Charmonium results from BES

Using ～ 14 × 10^6 ψ（2S） and ～ 58 × 10^ J/ ψ data collected at BES Ⅱ/BEPC, the branching fraction of ψ（2S）→Ω-Ω^＋ is measured with about 5a statistical significance. The A electric dipole and ∧ decay parameter are studied using the decay J/ψ →∧∧→ ppπ^＋π^-. Using （106±3）× 10^6 ψ（2S） decays collected at BESⅢ/BEPC Ⅱ, we have obtained some interesting physics results. The branching fractions of XcJ→π^0π^0, ηη are measured with precision improved. The mass and width of he（l^1P1） state, together with the branching fractions of Br（ψ（2S） →π^0hc） and Br（hc →γηc） are the first measurements. Surprisingly, the decays of Xc1→φφ, ωω, and ωφ are firstly observed in BESⅢ data.     

Charmonium results from BES

Using ～14×106ψ(2S) and ～58×106J/ψ data collected at BESⅡ/BEPC,the branching fraction of ψ(2S) →Ω+Ωˉ+ is measured with about 5σ statistical significance.The Λ electric dipole and Λ decay parameter are studied using the decay J/ψ→ΛΛ→ ppˉπ+π-.Using(106±3)×106 ψ(2S) decays collected at BESⅢ/BEPCⅡ,we have obtained some interesting physics results.The branching fractions of χcJ →π0π0,ηη are measured with precision improved.The mass and width of hc(11P1) state,together with the branching fractions of Br(ψ(2S) →π0hc) and Br(hc →γηc) are the first measurements.Surprisingly,the decays of χc1 →φφ,ωω,and ωφ are firstly observed in BESⅢ data.     

Determination of event start time at BESⅢ

The principle of the method for the BESⅢ event start time determination and the code construction are described. The investigation of influence of the noise, the method of rejecting noise and the performance checking by the Monte Carlo physics data sample are also presented. The preliminary results got from the Monte Carlo simulation are presented, the reconstruction efficiency of J/ψ→ anything events at noise level 0~60% can achieve above 99%, and the error rate is below 1%.     

Study of BESⅢ trigger efficiencies with the 2018 J/ψ data

Using a dedicated data sample taken in 2018 on the J/ψ peak, we perform a detailed study of the trigger efficiencies of the BESⅢ detector. The efficiencies are determined from three representative physics processes,namely Bhabha scattering, dimuon production and generic hadronic events with charged particles. The combined efficiency of all active triggers approaches 100% in most cases, with uncertainties small enough not to affect most physics analyses.     

Tuning and Validation of the Lundcharm Model with J/ψ Decays

Using J/ψ decays collected with the BES Ⅲ detector, Lundcharm model parameters are optimized with J/ψlight hadron decays. The dependence of the response function on model parameters is approximated up to the quadratic term, and the model parameters are optimized by simultaneously fitting J/ψ inclusive charged track distributions and event shapes. The Monte Carlo simulations show that optimal parameters yield satisfactory MC distributions as compared to both the J/ψ and ψ（2S） data distributions. These optimal values are suggested for the Lundcharm model to produce J/ψ and ψ（2S） decays to light hadrons.     

Determination of the number of ψ(3686)events at BESⅢ

The numbers of ψ(3686) events accumulated by the BESⅢ detector for the data taken during 2009 and2012 are determined to be(107.0±0.8)×10~6 and(341.1±2.1)×10~6, respectively, by counting inclusive hadronic events,where the uncertainties are systematic and the statistical uncertainties are negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of ψ(3686) events for the two data taking periods is(448.1±2.9)×10~6.     

Recent results on hadron spectroscopy from BES

The BES-Ⅲ Detector is a very versatile multipurpose device located at the Institute of High Energy Physics （IHEP） in Beijing, China. Concerning the physics program it ties stringently up to the past BES and BES-Ⅱ experiments. Since start of the data taking in the middle of 2008 the accumulated dataset of 200.10^6 J/ψ events and 100.10^6 ψ＇ events already exceeds the world data on these resonances. In addition to studies of the charmonium systems the data offers great opportunity for investigations in the light hadron sector. In detail it will be reported about the confirmation of the enhancement in pp invariant mass in radiative J/ψ decays, the search for decays Y（2175） → K＊0K＊0, observation of a charged K^± in K^±π^0 and observation of a new excited baryon N＊（2065） decaying to pπ^0 and charged onjugate. The first result is based on data taken by BES-Ⅱ and BES-Ⅲ, the latter three on data collected by BES-Ⅱ only.     

Study of ππ final state interactions in ψ（2S） →π^＋π^-J/ψ

The π^＋π^ transition of heavy quarkonia in decay ψ（2S） →π^＋π^-J/ψ is studied. With the BESII data on the decay ψ（2S） →π^＋π^-J/ψ, we update the values of coupling constants （gi） and chromopolarizability （αψ（2s）J/ψ） in this process.     

Strange quarkonium states at BESⅢ

We present physics opportunities and topics with the s states(strangeonia)that can be studied with the BES detector operating at the BEPC collider.Though the φ and η/ states have long been established experimentally,only a handful of strangeonia are well known,in contrast to the rich ccharmoium system.An overview of the s states and their experimental status is presented in this paper.The BES experiment has collected the world’s largest samples of J/ψ,ψ(2S),ψ(3770),and direct e+e-annihilations at energies below the J/ψand above 3.8 Ge V,and will continue to accumulate high quality,large integrated luminosity in theτ-charm energy region.These data,combined with the excellent performance of the BESⅢ detector,will offer unprecedented opportunities to explore the s system.In this paper we describe the experimental techniques to explore strangeonia with the BESⅢ detector.     

Determination of J/ψ Event Number via J/ψ → μ^＋μ^- and J/ψ → e^＋e^- at BESⅢ

The decays of J/ψ → μ^＋μ^- and J/ψ → e^＋e^- are studied by Monte-Carlo simulation, based on the Beijing Spectrometer （BES）Ⅲ offtine software system. The methods of determination of the J/ψ event number via J/ψ → μ^＋μ^- and J/ψ → e^＋e^- are presented, respectively. These methods can be used to determine the J/ψ event number for the coming BESⅢ J/ψ data sample.     

Further insights into the ＂ρπ puzzle＂

Based on a systematic investigation of J/ψ（ψ＇）→VP, where V and P stand for light vector and pseudoscalar mesons, we identify the role played by the electromagnetic （EM） transitions and intermediate meson loop transitions, which are essential ingredients for understanding the J/ψ and ψ＇ couplings to VP. We show that on the one hand, the EM transitions have relatively larger interferences in ψ＇→ρπ and K^＊^-K ＋c.c. as explicitly shown by vector meson dominance （VMD）. On the other hand, the strong decay of ψ＇ receives relatively larger destructive interferences from the intermediate meson loop transitions. By identifying these mechanisms in an overall study of J/ψ（ψ＇） → VP, we provide a coherent understanding of the so-called ＂ρπ puzzle＂.     

Event generators for η/η' decays at BESⅢ

The light unflavoured meson η/η' 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'→γl~+l~-, η/η'→γπ~+π~-, η'→ωe~+e~-, η→π~+π~-π~0, η/η'→π~0π~0π~0, η'→ηππ andη'→π~+π~-π~+π~-/π~+π~-π~0π~0, which have been developed for investigating η/ηdecay dynamics. For most of these generators, their usability has been validated in BESIII analyses for determining the detection efficiency, and background studies. The consistency between data and Monte Carlo shows that these generators work well in the BESⅢ simulation, and will also be useful for ongoing BESⅢ analyses and other experiments for studying η/η' physics.     

Study of tracking efficiency and its systematic uncertainty from J/ψ→ppπ~+π~- at BESIII

Based on J/ψ events collected with the BESIII detector,with corresponding Monte Carlo samples,the tracking efficiency and its systematic uncertainty are studied using a control sample of J/ψ→ppπ~+π~-.Validation methods and different factors influencing the tracking efficiency are presented in detail.The tracking efficiency and its systematic uncertainty for protons and pions with the transverse momentum and polar angle dependence are also discussed.     

Study of the online event filtering algorithm for BESⅢ

The results of a study of event tagging strategies for elementary physics processes in the τ-charm region are presented. The algorithm for online event filtering is optimized by adopting the information provided by different sub-detectors according to their strengths and capacities. The algorithm is tested with various generated physics and background events. The results indicate that the algorithm satisfies the requirements of BESⅢ physics analysis and its     

J/ψ→μ^＋μ^- reconstruction in the CMS experiment

In this paper the J/ψ→μ^＋μ^- reconstruction performance in the CMS experiment at the LHC is studied in detail by using B8→J/ψφ→μμKK events. The reconstruction efficiencies of J/ψ mesons and their decay muons are obtained as a function of the transverse momentum PT and the pseudo-rapidity η. We also study the muon trigger efficiency for this channel with the planned Level-1 trigger and High Level Trigger selection criteria. It was observed that the muon reconstruction efficiency decreases when the two decay muons have a small or large 3D angular separation, which further affects the overall J/ψ reconstruction efficiency.     

Determination of the number of J/ψ events with inclusive J/ψ decays

A measurement of the number of J/ψ events collected with the BESⅢ detector in 2009 and 2012 is performed using inclusive decays of the J/ψ. The number of J/ψ events taken in 2009 is recalculated to be(223.7±1.4)×10~6, which is in good agreement with the previous measurement, but with significantly improved precision due to improvements in the BESⅢ software. The number of J/ψ events taken in 2012 is determined to be(1086.9±6.0)×10~6. In total, the number of J/ψ events collected with the BESⅢ detector is measured to be(1310.6±7.0)×106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.     

Study a0(980)-f0(980)mixing in charmonium decays

In this proceeding,we propose to directly measure the a00(980)-f0(980)mixing in J/ψ→φ f0(980)φa00(980)and χc1 →π0a00(980)→π0f0(980)with the upgraded Beijing Electron Positron Collider(BEPCII)with BESⅢ detector.We show that a narrow peak of about 8 MeV will be produced by the a00(980)-f0(980)mixing,and the predominant feature makes it standing out from the background contributions.The predicted branching ratios for these two reactions are both expected to be about O(10-6),which is unambiguously accessible with109 J/ψ and 3 × 108 χc1 at BESⅢ.     

Observation of a p^-p mass threshold enhancement in ψ′→ π 〉＋π^-J/ψ（J/ψ 〉 γp^-p） decay

The decay channel ψ′→ π 〉＋π^-J/ψ（J/ψ 〉 γp^-p） is studied using a sample of 1.06 × 10^8 ψ′ events collected by the BESIII experiment at BEPCII. A strong enhancement at threshold is observed in the p^-p invariant mass spectrum. The enhancement can be fitted with an S-wave Breit-Wigner resonance function with a resulting peak mass of M = 1861-13^＋6 （stat）-26^＋7 （syst） MeV/c^2 and a narrow width that is Г 〈 38 MeV/c^2 at the 90% confidence level. These results are consistent with published BESII results. These mass and width values do not match with well established mesons.     

Recent results on hadron spectroscopy from BES

The BES-Ⅲ Detector is a very versatile multipurpose device located at the Institute of High Energy Physics(IHEP) in Beijing,China.Concerning the physics program it ties stringently up to the past BES and BES-Ⅱ experiments.Since start of the data taking in the middle of 2008 the accumulated dataset of 200·106 J/ψ events and 100·106 ψ events already exceeds the world data on these resonances.In addition to studies of the charmonium systems the data offers great opportunity for investigations in the light hadron sector.In detail it will be reported about the confirmation of the enhancement in p invariant mass in radiative J/ψ decays,the search for decays Y(2175) → K0 K0,observation of a charged κ± in K±π0 and observation of a new excited baryon N(2065) decaying to pπ0 and charged conjugate.The first result is based on data taken by BES-Ⅱ and BES-Ⅲ,the latter three on data collected by BES-Ⅱ only.     

Studies of dE/dx measurements with the BESⅢ

The Beijing Spectrometer Ⅲ（BESⅢ）is a general-purpose detector used for the study of τ-charm physics at the Beijing Electron-Positron Collider Ⅱ（BEPC Ⅱ）.This paper presents our studies of the dE/dx measurement in the drift chamber of BESⅢ,which is important for the identification of charged particles.Corrections applied to the dE/dx measurement in data reconstruction are discussed.After our current dE/dx calibration,a resolution of about 6% has been obtained for minimum ionization particles,and a 3σ K/πseparation is obtained for momenta up to 760 MeV/c.These results meet the design goals of the BESⅢ drift chamber.