Search for the Higgs particle Higgs gg Brbara

Search for the Higgs particle Higgs gg Bárbara Millán Mejías Eleni Petrakou Xiaohu Sun FAPPS 26 September 2008

Introduction • Search or exclusion Higgs Boson H gg • Characteristics • Select cuts • Sensitivity • Expectations FAPPS 26 September 2008 2

Atlas Detector • 40 million proton-proton collisions per second FAPPS 26 September 2008 2000 Thousand people 3

Higgs boson LEP lower limit: m. H > 114 Ge. V/c 2 @ 95% CL Tevatron EW limit: m. H < 154 Ge. V/c 2 @ 95% CL Combined: m. H < 185 Ge. V/c 2 @ 95% CL ( Because of the uncertainty) FAPPS 26 September 2008 4

H gg decay • Promising channel in the Higgs mass range 115<m. H<140 Ge. V • Branching ratio = 10 -3 H g g • Cross Section = 50 fb • Clear channel to detect FAPPS 26 September 2008 5

Background • ee from Drell-Yan events q e q • g+jet • jet+jet e q g g q g q • QCD gg continuum (irreducible background) g g FAPPS 26 September 2008 6

Preselection cuts (Triggering) • At least two γ’s with pt>20 Ge. V • Region in the detector of |η|<2. 45 • Isolated tracks (determined from calorimeter shower shapes). FAPPS 26 September 2008 7

Selection cuts • Et>40 Ge. V for first γ, Et>25 Ge. V for second • Hits on e/m calorimeter in the rapidity regions 1. 37<|η|<1. 52, 2. 37<|η|<2. 5 are excluded • π0 shower rejection from calorimeter • e rejection from isolated tracks in tracker FAPPS 26 September 2008 8

Will we see it? FAPPS 26 September 2008 9

Statistical significance studies Significance is defined as the amount of signal compared to the error on the background events. S= number of signal events B= number of background events s= number of standard deviations necessary to distinguish signal from statistical fluctuations Significance > 5 s necessary for claiming discovery of new physics FAPPS 26 September 2008 10

Expected results Statistical significance MH(Ge. V) (30 fb-1) (100 fb-1) FAPPS 26 September 2008 120 6. 1 130 6. 2 140 5. 4 9. 8 10. 1 8. 9 11

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BACK-UP SLIDES FAPPS 26 September 2008 13

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Mass resolution s. MH(Ge. V) 120 130 140 2 x 1033 cm-2 s-1 1. 36 1. 42 1. 51 1034 cm-2 s-1 1. 59 1. 65 1. 70 FAPPS 26 September 2008 15

Outline • • • Introduction H gg in ATLAS detector Signal and background characteristic Pre-selection & selection cuts Significance Expected results FAPPS 26 September 2008 16

H->gamma Drell-Yan g g -> j j q g -> gamma jet QCD gamma FAPPS 26 September 2008 17