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Institute
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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.
Using a sample of (10087Β±44)Γ106 J/Ο events, which is about 45 times larger than that was previously analyzed, a further investigation on the J/ΟβΞ³3(Ο+Οβ) decay is performed. A significant distortion at 1.84 GeV/c2 in the line-shape of the 3(Ο+Οβ) invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, X(1840) and X(1880). The new state X(1880) is observed with a statistical significance larger than 10Ο. The mass and width of X(1880) are determined to be 1882.1Β±1.7Β±0.7 MeV/c2 and 30.7Β±5.5Β±2.4 MeV, respectively, which indicates the existence of a ppΒ― bound state.
Measurement of the eβΊeβ» β Kβ°SKβ°LΟβ° cross sections from βs = 2.000 to 3.080 GeV
(2024)
Based on e+eβ collision data collected at center-of-mass energies from 2.000 to 3.080 GeV by the BESIII detector at the BEPCII collider, a partial wave analysis isperformed for the process e+eβ β K0SK0LΟ0. The results allow the Born cross sections of the process e+eβ β K0SK0LΟ0, as well as its subprocesses e+eβ β Kβ(892)0KΒ― 0 and Kβ2(1430)0KΒ― 0 to be measured. The Born cross sections for e+eβ β K0SK0 LΟ 0 are consistent with previous measurements by BaBar, but with substantially improved precision. The Born cross section lineshape of the process e+e β β Kβ(892)0KΒ― 0 is consistent with a vector meson state around 2.2 GeV with a signifcance of 3.2Ο. A Breit-Wigner ft determines its mass as MY = (2164.7 Β± 9.1 Β± 3.1) MeV/c2 and its width as ΞY = (32.4 Β± 21.0 Β± 1.8) MeV.
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.
Using a sample of (10087Β±44)Γ106 J/Ο events, which is about fifty times larger than that was previously analyzed, a further investigation on the J/ΟβΞ³3(Ο+Οβ) decay is performed. A significant distortion at 1.84 GeV/c2 in the line-shape of the 3(Ο+Οβ) invariant mass spectrum is observed for the first time, which is analogous to the behavior of X(1835) and could be resolved by two overlapping resonant structures, X(1840) and X(1880). The new state X(1880) is observed with a statistical significance of 14.7Ο. The mass and width of X(1880) are determined to be 1882.1Β±1.7Β±0.7 MeV/c2 and 30.7Β±5.5Β±2.4 MeV, respectively, which indicates the existence of a ppΒ― bound state.
The cross sections of the π+β’πββπβ’πβ² process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1ββfbβ1 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 π βπ/2 with π=4.35Β±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of π=3.5Β±0.9. In addition, the charmless decay πβ‘(3770)βπβ’πβ² is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of β¬β‘(πβ‘(3770)βπβ’πβ²) at the 90% confidence level is determined to be 2.3Γ10β5.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 (10087Β±44)Γ106 J/Ο events collected with the BESIII detector, the radiative hyperon decay Ξ£βpΞ³ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be (0.996Β±0.021stat.Β±0.018syst.)Γ10β3, which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be β0.652Β±0.056stat.Β±0.020syst.. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.