News from H->bb Ricardo Gonçalo on behalf of H->bb Note group HSG5 Meeting – 3 Dec. 2010

H->bb CONF Note Plans CONF note intended for Winter conferences: “Estimation of the Z+jets background to ZH→llbb Search with the ATLAS Detector at 7TeV” – Based on existing SM Z+jets analysis – Intend to use rel.16: updated Z-width calibrations from data/MC comparison, updated trigger, updated jet EDM – More info: te te2011 For Summer 2011 conferences: CONF note on WH->lvbb – Editors: Patricia Conde-Muino, Andrew Mehta, Paul Thompson – Plan is open-ended: get as far as possible in analysis before Summer – Hard constraint is to be finished for Summer conferences – Next meeting: 13 Dec 2010 Compare cut flows from Liverpool/Birmingham and Lisbon groups – More info:

Z+jets background to ZH→llbb Analysis plans: – Follow same cut flow up to “pre-tag” stage only, to avoid b-tagging calibration and b-jet energy scale issues – Follow same systematics as Z+jets analysis – Investigating sideband methods for Z+jets and tt background determination – Plan to use reprocessed WZphys D3PDs Hopefully to be available soon – Considering to use only latest data periods Avoid any complications that will delay the study – Finally: try to get this out in January for Moriond… if we fail we still gain the work done towards the analysis People: – Malachi focused on Z->μμ channel; starting to write first note draft – Koloina focusing on Z->ee channel – Ricardo ramping up on Z->μμ channel

Analysis Strategy Cut-based analysis with 2010 dataset to gain confidence in background estimation techniques, etc. There is 3 stages to this analysis: 1.Inclusive: Z-boson identification (using Z+jets selection cuts for now) 2.Pre-tag: Requiring at least 2 jets and apply kinematic cuts 3.Final: Apply b-tagging using Loose Double Tag (DT) or Tight Single Tag (ST) Inclusive stage allows: – Compare MC/data – Trigger and lepton performance corrections using tag-probe (via Z+jets analysis) – Re-weight Z boson pt and/or mass to agree with data Pre-tag stage allows: – Compare MC/data – Estimation of background using sideband – Normalization factors

Inclusive Selection Cuts

Pre-tag Selection Cuts

Latest Results QCD background estimates from Koloina Studies on ttbar sideband methods: – Tried reversing MET cut: Doesn’t work: sideband region contaminated by signal – Studying lepton flavour sideband: Request eμ instead of ee or μμ

QCD Background Electron isolation ratio is a good variable to control QCD background η η

Di-lepton Invariant Mass M ee [GeV]M eμ [GeV]