→π+π−J/ψ is determined to be Γee×B(X(3872)→π+π−J/ψ)<7.5×10−3eV at 90% confidence level under an assumption of total width of 1.19±0.21 MeV. This is an improvement of a factor of about 17 compared to the previous limit. Furthermore, using the latest result of B(X(3872)→π+π−J/ψ), an upper limit on the electronic width Γee of X(3872) is obtained to be <0.32eV at the 90% confidence level.
Based on a sample of (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/ψ→γηη′ is performed. An isoscalar state with exotic quantum numbers JPC=1−+, denoted as η1(1855), has been observed for the first time with statistical significance larger than 19σ. Its mass and width are measured to be (1855±9+6−1)~MeV/c2 and (188±18+3−8)~MeV, respectively. The product branching fraction B(J/ψ→γη1(1855)→γηη′) is measured to be (2.70±0.41+0.16−0.35)×10−6. The first uncertainties are statistical and the second are systematic. In addition, an upper limit on the branching ratio B(f0(1710)→ηη′)/B(f0(1710)→ππ) is determined to be 1.61×10−3 at 90\% confidence level, which lends support to the hypothesis that the f0(1710) has a large glueball component.
Study of ψ(3686) → ΛΛ¯ω
(2022)
Based on a data sample of (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the branching fraction of ψ(3686)→ΛΛ¯ω is measured to be (3.30±0.34(stat.)±0.29(syst.))×10−5 for the first time. In addition, the Λω (or Λ¯ω) invariant mass spectra is studied and the potential presence of excited Λ states has been investigated.
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.
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 data samples with an integrated luminosity of 19 fb−1 at twenty-eight center-of-mass energies from 3.872 GeV to 4.700 GeV collected with the BESIII detector at the BEPCII electron-positron collider, the process e+e− → ηπ+π− and the intermediate process e+e− → ηρ0 are studied for the first time. The Born cross sections are measured. No significant resonance structure is observed in the cross section lineshape.
Based on (10087±44)×106 J/ψ events collected with the BESIII detector, the process J/ψ→γπ+π−η′ is studied using two dominant decay channels of the η′ meson, η′→γπ+π− and η′→ηπ+π−,η→γγ. The X(2600) is observed with a statistical significance larger than 20σ in the π+π−η′ invariant mass spectrum, and it has a strong correlation to a structure around 1.5 GeV/{\it c}2 in the π+π− invariant mass spectrum. A simultaneous fit on the π+π−η′ and π+π− invariant mass spectra with the two η′ decay modes indicates that the mass and width of the X(2600) state are 2617.8±2.1+18.2−1.9 MeV/{\it c}2 and 200±8+20−17 MeV, respectively. The corresponding branching fractions are measured to be B(J/ψ→γX(2600))⋅B(X(2600)→f0(1500)η′)⋅B(f0(1500)→π+π−) = (3.39±0.18+0.91−0.66)×10−5 and B(J/ψ→γX(2600))⋅B(X(2600)→f′2(1525)η′)⋅B(f′2(1525)→π+π−) = (2.43±0.13+0.31−1.11)×10−5, where the first uncertainties are statistical, and the second systematic.