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.     

北京谱仪BESⅢ

北京谱仪是北京正负电子对撞机上的大型通用磁谱仪。对撞机中的正负电子束团在谱仪中心对撞,产生的末态带电粒子和中性粒子的空间位置、动量、能量等特性由谱仪记录,经过数据处理后进行粲-τ能区的物理研究。在BEPC上先后安装了北京谱仪BESⅠ和BESⅡ。在BEPCⅡ上安装的是新研制的北京谱仪BESⅢ包括主漂移室、电磁量能器、飞行时间计数器、μ子探测器和超导磁体,具有     

BESⅡ顶点探测器

介绍了BESⅡ上正在运行的顶点探测器基本结构、特点和性能(覆盖95%×4π立体角,空间分辨σ_rφ≈100μm,σ_z≈2mm),及工作方式和电子学读出,并进一步介绍它在北京谱仪上的作用.     

Tuning of the cosmic-ray test system of the BESⅢ drift chamber

The BESⅢ drift chamber and its subsystems need a cosmic-ray test after the chamber construction to check the chamber construction quality,testing the joint operation of the whole system and the performance of the chamber.The noise performance,drift time and charge measurements,and the scanning of channels were examined specifically.The preliminary results of the test indicate that the whole system works well.     

Study of low momentum track reconstruction for the BESⅢ main drift chamber

In order to overcome the difficulty brought by the circling charged tracks with transverse momentum less than 120 MeV in the BESⅢ Main Drift Chamber （MDC）, a specialized method called TCurlFinder was developed. This tracking method focuses on the charged track reconstruction under 120 MeV and possesses a special mechanism to reject background noise hits. The performance of the package has been carefully checked and tuned by both Monte Carlo data and real data. The study shows that this tracking method could obviously enhance the reconstruction efficiency in the low transverse momentum region, providing physics analysis with more and reliable data.     

北京谱仪（BESⅢ）的物理研究

世界上第一台粒子对撞机是20世纪60年代在意大利国家核物理实验室发展出来的。自原理验证样机ADA完成后,第一台正负电子对撞机ADONE于1969年在罗马郊外的小镇FRASCATI建成,并投入运行。稍后美国斯坦福大学建成了质心系能量为3．1GeV的正负电子对撞机,称作SPEAR,并在其上取得了极为丰硕的成果。     

Kinematics of τ two-body decay near τ threshold at BESⅢ

The kinematic properties of two-body decay near τ threshold are studied according to the special capacity of the BEPC accelerator and the BESⅢ detector.Explicitly presented are the transformations of energy and momentum of hadronic particles between different reference frames,and the corresponding distributions.A brand new method is proposed to obtain the energy spread of the accelerator by fitting the energy distribution of hadron from τ semi-leptonic decays.     

我为BEPC/BES的成功点赞——纪念BEPC对撞成功30年

北京正负电子对撞机BEPC及其实验装置北京谱仪BES是我国最大的基础科学实验研究设备之一,1984年开始工程建造,1988年建成并实现正负电子对撞,从1988年实现对撞和1989年投入实验运行到今天已经30年了。在这30年里,BEPCI升级到BEPCⅡ,BESI升级到BESⅡ再到BESⅢ,不间断的实验运行获取了大量的事例样本,取得了一个又一个高能物理界很有影响的物理成果。以北京谱仪BESI的“τ轻子质量精确测量”、BESⅡ的“2~5GeV能区强子反应截面（R值）测量”和“北京谱仪Ⅱ实验发现新粒子”…等为代表的物理成果,都是当年国际高能物理界公认的亮点和世界一流的物理成果,都获得了国家自然科学二等奖,也是国内当年十大科技新闻之一。这不仅表明了我国有能力在世界高科技领域“占有一席之地”,而且已经在一些领域占有了一席之地甚至领跑世界。实现了邓小平同志对中国高科技领域“占有一席之地”的希望,也是包括我在内的中科院高能物理所全体人员,特别是工作在BEPC和BES上科学家们和工程技术人员的共同愿望。     

北京谱仪（BESⅢ）上的粲物理研究

自J/Ψ粒子和τ轻子在20世纪70年代被发现后,τ-粲物理研究即蓬勃兴起,多个正负电子对撞机在此能量运行,取得了丰硕的成果.文章简要论述了国内外长期进行τ-粲物理研究的原因,介绍了其研究的主要内容与特点,并结合新近完成的北京正负电子对撞机重大改造工程（BEPCⅡ）及北京谱仪（BESⅢ）,举例介绍了BESⅢ在轻强子谱、粲物理、粲偶素物理研究,量子色动力学及强子产生性质研究和τ轻子物理研究方面的主要科学目标、任务及新近取得的主要成果.     

北京谱仪大型精密圆柱漂移室dE/dx粒子识别的研究

本文简要描述了北京谱仪主漂移室的dE/ds粒子识别方法,给出在物理实验应用中dE/dx性能测量的主要结果.经过系统效应的软件修正和绝对的能量刻度后,对最小电离粒子(0.4—0.5GeV/c的π)大于30次dE/dx取样的能量分辨率为7.5%.大于3σK/π分离的动量p≤0.65GeV/c.大于3σe/π分离的相应动量范围为0.2≤p≤4GeV/c.     

Trigger efficiencies at BESⅢ

Trigger efficiencies at BESⅢ were determined for both the J/ψ and ψ＇ data taking of 2009. Both dedicated runs and physics datasets are used; efficiencies are presented for Bhabha-scattering events, generic hadronic decay events involving charged tracks, dimuon events and ψ＇→π＋π-J/ψ, J/ψ→ 1＋1- events.The efficiencies are found to lie well above 99% for all relevant physics cases, thus fulfilling the BESⅢ design specifications.     

Track reconstruction in the BESⅢ muon counter

The reconstruction algorithm for BESⅢ Muon Counter, MucRecAlg, is developed with the objectoriented language C＋＋ in BESⅢ offine software environment. MucRecAlg consists of the following functions：to find track seeds either from extrapolation of tracks in the main drift chamber or from the fired strips in muon counter, to select fired strips associated to the candidate tracks, to fit the candidate tracks with a linear or quadratic function and to calculate other parameters of the tracks for muon identification. Monte Carlo samples are generated to check the performance of the reconstruction package, such as reconstruction effciency, muon remaining rate and pion rejection rate, etc. The preliminary results show that the pion rejection rate is around 3%—4% while the muon remaining rate is better than 90% in 0.4—1.6 GeV/c momentum region, which meets the requirement as shown in the design report.     

Measurement of the integrated luminosities of the data taken by BESⅢ at √s=3.650 and 3.773 GeV

Data sets were collected with the BESⅢ detector at the BEPCⅡ collider at the center-of-mass energy of √s=3.650 GeV during May 2009 and at √s=3.773 GeV from January 2010 to May 2011. By analyzing the large angle Bhabha scattering events, the integrated luminosities of the two data sets are measured to be （44.49±0.02±0.44） pb-1 and （2916.94±0.18±29.17） pb-1, respectively, where the first error is statistical and the second error is systematic.     

Coolant choice for the central beryllium pipe of the BESⅢ beam pipe

In order to take away much more heat on the BESⅢ beam pipe to guarantee the normal particle detection,EDM-1（oil No.1 for electric discharge machining）,with good thermal and flow properties was selected as the candidate coolant for the central beryllium pipe of the BESⅢ beam pipe.Its cooling character was studied and dynamic corrosion experiment was undertaken to examine its corrosion on beryllium.The experiment results show that EDM-1 would corrode the beryllium 19.9 μm in the depth in 10 years,which is weak and can be neglected.Finite element simulation and experiment research were taken to check the cooling capacity of EDM-1.The results show that EDM-1 can meet the cooling requirement of the central beryllium pipe.Now EDM-1 is being used to cool the central beryllium pipe of the BESⅢ beam pipe.     

Physics program of open charm and heavy cc states at the BES-Ⅲ experiment

We present the physics program of the open charm and heavy cc states above the DD production energy threshold, which will be studied with the BES-Ⅲ detector at the BEPC- Ⅱ collider in the coming years. Based on some full Monte Carlo simulations with the BES-Ⅲ detector, we predict the accuracy levels on measuring some physical quantities related to D^0, D^＋ and Ds^＋ decays as well as some non-charmed decays of the heavy cc states.     

Measurement of J/ψ leptonic width with the KEDR detector

We report a new precise determination of the leptonic widths of the J/psi meson performed with the KEDR detector at the VEPP-4M e^＋e^- collider. The measured values of the J/psi parameters are： Гee×Гee/P = 0.3323±0.0064 （stat.）±0.0048 （syst.） keV,Гee×Гμμ/Г = 0.3318±0.0052 （stat.） ±0.0063 （syst.） keY. Assuming eμ universality and using the table value of the branching ratios the leptonic Г11 = 5.59 ± 0.12 keV width and the total Г = 94.1±2.7 keV widths were obtained. We also discuss in detail a method to calculate radiative corrections at a narrow resonance.     

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.     

中国mτ数据被直接引用逾170次

 一项科研成果或测量数据公开发表后,是否被相关领域的理论文章,实验研究文章或学科综述文章引用,引用多少次,尤其是被权威刊物发表的论文引用多少次,是表现该科研成果（该测量数据）重要性的一个主要标志．引用次数由引用了该数据的ＳＣＩ刊物（ＳｃｉｅｎｔｉｆｉｃＧｉｔａｔｉｏｎＩｎｄｅｘ──科学论文引用数据;ＳＣＩ刊物是列入国际科学文献引文检索系列的刊物．）文章的篇数来代表．