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Monte Carlo simulation study of the e+e→Lambda Lamba-Bar reaction with the BESIII experiment
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.
2016 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

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.

Abstract [sv]

Att studera vad som händer vid reaktioner där elektroner och positroner kolliderar och annihilerar så att hadroner kan bildas ur energin kan vara till stor hjälp när vi vill förstå standardmodellen och dess krafter, i synnerhet den starka kraften, som kan studeras i sådana reaktioner. Genom att utföra precisa mätningar av tvärsnitt för hadronproduktion får man fram de elektromagnetiska formfaktorerna GE och GM som beskriver hadronernas inre struktur. Hadroner är sammansatta system av kvarkar och den starka kraften binder dessa kvarkar.\\Under mitt examensarbete har jag använt mig av data från detektorn BESIII som finns vid BEPC-II (Beijing Electron-Positron Collider) i Kina. Uppsala universitet har flera forskare som jobbar med BESIII experimentet. Målet var att kvalitetssäkra den tidigare analys som gjorts för reaktionen e+e- → Lambda Lambda-Bar vid 2.396 GeV. Jag började med att göra Monte Carlo-simuleringar. Reaktionerna har genererats med två olika generatorer, ConExc och PHSP. Dessa generatorer har använts till olika ändamål. De genererade partiklarnas färd genom detektorn har sedan simulerats. Då bildas data av samma typ som dem man får från experiment. Jag har analyserat dessa simulerade data för att hitta en metod som kan filtrera bort bakgrundsstörningar samtidigt som intressanta data sparas. Kriterier utarbetade av Dr. Cui Li har använts för att skapa denna metod. Min algortim gav en total effektivitet på 14%, vilket stämmer bra med den tidigare algoritmen som Cui Li skapade, även där var effektiviteten 14%. Detta ger förtroende för min algortim och den stärker även Cui Lis resultat.

Place, publisher, year, edition, pages
2016. , 30 p.
Keyword [en]
Hadron, Nuclear physics, Lambda, Monte Carlo-simulations, BES, BESIII, Event selection
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-297851OAI: oai:DiVA.org:uu-297851DiVA: diva2:943793
Educational program
Bachelor Programme in Physics
Available from: 2016-07-07 Created: 2016-06-28 Last updated: 2016-07-07Bibliographically approved

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