Researches Of The BESⅢ Offline Software And D Physics

The Beijing Electron Position Collider(BEPC) and Beijing Spectrometer(BES) have been upgraded again during the year 2004-2008,and have began to run since the middle of 2008.The newly upgraded BEPCâ…¡is a multi-bunch and double ring collider with designed peak luminosity of 10³³cm^-2s^-1,an improvement of a factor of 100 with respect to BEPC.The BESâ…¢detector mainly consists of a multilayer drift chamber,a plastic scintillator time-of-flight system,a Csâ… electromagnetic calorimeter and a RPC-based muon identifier.Comparing with the previous BESâ…¡detector,the performance of BESâ…¢has significantly improved.With the large sample and high precise data that will be produced by BEPCâ…¡/BESâ…¢,it's expected to achieve great results on the topics of eletroweak and strong interactions,search for new physics,et al.In order to meet the high luminosity of BEPCâ…¡,the online DAQ and offline data processing systems are completely redesigned and implemented with new technologies. The adoption of object-oriented C++ programming language and Gaudi framework brings us great conveniences in many areas,such as the software reuse,code maintenances,and the modularization design and implementation.The D physics, which corresponds to the researches of D_(s) mesons,is an important part of BESâ…¢physics analysis.The development of toolkits for D physics from now on will play an important role in the future researches.When BEPCâ…¡runs at the designed peak luminosity,the event rate will reach 10⁷ Hz.We have to filter these events so to reduce the various sources of background and ease the data storage system.Furthermore,we can also classify and tag the events that we are interested at the same time.To achieve this requirement,we applied a high level event filtering software system in addition to the first level fast trigger system.For the event filtering will be used in both the online and offline environments,we carefully designed the framework in order to maximize the software reuse.The framework is divided into 2 parts:the 1^st part is realized as an interface of the online environment; and the 2^nd part,which is named as step-handler and contains the main functionality of event filtering procedures,is realized as an environment independent module.The step-handler can execute as part of the online event filtering software,as well as execute directly in the offline BOSS framework.With the step-handler,various filtering algorithms and criterions can be used and fully configured by XML files.The event filtering software has been involved since the beginning of BESâ…¢operation,and the results are basically reliable.In future,the filtering algorithms and criterions should be optimized continuously according to the real data status.The electronic signals from detectors are coded and compressed with specific format,and then stored to disks or tapes as the binary raw data.In order to simplify the access to raw data by offline software,we developed the raw data conversion service. The complex details of the data format are hidden,and the compressed signals are decoded by the conversion service,so that users can access data with simple interfaces. Besides that,the conversion service can also be used to save the simulated data as raw format.For some online software have to reuse the raw data conversion service,we provide 2 different compiling mode to it,the offiine mode and the online mode.When it's compiled as online mode,the input data are received via the intranet instead of read from disks.We optimized the conversion service by adding a file buffer and reducing the data size with third-party library,and these efforts eased the data I/O bottleneck to a certain extent.We developed an additional data provider service to preprocessing the raw data,which is used to reject some abnormal signals.We have got more than 2 TB raw data since the BESâ…¢begin to run,the conversion service works steadily and reliably during the data processing.It meets the requirements of BESâ…¢.In the future,3×10⁷ D(?) pairs will be produced each year at BESâ…¢.We need to reconstruct the D mesons via a lot of hadronic modes to improve the efficiency,so as to use the data effectively.In order to simplify the development,maintenance and the usage of the reconstruction program,we designed the BESâ…¢D-tagging framework referred to the CLEO-c D-tagging software.The D meson reconstructed by the D-tagging software is called D-tag.Generally,all D physics researches should start from the D-tags.The framework is consists of particle list,combinatoric engine and the tag storage.The particle list and combinatoric engine are compositively implemented in the BesDChain package.BesDChain is an important component of the D-tagging software, however,it can be used as a general purpose toolkit in fact.The BesDChain will simplify reconstruction algorithms greatly,especially to complex decay channels.In BesDChain,C++ class templates are widely used to avoid similar code development; and lazy evaluations are adopted in many areas to avoid the waste of computing resources. The development of BesDChain has been finished,and it can cooperate with BOSS seamlessly.Based on the BesDChain,the tag storage and D reconstruction algorithms are being studied.When a D meson decays to 2 vector mesons,the decay angle of the 2 children are of great interest,for it can be used to measure the CP violation.To extract the decay rate and the longitudinal polarization fraction f_L of the D meson from the decay of D⁺→(?)^*(892)⁰ρ⁺(+ c.c.),a multi-variable fitting toolkit named D2vvTools is developed.VariablesΔE,m_bc,m_K^* and m_ρare used to distinguish backgrounds from signal,and the decay angle of K^*(892)⁰andρ⁺(θ₁ andθ₂) are used to distinguish the longitudinal polarized components from the transverse polarized components.So, totally 6 variables are used in D2vvTools.The parameterized PDF(probability density function) of each variable is determined by using MC data.In order to describe the data distribution precisely,besides the background,the signal are ulteriorly divided into true-signal and self-cross-feed(SCF) components.It's assumed that the 6 variables are uncorrelated,so the joint PDF for each component can be obtained by the product of sigle-variable PDFs.We mixed 80%longitudinal and 20%transverse polarized MC signal data to test the D2vvTools toolkit,and get f_L=(80.4±0.5)%.Currently we only made some simple check to the background.More studies of the background will undertake in the future.At the end of this thesis,we reviewed the most recent determinations of the decay constant f_Ds⁺ from different experiments.We find that the current experimental determination in the SM context differs from the most precise unquenched lattice QCD(LQCD) calculation at a 4σlevel.Meanwhile,the measured ratio,R_μ≡ BR(D_s⁺→μ⁺ν_μ)/BR(D⁺→μ⁺ν_μ),is larger than the SM prediction at a 2.0σlevel. With current data,the occurrence of new physics,in the case of the 2HDM,is disfavored. The measured ratio R_μsuggests that we need a new physics contribution with constructive interference.We discuss that the precise measurement of R_μat BESâ…¢will shed light on the presence of new intermediate particles by comparing with the theoretical predictions,especially the LQCD calculations.