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A light scalar X0 or vector X1 particles have been introduced as a possible explanation for the (g−2)μ anomaly and dark matter phenomena.
Using (8.998±0.039)×109 $\jpsi$ events collected by the BESIII detector, we search for a light muon philic scalar X0 or vector X1 in the processes J/ψ→μ+μ−X0,1 with X0,1 invisible decays. No obvious signal is found, and the upper limits on the coupling g′0,1 between the muon and the X0,1 particles are set to be between 1.1×10−3 and 1.0×10−2 for the X0,1 mass in the range of 1<M(X0,1)<1000 MeV/c2 at 90% confidence level.
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.
Using e+e− collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of e+e−→Λ+cΛ¯c(2595)−+c.c. and e+e−→Λ+cΛ¯c(2625)−+c.c. are measured for the first time at center-of-mass energies of s√=4918.0 and 4950.9 MeV. Non-zero cross sections are observed very close to the production threshold. The measured Born cross sections of e+e−→Λ+cΛ¯c(2625)−+c.c. are about 2∼3 times greater than those of e+e−→Λ+cΛ¯c(2595)−+c.c., thereby indicating that the exotic structure potentially exists in the excited charmed baryons. The Born cross sections are 15.6±3.1±0.9 pb and 29.4±3.7±2.7 pb for e+e−→Λ+cΛ¯c(2595)−+c.c., and are 43.4±4.0±4.1 pb and 76.8±6.5±4.2 pb for e+e−→Λ+cΛ¯c(2625)−+c.c. at s√=4918.0 and 4950.9 MeV, respectively. Based on the polar angle distributions of the Λ¯c(2625)− and Λc(2625)+, the form-factor ratios |GE|2+3|GM|2−−−−−−−−−−−−√/|GC| are determined for e+e−→Λ+cΛ¯c(2625)−+c.c. for the first time, which are 5.95±4.07±0.15 and 0.94±0.32±0.02 at s√=4918.0 and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic.
A massless particle beyond the Standard Model is searched for in the two-body decay Σ+→p+invisible using (1.0087±0.0044)×1010 J/ψ events collected at a center-of-mass energy of s√=3.097 GeV with the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction B(Σ+→p+invisible) is determined to be 3.2×10−5 at the 90% confidence level. This is the first search for a flavor-changing neutral current process with missing energy in hyperon decays which plays an important role in constraining new physics models.
A massless particle beyond the Standard Model is searched for in the two-body decay Σ+→p+invisible using (1.0087±0.0044)×1010 J/ψ events collected with the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction B(Σ+→p+invisible) is determined to be 3.2×10−5 at the 90% confidence level. This is the first search for a flavor-changing neutral current process with missing energy in hyperon decays which plays an important role in constraining new physics models.
With a data sample corresponding to an integrated luminosity of 11.5~fb−1 collected with the BESIII detector operating at the BEPCII storage ring, for the first time the light hadron decay χc1(3872)→π+π−η is searched for. While no significant signal is observed, the upper limits at the 90\% confidence level for σ[e+e−→γχc1(3872)]B[χc1(3872)→π+π−η] at center-of-mass energies from 4.13 to 4.34 GeV are determined. By normalizing to the χc1(3872)→π+π−J/ψ decay channel, a 90\% confidence level upper limit for the branching fraction ratio R=B[χc1(3872)→π+π−η]/B[χc1(3872)→π+π−J/ψ]<0.12 is given. These measurements provide important inputs for understanding the internal structure of the χc1(3872) resonance.
A massless particle beyond the Standard Model is searched for in the two-body decay Σ+→p+invisible using (1.0087±0.0044)×1010 J/ψ events collected at a center-of-mass energy of s√=3.097 GeV with the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction B(Σ+→p+invisible) is determined to be 3.2×10−5 at the 90% confidence level. This is the first search for a flavor-changing neutral current process with missing energy in hyperon decays which plays an important role in constraining new physics models.
We present cross sections for the reaction e+e−→K0SK0L at center-of-mass energies ranging from 3.51 GeV to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb−1. The ratio of neutral-to-charged kaon form factors at large momentum transfers (12 GeV2<Q2<25 GeV2) is determined to be 0.21±0.01, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and consequently excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction |F(π±)|/|F(K±)|=f2π/f2K, where F(π±) and F(K±) are the form factors, and fπ and fK are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay ψ(3770)→K0SK0L for the first time. Within a 1σ contour of the likelihood value, the the branching fraction for ψ(3770)→K0SK0L is determined to be B=(2.63+1.40−1.59)×10−5, and the relative phase between the continuum and ψ(3770) amplitudes is ϕ=(−0.39+0.05−0.10)π. The branching fraction is in good agreement with the S- and D-wave charmonia mixing scheme proposed in the interpretation of the "ρπ puzzle" between J/ψ and ψ(3686) decays.
We present cross sections for the reaction e+e−→K0SK0L at center-of-mass energies ranging from 3.51 GeV to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb−1. The ratio of neutral-to-charged kaon form factors at large momentum transfers (12 GeV2<Q2<25 GeV2) is determined to be 0.21±0.01, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and consequently excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction |F(π±)|/|F(K±)|=f2π/f2K, where F(π±) and F(K±) are the form factors, and fπ and fK are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay ψ(3770)→K0SK0L for the first time. Within a 1σ contour of the likelihood value, the the branching fraction for ψ(3770)→K0SK0L is determined to be B=(2.63+1.40−1.59)×10−5, and the relative phase between the continuum and ψ(3770) amplitudes is ϕ=(−0.39+0.05−0.10)π. The branching fraction is in good agreement with the S- and D-wave charmonia mixing scheme proposed in the interpretation of the "ρπ puzzle" between J/ψ and ψ(3686) decays.
Using 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 at the BEPCII collider, we search for a scalar partner of the X(3872), denoted as X(3700), via ψ(3770)→γηη′ and γπ+π−J/ψ processes. No significant signals are observed and the upper limits of the product branching fractions B(ψ(3770)→γX(3700))⋅B(X(3700)→ηη′) and B(ψ(3770)→γX(3700))⋅B(X(3700)→π+π−J/ψ) are determined at the 90\% confidence level, for the narrow X(3700) with a mass ranging from 3710 to 3740 MeV/c2, which are from 0.8 to 1.8 (×10−5) and 0.9 to 3.4 (×10−5), respectively.
Using 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 at the BEPCII collider, we search for a scalar partner of the X(3872), denoted as X(3700), via ψ(3770)→γηη′ and γπ+π−J/ψ processes. No significant signals are observed and the upper limits of the product branching fractions B(ψ(3770)→γX(3700))⋅B(X(3700)→ηη′) and B(ψ(3770)→γX(3700))⋅B(X(3700)→π+π−J/ψ) are determined at the 90\% confidence level, for the narrow X(3700) with a mass ranging from 3710 to 3740 MeV/c2, which are from 0.8 to 1.8 (×10−5) and 0.9 to 3.4 (×10−5), respectively.
Using 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 at the BEPCII collider, we search for a scalar partner of the X(3872), denoted as X(3700), via ψ(3770)→γηη′ and γπ+π−J/ψ processes. No significant signals are observed and the upper limits of the product branching fractions B(ψ(3770)→γX(3700))⋅B(X(3700)→ηη′) and B(ψ(3770)→γX(3700))⋅B(X(3700)→π+π−J/ψ) are determined at the 90\% confidence level, for the narrow X(3700) with a mass ranging from 3710 to 3740 MeV/c2, which are from 0.8 to 1.8 (×10−5) and 0.9 to 3.4 (×10−5), respectively.
The cross sections of the e+e−→ϕη′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn, and decrease as the center-of-mass energy increases as s−n/2 with n=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of n=3.5±0.9. In addition, the charmless decay ψ(3770)→ϕη′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of B(ψ(3770)→ϕη′) at the 90\% confidence level is determined to be 2.3×10−5.
The cross sections of the 𝑒+𝑒−→𝜙𝜂′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn and decrease as the center-of-mass energy increases as 𝑠−𝑛/2 with 𝑛=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of 𝑛=3.5±0.9. In addition, the charmless decay 𝜓(3770)→𝜙𝜂′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of ℬ(𝜓(3770)→𝜙𝜂′) at the 90% confidence level is determined to be 2.3×10−5.
The cross sections of the e+e−→ϕη′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn, and decrease as the center-of-mass energy increases as s−n/2 with n=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of n=3.5±0.9. In addition, the charmless decay ψ(3770)→ϕη′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of B(ψ(3770)→ϕη′) at the 90\% confidence level is determined to be 2.3×10−5.
Determination of U-spin breaking parameters with an amplitude analysis of the decay D⁰ → K⁰Lπ⁺π⁻
(2022)
We present a study of the resonant structure of the decay D0→K0Lπ+π−, using quantum-correlated D0D¯0 data produced at s√=3.773 GeV. The data sample was collected by the BESIII experiment and corresponds to an integrated luminosity of 2.93 fb−1. This study is the first amplitude analysis of a decay mode involving a K0L, which also results in the first measurement of the complex U-spin breaking parameters (ρ^) related to various CP-eigenstate resonant modes through which the three-body decay proceeds. The moduli of the ρ^ parameters have central values in a wide range from 0.4 to 12.1, which indicates substantial U-spin symmetry breaking. We present the fractional resonant contributions and average strong-phase parameters over regions of phase space for both K0Sπ+π− and K0Lπ+π− modes. We also report the ratio of the branching fractions between K0Lπ+π− and K0Sπ+π− decay modes and the CP-even fraction of the K0Lπ+π− state calculated using the U-spin breaking parameters.
Using e+e− collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of e+e−→Λ+cΛ¯c(2595)−+c.c. and e+e−→Λ+cΛ¯c(2625)−+c.c. are measured for the first time at center-of-mass energies of s√=4918.0 and 4950.9 MeV. Non-zero cross sections are observed very close to the production threshold. The measured Born cross sections of e+e−→Λ+cΛ¯c(2625)−+c.c. are about 2∼3 times greater than those of e+e−→Λ+cΛ¯c(2595)−+c.c., thereby indicating that the exotic structure potentially exists in the excited charmed baryons. The Born cross sections are 15.6±3.1±0.9 pb and 29.4±3.7±2.7 pb for e+e−→Λ+cΛ¯c(2595)−+c.c., and are 43.4±4.0±4.1 pb and 76.8±6.5±4.2 pb for e+e−→Λ+cΛ¯c(2625)−+c.c. at s√=4918.0 and 4950.9 MeV, respectively. Based on the polar angle distributions of the Λ¯c(2625)− and Λc(2625)+, the form-factor ratios |GE|2+3|GM|2−−−−−−−−−−−−√/|GC| are determined for e+e−→Λ+cΛ¯c(2625)−+c.c. for the first time, which are 5.95±4.07±0.15 and 0.94±0.32±0.02 at s√=4918.0 and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic.
Using (2712.4±14.3)×106 ψ(3686) events collected with the BESIII detector operating at the BEPCII collider, we search for the hadronic transition hc→π+π−J/ψ via ψ(3686)→π0hc. No significant signal is observed. We set the most stringent upper limits to date on the branching fractions B(ψ(3686)→π0hc)×B(hc→π+π−J/ψ) and B(hc→π+π−J/ψ) at the 90% confidence level, which are determined to be 6.7×10−7 and 9.4×10−4, respectively.
Model-independent determination of the strong-phase difference between D⁰ and D̄⁰ → π⁺π⁻π⁺π⁻ decays
(2024)
Measurements of the strong-phase difference between D0 and D¯0→π+π−π+π− are performed in bins of phase space. The study exploits a sample of quantum-correlated DD¯ mesons collected by the BESIII experiment in e+e− collisions at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 2.93~fb−1. Here, D denotes a neutral charm meson in a superposition of flavor eigenstates. The reported results are valuable for measurements of the CP-violating phase γ (also denoted ϕ3) in B±→DK±, D→π+π−π+π− decays, and the binning schemes are designed to provide good statistical sensitivity to this parameter. The expected uncertainty on γ arising from the precision of the strong-phase measurements, when applied to very large samples of B-meson decays, is around 1.5∘ or 2∘, depending on the binning scheme. The binned strong-phase parameters are combined to give a value of F4π+=0.746±0.010±0.004 for the CP-even fraction of D0→π+π−π+π− decays, which is around 30\% more precise than the previous best measurement of this quantity.
In this Letter, a systematic study of the weak radiative hyperon decay Ξ0→Λγ at an electron-positron collider using entangled Ξ0Ξ¯0 pair events is presented. The absolute branching fraction for this decay has been measured for the first time, and is (1.347±0.066stat.±0.054syst.)×10−3. The decay asymmetry parameter, which characterizes the effect of parity violation in the decay, is determined to be −0.741±0.062stat.±0.019syst.. The obtained results are consistent with the world average values within the uncertainties, offering valuable insights into the underlying mechanism governing the weak radiative hyperon decays. The charge conjugation parity (CP) symmetries of branching fraction and decay asymmetry parameter in the decay are also studied. No statistically significant violation of charge conjugation parity symmetry is observed.