BESIII Experiment Research Articles

Charmonium Decays at BESIII

The BESIII Experiment at the Beijing Electron Positron Collider (BEPCII) has accumulated the largest e+e− collisions data sets in the τ-charm region in the world. Using the 448.1 million ψ(3686) events, 1.31 billion J/ψ events, and data above 4 GeV, some charmonium decays are searched for and studied. The branching fractions of ψ(3686)→KS0+anything, Σ¯0Λ+c.c. and χcJ→ΛΛ¯, Σ−Σ¯+, Σ0p¯K++c.c. are measured. The spin-singlet charmonium decays ηc→ηηη′ and hc→K+K−π+π−π0 are observed for the first time. Some D-wave charmonium ψ2(3823) decays are also searched for.

Nucleon Electromagnetic Form Factors Measurements at BESIII

Electromagnetic form factors provide fundamental information to reveal the internal structure and dynamincs of nucleons. Using the energy scan data collected by BESIII experiment on BEPCII collider, the Born cross section of e+e−→pp¯ and e+e−→nn¯, and the proton and neutron electromagnetic form factors are measured at center-of-mass energies between 2.0 and 3.08 GeV, through the e+e− direct annihilation process. Through the initial-state-radiation process, the proton electromagnetic form factors are also measured from the pp¯ threshold to 3.0 GeV with the large data sets collected at center-of-mass energy between 3.773 and 4.6 GeV, while the Born cross section of e+e−→pp¯ is measured up to 3.8 GeV.

Light meson decays at BESIII

Due to the high production rate of light mesons in J/ψ radiative and hadronic decays, the largest sample of J/ψ events accumulated at the BESIII detector offers a unique laboratory for investigating light meson decays. In recent years the BESIII experiment has made significant progresses in the study of η′ decays, including the search for the η′→γγη and η′→π0π0π0π0 decays, the measurement of the branching fraction of and the search for a CP-violating asymmetry in the η′→π+π−e+e− decay, and the observation of the η′→π+π−μ+μ− decay. This paper gives brief introductions to these works.

Method for detector description transformation to Unity and application in BESIII

Detector and event visualization are essential parts of the software used in high-energy physics (HEP) experiments. Modern visualization techniques and multimedia production platforms such as Unity provide impressive display effects and professional extensions for visualization in HEP experiments. In this study, a method for automatic detector description transformation is presented, which can convert the complicated HEP detector geometry from GDML in offline software to 3D modeling in Unity. The method was successfully applied in the BESIII experiment and can be further developed into applications such as event displays, data monitoring, or virtual reality. It has great potential in detector design, offline software development, physics analysis, and outreach for next-generation HEP experiments as well as applications in nuclear techniques for the industry.

Two- and three-gluon glueballs within QCD sum rules

We study two- and three-gluon glueballs using the method of QCD sum rules. We systematically construct their interpolating currents and calculate their masses. We propose to search for the JPC=3±− three-gluon glueballs in their three-meson decay channels in future BESIII, GlueX, LHC, and PANDA experiments.

Role of meson interactions in the Ds+→π+π+π−η decay

We perform a theoretical study of the $D_s^{+}\to \pi^{+}\pi^{+}\pi^{-}\eta$ decay. We look first at the basic $D_s^{+}$ decay at the quark level from external and internal emission. Then hadronize a pair or two pairs of $q\bar{q}$ states to have mesons at the end. Posteriorly the pairs of mesons are allowed to undergo final state interaction, by means of which the $a_0(980)$, $f_0(980)$, $a_1(1260)$, and $b_1(1235)$ resonances are dynamically generated. The $G$-parity is used as a filter of the possible channels, and from those with negative $G$-parity only the ones that can lead to $\pi^{+}\pi^{+}\pi^{-}\eta$ at the final state are kept. Using transition amplitudes from the chiral unitary approach that generates these resonances, and a few free parameters, we obtain a fair reproduction of the six mass distributions reported in BESIII experiment.

Gluonic nature of the newly observed state X(2600)

Motivated by the newly observed resonance $X(2600)$ by BESIII Collaboration, we examine the trigluon glueball interpretation for it in the framework of QCD sum rules. We evaluate the mass spectra of the trigluon glueballs with quantum numbers $0^{-+}$ and $2^{-+}$ up to dimension 8 condensate in the operator product expansion. Our numerical results indicate that the mass of the $2^{-+}$ trigluon glueball is about $2.66\pm 0.06$ GeV, which is consistent with the mass of the X(2600) within the uncertainties, while $0^{-+}$ has a mass of $2.01\pm0.14$ GeV. The possible decay channels of the $2^{-+}$ state are analyzed, which are crucial in decoding $X(2600)$'s internal structure and are hopefully measurable in BESIII, BEllEII, PANDA, and LHCb experiments.

Possible structure of the newly found exotic state η1(1855)

Recently, a hadronic state named $\eta_1(1855)$, about 1.86 GeV, was observed in the BESIII experiment. This finding has a peculiar interest due to its exotic quantum number $J^{PC}=1^{-+}$. In this paper, we examine the tetraquark interpretation for the structure of $\eta_1(1855)$ in the configurations of $[1_c]_{\bar{s}s}\otimes[1_c]_{\bar{q}q}$ and $[1_c]_{\bar{s}q}\otimes[1_c]_{\bar{s}q}$, and perform a mass spectrum calculation in the framework of QCD sum rules. The results show that the observed $\eta_1(1855)$ could be embedded into the $[1_c]_{\bar{s}s}\otimes[1_c]_{\bar{q}q}$ configuration. The possible tetraquark and hybrid decay modes are analyzed, which are critical in decoding its inner structure. In the same way, we evaluate as well the $\bar{s}s\bar{s}s$ molecular state with $1^{-+}$ quantum number and find that there might exist two such ground states.

Precise Measurements of Decay Parameters and CP Asymmetry with Entangled Λ−Λ¯ Pairs

Based on 10billion J/ψ events collected at the BESIII experiment, a search for CP violation in Λ decay is performed in the difference between CP-odd decay parameters α_{-} for Λ→pπ^{-} and α_{+} for Λ[over ¯]→p[over ¯]π^{+} by using the process e^{+}e^{-}→J/ψ→ΛΛ[over ¯]. With a five-dimensional fit to the full angular distributions of the daughter baryon, the most precise values for the decay parameters are determined to be α_{-}=0.7519±0.0036±0.0024 and α_{+}=-0.7559±0.0036±0.0030, respectively. The Λ and Λ[over ¯] averaged value of the decay parameter is extracted to be α_{avg}=0.7542±0.0010±0.0024 with unprecedented accuracy. The CP asymmetry A_{CP}=(α_{-}+α_{+})/(α_{-}-α_{+}) is determined to be -0.0025±0.0046±0.0012, which is one of the most precise measurements in the baryon sector. The reported results for the decay parameter will play an important role in the studies of the polarizations and CP violations for the strange, charmed and beauty baryons.

Measurement of integrated luminosities at BESIII for data samples at center-of-mass energies between 4.0 and 4.6 GeV* *Supported in part by National Key R&D Program of China (2020YFA0406300, 2020YFA0406400); National Natural Science Foundation of China (NSFC) (11625523, 11635010, 11735014, 11822506, 11835012, 11935015, 11935016, 11935018, 11961141012, 12022510, 12025502, 12035009, 12035013, 12061131003); the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program;

The integrated luminosities of data samples collected in the BESIII experiment in 2016–2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010–2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur.

Luminosities and energies of e + e − collision data taken between =4.61 GeV and 4.95 GeV at BESIII* *Supported in part by National Key R&D Program of China (2020YFA0406400, 2020YFA0406300); National Natural Science Foundation of China (NSFC) (11635010, 11735014, 11805086, 11835012, 11935015, 11935016, 11935018, 11961141012, 12022510, 12025502, 12035009, 12035013, 12192260, 12192261, 12192262, 12192263, 12192264, 12192265); the Chinese Academy of

From December 2019 to June 2021, the BESIII experiment collected approximately 5.85 fb−1 of data at center-of-mass energies between 4.61 and 4.95 GeV. This is the highest collision energy BEPCII has reached to date. The accumulated annihilation data samples are useful for studying charmonium(-like) states and charmed-hadron decays. By adopting a novel method of analyzing the production of pairs in annihilation, the center-of-mass energies are measured with a precision of 0.6 MeV. Integrated luminosities are measured with a precision of better than 1% by analyzing the events of large-angle Bhabha scattering. These measurements provide important inputs to analyses based on these data samples.

Recent results on hyperon pair production and nucleon time-like form factors at BESIII

The BESIII experiment, based on the BEPCII collider at IHEP in Beijing, China, is capable of measuring nucleon form factors with unprecedented precision. We report recent results achieved by the BESIII collaboration concerning the nucleon time-like form factors and the hyperon pair production. Specifically, we outline the results obtained by the study of the process e^+e^- \to p \overline pe+e−→pp¯, using both the scan-energy and initial-state radiation techniques, those of the process e^+e^- \to n \overline ne+e−→nn¯, and the study of the \SigmaΣ polarization regarding the process e^+e^- \to J/\psi \to \Sigma^+\overline \Sigma{}^-e+e−→J/ψ→Σ+Σ¯−.

Light meson decays at BESIII

The world’s largest sample of J/\psiJ/ψ events accumulated at the BESIII detector offers a unique opportunity to investigate \etaη and \eta^\primeη′ physics via two body J/\psiJ/ψ radiative or hadronic decays. In recent years the BESIII experiment has made significant progresses in \eta/\eta^\primeη/η′ decays. A selection of recent highlights in light meson spectroscopy at BESIII are reviewed in this report, including the observation of \eta^\prime\rightarrow\pi^+\pi^-\mu^+\mu^-η′→π+π−μ+μ−, the study of \eta^\prime\rightarrow\pi^+\pi^-e^+e^-η′→π+π−e+e−, and search for CPCP-violation in this decay, search for the rare decays of \eta^\prime\rightarrow4\pi^0η′→4π0 and \eta^\prime\rightarrow\gamma\gamma\etaη′→γγη, as well as the precision measurement of the branching fraction of \eta^\primeη′ decays.

Operation and readout of the CGEM inner tracker

A recently approved ten-year extension of the BESIII experiment (IHEP, Beijing) motivated an upgrade program for both the accelerator and the detector. In particular, the current inner drift chamber is suffering from aging and the proposal is to replace it with a detector based on the cylindrical GEM technology. The CGEM inner tracker (CGEM-IT) consists of three coaxial layers of triple-GEM. The tracker is expected to restore efficiency, improve z-determination and secondary vertex position reconstruction with a spatial resolution of 130μm in the xy-plane and better than 300μm along the beam direction. A dedicated readout system was developed. Signals from the detector strips are processed by TIGER, a custom-made 64-channel ASIC that provides an analog charge readout via a fully digital output up to about 50fC and less than 3ns jitter. TIGER continuously streams over-threshold data in trigger-less mode to an FPGA-based readout module, called GEM Read Out Card, that organizes the incoming data by building the event packets when the trigger arrives. Two of the three layers are in operation in Beijing since December 2019 and remotely controlled since January 2020. Due to the pandemic situation the integration activity has been continued on a small-scale prototype. Recently, a test beam has been performed at CERN with the final electronics configuration. In this presentation, the general status of the CGEM-IT project will be presented with a particular focus on the results from the test beam data acquisition.

Suppression of top-up injection backgrounds with offline event filter in the BESIII experiment

Suppression of top-up injection backgrounds with offline event filter in the BESIII experiment

Recent results from BESIII

The BESIII experiment is using e+ e- annihilation in the tau-charm region to study various topics in hadron physics, from the spectroscopy of light and charmonium hadrons, studies on rare and symmetry violating decays to open-charm physics. An overview over a selection of recent BESIII contributions to the field of hadron physics is given, highlighted by the recent observation of a near threshold enhancement in the recoil mass of the K+ in the process e+ e- --> K+ (Ds- D*0 + Ds*- D0) as a possible Zcs candidate.

Cross section measurements of the e+e−→ D*+D*− and e+e−→ D*+D− processes at center-of-mass energies from 4.085 to 4.600 GeV

The Born cross sections of the e+e−→ D*+D*− and e+e−→ D*+D− processes are measured using e+e− collision data collected with the BESIII experiment at center-of-mass energies from 4.085 to 4.600 GeV, corresponding to an integrated luminosity of 15.7 fb−1. The results are consistent with and more precise than the previous measurements by the Belle, Babar and CLEO collaborations. The measurements are essential for understanding the nature of vector charmonium and charmonium-like states.

Recent results on nucleon electromagnetic form factors at BESIII


 
 
 We report recent results of Nucleon Electromagnetic Form Factors at the BESIII experiment. The BESIII detector is installed at the BEPCII electron-positron collider in Beijing (PRC) with a center-of-mass energy range between between 2.0 and 4.9 GeV. The Nucleon Electromagnetic Form Factors has been measured in BESIII both via direct e+e− annihilation and initial-state-radiation technique.
 
 

Hyperon pair production at BESIII

Hyperons provide a unique avenue to study the strong interaction. Due to their limited lifetime, the hyperon production in e +e − collisions is a new viable way to obtain information to understand the hyperon structure and internal dynamics, and even insight into the nature of the charmonium(-like) states. With the unique data sets obtained by the BESIII experiment, the recent results for the hyperon pair production in e +e − collisions are presented, such as observation of ψ(3686) → Ξ(1530)−Ξ(1530) ¯ +, determination of the Ω − spin, observation of the Ξ hyperon polarization, study of threshold effect in the sector of Ξ hyperon, search for Y (4230/4260) → Ξ −Ξ¯+ and so on.

Vector Charmonium-like States at BESIII

BESIII experiment is the only electron positron experiment working in the $\tau$-charm energy region in the world now, and on which the largest sample about Charmonium states has been taken. The Charmonium-like states, which are hadron states beyond the naive quark model are studied with this sample, in the Charmonium plus light hadron, light hadron only and leptonic final states.