Energy calibration of electrons and photons in ATLAS and impact on - - PowerPoint PPT Presentation

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Energy calibration of electrons and photons in ATLAS and impact on - - PowerPoint PPT Presentation

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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:

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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

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Outline

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Introduction: Higgs to diphoton in ATLAS

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Electron & photon energy calibration

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Higgs mass measurement

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Conclusion & Outlook

Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 1 / 26

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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? → 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)

arXiv:1205.6497 [hep-ph]

Good photon energy calibration needed to measure Higgs properties!

Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 2 / 26

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How to measure H → γγ with ATLAS?

Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 3 / 26

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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

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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

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Effect of the calibration

C

  • n

s i d e r t h e d i ff e r e n t y

  • s

c a l e s i n t h e r a t i

  • p

l

  • t

!

ATLAS-CONF-2017-046 Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 6 / 26

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Pseudorapidity

η = − ln tan θ

2

Saskia Falke Higgs mass & photon calibration in ATLAS 12/2017 7 / 26