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Travaux sur le neutralino dans le cadre de l’expérience LHCb Rapport stage 2A Abstract Work on the neutralino in LHCb experiment I did my internship of second year of the ENSPS, in the Laboratory for High Energy Physics (LPHE) at the Swiss Federal Institute of Technology Lausanne (EPFL) and under the management of Pr. Aurelio Bay. The LPHE is in charge of all activities related to elementary particle physics with several experiments such as LHCb which examine CP violation. This laboratory, under the direction of Professor Bay, employs fast forty researchers and PHD students and around fifteen technicians and administrative staff. It is located through the second and the sixth floor of the building named “cubotron”. During this internship, I made my study in Supersymmetry, a theory beyond the current reference in High Energy Physics: the Standard Model. It focuses on the neutralino, an hypothetical explanation for The Universe dark matter, if it does not decay. I had to generate events with the parameters of LHCb experiment. Through another program, I analyzed some properties of the neutralino such as lifetime, flight distance… Then another one conducted mass reconstruction and the evaluation of the number of tracks used for this mass reconstruction. Afterwards I analyzed my results thanks to graphics in order to find some answers: the probabilities to reveal neutralino, if exists, in the Vertex Locator, component of LHCb detector, are quite nice. Consequently I practiced several software and theories used in High Energy Physics and I met scientists in the LPHE or at the CERN, which made me know different looks of researchers work. 2008. 4/44
Travaux sur le neutralino dans le cadre de l’expérience LHCb Rapport stage 2A Table des matières Introduction ..................................................................................................................................... 8 I Contexte du stage, présentation. ............................................................................................. 9 I.1 L’Ecole Polytechnique Fédérale de Lausanne. ................................................................ 9 I.2 Le Laboratoire de Physique des Hautes Energies ........................................................... 9 I.3 Le LHCb ........................................................................................................................... 10 I.3.a Présentation générale .................................................................................................. 10 I.3.b Présentation technique ................................................................................................ 11 I.3.c Le Vertex Locator (VELO) ........................................................................................... 12 I.4 Outils informatiques/Contexte du stage ........................................................................ 13 II Travail effectué ........................................................................................................................ 15 II.1 Cadre Théorique de l’étude ............................................................................................. 15 II.1.a Le Modèle Standard ..................................................................................................... 15 II.1.b Les limites du modèle standard ................................................................................... 18 II.1.c La SuperSymétrie (SuSy) ............................................................................................. 19 II.1.d Le modèle d’Eboli et le modèle de Kaplan .................................................................. 22 II.2 L’étude ............................................................................................................................. 23 II.2.a Environnement et déroulement du stage ................................................................... 23 II.2.b Le programme génération ........................................................................................... 25 II.2.c Le programme lecture .................................................................................................26 II.2.d Le programme de reconstruction ............................................................................... 27 III Analyse des résultats obtenus ................................................................................................28 III.1 Résultats du programme génération ..............................................................................28 III.2 Résultats du programme lecture .................................................................................... 31 III.3 Résultats du programme reconstruction ........................................................................ 34 III.3.a Cas #1 ........................................................................................................................ 34 III.3.b Cas #2 ....................................................................................................................... 36 III.3.c Cas #3 ....................................................................................................................... 37 III.3.d Cas #4 ....................................................................................................................... 38 III.3.e Cas AMSB ................................................................................................................. 39 III.4 Résultats du modèle de Kaplan. .................................................................................... 40 Conclusion ...................................................................................................................................... 42 Bibliographie ................................................................................................................................... 43 2008. 5/44
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