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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

350GeV HZ Recoil Analysis

LCD WG Meeting, 19/06/2012

J.S. Marshall, University of Cambridge

Hz analyses
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






Hz recoil 350gev vs 500gev
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.

350gev hz recoil selection
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

350gev hz recoil fitting
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.

350gev hz recoil x
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:


350gev hz recoil eex
350GeV HZ Recoil: eeX

  • 1000 test samples for eeX channel:

350gev hz recoil b rem recovery
350GeV HZ Recoil: Brem. Recovery

Removes tail

Improves peak entries, but broader due to use of cluster energy

350gev hz recoil b rem recovery1
350GeV HZ Recoil: Brem. Recovery

  • Brem. recovery increases no. of entries in peak, but does increase peak width:

Comparison with ilc results
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

Comparison with ilc results1
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

Comparison with ilc results2
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.

Fit robustness
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.

Fit robustness1
Fit Robustness

1. Pol4a

2. Pol4b

3. Exponential



100 tests

for each

4. Gaussian

5. Pol5

6. Landau