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Matrix element analysis update

Matrix element analysis update. Gemma Wooden, Chris Hays, Shih- Chieh Hsu (LBNL), Daniel Whiteson (University of California, Irvine) Oxford Higgs meeting 01/04/11. Improvements. Currently have two implementations (mine & Shih- Chieh’s )

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Matrix element analysis update

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  1. Matrix element analysis update Gemma Wooden, Chris Hays, Shih-Chieh Hsu (LBNL), Daniel Whiteson(University of California, Irvine) Oxford Higgs meeting 01/04/11

  2. Improvements • Currently have two implementations (mine & Shih-Chieh’s) • Have carried out dedicated comparisons in past three weeks in terms of: • MCFM vsMadGraph • LHAPDF tools • Following Higgs Yellow Report recommendation for MH and GH • See complete agreement • Have added in some improvements: • Constructed KT distribution from MC (to account for ISR) for 0 and 1 jet channels • Constructed and verified transfer functions to account for detector effects for: • Leptons • MET • Compared two sets of integration variables: • MH, nux, nuy, nuz vs. MH, MW1, nux, nuy • The first set appears to perform better (large peak at zero for second set which isn’t understood yet) Gemma Wooden, Oxford Higgs meeting

  3. Higgs PT distributions • Plotted the Higgs PT distribution for 0, 1 and 2 jet channels after preselection • Use this in the matrix element calculation: • Draw at random from these distributions • Draw from 0 jet distribution for 0 jet events etc. • Apply a weight to each event based on the Higgs PT which is drawn MH = 170 GeV, 1 jet channel MH = 170 GeV, 0 jet channel MH = 170 GeV, 2 jet channel

  4. New integration ranges • Had been using a CDF parameterisation for integration to check with Shih-Chieh • Now switch to ATLAS parameterisation – assume flat distribution for nuX and nuY between -50 and 50 • Use fit to truth distribution for nuZ MH = 170 GeV, nuX MH = 170 GeV, nuZ Gemma Wooden, Oxford Higgs meeting

  5. Event selection • In order to get the best reduction in background, apply some preselection: • Two opposite sign, well-identified leptons • Require Mll > 15 GeV and |Mll – Mz| > 15 GeV • METproj > 35 GeV to reduce the Z background which is significant • Dphill < 2.25 • Finally calculate the ME likelihood: • PH(MH)/ (PH(MH) + PWW) • Use this to get the best possible separation between signal and background

  6. Matrix element likelihoods MH = 120 GeV MH = 160 GeV

  7. Matrix element likelihoods • Matrix element method shows nice improvement in significance wrt cuts-based method • Improvement is seen at all Higgs masses MH = 200 GeV

  8. Next steps • Running systematics samples as we speak: • JES • JER • Lepton resolution • Should add in lepton efficiency – this was found to be a large uncertainty in BDT analysis • Limit setting: • Can calculate the limits using a binned maximum likelihood fit without systematics • Adding in systematics could turn out to be some work • Planning on looking at RooStats in more detail • Plan: • Write up all of the description in the MVA note while the systematics samples are running • Also look into limit setting in the meantime • Update MVA note with final results as soon as possible Gemma Wooden, Oxford Higgs meeting

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