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Institute
The cross section of the process e+eββK+Kβ is measured at a number of center-of-mass energies sβ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M=2239.2Β±7.1Β±11.3~and a width of Ξ=139.8Β±12.3Β±20.6 MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process π+β’πββππβ’πβ’π+β’πβ. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The ππ meson is reconstructed in 16 exclusive decay modes. No signal is observed in the ππ mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.
Using a sample of 106 million πβ‘(3686) decays, πβ‘(3686)βπΎβ’ππβ’π½β‘(π½=0,1,2) and πβ‘(3686)βπΎβ’ππβ’π½,ππβ’π½βπΎβ’π½/πβ‘(π½=1,2) events are utilized to study inclusive ππβ’π½βanything, ππβ’π½βhadrons, and π½/πβanything distributions, including distributions of the number of charged tracks, electromagnetic calorimeter showers, and π0β’s, and to compare them with distributions obtained from the BESIII Monte Carlo simulation. Information from each Monte Carlo simulated decay event is used to construct matrices connecting the detected distributions to the input predetection βproducedβ distributions. Assuming these matrices also apply to data, they are used to predict the analogous produced distributions of the decay events. Using these, the charged particle multiplicities are compared with results from MARK I. Further, comparison of the distributions of the number of photons in data with those in Monte Carlo simulation indicates that G-parity conservation should be taken into consideration in the simulation.
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.
Using a 3.19ββfbβ1 data sample collected at an π+β’πβ center-of-mass energy of πΈcm=4.178ββGeV with the BESIII detector, we measure the branching fraction of the leptonic decay π·+π βπ+β’ππ to be β¬π·+π βπ+β’ππ=(5.49Β±0.1β’6statΒ±0.1β’5syst)Γ10β3. Combining our branching fraction with the masses of the π·+π and π+ and the lifetime of the π·+π , we determine ππ·+π β’|ππβ’π |=246.2Β±3.β’6statΒ±3.β’5systββMeV. Using the πβπ quark mixing matrix element |ππβ’π | determined from a global standard model fit, we evaluate the π·+π decay constant ππ·+π =252.9Β±3.β’7statΒ±3.β’6systββMeV. Alternatively, using the value of ππ·+π calculated by lattice quantum chromodynamics, we find |ππβ’π |=0.985Β±0.01β’4statΒ±0.01β’4syst. These values of β¬π·+π βπ+β’ππ, ππ·+π β’|ππβ’π |, ππ·+π and |ππβ’π | are each the most precise results to date.
Using a data sample of 448.1Γ106ββπβ‘(3686) events collected at βπ =3.686ββGeV with the BESIII detector at the Beijing Electron-Positron Collider II, we search for the rare decay π½/πβπβ’π+β’πβ via πβ‘(3686)βπ+β’πββ’π½/π. No signal events are observed and the upper limit on the branching fraction is set to be β¬β‘(π½/πβπβ’π+β’πβ)<1.2Γ10β7 at the 90% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.
he process e+eββpK0SnΒ―Kβ+c.c. and its intermediate processes are studied for the first time, using data samples collected with the BESIII detector at BEPCII at center-of-mass energies of 3.773, 4.008, 4.226, 4.258, 4.358, 4.416, and 4.600 GeV, with a total integrated luminosity of 7.4 fbβ1. The Born cross section of e+eββpK0SnΒ―Kβ+c.c. is measured at each center-of-mass energy, but no significant resonant structure in the measured cross-section line shape between 3.773 and 4.600 GeV is observed. No evident structure is detected in the pKβ, nK0S, pK0S, nK+, pnΒ―, or K0SKβ invariant mass distributions except for Ξ(1520). The Born cross sections of e+eββΞ(1520)nΒ―K0S+c.c. and e+eββΞ(1520)pΒ―K++c.c. are measured, and the 90\% confidence level upper limits on the Born cross sections of e+eββΞ(1520)ΞΒ―(1520) are determined at the seven center-of-mass energies.
The observed cross sections for π+β’πββπ+β’πβ 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 πβ‘(4040), πβ‘(4160), and πβ‘(4415) decaying to π+β’πβ, 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 4.220ββGeV/π2, which we denote as πβ‘(4220). Analyzing a coherent sum of amplitudes yields eight solutions, one of which gives a mass of ππβ‘(4220) = 4216.7Β±8.9Β±4.1ββMeV/π2, a total width of Ξtot Sβ‘(4220) = 47.2Β±22.8Β±10.5ββMeV, and a muonic width of Ξπβ’π πβ‘(4220) = 1.53Β±1.26Β±0.54ββkeV, 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 4219.4ββMeV/π2, from 36.4 to 49.6 MeV, and from 1.09 to 1.53 keV. The statistical significance of the πβ‘(4220) signal is 3.9β’π. Correcting the total dimuon cross section for radiative effects yields a statistical significance for this structure of 8.1β’π.
An amplitude analysis of the πΎπβ’πΎπ system produced in radiative π½/π decays is performed using the (1310.6Β±7.0)Γ106ββπ½/π decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parametrizing the πΎπβ’πΎπ invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the πΎπβ’πΎπ system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the π0β‘(1710), π0β‘(2200), and πβ²2β‘(1525). The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative π½/π decays to πΎπβ’πΎπ is measured to be (8.1Β±0.4)Γ10β4, where the uncertainty is systematic and the statistical uncertainty is negligible.
We report new measurements of the cross sections for the production of Dbar D final states at the Ο(3770) resonance. Our data sample consists of an integrated luminosity of 2.93 fbβ1 of e+eβ annihilation data produced by the BEPCII collider and collected and analyzed with the BESIII detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed Dbar D events ("double tags") to the yield of all reconstructed D or bar D mesons ("single tags") to determine the number of D0bar D0 and D+Dβ events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be Ο(e+eβ β D0bar D0) nb and Ο(e+eβ β D+Dβ) = (2.830 Β± 0.011 Β± 0.026) nb, where the uncertainties are statistical and systematic, respectively.
We study the hadronic decays of Ξ+c to the final states Ξ£+Ξ· and Ξ£+Ξ·β², using an e+eβ annihilation data sample of 567 pbβ1 taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays Ξ+cβΞ£+Ξ· and Ξ£+Ξ·β² with statistical significance of 2.5Ο and 3.2Ο, respectively. Normalizing to the reference decays Ξ+cβΞ£+Ο0 and Ξ£+Ο, we obtain the ratios of the branching fractions B(Ξ+cβΞ£+Ξ·)B(Ξ+cβΞ£+Ο0) and B(Ξ+cβΞ£+Ξ·β²)B(Ξ+cβΞ£+Ο) to be 0.35Β±0.16Β±0.03 and 0.86Β±0.34Β±0.07, respectively. The upper limits at the 90\% confidence level are set to be B(Ξ+cβΞ£+Ξ·)B(Ξ+cβΞ£+Ο0)<0.58 and B(Ξ+cβΞ£+Ξ·β²)B(Ξ+cβΞ£+Ο)<1.2. Using BESIII measurements of the branching fractions of the reference decays, we determine B(Ξ+cβΞ£+Ξ·)=(0.41Β±0.19Β±0.05)% (<0.68%) and B(Ξ+cβΞ£+Ξ·β²)=(1.34Β±0.53Β±0.21)% (<1.9%). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of Ξ+cβΞ£+Ξ· is consistent with the previous measurement, and the branching fraction of Ξ+cβΞ£+Ξ·β² is measured for the first time.
We study the electromagnetic Dalitz decay π½/πβπ+β’πββ’π and search for dielectron decays of a dark gauge boson (πΎβ²) in π½/πβπΎβ²β’π with the two π decay modes πβπΎβ’πΎ and πβπ+β’πββ’π0 using (1310.6Β±7.0)Γ106ββπ½/π events collected with the BESIII detector. The branching fraction of π½/πβπ+β’πββ’π is measured to be (1.43Β±0.04β’(stat)Β±0.06β’(syst))Γ10β5, with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be Ξ=2.84Β±0.11β’(stat)Β±0.08β’(syst)ββGeV/π2. We find no evidence of πΎβ² production and set 90% confidence level upper limits on the product branching fraction β¬β‘(π½/πβπΎβ²β’π)Γβ¬β‘(πΎβ²βπ+β’πβ) as well as the kinetic mixing strength between the standard model photon and πΎβ² in the mass range of 0.01β€ππΎβ²β€2.4ββGeV/π2.
Using a sample of 4.48Γ108 Ο(3686) events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons Ο0, Ξ·, Ξ·β², Ξ·(1405), Ξ·(1475), Ξ·(1760), and X(1835) in J/Ο radiative decays using Ο(3686)βΟ+ΟβJ/Ο events. The Ο0, Ξ· and Ξ·β² mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be B(J/ΟβΞ³Ο0β3Ξ³)=(3.57Β±0.12Β±0.16)Γ10β5, B(J/ΟβΞ³Ξ·β3Ξ³)=(4.42Β±0.04Β±0.18)Γ10β4, and B(J/ΟβΞ³Ξ·β²β3Ξ³)=(1.26Β±0.02Β±0.05)Γ10β4, where the first errors are statistical and the second systematic. No clear signal for Ξ·(1405), Ξ·(1475), Ξ·(1760) or X(1835) is observed in the two-photon mass spectra, and upper limits at the 90% confidence level on the product branching fractions are obtained.
Using a data sample of 448.1Γ106 Ο(3686) events collected at sβ= 3.686 GeV with the BESIII detector at the BEPCII, we search for the rare decay J/ΟβΟe+eβ via Ο(3686)βΟ+ΟβJ/Ο. No signal events are observed and the upper limit on the branching fraction is set to be B(J/ΟβΟe+eβ)<1.2Γ10β7 at the 90\% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.
We report on new measurements of Cabibbo-suppressed semileptonic D+s decays using 3.19 fbβ1 of e+eβ annihilation data sample collected at a center-of-mass energy of 4.178~GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions B(D+sβK0e+Ξ½e)=(3.25Β±0.38(stat.)Β±0.16(syst.))Γ10β3 and B(D+sβKβ0e+Ξ½e)=(2.37Β±0.26(stat.)Β±0.20(syst.))Γ10β3 which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For D+sβK0e+Ξ½e, we obtain f+(0)=0.720Β±0.084(stat.)Β±0.013(syst.), and for D+sβKβ0e+Ξ½e, we find form-factor ratios rV=V(0)/A1(0)=1.67Β±0.34(stat.)Β±0.16(syst.) and r2=A2(0)/A1(0)=0.77Β±0.28(stat.)Β±0.07(syst.).
Search for heavy Majorana neutrino in lepton number violating decays of DβββKΟeβΊeβΊ
(2019)
Using a data sample with an integrated luminosity of 2.93ββfbβ1 taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino (ππ) in the lepton number violating decays π·βπΎβ’πβ’π+β’π+. No significant signal is observed, and the upper limits on the branching fraction at the 90% confidence level are set to be β¬β‘(π·0βπΎββ’πββ’π+β’π+)<2.8Γ10β6, β¬β‘(π·+βπΎ0πβ’πββ’π+β’π+)<3.3Γ10β6 and β¬β‘(π·+βπΎββ’π0β’π+β’π+)<8.5Γ10β6. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0ββGeV/π2 in the decays π·0βπΎββ’π+β’ππ,ππβπββ’π+ and π·+βπΎ0πβ’π+β’ππ,ππβπββ’π+, and the upper limits on the branching fraction at the 90% confidence level are at the level of 10β7βΌ10β6, depending on the mass of the Majorana neutrino. The constraints on the mixing matrix element |ππβ’ππ|2 are also evaluated.
Using a low background data sample of 9.7Γ105ββπ½/πβπΎβ’πβ², πβ²βπΎβ’π+β’πβ events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of πβ²βπΎβ’π+β’πβ are studied with both model-dependent and model-independent approaches. The contributions of π and the πβ‘(770)βπ interference are observed for the first time in the decays πβ²βπΎβ’π+β’πβ in both approaches. Additionally, a contribution from the box anomaly or the πβ‘(1450) resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.
We report the first observation of the semimuonic decay π·+βπβ’π+β’ππ using an π+β’πβ collision data sample corresponding to an integrated luminosity of 2.93ββfbβ1 collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. The absolute branching fraction of the π·+βπβ’π+β’ππ decay is measured to be β¬π·+βπβ’π+β’ππ=(17.7Β±1.β’8statΒ±1.β’1syst)Γ10β4. Its ratio with the world average value of the branching fraction of the π·+βπβ’π+β’ππ decay probes lepton flavor universality and it is determined to be β¬π·+βπβ’π+β’ππ/β¬PDG π·+βπβ’π+β’ππ=1.05Β±0.14, in agreement with the standard model expectation within one standard deviation.
A partial-wave analysis of the decay π½/πβπΎ+β’πΎββ’π0 has been made using (223.7Β±1.4)Γ106ββπ½/π events collected with the BESIII detector in 2009. The analysis, which is performed within the isobar-model approach, reveals contributions from πΎ*2β’(1430)Β±, πΎ*2β’(1980)Β± and πΎ*4β’(2045)Β± decaying to πΎΒ±β’π0. The two latter states are observed in π½/π decays for the first time. Two resonance signals decaying to πΎ+β’πΎβ are also observed. These contributions cannot be reliably identified and their possible interpretations are discussed. The measured branching fraction π΅β‘(π½/πβπΎ+β’πΎββ’π0) of (2.88Β±0.01Β±0.12)Γ10β3 is more precise than previous results. Branching fractions for the reported contributions are presented as well. The results of the partial-wave analysis differ significantly from those previously obtained by BESII and BABAR.