BES, the Beijing Spectrometer, began its first groundbreaking physics run, thirty years ago, in 1989. This is the first high energy physics experiment in China, and has been unique throughout the world for its thorough and extended coverage of the tau and charm energy region. Since then, the BES detector has undergone steady improvements, upgrading to BESII in 1998 and to BESIII in 2008. Over the same period, the collaboration has expanded from 150 members, across 10 institutions in China and the United States, to about 500 members, across 72 institutions and 15 countries. The physics program, too, has extended from light hadron spectroscopy, tau, and charm physics to the discovery of exotic charmonium-like states, precision tests of the Standard Model of particle physics, and searches for new physics beyond the Standard Model.
This special volume collects the proceedings of the symposium held at the Institute of High Energy Physics, Beijing, in celebration of the 30-year span of achievements and progress at the BES, BESII, and BESIII experiments. Written by many leaders of the BES collaborations, these proceedings document the early days of the BES experiments, important milestones, and the future physics program at BESIII.
Sample Chapter(s)
Preface
1. Beginnings of BES Experiment
Contents:
Readership: Researchers in elementary particle physics.
https://doi.org/10.1142/9789811217739_fmatter
The following sections are included:
https://doi.org/10.1142/9789811217739_0001
This is a brief introduction of the early history of BES, the formation of BES collaboration. The article is composed by Prof. Zhipeng Zheng, the formal director of IHEP.
https://doi.org/10.1142/9789811217739_0002
The BES experiment has had a wonderful and productive 30 years. Why the BES experiment has lasted 30 years has a lot to do with the wide range of physics available in the tau-charm energy region. Also discussed are the beginnings of BES and the US connection, as well as some BES high points, a low point, and a few collaboration meeting outings.
https://doi.org/10.1142/9789811217739_0003
This is the story of the Beijing Spectrometer (BES) Publication Policy, the first self-governance document of the Beijing Spectrometer. The Publication Policy played an instrumental role in facilitating communication between collaborators and disseminating their measurements.
https://doi.org/10.1142/9789811217739_0004
The first measurement of the tau lepton mass by the BES collaboration performed in 1992 is presented. A short review of the Standard Model, the discovery at SLAC, and the key predictions are given. The BES mass measurement is described in detail including the optimization of the search method, the likelihood and the results.
https://doi.org/10.1142/9789811217739_0005
Purely leptonic decays of the Ds(D) meson in the reaction e+e−→D+sD−s(D*+D−) are observed by the BES group at the BEPC collider. Direct measurements of the weak decay constant fDs (fD) and the Ds(D) branching fractions to μνμ, ϕπ, eX, ϕX (μνμ) are obtained for the first time.
https://doi.org/10.1142/9789811217739_0006
In this article, I review the early years of the study of charmonium physics at the BES experiment and its consequences on the future research at the BESII and BESIII experiments, based on my own experience of working at BES since summer 1992 and material found from the IHEP archives.
https://doi.org/10.1142/9789811217739_0007
The birth, growth and maturity of studies of ψ(3770) non-DˉD decays and its related XabvDˉD physics as well as D physics at the BES experiment are briefly reviewed.
https://doi.org/10.1142/9789811217739_0008
This paper discusses the events leading up to, the instantiation in 1994 of the first permanent network connection between mainland China and the USA, and some of the impacts since.
https://doi.org/10.1142/9789811217739_0009
The BES II upgrade included the construction of a new Main Drift Chamber and the rebuilding of the MARK III Vertex Chamber. The manufacture and performance of high-voltage feedthroughs are a critical component of tracking chambers, and they need to maintain structural and dielectric integrity throughout their expected lifetime. Long term (years) and short term (weeks to months) damage to Delrin feedthroughs was found during the construction and operation of BES II.
https://doi.org/10.1142/9789811217739_0010
The τ-Charm physics required the upgrade of BEPC. Faced the strong competition from CESRc, The BEPC upgrade (BEPCII) adopted the double ring scheme in the existing short and narrow tunnel with the design luminosity of 1033 cm−2s−1, which is two orders of magnitudes higher than the one of BEPC before upgrade. The new detector BESIII provided the small systematics errors and the very high rate of the data taking. The BEPCII was successfully constructed on schedule and reached the design specification.
https://doi.org/10.1142/9789811217739_0011
This paper describes the update program for BESII and the design, construction, data taking and data quality for BESIII. The team members are introduced, and the major works for BESII and BESIII are detailed. BESIII reached the design goal and a lots of data have been taken, producing important physics results.
https://doi.org/10.1142/9789811217739_0012
This talk will give a brief history of the European involvement in BES(III), starting with the first group joining in 2002. In 2019, 14 institutions from six European countries are part of BESIII, with more than 120 active members participating.
https://doi.org/10.1142/9789811217739_0013
Two institutes located in Russia take part in the BESIII experiment for more than a decade. The first one is the Joint Institute for Nuclear Research (JINR), the international scientific organization located in Dubna, not far from Moscow. Another one is the Budker Institute of Nuclear Physics of the Siberian Branch of Russian Academy of Sciences (BINP), located in Novosibirsk. This report describes the history of their way to join the BESIII Collaboration and their contribution to the experiment.
https://doi.org/10.1142/9789811217739_0014
The study of non-conventional mesons in the charmonium system (the XYZ states) has evolved to become an integral part of the BESIII physics program. The following traces the evolution of this line of study from its origins in 2010, with a proposal to study ψ(4040) decays, to 2014, when the discovery of the Zc states had risen to prominence.
https://doi.org/10.1142/9789811217739_0015
High Energy Physic in China can be classified into four major categories: accelerator-based experiments, underground experiments, surface experiments particularly at high altitude, and space experiments. An overview of these experiments and their future prospects are presented.
https://doi.org/10.1142/9789811217739_0016
A brief review of light hadron physics achieved at the BES experiment is presented. In addition to the evaluation of the contributions to the light hadron spectroscopy from the BES and BESII experiment, we also highlighted the present status and the most recent developments at BESIII experiment. In particular, we made an discussion on the prospects for future improvements at the BESIII experiment.
https://doi.org/10.1142/9789811217739_0017
In this talk, I review the physics achievements of conventional charmonium and exotic charmonium-like states at BES, BESII, and BESIII three-generation experiments. I discuss the motivations, corresponding data sets, some important examples, and impacts of these exciting results during last 30 years.
https://doi.org/10.1142/9789811217739_0018
In BES experiments, studies of charmed meson decays were initially started with the BESI data taken at √s=4.04 GeV in the middle 1990s, and then extended with the BESII data taken around √s=3.773 GeV in 2000s. In 2010s, many important results from studies of charmed meson decays were reported, with the world largest threshold data samples at BESIII. Here gives a brief review on charmed meson physics at BESIII.
https://doi.org/10.1142/9789811217739_0019
This article describes the tau physics research at BESIII, some of which have been performed, other significant research has been prospected.
https://doi.org/10.1142/9789811217739_0020
A brief history of the measurements of R values and QCD studies at the BES experiments is reviewed. The BESII measured R values in the energy region between 2–5 GeV, achieving an accuracy of ∼ 6.6% on average. Prior to that, a pre-stduy with earlier data collected with the BESI detector gave R values around ττ production threshold. Nowadays the BESIII is devoted to measuring R values with unprecedented statistics and fine steps in the range of 2–4.6 GeV, with a goal of ∼ 3% precision. Thanks to the large data samples, QCD predictions are tested at BESIII from various aspects, including fragmentation function, form factors, threshold effect, phase between electroweak and strong interactions, etc.
https://doi.org/10.1142/9789811217739_0021
The year 2019 marks the 30th anniversary of BES and the 100th anniversary of Rutherford’s discovery of the proton. In spite of the fact that when BES operations started the proton was already 70 years old and the strange hyperons were all over 25, BES continues to make important and unique measurements of nucleon and hyperon properties, including some interesting discoveries.
https://doi.org/10.1142/9789811217739_0022
New physics search is a part of 30 years of BES physics program, which started during BESII days. The richness of physics features in the τ-charm energy region enabled many published results. At BESIII, the clean environments, high luminosity and excellent detector performance provide ideal opportunities for searches for new physics beyond standard model. Though most obtained upper limits are still above than the SM predictions, they may help to discriminate the different new physics models or to constrain the parameters in the different physics models. With the accumulation of large data sets and possible increase of luminosity and cms energy, as well as an ever-improving understanding of the detector performance, BESIII will have great potential in NP searches in the coming years.
https://doi.org/10.1142/9789811217739_0023
The Beijing spectrometer III (BESIII) is a high precision detector located at the Beijing electron positron collider II (BEPCII). After running ten years, the BESIII sub-systems are suffering from the aging problems that lead to a performance degradation. In order to ensure the study of the important physics topics in tau-charm energy region that can be further explored at the BESIII, the BESIII experiment has received several upgrades. We report the upgrades of the BESIII, including the inner part of the drift chamber, the end cap of the time-of-flight system and the valve box of the superconducting magnet.
https://doi.org/10.1142/9789811217739_0024
The mass of the τ lepton has been measured at the Beijing Electron-Positron Collider using the Beijing Spectrometer. A search near threshold for e+ e− → τ+ τ− was performed. Candidate events were identified by requiring that one τ decay via τ → evῡ, and the other via τ → μvῡ. The mass value, obtained from a fit to the energy dependence of the τ+ τ− cross section, is mτ=1776.9+0.4−0.5±0.2 MeV.
https://doi.org/10.1142/9789811217739_0025
The Beijing Spectrometer (BES) experiment has observed purely leptonic decays of the Ds meson in the reaction e+e−→D+sD−s at a c.m. energ y of 4.03 GeV. Three events are observed in which one Ds decays hadronically to ϕπ, ˉK*0K, or ˉK0K, and the other decays leptonically to μνμ or τντ. With the assumption of μ-τ universality , values of the branching fraction, B(Ds→μνμ)=(1.5+1.3+0.3−0.6−0.2)%, and the Ds, pseudoscalar decay constant, fDs=(4.3+1.5+0.4−1.3−0.4)×102 MeV, are obtained.
https://doi.org/10.1142/9789811217739_0026
The decays of the ψ(2S) into vector plus tensor meson final states have been studied for the first time using the BES detector. We determine upper limits on branching fractions for ψ(2S) decays into ωf2, ρa2, K*0ˉK*02+c.c., and ϕf′2(1525) that are, in each case, significantly smaller than the corresponding branching fractions for the J/ψ meson, scaled according to the expectations of perturbative QCD. [S0031-9007(98)07836-3]
https://doi.org/10.1142/9789811217739_0027
We report values of R = σ(e+e− → hadrons)/σ(e+e− → μ+μ−) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.
https://doi.org/10.1142/9789811217739_0028
We observe a narrow enhancement near 2mp in the invariant mass spectrum of pˉp pairs from radiative J/ψ→γpˉp decays. No similar structure is seen in J/ψ→π0pˉp decays. The results are based on an analysis of a 58 × 106 event sample of J/ψ decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit-Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2mp at M=1859+3−10(stat)+5−25(syst) MeV/c2 and the total width is Γ<30 MeV/c2 at the 90% confidence level. These mass and width values are not consistent with the properties of any known particle.
https://doi.org/10.1142/9789811217739_0029
The decay ψ(2S)→K0SK0L is observed using ψ(2S) data collected with the Beijing Spectrometer at the Beijing Electron-Positron Collider; the branching fraction is determined to be B(ψ(2S)→K0SK0L)=(5.24±0.47±0.48)×10−5. Compared with J/ψ→K0SK0L, the ψ(2S) branching fraction is enhanced relative to the prediction of the perturbative QCD “12%” rule. The result, together with the branching fractions of ψ(2S) decays to other pseudoscalar meson pairs (π+ π− and K+K−), is used to investigate the relative phase between the three-gluon and the one-photon annihilation amplitudes of ψ(2S) decays.
https://doi.org/10.1142/9789811217739_0030
Evidence of ψ(3770) decays to a non-DˉD final state is observed. A total of 11.8 ± 4.8 ± 1.3 ψ (3770) → J/ψπ+π− events are obtained from a data sample of 27.7 pb−1 taken at center-of-mass energies around 3.773 GeV using the BES-II detector at the BEPC. The branching fraction is determined to be BF(ψ(3770) → J/ψπ+π−) = (0.34 ± 0.14 ± 0.09)%, corresponding to the partial width of Γ (ψ(3770) → J/ψπ+π−) = (80 ± 33 ± 23) keV.
https://doi.org/10.1142/9789811217739_0031
The decay ψ′→π+π−π0 is analyzed using a sample of 14 million ψπ events taken with the BESII detector at the BEPC, and the branching fraction is measured to be B(ψ′→π+π−π0)=(18.1±1.8±1.9)×10−5 A partial wave analysis is carried out using the helicity amplitude method. ψπ → ρ(770)π is observed, and the branching fraction is measured to be B(ψ′→ρ(770)π)=(5.1±0.7±1.1)×10−5, where the first error is statistical and the second one is systematic. A high mass enhancement with mass around 2.15 GeV/c2 is also observed. Attributing this enhancement to the ρ(2150) resonance, the branching fraction is measured to be B(ψ′→ρ(2150)π→π+π−π0)=(19.4±2.5+11.5−3.4)×10−5. The results will help in the understanding of the longstanding “ρπ puzzle” between J/ψ and ψπ hadronic decays.
https://doi.org/10.1142/9789811217739_0032
The decay channel J/ψ→γπ+π−η′ is analyzed using a sample of 5.8 × 107 J/ψ events collected with the BESII detector. A resonance, the X(1835), is observed in the π+π−η′ invariant-mass spectrum with a statistical significance of 7.7σ. A fit with a Breit-Wigner function yields a mass M = 1833.7 ± 6.1(stat) ± 2.7(syst) MeV/c2, a width Γ = 67.7 ± 20.3(stat) ± 7.7(syst) MeV/c2, and a product branching fraction B(J/ψ→γX)⋅B(X→π+π−η′)=[2.2±0.4(syst)±0.4(syst)]×10−4. The mass and width of the X(1835) are not compatible with any known meson resonance. Its properties are consistent with expectations for the state that produces the strong pˉp mass threshold enhancement observed in the J/ψ→γpˉp process at BESII.
https://doi.org/10.1142/9789811217739_0033
We study the process e+e−→π+π−J/ψ at a center-of-mass energy of 4.260 GeV using a 525 pb−1 data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9 ± 1.9 ± 3.7) pb, consistent with the production of the Y(4260). We observe a structure at around 3.9 GeV/c2 in the π±J/ψ mass spectrum, which we refer to as the Zc(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the π±J/ψ invariant mass spectrum, neglecting interference, results in a mass of R=(σ(e+e−→π±Zc(3900)∓→π+π−J/ψ)/σ(e+e−→π+π−J/ψ))=(21.5±3.3±7.5)%. In all measurements the first errors are statistical and the second are systematic.
https://doi.org/10.1142/9789811217739_0034
We study e+e−→π+π−hc at center-of-mass energies from 3.90 to 4.42 GeV by using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies and are found to be of the same order of magnitude as those of e+e−→π+π−J/ψ but with a different line shape. In the π±hc mass spectrum, a distinct structure, referred to as Zc(4020), is observed at 4.02 GeV/c2. The Zc(4020) carries an electric charge and couples to charmonium. A fit to the π±hc invariant mass spectrum, neglecting possible interferences, results in a mass of (4022.9 ± 0.8 ± 2.7) MeV/c2 and a width of (7.9 ± 2.7 ± 2.6) MeV for the Zc(4020), where the first errors are statistical and the second systematic. The difference between the parameters of this structure and the Zc(4025) observed in the D*ˉD* final state is within 1.5σ, but whether they are the same state needs further investigation. No significant Zc(3900) signal is observed, and upper limits on the Zc(3900) production cross sections in π±hc at center-of-mass energies of 4.23 and 4.26 GeV are set.
https://doi.org/10.1142/9789811217739_0035
With data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.009 to 4.420 GeV, the process e+e− → γX(3872) is observed for the first time with a statistical significance of 6.3σ. The measured mass of the X(3872) is (3871.9 ± 0.7stat ± 0.2syst) MeV/c2, in agreement with previous measurements. Measurements of the product of the cross section σ[e+e− → γX(3872)] and the branching fraction B[X(3872)→π+π−J/ψ] at center-of-mass energies 4.009, 4.229, 4.260, and 4.360 GeV are reported. Our measurements are consistent with expectations for the radiative transition process Y(4260) → γX(3872).
https://doi.org/10.1142/9789811217739_0036
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 |Fπ|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 aππ,LOμ(600−900 MeV)=(368.2±2.5stat±3.3sys)⋅10−10, which is between the corresponding values using the BaBar or KLOE data.
https://doi.org/10.1142/9789811217739_0037
We report the first measurement of absolute hadronic branching fractions of Λ+c baryon at the Λ+cˉΛ−c production threshold, in the 30 years since the Λ+c discovery. In total, 12 Cabibbo-favored Λ+c hadronic decay modes are analyzed with a double-tag technique, based on a sample of 567 pb−1 of e+e− collisions at √s=4.599 GeV recorded with the BESIII detector. A global least-squares fitter is utilized to improve the measured precision. Among the measurements for twelve Λ+c decay modes, the branching fraction for Λ+c→pK−π+ is determined to be (5.84 ± 0.27 ± 0.23)%, where the first uncertainty is statistical and the second is systematic. In addition, the measurements of the branching fractions of the other 11 Cabibbo-favored hadronic decay modes are significantly improved.
https://doi.org/10.1142/9789811217739_0038
Using 1.09 × 109 J/ψ events collected by the BESIII experiment in 2012, we study the J/ψ→γη′π+π− process and observe a significant abrupt change in the slope of the η′π+π− invariant mass distribution at the proton-antiproton (pˉp) mass threshold. We use two models to characterize the η′π+π− line shape around 1.85 GeV/c2: one that explicitly incorporates the opening of a decay threshold in the mass spectrum (Flatté formula), and another that is the coherent sum of two resonant amplitudes. Both fits show almost equally good agreement with data, and suggest the existence of either a broad state around 1.85 GeV/c2 with strong couplings to the pˉp final states or a narrow state just below the pˉp mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a pˉp moleculelike state or bound state with greater than 7σ significance.
https://doi.org/10.1142/9789811217739_0039
The cross section for the process e+e−→π+π−J/ψ is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb−1 of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (4222.0 ± 3.1 ± 1.4) MeV/c2 and a width of (44.1 ± 4.3 ± 2.0) MeV, while the second one has a mass of (4320.0 ± 10.4 ± 7.0) MeV/c2 and a width of (101.4+25.3−19.7±10.2)MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y(4260) resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in e+e−→π+π−J/ψ for the first time. The statistical significance of this resonance is estimated to be larger than 7.6σ. The mass and width of the second resonance agree with the Y(4360) resonance reported by the BABAR and Belle experiments within errors. Finally, the Y(4008) resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.
https://doi.org/10.1142/9789811217739_0040
Particles directly produced at electron–positron colliders, such as the J/ψ meson, decay with relatively high probability into a baryon–antibaryon pair1. For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase ΔΦ between the transition amplitudes to these helicity states results in a transverse polarization of the baryons. From the joint angular distribution of the decay products of the baryons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of ΔΦ = 42.4 ± 0.6 ± 0.5° using Λ → pπ− and ˉΛ→ˉpπ+,ˉnπ0 decays at BESIII. We find a value for the Λ → pπ− decay parameter of α− = 0.750 ± 0.009 ± 0.004, 17 ± 3% higher than the current world average, which has been used as input for all Λ polarization measurements since 1978. For ˉΛ→ˉpπ+ we find α+ = −0.758 ± 0.010 ± 0.007, giving ACP = (α− + α+)/(α− − α+) = −0.006 ± 0.012 ± 0.007, a precise direct test of charge–parity symmetry (CP) violation in Λ decays.
https://doi.org/10.1142/9789811217739_0041
Using e+e− annihilation data of 2.93 fb−1 collected at center-of-mass energy √s=3.773 GeV with the BESIII detector, we measure the absolute branching fraction of D0 → K−μ+νμ with significantly improved precision: BD0→K−μ+νμ=(3.413±0.019stat±0.035syst)%. Combining with our previous measurement of BD0→K−μ+νe, the ratio of the two branching fractions is determined to be BD0→K−μ+νμ/BD0→K−μ+νe=0.974±0.007stat±0.012syst, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentum transfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine fK+(0)=0.7327±0.0039stat±0.0030syst and |Vcs|=0.955±0.005stat±0.004syst±0.024LQCD.
https://doi.org/10.1142/9789811217739_0042
Using a 3.19 fb−1 data sample collected at an e+e− center-of-mass energy of Ecm = 4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay D+s→μ+νμ to be BD+s→μ+νμ=(5.49±0.16stat±0.15syst)×10−3. Combining our branching fraction with the masses of the D+s and μ+ and the lifetime of the D+s, we determine fD+s|Vcs|=246.2±3.6stat±3.5syst MeV. Using the c → s quark mixing matrix element |Vcs| determined from a global standard model fit, we evaluate the D+s decay constant fD+s=252.9±3.7stat±3.6syst MeV. Alternatively, using the value of fD+s calculated by lattice quantum chromodynamics, we find |Vcs|=0.985±0.014stat±0.014syst. These values of BD+s→μ+νμ,fD+s|Vcs|,fD+s and |Vcs| are each the most precise results to date.
https://doi.org/10.1142/9789811217739_0043
Time flies so fast, back to 30 years ago, on April 1989, BES was moved from the spectrometer assembly hall into the collider tunnel, to be connected to the collider. After more than two months debugging, on June 22 the J/ψ particles were first observed by BES, it marked the official start of the BES physics experiment.
https://doi.org/10.1142/9789811217739_bmatter
The following sections are included:
"Warmest congratulations on the 30th anniversary of the BES collaboration. BES has made remarkable achievements in tau physics, charm physics, as well as hadronic physics, which earn China a worldwide reputation in this field."
Sample Chapter(s)
Preface
1. Beginnings of BES Experiment