comphep automatic computations from lagrangians to events ivan melo university of zilina fyzika za...
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CompHEP Automatic Computations from
Lagrangians to Events
Ivan MeloUniversity of Zilina
Fyzika za Štandardným modelom klope na dvere Svit, 9.-16.9. 2007
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CompHEP
• A good tool for learning particle physics
• A good tool for research
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TheoryExperiment
PYTHIA, HERWIG
ATLFAST
Root ATLAS
CompHEP, GRACE, MadGraph,AlpGen, O’Mega, WHIZARD, Amegic, …
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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 particlesLEP2 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 CompHEP
the 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
• γ + e- γ + e- (QED)
• e+ + e- μ+μ- (SM scattering, e+e- collider)
• H 2 * x (SM decay)
• pp ttH +X tt bb + X (pp collider)
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γ + e- γ + e- (Compton scattering)
x << 1 (nonrelat.)Thomson scattering
x >> 1 (relat.)Klein-Nishina limit
Thomson
Klein-Nishina limit
(α=1/137)
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e+ + e- μ+μ-
σCompHEP= 2.0899 nbσLEP=1.9993+- 0.0026 nb
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e+ + e- μ+μ-
Tevatron LEP
= 0.01627
CompHEP
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Higgs decay, H 2*x
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t
Hg
g g
t
uud
uud
b
b
p
p
pp ttH +X tt bb + X
Proton structure functions fi(x,q2)
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pp ttH +X tt bb + X
Signalgg ttH σ = 0.729 pbuu ttH σ = 0.075 pbdd ttH σ = 0.045 pb
Backgroundgg ttgg σ = 400 pbgg ttbb σ = 6 pb
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gg -> ttbb (regularization and gauge invariant
set)
• 131 diagrams: choose diagrams without A,Z, W+,W-
• 59 left : keep just 8 with H->bb• 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