Spin structure is one of the fundamental subjects in the study of nucleon structure. Recently it is found that Generalized Parton Distributions(GPDs) are related to the total angular momentum carried by partons,which offers a possible solution to the spin puzzle in the first time. We get access to certain GPDs by looking at the azimuthal angle asymmetries attributed to the interference between Deeply Virtual Compton Scattering(DVCS) and Bethe-Heilter processes in HERMES experiment. By measuring the asymmetry with respect to transverse target polarization from proton target,a model-dependent constraint on Ju vs Jd is obtained. Another worldwide unique channel is nuclear DVCS. The preliminary results on asymmetries with respect to beam spin and beam charge are reported.
YE Hong-xue,MAO Ya-jun (School of Physics and State Key Laboratory of Nuclear Physics and Technology,Peking University,Beijing 100871,China)
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.
GEANT3 and GEANT4 are the detector simulation software programs that are widely used in most nuclear and particle physics experiments.ROOT is a program for framework,data analysis,online and offline software.Detector description is an important function in all these programs.Due to different detector construction methods and respective detector data representative,it is difficult to exchange the detector data among them.A new method based on GDML is developed to automatically convert the detector data among ROOT,GEANT4 and GEANT3.Any existing detector geometry in one program can be mapped to the geometry in the other two programs.In the software development of an experiment,different applications can share and reuse the same detector description.The application of this method in the PHENIX experiment upgrade and PHENIX Forward Vertex Silicon detector design is introduced.
