Time calibration for the end cap TOF system of BESⅢ

The time calibration for end cap TOF system of BESⅢ is studied in this paper. It has achieved about 110 ps time resolution for muons in dimu events. The pulse height correction using electronic scan curve and the predicted time calculated using Kalman filter method are introduced. This paper also describes the study of using electrons and muons as calibration samples.     

Lagrange multiplier method used in BESⅢ

In this paper, the kinematic fitting with the Lagrange multiplier method has been studied for BESⅢ experiment. First we introduce the Lagrange multiplier method and implement kinematic constraints. Then we present the performance of the kinematic fitting algorithm. With the kinematic fitting, we can improve the resolution of track parameters and reduce the background.     

Primary vertex reconstruction based on the Kalman filter technique at BESⅢ

Primary vertex reconstruction is crucial to estimate the beam profile in collision experiments. We study the principle of an iterative process, called the Kalman filter method, and apply it to primary vertex reconstruction at BESⅢ. A Newton procedure to find the zero point of the distance function＇s gradient is used for primary vertex finding in 3-dimensional space. Results are obtained based on raw data at BESⅢ.     

BESIII barrel time-of-flight （TOF） calibration using cosmic ray data

The principle of the method for the BESIII TOF calibration using cosmic ray data without magnetic field are reported in this paper. After applying calibration constants, the single-end readout time resolution could reach about 150 ps, and the time resolution for one layer is achieved to be about 110 ps. The paper also described the extraction scheme for the event start time of cosmic events.     

北京谱仪(NESⅡ)飞行时间测量修正的系统研究

飞行时间计数器(TOF)是北京谱仪(BESⅡ)中用于带电粒子鉴别的主要子探测器.鉴于粒子鉴别在物理分析中具有特殊重要的地位,本文对TOF测量时间的系统偏离和分辨率进行了研究.利用J/ψ能区的强子事例样本,对输出脉冲幅度Q,z向坐标位置和粒子的βγ值与时间偏离以及分辨率的关系进行了分析,分别构造了时间偏离和分辨率的修正函数.最后给出用ψ″能区的强子事例样本对修正函数进行检验的结果.     

Decay vertex reconstruction and 3-dimensional lifetime determination at BESⅢ

This paper focuses mainly on the vertex reconstruction of resonance particles with a relatively long lifetime such as Ks^0, A, as well as on lifetime measurements using a 3-dimensional fit. The kinematic constraints between the production and decay vertices and the decay vertex fitting algorithm based on the least squares method are both presented. Reconstruction efficiencies including experimental resolutions are discussed. The results and systematic errors are calculated based on a Monte Carlo simulation.     

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.     

在BEPCⅡ/BESⅢ上测量K((892)质量劈裂的Monte Carlo研究

对BEPCⅡ BESⅢ上的J ψ→K±K (892 ) 和J ψ→K0 K (892 ) 0 过程进行了MonteCarlo模拟,对测量K (892 )的质量劈裂的可行性进行了研究.在BESⅢ探测器的设计指标下,采用6×10 8J ψ数据,若输入K (892)0 和K(892)±的质量差为6 0 0MeV ,经过BESⅢ模拟和拟合后的质量差则是5 79±0 16±0 13MeV ,其中第一项误差为统计误差,第二项误差为系统误差.这表明,BESⅢ的建造将为精确测量K (892 )质量劈裂提供极佳机遇.     

利用BESⅢ的双层TOF寻找D~0-■混合的研究(英文)

在ψ(3770)处,D0→K-π+是研究D0-■混合的非常理想的衰变道．实验上,良好的K／π识别技术将对寻找D0-■混合过程起着决定性的作用．在BESⅢ实验的物理预研究中,发现利用飞行时间的信息,能够精确测定末态中含有多条带电径迹事例的起始时间,从而可以改善飞行时间计数器的时间分辨率．进一步的研究表明,应用该方法后,BESⅢ双层TOF的时间分辨率从～78ps降到～64ps．按照20fb-1的ψ(3770)数据量进行估算,在95％置信度下,D0-■混合率的上限值可以提高7％左右．