Narrow Results

The BESIII experiment, serving as the only operational $\tau$-charm factory, has made significant strides in advancing our understanding of baryons. Notably, it has achieved a remarkable series of breakthroughs encompassing baryon decays, mass spectra, and production mechanisms. This mini review serves as the one-stop shop for readers who would like to know what has been studied about baryons at BESIII, and of course, it could be a starting point for studies about baryons at BESIII or even a super-Tau-Charm factory.

Recent results of the BESIII experiment are presented, including the first observation of the M1 transition ψ(3686) → γη_c(2S), the measurement of J/ψ → 3γ, η_c decays into baryon anti-baryon pairs, the discovery of Z_c(3900), and the study of .

Based on 106×10⁶ ψ(3686) events collected with BESIII at BEPCII, partial wave analysis (PWA) of and are performed. Clear signals for N(1535) are observed and the mass, width and spin-parity are measured from . 7 N* intermediate resonances including two significant new resonances N(2300) and N(2570) are observed and the mass, width and spin-parity are also measured from .

An end-cap Time-of-Flight (E-TOF) system with higher granularity and intrinsic time resolution of better than 50 ps will extend the K/pion separation (2 sigma) pT range to 1.4 GeV/c and enhance the physics capability of Beijing Spectrometer (BESIII). A R&D work was carried out aiming at upgrading the current BESIII E-TOF with the Multi-gap resistive Plate Chamber (MRPC) detector. The latest best test for the prototype MRPC, together with the custom designed Front End Electronics (FEE) and TDC boards, was performed at the BEPC E3 line in July 2012. The test results show that time resolution of less than 50 ps can be achieved with such a system.

Based on 2.92 fb^-1 of e⁺e^- collision data collected with the BESIII detector at GeV, we measured the asymmetry of the branching fractions of D^CP± → K^-π⁺ (D^CP± are the CP-odd and CP-even eigenstates) to be . is used to extract the strong phase difference δ_Kπ between the doubly Cabibbo-suppressed process and Cabibbo-favored D⁰ → K^-π⁺. By taking inputs of other parameters in world measurements, we obtain cosδ_Kπ = 1.03 ± 0.12 ± 0.04 ± 0.01. This is the most accurate result of cosδ_Kπ to date and can improve the world constrains on the mixing parameters and on γ/ϕ₃ in the CKM matrix.

The BESIII experiment in Beijing takes data in τ-charm domain since 2009. For the moment the world largest samples of J/ψ, ψ(3686), ψ(3770) and ψ(4040) data have been collected. Hadron spectroscopy is a unique way to access QCD, which is one of the most important physics goals of BESIII. Experimental search of new forms of hadrons and subsequent investigation of their properties would provide validation of and valuable input to the quantitative understanding of QCD. The key to success lies in high levels of precision during the measurement and high statistics in the recorded data set complemented with sophisticated analysis methods. Partial wave analysis (PWA) is a powerful tool to study the hadron spectroscopy, that allows one to extract the resonance's spin-parity, mass, width and decay properties with high sensitivity and accuracy. In this poster, we present the working PWA framework of BESIII – GPUPWA and the recent results of PWA of J/ψ → γηη. GPUPWA is a PWA framework for high statistics partial wave analyses harnessing the GPU parallel computing.

Due to the beam related background, the inner chamber of BESIII MDC has aging effect after 5 years running. The gains of the inner chamber cells decrease obviously, and the max gain decrease is about 26% for the first layer cells. A new inner drift chamber with eight stereo sense wire layers as a backup for MDC is under construction, which is almost the same as the current one but using stepped endplates to shorten the wire length beyond the effective solid angle. This new structure will be of benefit to reducing the counting rate of single cell. The manufacture of each component is going smoothly, and the new inner drift chamber will be finished by the end of April 2014.

The recent results about charmonium and charmonium-like spectroscopy and decays from BESIII are presented in this talk. We report the observation of X(3872) from Y(4260) radiative transition, π⁺π^-h_c line shape measurement and Z_c states. In addition, the accurate measurement of η_c parameters, the analysis on h_c exclusive decays into γη_c, and the first observation of the M1 transition ψ′ → γη_c(2S) are included in this talk.

We present the preliminary results of the measurement of the azimuthal asymmetries of two charged pions in the inclusive process $e^{+}{e}^{-}\to \pi \pi X$ in the BESIII experiment. These asymmetries are attributed to the so-called Collins fragmentation function, which depict the behavior of a hadron produced from a transversely polarized quark. This spin-dependent function is an important input for the global analysis of extracting the transversity inside the nucleon. In addition, by comparison with the measured asymmetries at Belle, this measurement provides the first data to explore the $Q^2$ evolution of the spin-dependent fragmentation function. This work is performed based on about 62${\mathrm{\text{pb}}}^{-1}$ data collected with the BESIII detector at BEPCII at $\sqrt{s}$=3.65GeV.

BESIII has collected $1.3\times 10^{8}J/\psi$ and $0.4\times 10^8$ of ${\psi }^{\prime }$, which are the world’s largest data samples of $J/\psi$ and ${\psi }^{\prime }$ from $e^{+}{e}^{-}$ collision. Radiative decays of charmonium provide a gluon-rich environment and are therefore regarded as one of the most promising hunting grounds for gluonic excitations. Significant progresses in the light-quark sector have been made with the unprecedented high statistics data sets. Several recent results on light hadron spectroscopy and light hadron decays will be reported, including: 1, the observation of the anomalous line shape of $X(1835)$ near $p\bar{p}$ mass threshold and related studies; 2, studies of glueballs in $J/\psi$ radiative decays; 3, search for $1^{-+}$ exotic in ${\chi }_{c1}\to \eta \pi \pi$.

The data sample of $1.3\times 10^9$$J/\psi$ events accumulated at BESIII provides us with a clean environment to study the decay of the ${\eta }^{\prime }$. In this proceeding, several recent results are reported, including the observation of the doubly radiative decay ${\eta }^{\prime }\to \gamma \gamma {\pi }^0$, amplitude analysis of the decays ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\pi }^0$ and ${\pi }^0{\pi }^0{\pi }^0$, the observation of the Dalitz decay ${\eta }^{\prime }\to \gamma e^{+}{e}^{-}$, and search for the weak decay ${\eta }^{\prime }\to K^{\pm }{\pi }^{\mp }$.

The BESIII Experiment at the Beijing Electron Positron Collider (BEPCII) has accumulated the largest $e^{+}{e}^{-}$ collisions data sets in the $\tau$-charm region in the world. Using the data sets of 448.1 million $\psi (3686)$ events and 1.3 billion $J/\psi$ events, the branching fractions and the angular distributions of $J/\psi$ and $\psi (3686)$ decay to $\mathrm{\Lambda }\bar{\mathrm{\Lambda }}$, ${\mathrm{\Sigma }}^0{\bar{\mathrm{\Sigma }}}^0$, $\mathrm{\Sigma }{(1385)}^0\bar{\mathrm{\Sigma }}{(1385)}^0$ and ${\mathrm{\Xi }}^0{\bar{\mathrm{\Xi }}}^0$ are measured. The branching fractions of $\psi (3686)\to \gamma {\chi }_{cJ}$ are reported with improved precision. The higher-order multipole amplitudes in $\psi (3686)\to \gamma {\chi }_{c1,2}$ with ${\chi }_{c1,2}\to \gamma J/\psi$ are measured, as a byproduct the ${\eta }_c(2S)\to \gamma J/\psi$ transition is searched. The Dalitz decays of $\psi (3686)\to e^{+}{e}^{-}{\chi }_{cJ}$ and ${\chi }_{cJ}\to e^{+}{e}^{-}J/\psi$ are observed and the branching fractions are measured. $h_c$ radiative decays $h_c\to \gamma {\eta }^{\prime }(\eta )$ are observed for the first time. Improved measurement of ${\eta }_c\to \varphi \varphi$ and search for ${\eta }_c\to \omega \varphi$ are reported.

The anomalous part of the magnetic moment of the muon, (g-2)${}_{\mu }$, allows for one of the most precise tests of the Standard Model of particle physics. We report on recent results by the BESIII Collaboration of exclusive hadronic cross section channels, such as the 2$\pi$, 3$\pi$, and 4$\pi$ final states. These measurements are of utmost importance for an improved calculation of the hadronic vacuum polarization contribution of (g-2)${}_{\mu }$, which currenty is limiting the overall Standard Model prediction of this quantity. BESIII has furthermore also intiatated a programme of spacelike transition form factor measurements, which can be used for a determination of the hadronic light-by-light contribution of (g-2)${}_{\mu }$ in a data-driven approach. These results are of relevance in view of the new and direct measurements of (g-2)${}_{\mu }$ as foreseen at Fermilab/USA and J-PARC/Japan.

Form factors of hadron provide fundamental information about its structure and dynamics. They constitute a rigorous test of non-perturbative QCD as well as of phenomenological models. Based on data samples collected with BESIII detector at BEPCII collider, born cross section of $e^{+}{e}^{-}\to p\bar{p}$ and proton effective form factors are measured at 12 center-of-mass energies between 2.2324 and 3.671 GeV. The ratio $|G_E/G_M|$s are extracted by fitting polar angle distribution of proton for data samples with large statistics. For data between 3.773 and 4.6 GeV, we use initial state radiation (ISR) method to study $e^{+}{e}^{-}\to p\bar{p}$ by tagged or un-tagged ISR photon, where the pair cross section, effective form factors and $|G_E/G_M|$s are obtained from proton pair threshold to about 3 GeV. For $e^{+}{e}^{-}\to \mathrm{\Lambda }\bar{\mathrm{\Lambda }}$ and $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Lambda }}}_c^{-}$, the pair cross section and $\mathrm{\Lambda }/{\mathrm{\Lambda }}_c$ form factors are measured near threshold. With data scanned in 2015 from 2-3.08 GeV, charged Kaon pair cross section and form factors are measured at 21 center-of-mass energies.

Many models beyond the Standard Model, motivated by the recent astrophysical anomalies, predict a new type of weak-interacting degrees of freedom. Typical models include the possibility of the low-mass dark gauge bosons of a few GeV and thus making them accessible at the BESIII experiment running at the tau-charm region. The BESIII has recently searched such dark bosons in several decay modes using the high statistics data set collected at charmonium resonaces. This talk will summarize the recent BESIII results of these dark photon searches and related new physics studies.

In 2014 BESIII collected a data sample of 567 $p{b}^{-1}$ at $E_{cm}$ = 4.6 GeV, which is just above the ${\mathrm{\Lambda }}_c^{+}$ pair production threshold. By analyzing this data sample, we have measured the absolute branching fractions for many decays of ${\mathrm{\Lambda }}_c^{+}$ for the first time. These decays include the semileptonic decays of $\mathrm{\Lambda }{e}^{+}\nu$, $\mathrm{\Lambda }{\mu }^{+}\nu$, the hadronic decays of $p{K}_s$, $p{K}^{-}{\pi }^{+}$, $p{K}^{-}{\pi }^{+}{\pi }^0$, $\mathrm{\Lambda }{\pi }^{+}$, $\mathrm{\Lambda }{\pi }^{+}{\pi }^0$, ${\mathrm{\Sigma }}^{+}{\pi }^{+}{\pi }^0$, $p{K}_s{\pi }^0$, $\mathrm{\Lambda }{\pi }^{+}{\pi }^{+}{\pi }^{-}$, $p{K}_s{\pi }^{+}{\pi }^{-}$, ${\mathrm{\Sigma }}^0{\pi }^{+}$, ${\mathrm{\Sigma }}^{+}{\pi }^0$, ${\mathrm{\Sigma }}^{+}\omega$, $p\varphi$, $p{K}^{+}{K}^{-}(\mathrm{\text{non}}-\varphi )$, $p{\pi }^{+}{\pi }^{-}$, $n{K}_s\pi +$, ${\mathrm{\Sigma }}^{-}{\pi }^{+}{\pi }^{+}({\pi }^0)$ and inclusive decay $\mathrm{\Lambda }$ + anything. The decays of $p{\pi }^{+}{\pi }^{-}$, $n{K}_s{\pi }^{+}$ and ${\mathrm{\Sigma }}^{-}{\pi }^{+}{\pi }^{+}{\pi }^0$ are observed for the first time and the others are measured with significantly improved precision. These results are important to benefit the development of the related theories, and provide important inputs for both charmed baryons and $B$ physics.

In this paper the new endcap Time-of-Flight system (ETOF) of BESIII experiment at the IHEP is described. The new detector module is composed of multi-gap resistive plate chamber (MRPC) with the gas mixture 90% Freon+5% S$F_6$+5% iso-$C_4{H}_{10}$. The whole system including the detectors, the gas system, the high voltage (HV) system, the readout electronics system is described. Finally the installation and commissioning of the whole system is introduced briefly. After the calibration with Bhabha events, the very promising time resolutions of 69 and 60 ps for one-end and two-ends of MRPCs are obtained. The average detection efficiency of two-ends is about 97.5%.

We extract the e⁺e⁻ → π⁺π⁻ cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb⁻¹ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor |F_π|² as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (g − 2)_μ. We find this value to be $a_{\mu }^{\pi \pi ,\text{LO}}\left(600-900\text{MeV}\right)=\left(368.2\pm {2.5}_{\text{stat}}\pm {3.3}_{\text{sys}}\right)\cdot {10}^{-10}$, which is between the corresponding values using the BaBar or KLOE data.