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The Born cross sections for the process e+eββΟΞ·β² are measured at 22 center-of-mass energies from 2.000 to 3.080 GeV using data collected with the BESIII detector at the BEPCII collider. A resonant structure is observed with a statistical significance of 9.6Ο. A Breit-Wigner fit determines its mass to be MR=(2153Β±30Β±31) MeV/c2 and its width to be ΞR=(167Β±77Β±7) MeV, where the first uncertainties are statistical and the second are systematic.
Evidence for the singly Cabibbo suppressed decay Ξ+cβpΟ0 is reported for the first time with a statistical significance of 3.7Ο based on 6.0 fbβ1 of e+eβ collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Ξ+cβpΟ0 is measured to be (1.56+0.72β0.58Β±0.20)Γ10β4. Combining with the branching fraction of Ξ+cβnΟ+, (6.6Β±1.3)Γ10β4, the ratio of the branching fractions of Ξ+cβnΟ+ and Ξ+cβpΟ0 is calculated to be 3.2+2.2β1.2. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Ξ+cβpΞ· is measured to be (1.63Β±0.31statΒ±0.11syst)Γ10β3.
Evidence for the singly Cabibbo suppressed decay Ξ+cβpΟ0 is reported for the first time with a statistical significance of 3.7Ο based on 6.0 fbβ1 of e+eβ collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Ξ+cβpΟ0 is measured to be (1.56+0.72β0.58Β±0.20)Γ10β4. Combining with the branching fraction of Ξ+cβnΟ+, (6.6Β±1.2Β±0.4)Γ10β4, the ratio of the branching fractions Ξ+cβnΟ+ and Ξ+cβpΟ0 is calculated to be 4.2+2.2β1.9; this is an important input for the understanding of the decay mechanisms of charmed baryons. In addition, the absolute branching fraction of Ξ+cβpΞ· is measured to be (1.63Β±0.31statΒ±0.11syst)Γ10β3, which is consistent with previous measurements.
Using a sample of (10087Β±44)Γ106ββπ½/π events, which is about 45 times larger than that was previously analyzed, a further investigation on the π½/πβπΎβ’3β’(π+β’πβ) decay is performed. A significant distortion at 1.84ββGeV/π2 in the line shape of the 3β’(π+β’πβ) invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, πβ‘(1840) and πβ‘(1880). The new state πβ‘(1880) is observed with a statistical significance larger than 10β’π. The mass and width of πβ‘(1880) are determined to be 1882.1Β±1.7Β±0.7ββMeV/π2 and 30.7Β±5.5Β±2.4ββMeV, respectively, which indicates the existence of a πβ’Β― π bound state.
Amplitude analysis and branching fraction measurement of the decay DβΊ β Kββ°ΟβΊΟβ°Οβ°
(2023)
Using 2.93 fbβ1 of e+eβ collision data collected with the BESIII detector at the center-of-mass energy 3.773 GeV, we perform the first amplitude analysis of the decay D+ β Ο+Ο0Ο0 and determine the relative magnitudes and phases of different intermediate processes. The absolute branching fraction of D+ β Ο+Ο0Ο0 is measured to be (2.888 Β± 0.058stat. Β± 0.069syst.)%. The dominant intermediate processes are D+ β a1(1260)+(β Ο+Ο0) and D+ β *0Ο+, with branching fractions of (8.66 Β± 1.04stat. Β± 1.39syst.) Γ 10β3 and (9.70 Β± 0.81stat. Β± 0.53syst.) Γ 10β3, respectively.
Quantum-correlated π·β’Β―π· pairs collected by the BESIII experiment at the πβ‘(3770) resonance corresponding to an integrated luminosity of 2.93ββfbβ1 are used to study the π·0βπΎ0πβ’π+β’πββ’π0 decay mode. The πΆβ’π-even fraction of π·0βπΎ0πβ’π+β’πββ’π0 decays is determined to be 0.235Β±0.010Β±0.002, where the first uncertainty is statistical and the second is systematic.
The quantum entangled J/ΟβΞ£+Σ¯β pairs from (1.0087Β±0.0044)Γ1010 J/Ο events taken by the BESIII detector are used to study the non-leptonic two-body weak decays Ξ£+βnΟ+ and Σ¯ββnΒ―Οβ. The CP-odd weak decay parameters of the decays Ξ£+βnΟ+ (Ξ±+) and Σ¯ββnΒ―Οβ (Ξ±Β―β) are determined to be β0.0565Β±0.0047statΒ±0.0022syst and 0.0481Β±0.0031statΒ±0.0019syst, respectively. The decay parameter Ξ±Β―β is measured for the first time, and the accuracy of Ξ±+ is improved by a factor of four compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of ACP=(Ξ±++Ξ±Β―β)/(Ξ±+βΞ±Β―β) = β0.080Β±0.052statΒ±0.028syst. Assuming CP conservation, the average decay parameter is determined as β¨Ξ±+β©=(Ξ±+βΞ±Β―β)/2 = β0.0506Β±0.0026statΒ±0.0019syst, while the ratios Ξ±+/Ξ±0 and Ξ±Β―β/Ξ±Β―0 are β0.0490Β±0.0032statΒ±0.0021syst and β0.0571Β±0.0053statΒ±0.0032syst, where Ξ±0 and Ξ±Β―0 are the decay parameters of the decays Ξ£+βpΟ0 and Σ¯ββpΒ―Ο0, respectively.
The quantum entangled J=Ο β ΣþΣ¯ β pairs from Γ°1.0087 0.0044Γ Γ 1010 J=Ο events taken by the BESIII detector are used to study the nonleptonic two-body weak decays Σþ β nΟΓΎ and Σ¯ β β nΒ―Οβ. The CP-odd weak decay parameters of the decays Σþ β nΟΓΎ (Ξ±ΓΎ) and Σ¯ β β nΒ―Οβ (Ξ±Β―β) are determined to be 0.0481 0.0031stat 0.0019syst and β0.0565 0.0047stat 0.0022syst, respectively. The decay parameter Ξ±Β―β is measured for the first time, and the accuracy of Ξ±ΓΎ is improved by a factor of 4 compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of ACP ΒΌ ðαþ ΓΎ Ξ±Β―βΓ=ðαþ β Ξ±Β―βΓ ΒΌ β0.080 0.052stat 0.028syst. Assuming CP conservation, the average decay parameter is determined as hΞ±ΓΎi¼ðαþ β Ξ±Β―βΓ=2 ΒΌ β0.0506 0.0026stat 0.0019syst, while the ratios Ξ±ΓΎ=Ξ±0 and Ξ±Β―β=Ξ±Β― 0 are β0.0490 0.0032stat 0.0021syst and β0.0571 0.0053stat 0.0032syst, where Ξ±0 and Ξ±Β― 0 are the decay parameters of the decays Σþ β pΟ0 and Σ¯ β β pΒ― Ο0, respectively.
We report the measurement of the cross sections for e+eββhadrons at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe a new resonance R(3810) in the cross sections for the first time, and observe the R(3760) resonance with high significance in the cross sections. The R(3810) has a mass of (3804.5Β±0.9Β±0.9) ~MeV/c2, a total width of (5.4Β±3.5Β±3.2)~MeV, and an electronic partial width of (19.4Β±7.4Β±12.1)~eV. Its significance is 7.7Ο. The R(3810) could be interpreted as a hadro-charmonium resonance predicted by Quantum Chromodynamics (QCD). In addition, we measure the mass (3751.9Β±3.8Β±2.8) ~MeV/c2, the total width (32.8Β±5.8Β±8.7)~MeV, and the electronic partial width (184Β±75Β±86)~eV with improved precision for the R(3760). Furthermore, for the R(3780) we measure the mass (3778.7Β±0.5Β±0.3) ~MeV/c2 and total width (20.3Β±0.8Β±1.7)~MeV with improved precision, and the electronic partial width (265Β±69Β±83)~eV. The R(3780) can be interpreted as the 13D1 state of charmonium. Its mass and total width differ significantly from the corresponding fitted values given by the Particle Data Group in 2022 by 7.1 and 3.2 times the uncertainties for Ο(3770), respectively. Ο(3770) has been interpreted as the 13D1 state for 45 years.
Using 7.33 fbβ1 of e+eβ collision data collected by the BESIII detector at center-of-mass energies between 4.128 and 4.226~GeV, we observe for the first time the decay DΒ±sβΟΟΒ±Ξ· with a statistical significance of 7.6Ο. The measured branching fraction of this decay is (0.54Β±0.12Β±0.04)%, where the first uncertainty is statistical and the second is systematic.
Using 10.1 Γ 109 J/Ο events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy βs = 3.097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/Ο β Dβe+Ξ½e + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction β¬(J/ΟβββDβe+Ξ½eβ+βc. c.)β<β7.1βΓβ10β8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.
Based on an e+eβ collision data sample corresponding to an integrated luminosity of 2.93 fbβ1 collected with the BESIII detector at βs=3.773 GeV, the first amplitude analysis of the singly Cabibbo-suppressed decay D+βK+K0SΟ0 is performed. From the amplitude analysis, the Kβ(892)+K0S component is found to be dominant with a fraction of (57.1Β±2.6Β±4.2)%, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction B(D+βK+K0SΟ0) measured by BESIII, we obtain B(D+βKβ(892)+K0S)=(8.69Β±0.40Β±0.64Β±0.51)Γ10β3, where the third uncertainty is due to the branching fraction B(D+βK+K0SΟ0). The precision of this result is significantly improved compared to the previous measurement. This result also differs from most of theoretical predictions by about 4Ο, which may help to improve the understanding of the dynamics behind.
The process e+eββΟΞ· is studied at 22 center-of-mass energy points (βs) between 2.00 and 3.08 GeV using 715ββpbβ1 of data collected with the BESIII detector. The measured Born cross section of e+eββΟΞ· is found to be consistent with BABAR measurements, but with improved precision. A resonant structure around 2.175 GeV is observed with a significance of 6.9Ο with mass (2163.5Β±6.2Β±3.0)ββMeV/c2 and width (31.1+21.1β11.6Β±1.1)ββMeV, where the first uncertainties are statistical and the second are systematic.
Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matterβantimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry1. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryonβantibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξβ baryon and its antiparticle2 ΞΒ―+
, has enabled a direct determination of the weak-phase difference, (ΞΎPβββΞΎS)β= (1.2βΒ±β3.4βΒ±β0.8)βΓβ10β2βrad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods3. Finally, we provide an independent measurement of the recently debated Ξ decay parameter Ξ±Ξ (refs.β4,5). The ΞΞΒ―
asymmetry is in agreement with and compatible in precision to the most precise previous measurement.
Measurement of the branching fraction of leptonic decay D+s β Ο+Ξ½Ο via Ο+ β Ο+Ο0Β―Ξ½Ο
(2021)
By analyzing 6.32 fb β 1 of e+ eβ annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay D + s β Ο + Ξ½Ο, with Ο+ β Ο + Ο0Β―Ξ½Ο, to be B D + s β Ο + Ξ½ Ο = (5.29 Β± 0.25 stat Β± 0.20 syst) %. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element |Vcs|and the D + s decay constant f D + s to be f D + s|Vcs| = (244.8 Β± 5.8 stat Β± 4.8syst) MeV, using the known values of the Ο + and D + s masses as well as the D + s lifetime, together with our branching fraction measurement. Combining the value of |Vcs| obtained from a global fit in the standard model and f D + s from lattice quantum chromodynamics, we obtain f D + s = (251.6 Β± 5.9 stat Β± 4.9syst) MeV and |Vcs| = 0.980 Β± 0.023 stat Β± 0.019 syst. Using the branching fraction of B D + s β ΞΌ + Ξ½ΞΌ = (5.35Β±0.21)Γ10β3, we obtain the ratio of the branching fractions B D + s β Ο + Ξ½Ο/B D +s β ΞΌ+Ξ½ΞΌ = 9.89Β±0.71, which is consistent with the standard model prediction of lepton flavor universality.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process eΓΎeβ β Ο0XΓ°3872ΓΞ³ and search for ZcΓ°4020Γ0 β XΓ°3872ΓΞ³. We find no significant signal and set upper limits on ΟΓ°eΓΎeβ β Ο0XΓ°3872ΓΞ³Γ Β· BΓ°XΓ°3872Γ β ΟΓΎΟβJ=ΟΓ and ΟΓ°eΓΎeβ β Ο0ZcΓ°4020Γ0Γ Β· BΓ°ZcΓ°4020Γ0 β XΓ°3872ΓΞ³Γ Β· BΓ°XΓ°3872Γ β ΟΓΎΟβJ=ΟΓ for each energy point at 90% confidence level, which is of the order of several tenths pb.
We measure the inclusive semielectronic decay branching fraction of the D+s meson. A double-tag technique is applied to e+eβ annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range 4.178β4.230 GeV. We select positrons fromD+sβXe+Ξ½e with momenta greater than 200 MeV/c and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the D+s semielectronic branching fraction to be(6.30Β±0.13(stat.)Β±0.09(syst.)Β±0.04(ext.))%, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the D+s and D0 semielectronic widths, Ξ(D+sβXe+Ξ½e)Ξ(D0βXe+Ξ½e)=0.790Β±0.016(stat.)Β±0.011(syst.)Β±0.016(ext.). Our results are consistent with and more precise than previous measurements.
The electromagnetic process is studied with the initial-state-radiation technique using 7.5 fbβ1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/ using the invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
Using a sample of (10.09Β±0.04)Γ109 J/Ο events collected with the BESIII detector, a partial wave analysis of J/ΟβΞ³Ξ·β²Ξ·β² is performed.The masses and widths of the observed resonances and their branching fractions are reported. The main contribution is from J/ΟβΞ³f0(2020) with f0(2020)βΞ·β²Ξ·β², which is found with a significance of greater than 25Ο. The product branching fraction B(J/Ο β Ξ³f0(2020))β
B(f0(2020) β Ξ·β²Ξ·β² is measured to be (2.63Β±0.06(stat.) + 0.31β0.46(syst.))Γ10β4.
We present the first experimental search for the rare charm decay D0βΟ0Ξ½Β―Ξ½. It is based on an e+eβ collision sample consisting of 10.6Γ10^6 pairs of D0Β―D0 mesons collected by the BESIII detector at βs=3.773 GeV, corresponding to an integrated luminosity of 2.93 fb^β1. A data-driven method is used to ensure the reliability of the background modeling. No significant D0βΟ0Ξ½Β―Ξ½ signal is observed in data and an upper limit of the branching fraction is set to be 2.1Γ10^-4 at the 90% confidence level. This is the first experimental constraint on charmed-hadron decays into dineutrino final states.
The process π+β’πββπβ’πβ² 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 π½πβ’πΆ=1ββ is observed with mass π=(2177.5Β±4.8β’(stat)Β±19.5β’(syst))β’MeV/π2 and width Ξ=(149.0Β±15.6β’(stat)Β±8.9β’(syst))ββMeV with a statistical significance larger than 10β’π, including systematic uncertainties. If the observed structure is identified with the πβ‘(2170), then the ratio of partial width between the πβ’πβ² by BESIII and πβ’π by BABAR is (β¬π
πβ’πβ’Ξπ
πβ’π)/(β¬π
πβ’πβ²β’Ξπ
πβ’π)=0.23Β±0.10β’(stat)Β±0.18β’(syst), which is smaller than the prediction of the π β’Β―π β’π hybrid models by several orders of magnitude.
We report a measurement of the observed cross sections of e+ eβ β J/ΟX based on 3.21 fb β 1 of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. In analysis of the cross sections, we measured the decay branching fractions of B(Ο(3686) β J/ΟX) = (64.4 Β± 0.6 Β± 1.6)% and B(Ο(3770) β J/ΟX) = (0.5 Β± 0.2 Β± 0.1)% for the first time. The energy-dependent line shape of these cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays Ο (3686) β J/ΟX and Ο(3770) β J/ΟX. Instead, it can be better described with one more BW amplitude of the decay R(3760)β J/ΟX. Under this assumption, we extracted the R (3760) mass M R (3760 ) = 3766.2 Β± 3.8 Β± 0.4 MeV/c2, total width Ξ tot R ( 3760 ) = 22.2 Β± 5.9 Β± 1.4 MeV, and product of leptonic width and decay branching fraction
ΞeeR(3760) B[R(3760) β J/ΟX] = (79.4 Β± 85.5 Β± 11.7) eV. The significance of the R(3760) is 5.3Ο. The first uncertainties of these measured quantities are from fits to the cross sections and second systematic.
Using (1.0087Β±0.0044)Γ1010ββπ½/π events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays Ξ0βπΎββ’π+ with Ξβ’(π΅βπΏ)=0 and Ξ0βπΎ+β’πβ with |Ξβ’(π΅βπΏ)|=2, where π΅ (πΏ) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to β¬β‘(Ξ0βπΎββ’π+)<3.6Γ10β6 and β¬β‘(Ξ0βπΎ+β’πβ)<1.9Γ10β6 at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.
Precision measurements of DβΊβ β πeβΊβ’πβ and DβΊβ β πβ²β’eβΊβ’πβ
(2023)
Precision measurements of the semileptonic decays π·+π βπβ’π+β’ππ and π·+π βπβ²β’π+β’ππ are performed with 7.33ββfbβ1 of π+β’πβ collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector. The branching fractions obtained are β¬β‘(π·+π βπβ’π+β’ππ) = (2.255Β±0.03β’9statΒ±0.05β’1syst)% and β¬β‘(π·+π βπβ²β’π+β’ππ)=(0.810Β±0.03β’8statΒ±0.02β’4syst)%. Combining these results with the β¬β‘(π·+βπβ’π+β’ππ) and β¬β‘(π·+βπβ²β’π+β’ππ) obtained from previous BESIII measurements, the πβπβ² mixing angle in the quark flavor basis is determined to be πP=(40.0Β±2.0statΒ±0.6syst)Β°. Moreover, from the fits to the partial decay rates of π·+π βπβ’π+β’ππ and π·+π βπβ²β’π+β’ππ, the products of the hadronic transition form factors ππ(β²)+β‘(0) and the modulus of the πβπ Cabibbo-Kobayashi-Maskawa matrix element |ππβ’π | are determined by using different hadronic transition form factor parametrizations. Based on the two-parameter series expansion, the products ππ+β‘(0)β’|ππβ’π | = 0.4519Β±0.007β’1statΒ±0.006β’5syst and ππβ²+β‘(0)β’|ππβ’π | = 0.525Β±0.02β’4statΒ±0.00β’9syst are extracted. All results determined in this work supersede those measured in the previous BESIII analyses based on the 3.19ββfbβ1 subsample of data at 4.178 GeV.
Using Γ°1.0087 0.0044Γ Γ 1010 J=Ο events collected with the BESIII detector at the BEPCII storage ring, the process Ξ0n β Ξβp is studied, where the Ξ0 baryon is produced in the process J=Ο β Ξ0ΞΒ― 0 and the neutron is a component of the 9 Be, 12C, and 197Au nuclei in the beam pipe. A clear signal is observed with a statistical significance of 7.1Ο. The cross section of the reaction Ξ0 ΓΎ 9 Be β Ξβ ΓΎ p ΓΎ 8 Be is determined to be ΟΓ°Ξ0 ΓΎ 9 Be β Ξβ ΓΎ p ΓΎ 8 BeΓΒΌΓ°22.1 5.3stat 4.5sysΓ mb at the Ξ0 momentum of 0.818 GeV=c, where the first uncertainty is statistical and the second is systematic. No significant H-dibaryon signal is observed in the Ξβp final state. This is the first study of hyperon-nucleon interactions in electron-positron collisions and opens up a new direction for such research.
Measurement of branching fractions of _Ξ__(c)βΊ decays to Ξ£+K+Kβ, Ξ£+Ο and Ξ£+K+Οβ(Ο0)
(2023)
Based on 4.5 fbβ1 data taken at seven center-of-mass energies ranging from 4.600 to 4.699 GeV with the BESIII detector at the BEPCII collider, we measure the branching fractions of Ξ + c β Ξ£ + + hadrons relative to Ξ + c β Ξ£ +Ο +Ο β. Combining with the world average branching fraction of Ξ + c β Ξ£ +Ο +Ο β, their branching fractions are measured to be (0.377 Β± 0.042 Β± 0.020 Β± 0.021)% for Ξ + c β Ξ£ +K+Kβ, (0.200 Β± 0.023 Β± 0.011 Β± 0.011)% for Ξ + c β Ξ£+K+Οβ, (0.414 Β± 0.080 Β± 0.030 Β± 0.023)% for Ξ + c β Ξ£ +Ο and (0.197 Β± 0.036 Β± 0.009 Β± 0.011)% for Ξ + c β Ξ£ +K+Kβ(non-Ο). In all the above results, the first uncertainties are statistical, the second are systematic and the third are from external input of the branching fraction of Ξ + c β Ξ£ +Ο +Ο β. Since no signal for Ξ + c β Ξ£ +K+ΟβΟ 0 is observed, the upper limit of its branching fraction is determined to be 0.13% at the 90% confidence level.
With data samples collected with the BESIII detector at seven energy points at βs = 3.68 β 3.71 GeV, corresponding to an integrated luminosity of 333 pbβ1, we present a study of the Ξ transverse polarization in the e+eβ β ΞΞΒ― reaction. The signifcance of polarization by combining the seven energy points is found to be 2.6Ο including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the ΞΞΒ― helicity states. The modulus ratio and the relative phase of EM-psionic form factors combined with all energy points are measured to be RΞ¨ = 0.71+0.10β0.10 Β± 0.03 and βΦΨ = 23+8.8β8.0 Β± 1.6β¦, where the frst uncertainties are statistical and the second systematic.
We search for the semi-leptonic decays Ξ + c β ΞΟ+Οβe+Ξ½e and Ξ + c β pK0 SΟβe+Ξ½e in a sample of 4.5 fbβ1 of e+eβ annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Ξ+c β ΞΟ+Οβe+Ξ½e ) < 3.9 Γ 10β4 and B(Ξ + c β pK0SΟβe+Ξ½e ) < 3.3 Γ 10β4 at the 90% confidence level, respectively.
Using an π+β’πβ collision data sample of (27.08Β±0.14)Γ108ββπβ‘(3686) events collected by the BESIII detector, we report the first observation of ππβ’π½βΞ©ββ’Β―Ξ©+ (π½=0, 1, 2) decays with significances of 5.6β’π, 6.4β’π, and 18β’π, respectively, where the ππβ’π½ mesons are produced in the radiative πβ‘(3686) decays. The branching fractions are determined to be β¬β‘(ππβ’0βΞ©ββ’Β―Ξ©+) = (3.51Β±0.54Β±0.29)Γ10β5, β¬β‘(ππβ’1βΞ©ββ’Β―Ξ©+)=(1.49Β±0.23Β±0.10)Γ10β5, and β¬β‘(ππβ’2βΞ©ββ’Β―Ξ©+)=(4.52Β±0.24Β±0.18)Γ10β5, where the first and second uncertainties are statistical and systematic, respectively.
The Ξ0 asymmetry parameters are measured using entangled quantum Ξ0 β ΞΒ― 0 pairs from a sample of Γ°448.1 2.9Γ Γ 106 ΟΓ°3686Γ events collected with the BESIII detector at BEPCII. The relative phase between the transition amplitudes of the Ξ0ΞΒ― 0 helicity states is measured to be ΞΞ¦ ΒΌ β0.050 0.150 0.020 rad, which implies that there is no obvious polarization at the current level of statistics. The decay parameters of the Ξ0 hyperon ðαΞ0 ; Ξ±ΞΒ― 0 ; ΟΞ0 ; ΟΞΒ― 0 Γ and the angular distribution parameter Β½Ξ±ΟΓ°3686Γ and ΞΞ¦ are measured simultaneously for the first time. In addition, the CP asymmetry observables are determined to be AΞ0 CP ΒΌ ðαΞ0 ΓΎ Ξ±ΞΒ― 0 Γ=ðαΞ0 β Ξ±ΞΒ― 0 Γ ΒΌ β0.007 0.082 0.025 and ΞΟΞ0 CP ΒΌ Γ°ΟΞ0 ΓΎ ΟΞΒ― 0 Γ=2 ΒΌ β0.079 0.082 0.010 rad, which are consistent with CP conservation.
We report a search for a heavier partner of the recently observed Zcs(3985)β state, denoted as Zβ²βcs, in the process e+eββK+DββsDβ0+c.c., based on e+eβ collision data collected at the center-of-mass energies of sβ=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Zβ²βcs 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 Zβ²βcsβDββsDβ0 (c.c.). We find an excess of Zβ²βcsβDββsDβ0 (c.c.) candidates with a significance of 2.9Ο, after considering systematic uncertainties, at a mass of (4123.5Β±0.7stat.Β±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 Zβ²βcsβDββsDβ0, ΟBornβ
B at the three energy points, under different assumptions of the Zβ²βcs 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 ΟBornβ
B are found to lie in the range of 2βΌ6, 3βΌ7 and 3βΌ6 pb at sβ=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 Zβ²βcs state.
We search for an axion-like particle (ALP) a through the process Ο(3686)βΟ+ΟβJ/Ο, J/ΟβΞ³a, aβΞ³Ξ³ in a data sample of (2.71Β±0.01)Γ109 Ο(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ΟβΞ³a and the ALP-photon coupling constant gaΞ³Ξ³ are set at 95% confidence level in the mass range of 0.165β€maβ€2.84GeV/c2. The limits on B(J/ΟβΞ³a) range from 8.3Γ10β8 to 1.8Γ10β6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165β€maβ€1.468GeV/c2.
We search for an axion-like particle (ALP) a through the process Ο(3686)βΟ+ΟβJ/Ο, J/ΟβΞ³a, aβΞ³Ξ³ in a data sample of (2.71Β±0.01)Γ109 Ο(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ΟβΞ³a and the ALP-photon coupling constant gaΞ³Ξ³ are set at 95% confidence level in the mass range of 0.165β€maβ€2.84GeV/c2. The limits on B(J/ΟβΞ³a) range from 8.3Γ10β8 to 1.8Γ10β6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165β€maβ€1.468GeV/c2.
Search for hidden-charm tetraquark with strangeness in eβΊeβ» β KβΊD*β»β D*β° + c.c.
(2023)
We report a search for a heavier partner of the recently observed Zcs(3985)β state, denoted as Zβ²βcs, in the process e+eββK+DββsDβ0+c.c., based on e+eβ collision data collected at the center-of-mass energies of sβ=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Zβ²βcs 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 Zβ²βcsβDββsDβ0 (c.c.). We find an excess of Zβ²βcsβDββsDβ0 (c.c.) candidates with a significance of 2.1Ο, after considering systematic uncertainties, at a mass of (4123.5Β±0.7stat.Β±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 (ΟBorn) and the branching fraction (B) of Zβ²βcsβDββsDβ0, under different assumptions of the Zβ²βcs 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 ΟBornβ
B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Zβ²βcs state and clarify its nature in the coming years.
Search for hidden-charm tetraquark with strangeness in eβΊeβ» β KβΊD*β»β D*β° + c.c.
(2022)
We report a search for a heavier partner of the recently observed Zcs(3985)β state, denoted as Zβ²βcs, in the process e+eββK+DββsDβ0+c.c., based on e+eβ collision data collected at the center-of-mass energies of sβ=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Zβ²βcs 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 Zβ²βcsβDββsDβ0 (c.c.). We find an excess of Zβ²βcsβDββsDβ0 (c.c.) candidates with a significance of 2.1Ο, after considering systematic uncertainties, at a mass of (4123.5Β±0.7stat.Β±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 (ΟBorn) and the branching fraction (B) of Zβ²βcsβDββsDβ0, under different assumptions of the Zβ²βcs 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 ΟBornβ
B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Zβ²βcs state and clarify its nature in the coming years.
We search for an axion-like particle (ALP) a through the process Ο(3686)βΟ+ΟβJ/Ο, J/ΟβΞ³a, aβΞ³Ξ³ in a data sample of (2.71Β±0.01)Γ109 Ο(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ΟβΞ³a and the ALP-photon coupling constant gaΞ³Ξ³ are set at 95% confidence level in the mass range of 0.165β€maβ€2.84GeV/c2. The limits on B(J/ΟβΞ³a) range from 8.3Γ10β8 to 1.8Γ10β6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165 β€ ma β€ 1.468GeV/c2.
We report a search for a dark photon using 14.9~fbβ1 of e+eβ annihilation data taken at center-of-mass energies from 4.13 to 4.60~GeV with the BESIII detector operated at the BEPCII storage ring. The dark photon is assumed to be produced in the radiative annihilation process of e+eβ and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9~GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90% confidence level on the coupling strength parameter Ο΅ for a dark photon coupling with an ordinary photon vary between 1.6Γ10β3 and 5.7Γ10β3.
Observation of the decay Ο(3686) β Ξ£β»Ξ£βΎβΊ and measurement of its angular distribution
(2022)
Using (448.1Β±2.9)Γ106 Ο(3686) events collected with the BESIII detector at the BEPCII collider, the decay Ο(3686)βΞ£βΣ¯+ is observed for the first time with a branching fraction of (2.84Β±0.04stat.Β±0.08syst.)Γ10β4, and the angular parameter Ξ±Ξ£β is measured to be 0.96Β±0.09stat.Β±0.03syst..
Observation of the decay Ο(3686) β Ξ£β»Ξ£βΎβΊ and measurement of its angular distribution
(2022)
Using (448.1Β±2.9)Γ106 Ο(3686) events collected with the BESIII detector at the BEPCII collider, the decay Ο(3686)βΞ£βΣ¯+ is observed for the first time with a branching fraction of (2.82Β±0.04stat.Β±0.08syst.)Γ10β4, and the angular parameter Ξ±Ξ£β is measured to be 0.96Β±0.09stat.Β±0.03syst..
Study of the eβΊeβ» β ΟβΊΟβ»Ο process at center-of-mass energies between 4.0 and 4.6 GeV
(2023)
Using 15.6 fbβ1 of e+eβ collision data collected at twenty-four center-of-mass energies from 4.0 to 4.6 GeV with the BESIII detector, the helicity amplitudes of the process e+eββΟ+ΟβΟ are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5Ο are presented, such as f0(500), f0(980), f2(1270), f0(1370), b1(1235)Β±, and Ο(1450)Β±. In addition, evidence of a resonance state in e+eββΟ+ΟβΟ production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/c2, which is consistent with the production of Ο(4160) or Y(4220).
Study of the eβΊeβ» β ΟβΊΟβ»Ο process at center-of-mass energies between 4.0 and 4.6 GeV
(2023)
Using 15.6 fbβ1 of e+eβ collision data collected at twenty-four center-of-mass energies from 4.0 to 4.6 GeV with the BESIII detector, the helicity amplitudes of the process e+eβ β Ο+ΟβΟ are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5Ο are presented, such as f0(500), f0(980), f2(1270), f0(1370), b1(1235)Β±, and Ο(1450)Β±. In addition, evidence of a resonance state in e+eβ β Ο+ΟβΟ production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/c2, which is consistent with the production of Ο(4160) or Y(4220).
Using a data sample corresponding to an integrated luminosity of 11.3 fbβ1 collected at center-of-mass energies from 4.23 to 4.70 GeV with the BESIII detector, we observe the process e+eβ β Ο0Ο0Ο2(3823) for the first time with a statistical significance of 6.0 standard deviations. The ratio of average cross sections for e+eβ β Ο0Ο0Ο2(3823) and Ο+ΟβΟ2(3823) is determined to be R = Ο[e+eβ β Ο0Ο0Ο2(3823)] Ο[e+eββΟ+ΟβΟ2(3823)] = 0.57 Β± 0.14 Β± 0.05, which is consistent with expectations from isospin symmetry. Here and below, the first uncertainties are statistical and the second are systematic. The mass of the Ο2(3823) is measured to be M[Ο2(3823)] = 3824.5Β±2.4Β±1.0 MeV/c2. Due to the limited data sample, an upper limit of 18.8 MeV at 90% confidence level is set on the intrinsic width of Ο2(3823).
Observation of the decay Ο(3686) β Ξ£β»Ξ£βΎβΊ and measurement of its angular distribution
(2022)
Using (448.1 Β± 2.9) Γ 106 Ο(3686) events collected with the BESIII detector at the BEPCII collider, the decay Ο(3686) β Ξ£β»Ξ£βΎβΊ is observed for the first time with a branching fraction of (2.82 Β± 0.04stat. Β± 0.08syst.) Γ 10β4, and the angular parameter Ξ±Ξ£β is measured to be 0.96 Β± 0.09stat. Β± 0.03syst..
Based on (10087Β±44)Γ106ββπ½/π events collected with the BESIII detector at BEPCII, the double Dalitz decay πβ²βπ+β’πββ’π+β’πβ is observed for the first time via the π½/πβπΎβ’πβ² decay process. The significance is found to be 5.7β’π with systematic uncertainties taken into consideration. Its branching fraction is determined to be β¬β‘(πβ²βπ+β’πββ’π+β’πβ)=(4.5Β±1.0β’(stat)Β±0.5β’(sys))Γ10β6.
By using 6.32 fbβ1 of data collected with the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, we perform an amplitude analysis of the decay D+s ! K0S +β0 and determine the relative fractions and phase differences of different intermediate processes, which include K0S (770)+, K0S (1450)+, Kβ(892)0β+, Kβ(892)+β0, and Kβ(1410)0β+. With the detection efficiency based on the amplitude analysis results, the absolute branching fraction is measured to be B(D+s ! K0S +β0) = (5.43 Β± 0.30stat Β± 0.15syst) Γ 10β3.
Using e+eβ annihilation data sets collected with the BESIII detector, we measure the cross sections of the processes e+eββe+eβ and e+eββΞΌ+ΞΌβ at fifteen center-of-mass energy points in the vicinity of the J/Ο resonance. By a simultaneous fit to the measured, center-of-mass energy dependent cross sections of the two processes, the combined quantities ΞeeΞee/Ξtot and ΞeeΞΞΌΞΌ/Ξtot are determined to be (0.346Β±0.009) and (0.335Β±0.006) keV, respectively, where Ξee, ΞΞΌΞΌ, and Ξtot are the electronic, muonic, and total decay widths of the J/Ο resonance, respectively. Using the resultant ΞeeΞΞΌΞΌ/Ξtot and ΞeeΞee/Ξtot, the ratio Ξee/ΞΞΌΞΌ is calculated to be 1.031Β±0.015, which is consistent with the expectation of lepton universality within about two standard deviations. Assuming lepton universality and using the branching fraction of the J/Ο leptonic decay measured by BESIII in 2013, Ξtot and Ξll are determined to be (93.0Β±2.1) and (5.56Β±0.11) keV, respectively, where Ξll is the average leptonic decay width of the J/Ο resonance.
Using a data sample of (448.1Β±2.9)Γ106ββπβ‘(3686) decays collected at an π+β’πβ center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay πβ‘(3686)βπ+β’πββ’ππ with a significance of 7.9β’π. The branching fraction is determined to be β¬β‘(πβ‘(3686)βπ+β’πββ’ππ)=(3.77Β±0.4β’0statΒ±0.1β’8syst)Γ10β5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the πβ‘(3686) and the ππ, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ππ decays.
The hadronic decay ππβ‘(2β’π)β3β’(π+β’πβ) is observed with a statistical significance of 9.3 standard deviations using (448.1Β±2.9)Γ106ββπβ‘(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ππβ‘(2β’π) are (3643.4Β±2.3β(stat)Β±4.4β(syst))ββMeV/π2 and (19.8Β±3.9β(stat)Β±3.1β(syst))ββMeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction β¬β‘[πβ‘(3686)βπΎβ’ππβ‘(2β’π)]Γβ¬β‘[ππβ‘(2β’π)β3β’(π+β’πβ)] is measured to be (9.2Β±1.0β(stat)Β±1.2β(syst))Γ10β6. Using β¬β‘[πβ‘(3686)βπΎβ’ππβ‘(2β’π)]=(7.β’0+3.4β2.5)Γ10β4, we obtain β¬β‘[ππβ‘(2β’π)β3β’(π+β’πβ)]=(1.31Β±0.15β(stat)Β±0.17β(syst) (+0.64β0.47)β(extr))Γ10β2, where the third uncertainty is from β¬β‘[πβ‘(3686)βπΎβ’ππβ‘(2β’π)]. We also measure the ππβ’π½β3β’(π+β’πβ) (π½=0, 1, 2) decays via πβ²βπΎβ’ππβ’π½ transitions. The branching fractions are β¬β‘[ππβ’0β3β’(π+β’πβ)]=(2.080Β±0.006β(stat)Β±0.068β(syst))Γ10β2, β¬β‘[ππβ’1β3β’(π+β’πβ)]=(1.092Β±0.004β(stat)Β±0.035β(syst))Γ10β2, and β¬β‘[ππβ’2β3β’(π+β’πβ)]=(1.565Β±0.005β(stat)Β±0.048β(syst))Γ10β2.
The hadronic decay Ξ·c(2S)β3(Ο+Οβ) is observed with a statistical significance of 9.3 standard deviations using (448.1Β±2.9)Γ106 Ο(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of Ξ·c(2S) are (3643.4Β±2.3(stat.)Β±4.4(syst.)) MeV/c2 and (19.8Β±3.9(stat.)Β±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[Ο(3686) β Ξ³Ξ·c(2S)]ΓB[Ξ·c(2S)β3(Ο+Οβ)] is measured to be (9.2Β±1.0(stat.)Β±0.9(syst.))Γ10β6. Using B[Ο(3686)βΞ³Ξ·c(2S)]=(7.0+3.4β2.5)Γ10β4, we obtain B[Ξ·c(2S)β3(Ο+Οβ)]=(1.31Β±0.15(stat.)Β±0.13(syst.)(+0.64β0.47)(extr))Γ10β2, where the third uncertainty is from B[Ο(3686)βΞ³Ξ·c(2S)]. We also measure the ΟcJβ3(Ο+Οβ) (J=0,1,2) decays via Ο(3686)βΞ³ΟcJ transitions. The branching fractions are B[Οc0β3(Ο+Οβ)]=(2.080Β±0.006(stat.)Β±0.068(syst.))Γ10β2, B[Οc1β3(Ο+Οβ)]=(1.092Β±0.004(stat.)Β±0.035(syst.))Γ10β2, and B[Οc2β3(Ο+Οβ)]=(1.565Β±0.005(stat.)Β±0.048(syst.))Γ10β2.