CompHEP Automatic Computations from Lagrangians to Events

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CompHEP Automatic Computations from Lagrangians
to Events
Fyzika za Štandardným modelom klope na dvere
Svit, 9.-16.9. 2007

• Ivan Melo
• University of Zilina

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CompHEP

• A good tool for learning particle physics
• A good tool for research

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CompHEP, GRACE, MadGraph,AlpGen, OMega, WHIZARD,
Amegic,
PYTHIA, HERWIG
Theory Experiment
ATLFAST
Root
ATLAS
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Useful features of CompHEP

• Tool for calculating cross-sections and widths at
  tree-level starting from Lagrangian
• Event generation plus CompHEP PYTHIA and
  CompHEP HERWIG interface
• Up to 7 particles in final state
• Built-in models QED, effective 4-fermion, SM,
  MSSM, SUGRA, GMSB
• With LanHEP one can add his/her own model
• Simplicity

LEP1 2 particles LEP2 4
LHC, ILC 5,6,8
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CompHEP limitations

• No loop diagrams
• Computation of squared amplitudes time-consuming
  for large number of FD
• No polarized (helicity) cross-sections
• No hadronization of quarks and gluons

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CompHEP Collaboration

• E. Boos, V. Bunichev, M. Dubinin, L. Dudko,
  V. Edneral, V. Ilyin, A. Kryuokov, V. Savrin,
  A. Semenov, A. Sherstnev
• Lomonosov Moscow State University

CompHEP home page http//comphep.sinp.msu.ru
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Beyond the SM with CompHEP
CompHEP Collaboration
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Beyond the SM with CompHEPthe list of topics
based on 1000 theory papers quoting CompHEP
CompHEP Collaboration
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Published experimental analyses quoting CompHEP
CompHEP Collaboration
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Learning particle physics with CompHEP

• ? e- ? e- (QED)
• e e- µµ- (SM scattering, ee-
  collider)
• H 2 x (SM decay)
• pp ttH X tt bb X (pp collider)

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? e- ? e- (Compton scattering)
(a1/137)
Thomson
Klein-Nishina limit
x ltlt 1 (nonrelat.) Thomson scattering
x gtgt 1 (relat.) Klein-Nishina limit
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e e- µµ-
sCompHEP 2.0899 nb sLEP1.9993- 0.0026 nb
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e e- µµ-
CompHEP
Tevatron
LEP
0.01627
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Higgs decay, H 2x
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pp ttH X tt bb X
Proton structure functions fi(x,q2)
u
u
p
d
t
g
b
H
g
g
b
t
u
u
p
d
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pp ttH X tt bb X
Signal gg ttH s 0.729 pb uu ttH
s 0.075 pb dd ttH s 0.045 pb
Background gg ttgg s 400 pb gg
ttbb s 6 pb
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gg -gt ttbb (regularization and gauge invariant
set)

• 131 diagrams choose diagrams without A,Z, W,W-
• 59 left keep just 8 with H-gtbb
• Run without regularization
• Run with regularization

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Research with CompHEP

• Add your own model with OneHEP
• Send events to PYTHIA or HERWIG

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Future developments

• Loops
• Polarized cross-sections
• Grid and new algorithm