The standard model of particle physics is a well-tested theoretical framework, but there are still a number of issues that deserve further experimental and theoretical investigation. For quark physics, such questions include: the nature of quark confinement, the mechanism that connects the quarks and gluons of the standard model theory to the strongly interacting particles; and the weak decays of quarks, which may provide insights into new physics mechanisms responsible for the matter-antimatter asymmetry of the Universe. These issues are addressed by the Beijing Spectrometer III (BESIII) experiment at the Beijing Electron-Positron Collider II (BEPCII) storage ring, which for the past decade has been studying particles produced in electron-positron collisions in the tau-charm energy-threshold region, and has by now accumulated the world's largest datasets that enables searches for nonstandard hadrons, weak decays of the charmed particles, and new physics phenomena beyond the standard model. Here, we review the contributions of BESIII to such studies and discuss future prospects for BESIII and other experiments.
Using the largest $J/ψ$ and $ψ(3686)$ data samples collected at the BESIII experiment, the hyperon anti-hyperon pairs are generated in their quantum entangle system. The polarization of hyperon has been observed, which makes it possible to measure the decay parameters of hyperon and anti-hyperon precisely. The CP conservation observables have been estimated which is important to test the Standard Model. In the meanwhile, the branching fractions and angular distributions related to hyperon pair production have been measured.
Studies of light meson decays are important tools to perform precision tests of the effective field theories, determine transition form factors, and test fundamental symmetries. With very high statistics data samples, the BESIII experiment provides a unique laboratory for light meson studies and is contributing significantly to a variety of these investigations. A brief review of recent progress in light meson decay studied at the BESIII experiment, including detailed studies of common decay dynamics, searches for rare/forbidden decays and new particles, is presented. Finally, together with de…
The Beijing Spectrometer (BESIII) collaboration uses $e^+e^-$ collisions in the tau-charm energy region to study a broad spectrum of topics. These include studies of light mesons and light baryons, studies of charmonium, including exotic mesons and baryons containing charmonium, studies of charmed mesons and baryons, studies of QCD and tau physics, as well as searches for new physics. The following is a Snowmass white paper that outlines the BESIII accomplishments and potential in each of these areas.
With the help of the largest data samples of $J/ψ$ and $ψ(2S)$ events ever produced in $e^+e^-$ annihilations, the three singlet charmonium states, $η_c(1S)$, $η_c(2S)$ and $h_c(1P)$, have been extensively studied at the BESIII experiment. In this review, a survey on the most recent results, including a series of precision measurements and observations of their new decay modes, is presented, which indicates the further investigations on their decays are needed to understand their decay mechanisms and have precision tests of the theoretical models. At present, about eight times larger data samp…
Spin polarization and entanglement are utilized by the BESIII experiment to learn more about the production and decay properties of hyperon-antihyperon pairs in a series of recent analyses of its unprecedented datasets at the $J/ψ$ and $ψ'$ resonances. This has lead to the observation of significant transverse polarisation in decays of $J/ψ$ or $ψ'$ into $Λ\barΛ$, $Σ\barΣ$, $Ξ\barΞ$, and $Ω\barΩ$. Because of the non-zero polarization, the decay parameters for the most common hadronic weak decays of both hyperons and antihyperons could be determined independently for the first time. Comparing t…
The light unflavoured meson $η/η^{\prime}$ decays are valuable for testing non-perturbative quantum chromodynamics and exploring new physics beyond the Standard Model. This paper describes a series of event generators, including $η/η^{\prime}\toγl^{+}l^{-}$, $η/η^{\prime}\toγπ^{+}π^{-}$, $η^{\prime}\toωe^{+}e^{-}$, $η\toπ^{+}π^{-}π^{0}$, $η/η^{\prime}\toπ^{0}π^{0}π^{0}$, $η^{\prime}\toηππ$ and $η^{\prime}\toπ^{+}π^{-}π^{+}π^{-}/π^{+}π^{-}π^{0}π^{0}$, which have been developed for investigating $η/η^\prime$ decay dynamics. For most of these generators, their usability has been validated in BESI…
School of Physical Science and Technology, Lanzhou University（兰州大学物理科学与技术学院）；Frontiers Science Center for Rare Isotopes, Lanzhou University（兰州大学稀有同位素前沿科学中心）
The BESIII experiment at the electron-positron collider BEPCII in Beijing (China) is successfully operating since 2008 and has collected large data samples in the tau-mass region, including the world's largest data samples at the $J/ψ$ and $ψ'$ resonances. The recent observations of hyperon polarizations at BESIII opens a new window for testing CP violation, as it allows for simultaneous production and detection of hyperon and anti-hyperon pair two-body weak decays. The CP-symmetry tests can be performed in processes like e.g. $J/ψ\toΛ\barΛ$, $J/ψ,ψ'\toΣ^+\barΣ^-$ and $J/ψ\toΞ^-\barΞ^+$. For t…
Hadron spectroscopy is one of the most important physics goals of BESIII. BESIII brings great opportunities to study the XYZ states of charmonium by directly producing the Y states up to 4.6 GeV. High statistics of charmonium decays collected at BESIII provide an excellent place for hunting gluonic excitations and studying the excited baryons. Recent results of light hadron spectroscopy and charmonium spectroscopy from BESIII will be reported.
A fast physics analysis framework has been developed based on SNiPER to process the increasingly large data sample collected by BESIII. In this framework, a reconstructed event data model with SmartRef is designed to improve the speed of Input/Output operations, and necessary physics analysis tools are migrated from BOSS to SNiPER. A real physics analysis $e^{+}e^{-} \rightarrow π^{+}π^{-}J/ψ$ is used to test the new framework, and achieves a factor of 10.3 improvement in Input/Output speed compared to BOSS. Further tests show that the improvement is mainly attributed to the new reconstructed …
The Standard Model (SM) of particle physics, comprised of the unified electro-weak (EW) and Quantum Chromodynamic (QCD) theories, accurately explains almost all experimental results related to the micro-world, and has made a number of predictions for previously unseen particles, most notably the Higgs scalar boson, that were subsequently discovered. As a result, the SM is currently universally accepted as the theory of the fundamental particles and their interactions. However, in spite of its numerous successes, the SM has a number of apparent shortcomings including: many free parameters that …
The study of mesons and baryons which contain at least one charm quark is referred to as open charm physics. It offers the possibility to study up-type quark transitions. Since the $c$ quark can not be treated in any mass limit, theoretical predictions are difficult and experimental input is crucial. BESIII collected large data samples of $e^{+}e^{-}$ collisions at several charm thresholds. The at-threshold decay topology offers special opportunities to study open charm decays. We present a selection of recent BESIII results. Branching fractions and the $D_{s}^{+}$ decay constant are measured …
The world's largest sample of 1.31 billion $J/ψ$ events accumulated at the BESIII detector, provides a unique opportunity to investigate $η$ and $η^\prime$ physics via two body $J/ψ$ radiative or hadronic decays. For many $η^\prime$ decay channels the low background data samples are up to three orders of magnitude larger than collected in any previous experiment. Here we review the most significant results on $η$ and $η^\prime$ obtained at BESIII so far. The analyses range from detailed studies of the common decays dynamics, observations of new radiative and Dalitz decays, and search for rare/…
A comprehensive review of weak decays of charmed hadrons ($D^{0/+}$, $D^+_s$ and $Λ^+_c$) based on analyses of the threshold data from $e^+e^-$ annihilation in the BESIII experiment is presented. Current experimental challenges and successes in understanding decays of the charmed hadrons are discussed. Precise calibrations of QCD and tests of the Standard Model are provided by measurements of purely leptonic and semi-leptonic decays of charmed hadrons, and lepton universality is probed in purely leptonic decays of charmed mesons to three generations of leptons. Quantum correlations in threshol…
Learning transferable event representations for charmed baryon physics at BESIII
University of Chinese Academy of Sciences（中国科学院大学）；Lanzhou University（兰州大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）
The particle identification of charged hadrons, especially for the separation of $K$ and $π$, is crucial for the flavour physics study. Ionization measurement with the cluster counting technique, which has much less fluctuation than traditional $dE/dx$ measurement, is expected to provide better particle identification for the BESIII experiment. Simulation studies, including a Garfield++ based waveform analysis and a performance study of K/πidentification in the BESIII, offline software system have been performed. The results show that $K/π$ separation power and PID efficiency would be improved…
A high-energy $e^+e^-$ Linear Collider has been considered since a long time as an important complement to the LHC. Unprecedented precision measurements as well as the exploration of so far untouched phase space for direct production of new particles will provide unique information to advance the limits of our understanding of our universe. Within this project, the physics prospects of such a collider as well as their interplay with design of the accelerator and the detectors have been investigated in a quantitative way. This kind of study required a close collaboration between theory and expe…
The third generation of the Beijing Electron Spectrometer, BESIII, is an apparatus for high energy physics research. The hunting of new particles and the measurement of their properties or the research of rare processes are sought to understand if the measurements confirm the Standard Model and to look for physics beyond it. The detectors ensure the reconstruction of events belonging to the sub-atomic domain. The operation and the efficiency of the BESIII inner tracker is compromised due to the the radiation level of the apparatus. A new detector is needed to guarantee better performance and t…
There has recently been a dramatic renewal of interest in the subjects of hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like $XYZ$ states at BESIII and $B$ factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related $X(1835)$ meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons. We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII over the remai…
Colloquium: Hadron Production in Open-charm Meson Pair at $e^+e^-$ Collider
School of Physical Science and Technology, Lanzhou University（兰州大学物理科学与技术学院）；Lanzhou Center for Theoretical Physics, Key Laboratory of Theoretical Physics of Gansu Province, and Key Laboratory for Quantum Theory and Applications of MoE, Gansu Provincial Research Center for Basic Disciplines of Quantum Physics, Lanzhou University（兰州大学理论物理研究中心、甘肃省理论物理重点实验室、教育部量子理论与应用重点实验室、甘肃省量子物理基础学科省级研究中心）；School of Physics and Center of High Energy Physics, Peking University（北京大学物理学院高能物理中心）
We review the context, the motivations and the expected performances of a comprehensive and ambitious fixed-target program using the multi-TeV proton and ion LHC beams. We also provide a detailed account of the different possible technical implementations ranging from an internal wire target to a full dedicated beam line extracted with a bent crystal. The possibilities offered by the use of the ALICE and LHCb detectors in the fixed-target mode are also reviewed.
In parallel to the study of proton-proton collisions, LHCb is developing a unique heavy-ion programme and is pioneering beam-gas fixed-target physics at the CERN LHC. In this document, a selection of some recent results from both programmes is presented.
A variety of possible future analyses of HERA data in the context of the HERA data preservation programme is collected, motivated, and commented. The focus is placed on possible future analyses of the existing $ep$ collider data and their physics scope. Comparisons to the original scope of the HERA programme are made, and cross references to topics also covered by other participants of the workshop are given. This includes topics on QCD, proton structure, diffraction, jets, hadronic final states, heavy flavours, electroweak physics, and the application of related theory and phenomenology topic…
