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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