higgs search in the h➝bb channel in atlas

H->+- and H+-> with the ATLAS Detector at the LHC

Higgs search in the Hbb channel in ATLASRicardo Gonalo Royal Holloway University of Londonon behalf of the ATLAS Collaboration

International Europhysics Conference on High Energy Physics, Grenoble, July 21-27 2011OutlineATLAS and the LHC

Higgs physics at the LHC

ZH/WH Hbb in ATLASEvent selectionBackgroundsSystematic errorsResults

Boosted VH

Summary and OutlookRicardo GonaloEPS-HEP 2011 - Grenoble - July 20112

ATLAS and the LHCRicardo GonaloEPS-HEP 2011 - Grenoble - July 20113Ricardo GonaloEPS-HEP 2011 - Grenoble - July 20114

JINST (2008) 3 S08003Inner Tracker: ||20GeV) or (pT>18GeV)Exactly 1 lepton pT > 25GeVMT = 2pTlpT(1 - cos l ) > 40 GeVETmiss > 25GeV Exactly 2 jets (anti-kT 0.4; ET > 25GeV) to reduce top backgroundBoth jets b taggedRicardo GonaloEPS-HEP 2011 - Grenoble - July 201113To be included if approvedTo be included if approvedTo be included if approvedWHlbb BackgroundsW+jets and top dominant:W+jets important at low mbb:Use mjj from data as templateTop dominant at high mbb:Describe shape with MCCross check mbb in 3-jet binNormalisation from mbb sidebands [40GeV, 80 GeV] and [140GeV, 250GeV] Z+jets: use same normalisation of MC as measured in ZHMultijet Data templates from QCD enhanced samples (anti-isolation)Diboson WW , WZ from Monte CarloRicardo GonaloEPS-HEP 2011 - Grenoble - July 201114To be included if approvedTo be included if approved

Dominant systematic errors from b-tagging efficiency in both analyses

Followed by jet energy scale

Points at the next things things to improve!

Ricardo GonaloEPS-HEP 2011 - Grenoble - July 201115Size of Systematic UncertaintiesZHllbb WHlbb To be included if approvedTo be included if approvedHbb Analysis ResultsRicardo GonaloEPS-HEP 2011 - Grenoble - July 201116ZHllbb Good description of the backgroundNo excess observedSingle-channel exclusion of 20x Standard ModelRicardo GonaloEPS-HEP 2011 - Grenoble - July 201117To be included if approvedTo be included if approvedTo be included if approved

WHlbb Good description of the backgroundNo excess observedSingle-channel exclusion of 20-30x Standard ModelRicardo GonaloEPS-HEP 2011 - Grenoble - July 201118To be included if approvedTo be included if approvedTo be included if approved

Boosted VH with HbbRicardo GonaloEPS-HEP 2011 - Grenoble - July 201119Select Wl events and search for a Hbb jet Search for high-pT jet (Cambridge-Aachen algorithm, R=1.2)Search jet clustering history in reverse and look for large mass dropRe-cluster with small R parameter to find sub jets

Peak consistent with Wjj in tt events Proof of principle for future analysisAlternative to inclusive channels: search for high-pT Higgs to bb: J. M. Butterworth, A. R. Davison, M. Rubin, and G. P. Salam, Phys. Rev. Lett. 100 (2008) 242001, arXiv:0802.2470 [hep-ph]pTH > 200GeV 5% of inclusive cross section but improved significanceRicardo Gonalo20

To be included if approvedConclusions & OutlookRicardo GonaloEPS-HEP 2011 - Grenoble - July 201121First direct search for Hbb at the LHC in WH and ZH channels

Room for improvement! Reduce systematicsNew channels to exploreMultivariate analysesLots of data expected!

Proof of principle for boosted Higgs analysis

Watch this space! Ricardo GonaloEPS-HEP 2011 - Grenoble - July 201122To be included if approvedTo be included if approvedBackupRicardo GonaloEPS-HEP 2011 - Grenoble - July 201123ATLAS & LHC: Efficiency and PileupVery good ATLAS performanceData-taking efficiency above 95%Luminosity-weighted distribution of the mean number of interactions per crossing for 2011Calculated from the instantaneous luminosity as: =L x inel / (nbunch x fr) L: instantaneous luminosityinel : inelastic cross section (71.5 mb)nbunch: number of colliding bunchesfr: LHC revolution frequencyEntries at 0 from pilot bunches See: arXiv:1101.2185

Ricardo GonaloEPS-HEP 2011 - Grenoble - July 201124

Monte Carlo SamplesaRicardo GonaloEPS-HEP 2011 - Grenoble - July 201125

Common event selection:

Lepton Identification:

Jet reconstruction:Ricardo GonaloEPS-HEP 2011 - Grenoble - July 201126

Detector related uncertaintiesRicardo GonaloEPS-HEP 2011 - Grenoble - July 201127

Normalization Systematic UncertaintiesRicardo GonaloEPS-HEP 2011 - Grenoble - July 201128

Guessing the Tevatron sensitivityProbably close to excluding (or not) the Higgs at low massAt 4x SM with ZH->bb last yearSeveral factors 2x wrt now: 2 experimentsadding lepton channelsincreased luminosityRicardo GonaloEPS-HEP 2011 - Grenoble - July 201129NOT to show at conferencehttp://tevnphwg.fnal.gov/July 2010http://tevnphwg.fnal.gov/March 2011ZH->bb; March 2011On high-pT jet massCut applied here at 300GeV gives peak at 50-100Partially removed by jet filtering but shoulder still visible in boosted W->jj plotRicardo GonaloEPS-HEP 2011 - Grenoble - July 201130

NOT to show at conference

Day in 201127/02 01/04 04/05 06/06 10/07

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higgs search in the h➝bb channel in atlas

Documents

hbbricardo gonaloepshep

lhcricardo gonaloepshep

hbb jet search

gev z jets

lhc higgs search

high mbb

highpt higgs

hbb channel