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
CompHEP
• A good tool for learning particle physics
• A good tool for research
TheoryExperiment
PYTHIA, HERWIG
ATLFAST
Root ATLAS
CompHEP, GRACE, MadGraph,AlpGen, O’Mega, WHIZARD, Amegic, …
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
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
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
Beyond the SM with CompHEP
CompHEP Collaboration
Beyond the SM with CompHEP
the list of topics based on ~ 1000 theory papers quoting CompHEP
CompHEP Collaboration
Published experimental analyses quoting CompHEP
CompHEP Collaboration
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)
γ + e- γ + e- (Compton scattering)
x << 1 (nonrelat.)Thomson scattering
x >> 1 (relat.)Klein-Nishina limit
Thomson
Klein-Nishina limit
(α=1/137)
e+ + e- μ+μ-
σCompHEP= 2.0899 nbσLEP=1.9993+- 0.0026 nb
e+ + e- μ+μ-
Tevatron LEP
= 0.01627
CompHEP
Higgs decay, H 2*x
t
Hg
g g
t
uud
uud
b
b
p
p
pp ttH +X tt bb + X
Proton structure functions fi(x,q2)
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
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
Research with CompHEP
• Add your own model with OneHEP
• Send events to PYTHIA or HERWIG
Future developments
• Loops
• Polarized cross-sections
• Grid and new algorithm