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We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative J/ψ decays, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a signal and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.7−48.5)×10−8 and (2.2−101.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative decays of the J/ψ, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a narrow resonance and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.6−49.8)×10−8 and (2.2−103.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
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.
We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative J/ψ decays, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a signal and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.7−48.5)×10−8 and (2.2−101.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
Based on (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII collider, a partial wave analysis of the decay J/ψ→ϕπ0η is performed. We observe for the first time two new structures on the ϕη invariant mass distribution, with statistical significances of 24.0σ and 16.9σ; the first with JPC = 1+−, mass M = (1911 ± 6 (stat.) ± 14 (sys.))~MeV/c2, and width Γ= (149 ± 12 (stat.) ± 23 (sys.))~MeV, the second with JPC = 1−−, mass M = (1996 ± 11 (stat.) ± 30 (sys.))~MeV/c2, and width Γ = (148 ± 16 (stat.) ± 66 (sys.))~MeV. These measurements provide important input for the strangeonium spectrum. In addition, the f0(980)−a0(980)0 mixing signal in J/ψ→ϕf0(980)→ϕa0(980)0 and the corresponding electromagnetic decay J/ψ→ϕa0(980)0 are measured with improved precision, providing crucial information to understand the nature of a0(980)0 and f0(980).
Based on (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII collider, a partial wave analysis of the decay J/ψ→ϕπ0η is performed. We observe for the first time two new structures on the ϕη invariant mass distribution, with statistical significances of 24.0σ and 16.9σ; the first with JPC = 1+−, mass M = (1911 ± 6 (stat.) ± 14 (sys.))~MeV/c2, and width Γ= (149 ± 12 (stat.) ± 23 (sys.))~MeV, the second with JPC = 1−−, mass M = (1996 ± 11 (stat.) ± 30 (sys.))~MeV/c2, and width Γ = (148 ± 16 (stat.) ± 66 (sys.))~MeV. These measurements provide important input for the strangeonium spectrum. In addition, the f0(980)−a0(980)0 mixing signal in J/ψ→ϕf0(980)→ϕa0(980)0 and the corresponding electromagnetic decay J/ψ→ϕa0(980)0 are measured with improved precision, providing crucial information to understand the nature of a0(980)0 and f0(980).
We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative J/ψ decays, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a signal and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.7−48.5)×10−8 and (2.2−101.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
Using e+e− collision data, corresponding to an integrated luminosity of 892pb−1 collected at center-of-mass energies from 4.84 to 4.95\,GeV with the BESIII detector, we search for the process e+e−→K+K−ψ(3770) by reconstructing two charged kaons and one D meson from ψ(3770). No significant signal of e+e−→K+K−ψ(3770) is found and the upper limits of the Born cross sections are reported at 90\% confidence level.
A search has been performed for the semileptonic decays D0→K0SK−e+νe, D+→K0SK0Se+νe and D+→K+K−e+νe, using 7.9 fb−1 of e+e− annihilation data collected at the center-of-mass energy s√=3.773 GeV by the BESIII detector operating at the BEPCII collider. No significant signals are observed, and upper limits are set at the 90\% confidence level of 2.13×10−5, 1.54×10−5 and 2.10×10−5 for the branching fractions of D0→K0SK−e+νe, D+→K0SK0Se+νe and D+→K+K−e+νe, respectively.
Using a sample of 448.1×106 ψ(2S) events collected with the BESIII detector, we perform a study of the decay J/ψ→K+K− via ψ(2S)→π+π−J/ψ.
The branching fraction of J/ψ→K+K− is determined to be BK+K−=(3.072±0.023(stat.)±0.050(syst.))×10−4, which is consistent with previous measurements but with significantly improved precision.
Using 2.93 fb−1 of 𝑒+𝑒− collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, the first observation of the doubly Cabibbo-suppressed decay 𝐷+→𝐾+𝜋+𝜋−𝜋0 is reported. After removing decays that contain narrow intermediate resonances, including 𝐷+→𝐾+𝜂, 𝐷+→𝐾+𝜔, and 𝐷+→𝐾+𝜙, the branching fraction of the decay 𝐷+→𝐾+𝜋+𝜋−𝜋0 is measured to be (1.13±0.08stat±0.03syst)×10−3. The ratio of branching fractions of 𝐷+→𝐾+𝜋+𝜋−𝜋0 over 𝐷+→𝐾−𝜋+𝜋+𝜋0 is found to be (1.81±0.15)%, which corresponds to (6.28±0.52)tan4𝜃𝐶, where 𝜃𝐶 is the Cabibbo mixing angle. This ratio is significantly larger than the corresponding ratios for other doubly Cabibbo-suppressed decays. The asymmetry of the branching fractions of charge-conjugated decays 𝐷±→𝐾±𝜋±𝜋∓𝜋0 is also determined, and no evidence for 𝐶𝑃 violation is found. In addition, the first evidence for the 𝐷+→𝐾+𝜔 decay, with a statistical significance of 3.3𝜎, is presented and the branching fraction is measured to be ℬ(𝐷+→𝐾+𝜔) = (5.7+2.5−2.1stat±0.2syst)×10−5.
Using a sample of 1.31×109 𝐽/𝜓 events collected with the BESIII detector, we perform a study of 𝐽/𝜓→𝛾𝜂𝜂𝜂′ to search for the 𝑋(2370) and 𝜂𝑐 in the 𝜂𝜂𝜂′ invariant mass distribution. No significant signal for the 𝑋(2370) is observed, and we set an upper limit for the product branching fraction of ℬ(𝐽/𝜓→𝛾𝑋(2370)·ℬ(𝑋(2370)→𝜂𝜂𝜂′)<9.2×10−6 at the 90% confidence level. A clear 𝜂𝑐 signal is observed for the first time, yielding a product branching fraction of ℬ(𝐽/𝜓→𝛾𝜂𝑐)·ℬ(𝜂𝑐→𝜂𝜂𝜂′)=(4.86±0.62(stat)±0.45(sys))×10−5.
Based on 586 pb−1 of e+e− annihilation data collected at a center-of-mass energy of s√=4.6 GeV with the BESIII detector at the BEPCII collider, the absolute branching fraction of Λ+c→pK0Sη decays is measured for the first time to be B(Λ+c→pK0Sη)=(0.414±0.084±0.028)%, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction B(Λ+c→pK0Sη)B(Λ+c→pK−π+), and consistent with theoretical predictions of SU(3) flavor symmetry.
The process 𝑒+𝑒−→𝜙𝜂′ has been studied for the first time in detail using data sample collected with the BESIII detector at the BEPCII collider at center of mass energies from 2.05 to 3.08 GeV. A resonance with quantum numbers 𝐽𝑃𝐶=1−− is observed with mass 𝑀=(2177.5±4.8(stat)±19.5(syst))MeV/𝑐2 and width Γ=(149.0±15.6(stat)±8.9(syst)) MeV with a statistical significance larger than 10𝜎, including systematic uncertainties. If the observed structure is identified with the 𝜙(2170), then the ratio of partial width between the 𝜙𝜂′ by BESIII and 𝜙𝜂 by BABAR is (ℬ𝑅𝜙𝜂Γ𝑅𝑒𝑒)/(ℬ𝑅𝜙𝜂′Γ𝑅𝑒𝑒)=0.23±0.10(stat)±0.18(syst), which is smaller than the prediction of the 𝑠¯𝑠𝑔 hybrid models by several orders of magnitude.
Using 2.93 fb−1 of 𝑒+𝑒− annihilation data collected at a center-of-mass energy √𝑠=3.773 GeV with the BESIII detector operating at the BEPCII collider, we search for the semileptonic 𝐷0(+) decays into a 𝑏1(1235)−(0) axial-vector meson for the first time. No significant signal is observed for either charge combination. The upper limits on the product branching fractions are ℬ𝐷0→𝑏1(1235)−𝑒+𝜈𝑒·ℬ𝑏1(1235) −→ 𝜔𝜋−<1.12×10−4 and ℬ𝐷+→𝑏1(1235)0𝑒+𝜈𝑒·ℬ𝑏1(1235)0→𝜔𝜋0<1.75×10−4 at the 90% confidence level.
The rare decay 𝜂′→𝜋+𝜋−𝑒+𝑒− is studied using a sample of 1.3×109 𝐽/𝜓 events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be (2.42±0.05stat±0.08syst)×10−3. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the 𝐶𝑃-violating asymmetry in the angle between the decay planes of the 𝜋+𝜋−-pair and the 𝑒+𝑒−-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is 𝒜𝐶𝑃=(2.9±3.7stat±1.1syst)%, which is consistent with the standard model expectation of no 𝐶𝑃-violation. The precision is comparable to the asymmetry measurement in the 𝐾0𝐿→𝜋+𝜋−𝑒+𝑒− decay where the observed (14±2)% effect is driven by a standard model mechanism.
Using 5.9 pb−1 of e+e− annihilation data collected at center-of-mass energies from 3.640 to 3.701 GeV with the BESIII detector at the BEPCII Collider, we measure the observed cross sections of e+e−→K0SX (where X=anything). From a fit to these observed cross sections with the sum of continuum and ψ(3686) and J/ψ Breit-Wigner functions and considering initial state radiation and the BEPCII beam energy spread, we obtain for the first time the inclusive decay branching fraction B(ψ(3686)→K0SX)=(16.04±0.29±0.90)%, where the first uncertainty is statistical and the second is systematic.
Measurement of cross sections for e⁺e⁻ → μ⁺μ⁻ at center-of-mass energies from 3.80 to 4.60 GeV
(2020)
The observed cross sections for 𝑒+𝑒−→𝜇+𝜇− at energies from 3.8 to 4.6 GeV are measured using data samples taken with the BESIII detector operated at the BEPCII collider. We measure the muonic widths and determine the branching fractions of the charmonium states 𝜓(4040), 𝜓(4160), and 𝜓(4415) decaying to 𝜇+𝜇−, as well as making a first determination of the phase of the amplitudes. In addition, we observe evidence for a structure in the dimuon cross section near 4.220 GeV/𝑐2, which we denote as 𝑆(4220). Analyzing a coherent sum of amplitudes yields eight solutions, one of which gives a mass of 𝑀𝑆(4220) = 4216.7±8.9±4.1 MeV/𝑐2, a total width of Γtot S(4220) = 47.2±22.8±10.5 MeV, and a muonic width of Γ𝜇𝜇 𝑆(4220) = 1.53±1.26±0.54 keV, where the first uncertainties are statistical and the second systematic. The eight solutions give the central values of the mass, total width, muonic width to be, respectively, in the range from 4212.8 to 4219.4 MeV/𝑐2, from 36.4 to 49.6 MeV, and from 1.09 to 1.53 keV. The statistical significance of the 𝑆(4220) signal is 3.9𝜎. Correcting the total dimuon cross section for radiative effects yields a statistical significance for this structure of 8.1𝜎.
We report an amplitude analysis and branching fraction measurement of 𝐷+
𝑠→𝐾+𝐾−𝜋+ decay using a data sample of 3.19 fb−1 recorded with BESIII detector at a center-of-mass energy of 4.178 GeV. We perform a model-independent partial wave analysis in the low 𝐾+𝐾− mass region to determine the 𝐾+𝐾− S-wave line shape, followed by an amplitude analysis of our very pure high-statistics sample. With the detection efficiency based on the amplitude analysis results, the absolute branching fraction is measured to be ℬ(𝐷+𝑠→𝐾+𝐾−𝜋+)=(5.47±0.08stat±0.13sys)%.
By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the 𝐷+→𝜂𝜇+𝜈𝜇 decay to be ℬ𝐷+→𝜂𝜇+𝜈𝜇=(10.4±1.0stat±0.5syst)×10−4. Using the world averaged value of ℬ𝐷+→𝜂𝑒+𝜈𝑒, the ratio of the two branching fractions is determined to be ℬ𝐷+→𝜂𝜇+𝜈𝜇/ℬ𝐷+→𝜂𝑒+𝜈𝑒=0.91±0.13(stat+syst), which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor 𝑓𝜂+(0) and the 𝑐→𝑑 Cabibbo-Kobayashi-Maskawa matrix element |𝑉𝑐𝑑| to be 𝑓𝜂+(0)|𝑉𝑐𝑑|=0.087±0.008stat±0.002syst. Taking the input of |𝑉𝑐𝑑| from the global fit in the standard model, we determine 𝑓𝜂+(0)=0.39±0.04stat±0.01syst. On the other hand, using the value of 𝑓𝜂+(0) calculated in theory, we find |𝑉𝑐𝑑| = 0.242±0.022stat±0.006syst±0.033theory.