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Identification and Determination of Particle Mass through Z0 Decay

Explore the detection and identification of Z0 particles and their decay products using the ALEPH detector. Learn about the DALI identification system and event selection for mass determination. Dive into quantum mechanics concepts such as width measurements and perform real event analysis for MZ determination.

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Identification and Determination of Particle Mass through Z0 Decay

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  1. Identification du Z0 et détermination de sa masse • Désintégration du Z0 • Le détecteur ALEPH • Identification des produits de désintégration du Z0 (DALI)‏ • Sélection des évènements associés au Z0 et • détermination de sa masse (QTALEPH)‏

  2. Table des Particules Elémentaires

  3. Désintégration du Z0 Z0 m+m- t+t- nn e+e- qq e+- nent m+-nmnt p+- p+ p-nt p+- nt

  4. Le détecteur ALEPH

  5. Système d'identification

  6. DALI: e+e- Ecm = 91.2 Pch = 82.9 Ewi = 85.3 Eha = 0

  7. DALI: m+m- Ecm = 91.2 Pch = 90.8 Ewi = 1.23 Eha = 8.32

  8. DALI: t+t- Ecm = 91.2 Pch = 57.7 Ewi = 61.2 Eha = 17.1

  9. DALI: qqbar Ecm = 91.2 Pch = 74.4 Ewi = 42.8 Eha = 10.1

  10. DALI: Table

  11. QTALEPH: Sélection (évènements simulés)‏

  12. Notion de largeur En mécanique quantique, la théorie nous dit que l'on ne peut pas mesurer l'énergie et le temps de vie avec une précision infinie : • Si on mesure la masse d'une particule, on aura une courbe, et pas un pic infiniment étroit. La courbe est caractérisée par: • sa valeur moyenne • sa largeur

  13. QTALEPH: Ajustement de MZ (évènements réels)‏

  14. Maintenant,à vous de jouer !

  15. Résultats MZ0 = 91.188 ± 0.002 GeV GZ0 = 2.495 ± 0.003 GeV Nnu = 2.9840 ± 0.0082

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