Energy calibration of electrons and photons in ATLAS and impact on precision measurements of the Higgs boson properties in the diphoton channel Saskia Falke Journ´ ees de Rencontre de Jeunes Chercheurs December 2017
Outline Introduction: Higgs to diphoton in ATLAS 1 Electron & photon energy calibration 2 Higgs mass measurement 3 Conclusion & Outlook 4 Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 1 / 26
Introduction: why to measure the Higgs properties Is the particle discovered in 2012 the Standard Model Higgs boson? → precision measurement of couplings and cross-sections → use H → γγ channel: clean, easy to trigger Alternative theories: → light boson of a two-Higgs-doublet-model? arXiv:1205.6497 [hep-ph] → composite particle? What is the mass of the new particle? → is our universe stable or meta-stable? → only free parameter in the couplings prediction; can be used as input for measurements (also in other channels) Good photon energy calibration needed to measure Higgs properties! Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 2 / 26
How to measure H → γγ with ATLAS? Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 3 / 26
Electron & photon reconstruction Electron: track + cluster in electromagnetic calorimeter Photon: only cluster in electromagnetic calorimeter (unconverted) cluster with conversion vertex and track(s) (converted) Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 4 / 26
Electron and photon energy calibration Calorimeter showers of electrons and photons are very similar: calibrated using mainly same procedure Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 5 / 26
Effect of the calibration C o n s i y d - e s r c a t h l e e s d i n i ff t e h r e e n r t a t i o p ATLAS-CONF-2017-046 l o t ! Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 6 / 26
Pseudorapidity η = − ln tan θ 2 Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 7 / 26
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