Transcript TESLA - The TEV-Energy Superconducting Linear Accelerator Towards a measurement of the two photon width of the Higgs boson at the Tesla Photon.

TESLA - The TEV-Energy Superconducting Linear Accelerator
Towards a measurement of the two photon
width of the Higgs boson at the Tesla
Photon Collider
Aura Rosca
West University, Timişoara, Romania
Durham, U.K., 1-4 September 2004
TESLA - The TeV-Energy Superconducting Linear Accelerator
Motivation
• Measure the two-photon partial width:
– Contribution to the two photon decay width
from any kind of massive charged particles.
Deviation of the partial width from Standard
Model prediction:
• Evidence for new physics;
• Can be directly compared to predictions of alternative
models (MSSM, NMSSM, general 2HDM).
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
How to Get Widths?
• The Higgs mass peak gives
Γ(h  γγ)  BR(h  bb) (mh  140 GeV)
• Taking BR(h  bb) and BR(h  γγ) from LHC or
LC,
Γ γγ 
Γ(h  γγ)  BR(h  b b )
BR(h  b b )
Γ γγ
Γ tot 
BR(h  γγ)
• This is proposed as way to get the total Higgs
width. Model-independent result.
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Results of Amsterdam ‘03
• Realistic photon spectrum for ++ and +- photon
helicities simulated with CIRCE 2.0;
• Signal MC generated with PYTHIA and passed through
the TESLA fast simulation, Simdet 4.02;
• Background MC generated with PYTHIA and passed
through the TESLA fast simulation:
– s γγ  80 GeV
– Convolution with the realistic photon spectrum for ++ and +photon helicities
– Events weighted by the NLO (Jikia, Tkabladze) cross sections
for ++ and +- photon helicities
• B-tagging based on NN
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Invariant Mass Spectrum
• Possible to isolate the signal from the background.
N sig  6018 events
N bkg  7111 events



Δ Γ (h  γγ )BR(h  bb

Γ (h  γγ )BR(h  bb)

N obs

 1.9%
N obs  N b
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
New Results
• Background MC generated with SHERPA
(CERN-TH/2003-284) and passed through the
TESLA fast simulation:
– s γγ  80 GeV
– Convolution with the realistic photon spectrum for
++ and +- photon helicities
• Selection:
–
–
–
–
N jet  2,3
cosθ T  0.7
E vis  95 GeV, E long/E vis  0.1
jet
2nd fast jet
NNfastest

0.95,
NN
 0.2
out
out
September 2004
Aura Rosca
New!
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Background Cross Sections
1000
100
0.99
10
0.9
2.8
Jikia bbg ++
Jikia bbg +Jikia jjg ++
Jikia jjg +Sherpa bbg ++
Sherpa bbg +Sherpa ccg ++
Sherpa ccg +-
1
1.9
0.1
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80
100
100
120
120
Aura Rosca
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160
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Sherpa versus Pythia
Pythia ++
Pythia +-
Sherpa ++
Sherpa +-
N jet
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Sherpa versus Pythia
Pythia ++
Pythia +-
Sherpa ++
Sherpa +-
cos θ T
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Sherpa versus Pythia
Pythia ++
Pythia +-
Sherpa ++
Sherpa +-
E vis
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Sherpa versus Pythia
Pythia ++
Pythia +-
Sherpa ++
Sherpa +-
E long/E vis
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Invariant Mass Spectrum
N sig  3207 events
N bkg  1229 events



Δ Γ (h  γγ )BR(h  bb

Γ (h  γγ )BR(h  bb)

N obs

 1.5%
N obs  N b
(However, more statistics required!)
September 2004
Aura Rosca
West University Timisoara
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TESLA - The TeV-Energy Superconducting Linear Accelerator
Summary
• Measure Γ(h  γγ)  BR(h  bb) with a
precision below 2% by:
– Taking into account the QCD radiative corrections
to the background process γγ  qq ;
– Adapting a b-quark tagging algorithm based on a
neural network.
September 2004
Aura Rosca
West University Timisoara
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