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350GeV HZ Recoil Analysis

350GeV HZ Recoil Analysis. LCD WG Meeting, 19/06/2012 J.S. Marshall, University of Cambridge. HZ Analyses. Relevant processes for this study are the recoil reaction e + e -  HZ  Hff , commonly called Higgsstrahlung. Model independent recoil analysis:

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350GeV HZ Recoil Analysis

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  1. 350GeV HZ Recoil Analysis LCD WG Meeting, 19/06/2012 J.S. Marshall, University of Cambridge

  2. HZ Analyses • Relevant processes for this study are the recoil reaction e+e-HZHff, commonly called Higgsstrahlung. • Model independent recoil analysis: • Z decays to charged leptons. Identify leptons and compute recoil mass: • Model dependent analysis, with direct Higgs mass reconstruction: • HZqq channel, hadronic decay of Z • HZ channel, Z decays to neutrinos s = 500GeV Lint = 500fb-1 mH= 120GeV No polarization

  3. Previously... 1. 2. 3. 4.

  4. HZ Recoil: 350GeV vs. 500GeV • Move from 500GeV to 350GeV associated with increase in signal cross-section. • e1e1ff background falls, whilst only modest rise for e2e2ff background. • Recoil mass peak noticeably sharper, with radiative effects tail reduced. Reco. lepton id.

  5. 350GeV HZ Recoil: Selection • Lepton selection as previously described: • Simple selection cuts before TMVA training: 40 GeV < Mdl < 120 GeV95 GeV < Mrecoil < 290 GeV60 GeV < PTdl

  6. 350GeV HZ Recoil: Selection

  7. 350GeV HZ Recoil: BDT

  8. 350GeV HZ Recoil: Fitting • Fit uses MINUIT to vary mH, nSig and nBkg. A predicted distribution is created for these parameters and compared to the data, producing a 2 value. • Use Simplified Kernel Estimation to approx. signal shape by sum of many Gaussians. • Transformation x’ = x – mH allows sensitivity to mH. Scaling allows sensitivity to nSig. • Fit shape of selected background: 4th order polynomial seems OK – see later checks. • Scaling distribution allows sensitivity to nBkg. Background shape does not change.

  9. 350GeV HZ Recoil: X • Fluctuate high statistics signal sample, and the smooth background fit, to produce test samples. • Fit different test samples and examine fitted values and reported precisions: X

  10. 350GeV HZ Recoil: eeX • 1000 test samples for eeX channel:

  11. 350GeV HZ Recoil: Brem. Recovery Removes tail Improves peak entries, but broader due to use of cluster energy

  12. 350GeV HZ Recoil: Brem. Recovery • Brem. recovery increases no. of entries in peak, but does increase peak width:

  13. Comparison with ILC Results • Event generation using PYTHIA • Beam Pol. (e-: -80%, e+: +30%), • s=350 GeV, L=175 fb-1 • Details taken from LCWS10 talk in Beijing, by Hengne Li, available via this link • Event generation using WHIZARD • No beam polarization • s=350GeV • Scale to L=175 fb-1 for comparison

  14. Comparison with ILC Results Starting point:No selection cuts Pick true or reco leptons, relatively small difference Reco quantities,full selection • Comparison of results for X channel: Selection must work harder than at ILC, but achieves similar S/B

  15. Comparison with ILC Results • Try to understand remaining shape differences between recoil mass distributions at ILC/CLIC, so obtained ILC/CLIC E’ distributions from Frank. Use distributions to obtain E’ weight: CLICILC.

  16. Fit Robustness • Quick test of remaining free parameters in analysis.Look at reported Higgs mass precision as function of: • Number of bins used for simplified Kernel estimation. • Number of bins used in fit to recoil mass distribution. • Mass range considered in fit; experiment with different windows around true Higgs mass.

  17. Fit Robustness 1. Pol4a 2. Pol4b 3. Exponential mH(MeV) nsig(%) 100 tests for each 4. Gaussian 5. Pol5 6. Landau

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