Monte Carlo simulation study of the e+e- →Lambda Lamba-Bar reaction with the BESIII experiment

University essay from Uppsala universitet/Kärnfysik

Abstract: Studying the reactions where electrons and positrons collide and annihilate so that hadrons can be formed from their energy is an excellent tool when we try to improve our understanding of the standard model. Hadrons are composite quark systems held together by the strong force. By doing precise measurements of the, so called, cross section of the hadron production that was generated during the annihilation one can obtain information about the electromagnetic form factors, GE and GM, which describe the inner electromagnetic structure of hadrons. This will give us a better understanding of the strong force and the standard model.During my bachelor degree project I have been using data from the BESIII detector located at the Beijing Electron-Positron Collider (BEPC-II) in China. Uppsala university has several scientists working with the BESIII experiment. My task was to do a quality assurance of previous results for the reaction e+e-→ Lambda Lambda-Bar at a center of mass energy of 2.396 GeV. During a major part of the project I have been working with Monte Carlo data. Generating the reactions was done with two generators, ConExc and PHSP. The generators was used for different means. I have analyzed the simulated data to find a method of filtering out the background noise in order to extract a clean signal. Dr Cui Li at the hadron physics group at Uppsala university have worked with several selection criteria to extract these signals. The total efficiency of Cui Li's analysis was 14%. For my analysis I also obtained total efficiency of 14%. This gave me confidence that my analysis have been implemented in a correct fashion and that my analysis now can be transferred over to real data. It is also reassuring for Cui Li and the rest of the group that her analysis has been verified by and independently implemented selection algorithm.

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