Fyzika za Štandardným modelom klope na dvere
Svit, 9.-16.9. 2007
CompHEP
Automatic Computations from Lagrangians to
Events
Ivan Melo
University of Zilina
CompHEP
• A good tool for learning particle physics
• A good tool for research
CompHEP, GRACE, MadGraph,AlpGen, O’Mega, WHIZARD, Amegic, …
PYTHIA, HERWIG
Theory
Experiment
ATLFAST
Root
ATLAS
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
LEP1
LEP2
LHC, ILC
2 particles
4
5,6,8
• Built-in models: QED, effective 4-fermion, SM, MSSM,
SUGRA, GMSB
• With LanHEP one can add his/her own model
• Simplicity
CompHEP limitations
• No loop diagrams
• Computation of squared amplitudes timeconsuming 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
• pp
2*x
ttH +X
(SM decay)
tt bb + X (pp collider)
γ + e-
γ + e- (Compton scattering)
Thomson (α=1/137)
Klein-Nishina limit
x << 1 (nonrelat.)
Thomson scattering
x >> 1 (relat.)
Klein-Nishina limit
e+ + e-
μ+μσCompHEP= 2.0899 nb
σLEP=1.9993+- 0.0026 nb
e+ + e-
μ+μ-
Tevatron
CompHEP
LEP
= 0.01627
Higgs decay, H
2*x
pp
ttH +X
tt bb + X
Proton structure functions fi(x,q2)
u
u
d
p
t
g
g
u
u
d
b
H
g
b
t
p
pp
ttH +X
Signal
gg
ttH
uu
ttH
dd
ttH
tt bb + X
σ = 0.729 pb
σ = 0.075 pb
σ = 0.045 pb
Background
gg
ttgg σ = 400 pb
gg
ttbb σ = 6 pb
gg -> ttbb
(regularization and gauge invariant set)
•
•
•
•
131 diagrams: choose diagrams without A,Z, W+,W59 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