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We perform the first investigation of the process e+e−→K+K−ψ(2S) and report its Born cross sections over a range of center-of-mass energies from 4.699 to 4.951~GeV. The measurements are carried out using several partial reconstruction techniques using data samples collected by the BESIII detector with a total integrated luminosity of 2.5~fb−1. We search for new tetraquark candidates Z±cs in the decays Z±cs→K±ψ(2S). No significant Z±cs signals are observed.
Using (2712±14) × 106 ψ(2S) events collected with the BESIII detector at the BEPCII collider, we search for the decays ηc(2S)→ωω and ηc(2S)→ωϕ via the process ψ(2S)→γηc(2S). Evidence of ηc(2S)→ωω is found with a statistical significance of 3.2σ. The branching fraction is measured to be B(ηc(2S)→ωω)=(5.65±3.77(stat.)±5.32(syst.))×10−4. No statistically significant signal is observed for the decay ηc(2S)→ωϕ. The upper limit of the branching fraction at the 90\% confidence level is determined to be B(ψ(2S)→γηc(2S),ηc(2S)→ωϕ)<2.24×10−7. We also update the branching fractions of χcJ→ωω and χcJ→ωϕ decays via the ψ(2S)→γχcJ transition. The branching fractions are determined to be B(χc0→ωω)=(10.63±0.11±0.46)×10−4, B(χc1→ωω)=(6.39±0.07±0.29)×10−4, B(χc2→ωω)=(8.50±0.08±0.38)×10−4, B(χc0→ωϕ)=(1.18±0.03±0.05)×10−4, B(χc1→ωϕ)=(2.03±0.15±0.12)×10−5, and B(χc2→ωϕ)=(9.37±1.07±0.59)×10−6, where the first uncertainties are statistical and the second are systematic.
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.
The CP-even fractions (F+) of the decays D0→π+π−π0 and D0→K+K−π0 are measured with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment corresponding to an integrated luminosity of 7.93 fb−1. The results are Fπ+π−π0+=0.9406±0.0036±0.0021 and FK+K−π0+=0.631±0.014±0.011, where the first uncertainties are statistical and the second systematic. These measurements are consistent with the previous determinations, and the uncertainties for Fπ+π−π0+ and FK+K−π0+ are reduced by factors of 3.9 and 2.6, respectively. The reported results provide important inputs for the precise measurement of the angle γ of the Cabibbo-Kobayashi-Maskawa matrix and indirect CP violation in charm mixing.
In the effective field theory, the massless dark photon γ′ can only couple with the Standard Model particle through operators of dimension higher than four, thereby offering a high sensitivity to the new physics energy scale. Using 7.9 fb−1 of e+e− collision data collected at s√=3.773 GeV with the BESIII detector at the BEPCII collider, we measure the effective flavor-changing neutral current coupling of cuγ′ in D0→ωγ′ and D0→γγ′ processes to search for the massless dark photon. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be 1.1×10−5 and 2.0×10−6 for D0→ωγ′ and D0→γγ′, respectively. These results provide the most stringent constraint on the new physics energy scale associated with cuγ′ coupling in the world, with the new physics energy scale related parameter |C|2+|C5|2<8.2×10−17 GeV−2 at the 90% confidence level, playing a unique role in the dark sector search with the charm sector.
Using e+e− collision data samples with center-of-mass energies ranging from 2.000 to 2.644 GeV, collected by the BESIII detector at the BEPCII collider, and with a total integrated luminosity of 300 pb^{-1}, a partial-wave analysis is performed for the process e+e−→K+K−π0π0. The total Born cross sections for the process e+e−→K+K−π0π0, as well as the Born cross sections f or the subprocesses e+e−→ϕπ0π0, K+(1460)K−, K+1(1400)K−, K+1(1270)K− and K∗+(892)K∗−(892), are measured versus the center-of-mass energy. The corresponding results for e+e−→K+K−π0π0 and ϕπ0π0 are consistent with those of BaBar and have much improved this http URL analyzing the cross sections for the four subprocesses, K+(1460)K−, K+1(1400)K−, K+1(1270)K− and K∗+K∗−, a structure with mass M = (2126.5 ± 16.8 ± 12.4)~MeV/c^{2} and width Γ = (106.9 ± 32.1 ± 28.1)~MeV is observed with an overall statistical significance of 6.3 σ, although with very limited significance in the subprocesses e+e−→K+1(1270)K− and K∗+(892)K∗−(892). The resonant parameters of the observed structure suggest it can be identified with the ϕ(2170), thus the results provide valuable input to the internal nature of the ϕ(2170).
Using e+e− collision data samples with center-of-mass energies ranging from 2.000 to 2.644 GeV, collected by the BESIII detector at the BEPCII collider, and with a total integrated luminosity of 300 pb^{-1}, a partial-wave analysis is performed for the process e+e−→K+K−π0π0. The total Born cross sections for the process e+e−→K+K−π0π0, as well as the Born cross sections f or the subprocesses e+e−→ϕπ0π0, K+(1460)K−, K+1(1400)K−, K+1(1270)K− and K∗+(892)K∗−(892), are measured versus the center-of-mass energy. The corresponding results for e+e−→K+K−π0π0 and ϕπ0π0 are consistent with those of BaBar and have much improved this http URL analyzing the cross sections for the four subprocesses, K+(1460)K−, K+1(1400)K−, K+1(1270)K− and K∗+K∗−, a structure with mass M = (2126.5 ± 16.8 ± 12.4)~MeV/c^{2} and width Γ = (106.9 ± 32.1 ± 28.1)~MeV is observed with an overall statistical significance of 6.3 σ, although with very limited significance in the subprocesses e+e−→K+1(1270)K− and K∗+(892)K∗−(892). The resonant parameters of the observed structure suggest it can be identified with the ϕ(2170), thus the results provide valuable input to the internal nature of the ϕ(2170).
Using a data sample of (448.1±2.9)×106 ψ(3686) decays collected by the BESIII detector at the Beijing Electron Positron Collider (BEPCII), we observe the decays χcJ→ϕϕη (J=0, 1, 2), where the χcJ are produced via the radiative processes ψ(3686)→γχcJ. The branching fractions are measured to be B(χc0→ϕϕη)=(8.41±0.74±0.62)×10−4, B(χc1→ϕϕη)=(2.96±0.43±0.22)×10−4, and B(χc2→ϕϕη)=(5.33±0.52±0.39)×10−4, where the first uncertainties are statistical and the second are systematic. We also search for intermediate states in the ϕϕ or ηϕ combinations, but no significant structure is seen due to the limited statistics.
By analyzing (27.12±0.14)×108 ψ(3686) events accumulated with the BESIII detector, the decay ηc(2S)→K+K−η is observed for the first time with a significance of 6.2σ after considering systematic uncertainties. The product of the branching fractions of ψ(3686)→γηc(2S) and ηc(2S)→K+K−η is measured to be B(ψ(3686)→γηc(2S))×B(ηc(2S)→K+K−η)=(2.39±0.32±0.34)×10−6, where the first uncertainty is statistical, and the second one is systematic. The branching fraction of ηc(2S)→K+K−η is determined to be B(ηc(2S)→K+K−η)=(3.42±0.46±0.48±2.44)×10−3, where the third uncertainty is due to the branching fraction of ψ(3686)→γηc(2S). Using a recent BESIII measurement of B(ηc(2S)→K+K−π0), we also determine the ratio between the branching fractions of ηc(2S)→K+K−η and ηc(2S)→K+K−π0 to be 1.49±0.22±0.25, which is consistent with the previous result of BaBar at a comparable precision level.
The branching fraction of D+→K0Sπ0e+νe is measured for the first time using 7.93 fb−1 of e+e− annihilation data collected at the center-of-mass energy s√=3.773~GeV with the BESIII detector operating at the BEPCII collider, and is determined to be B(D+→K0Sπ0e+νe) = (0.881 ± 0.017stat. ± 0.016syst.)\%. Based on an analysis of the D+→K0Sπ0e+νe decay dynamics, we observe the S-wave and P-wave components with fractions of fS-wave = (6.13 ± 0.27stat. ± 0.30syst.)% and fK¯∗(892)0 = (93.88 ± 0.27stat. ± 0.29syst.)\%, respectively. From these results, we obtain the branching fractions B(D+→(K0Sπ0)S-wave e+νe) = (5.41 ± 0.35stat. ± 0.37syst.)×10−4 and B(D+→K¯∗(892)0e+νe) = (4.97 ± 0.11stat. ± 0.12syst.)\%. In addition, the hadronic form-factor ratios of D+→K¯∗(892)0e+νe at q2=0, assuming a single-pole dominance parameterization, are determined to be rV=V(0)A1(0)=1.43 ± 0.07stat. ± 0.03syst. and r2=A2(0)A1(0)=0.72 ± 0.06stat. ± 0.02syst.