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CompHEP Automatic Computations from Lagrangians to Events Ivan Melo University 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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Theory Experiment 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 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.ruhttp://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 - σ CompHEP = 2.0899 nb σ LEP =1.9993+- 0.0026 nb

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e + + e - μ + μ - TevatronLEP = 0.01627 CompHEP

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Higgs decay, H 2*x

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t H g g g t u u d u u d b b p p pp ttH +X tt bb + X Proton structure functions f i (x,q 2 )

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pp ttH +X tt bb + X Signal gg ttH σ = 0.729 pb uu ttH σ = 0.075 pb dd ttH σ = 0.045 pb Background gg ttgg σ = 400 pb gg 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

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