Track reconstruction using the TSF method for the BESm main drift chamber

We describe the algorithm to reconstruct the charged tracks for BESⅢmain drift chamber at BEPCⅡ,including the track finding and fitting.With a new method of the Track Segment Finder(TSF), the results of present study indicate that the algorithm can reconstruct the charged tracks over a wide range of momentum with high efficiency,while improving the robustness against the background noise in the drift chamber.The overall performances,including spatial resolution,momentum resolution and secondary vertices reconstruction efficiency,etc.satisfy the requirements of BESⅢexperiment.     

An extended segment pattern dictionary for a pattern matching tracking algorithm at BESⅢ

A pattern matching based tracking algorithm, named MdcPatRec, is used for the reconstruction of charged tracks in the drift chamber of the BES detector. This paper addresses the shortage of segment finding in the MdcPatRec algorithm. An extended segment construction scheme and the corresponding pattern dictionary are presented. Evaluation with Monte-Carlo and experimental data show that the new method can achieve higher efficiency for low transverse momentum tra     

Software alignment of the BESⅢ main drift chamber using the Kalman Filter method

Software alignment is quite important for a tracking detector to reach its ultimate position accuracy and momentum resolution. We developed a new alignment algorithm for the BESⅢ Main Drift Chamber using the Kalman Filter method. Two different types of data which are helix tracks and straight tracks are used to test this algorithm, and the results show that the design and implementation is successful.     

Calibration study of the X-T relation for the BESⅢ drift chamber

Offline calibration plays an important role in BES offline data processing. In order to achieve good spatial and momentum resolution, it is necessary to implement high precision offline calibration for the BES drift chamber. This paper studies the time-to-distance relations, which are important calibration constants for track reconstruction. The parameterization of the time-to-distance relation, studies of left-right asymmetry and studies of variation with entrance angle are performed. The impact of dead channels on the time-to-distance relation is given special attention in order to reduce the shift in measured momentum for tracks passing near dead cells. Finally we present the resolutions for barrel Bhabha events(|cos θ|< 0.8) from a J/ψ data set taken in 2012. The average spatial resolution is 123 μm and the momentum resolution for 1.548 Ge V/c Bhabha tracks is 11.9 Me V/c.     

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.     

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.     

Installation and cosmic ray test of the high voltage system of the BESⅢ drift chamber

After examination of the designed high voltage power supply system of the BESⅢ drift chamber in the beam test of the full length prototype of drift chamber, a full system covering all the channels of high voltage was installed. The system's training and the high voltage value adjustment were carried out in the cosmic ray test of the BESⅢ drift chamber. The cosmic ray test for the full system and its final installation on the BESⅢ drift chamber were reported. The full system of high voltage power supply works stably and reliably.     

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.     

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.     

A prototype MRPC beam test for the BESⅢ ETOF upgrade

A prototype multi-gap resistive plate chamber (MRPC) with a 2×6 gap structure is developed for the upgrading of the endcap time-of-flight (ETOF) detector in the Beijing Spectrometer (BESⅢ). The prototype MRPC is tested in the E3 beam line of the Beijing Electron Positron Collider (BEPC) with secondary charged particles (π and p, etc) of 600 MeV/c. The test results show that the time resolution of the MRPC can reach 50 ps and that the detection efficiency is greater than 98%.