Constraints from "Higgs mass and Cross-Section Measurements at a 500GeV CLIC Machine, Operating at sqrt(s)= 350GeV and 500GeV"

The 350 GeV HZ Recoil Analysis:

For both muon and electron channels, the background has a total cross section of roughly 1000 times greater than the signal. Given the small signal cross-sections, excess events in the Higgs note were generated, simulated and reconstructed. A safety factor of 50 was applied, and events were then weighted to the correct normalisation throughout the analysis. This helped remove the effects of statistical fluctuations in the signal sample.

For the background sample, cuts at generator level are required:

  • Transverse momentum of the leptons (l+ l-) must be greater than 10 GeV- Higgsstrahlung process will to produce a high Z transverse momentum, and hence a high lepton transverse momentum.
  • Ιcos (θ)Ι of l+ l- < 0.95. Cross-section for Higgsstrahlung process are expected to decrease the forward/backward regions, whilst their directions are favoured for processes involving the production of W or Z pairs.

Following the selection of the lepton pair: the Transverse momentum and polar angle of the lepton pair were calculated. Also Acollinearity and Acopolanarity of the leptons were calculated.

Background Rejection

In mumuX channel, the mass of the selected lepton pair, Transverse momentum of lepton pair, and the recoil mass were investigated. The made distributions made from the properties motivated the cuts:

Selection Cuts:

  • 40 Gev < M (l+ l-) < 120 GeV
  • 95 GeV < M (recoil) < 290 GeV
  • Transverse momentum of l+ l- > 60 GeV

500 GeV HZ Recoil Analysis

Hard selection cuts:

  • 30 GeV < M (l+ l-) < 120 GeV
  • 0 Gev < M (recoil) < 380 GeV
  • Transverse momentum of l+ l- > 65 GeV

500 GeV HZqq Analysis

Jet reconstruction: 3 different values for jet cone size:

R=0.7, 1.0 and 1.3

Kinematic Fit:

  • Energy conservation ∑ Ei = 500 GeV
  • Momentum conservation ∑ (pxi, pyi, pzi)= (5,0,0) GeV
  • Mass constraint: mass of one pair of jets is contrained to be equal to Z mass.

The variation of the jet parameters, and calculation of the fit probability used the following jet energy and angular resolutions:

  • σ(e) = 4.5% . Ejet
  • σ(θ) = 0.27 rad GeV / (sqrt(Ejet))
  • σ(Φ) = 0.25 rad GeV / (sqrt(Ejet))

Fit Procedure

To get the mass of the Higgs, Mh, Simplified Kernal Estimation used the shape of the fitted Higgs mass distribution for the signal sample.

Mass range 90 GeV < Mh < 200 GeV

500 GeV Hmumu Analysis

Monte Carlo fit: if invariant mass was within 5 GeV of Z mass the event was declared to be Higgsstrahlung. The remaining were flagged as WW fusion.

-- DominicSmith - 2012-11-20

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Topic revision: r3 - 2012-11-22 - DominicSmith
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