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350GeV HZ Recoil AnalysisPowerPoint Presentation

350GeV HZ Recoil Analysis

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350GeV HZ Recoil Analysis

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350GeV HZ Recoil Analysis

LCD WG Meeting, 19/06/2012

J.S. Marshall, University of Cambridge

- Relevant processes for this study are the recoil reaction e+e-HZHff, 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

1.

2.

3.

4.

- 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.

- Lepton selection as previously described:

- Simple selection cuts before TMVA training:

40 GeV<Mdl< 120 GeV95 GeV< Mrecoil< 290 GeV60 GeV<PTdl

- 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.

- 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

- 1000 test samples for eeX channel:

Removes tail

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

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

- 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

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

- 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: CLICILC.

- 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.

1. Pol4a

2. Pol4b

3. Exponential

mH(MeV)

nsig(%)

100 tests

for each

4. Gaussian

5. Pol5

6. Landau