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