1. CompHEP Automatic Computations from Lagrangians to Events
Urýchľovačová fyzika 3
CompHEP Automatic Computations from Lagrangians to Events
Ivan Melo

2. CompHEP A good tool for learning particle physics
A good tool for research

3. Cross section calculation3 4 5 1 2 7 6 8
amplitúda
počet možných stavov,
fázový priestor
zachovanie energie a hybnosti

4. + ... + e- e+  e- e+ Dynamika procesu je skrytá v amplitúde Mg e- e+ +
+ ...
M = M1(α) M2(α2)
ak  < 1 potom M1(α) > M2(α2) > ...
v prípade elektrónov a fotónov:  = 1/137
Urýchľovačová fyzika 5
M.Gintner

5. Great simulation chain
CompHEP, GRACE, MadGraph,AlpGen, O’Mega, WHIZARD, Amegic, …
PYTHIA, HERWIG
Theory
Experiment
ATLFAST
Root
ATLAS

6. 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
LEP particles
LEP
LHC, ILC ,6,8

7. 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

8. 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:

9. Beyond the SM with CompHEP
CompHEP Collaboration

10. Beyond the SM with CompHEP the list of topics based on ~ 1000 theory papers quoting CompHEP
CompHEP Collaboration

11. Published experimental analyses quoting CompHEP
CompHEP Collaboration

12. Learning particle physics with CompHEP
γ + e γ + e- (QED)
e+ + e μ+μ- (SM scattering, e+e- collider)
H * x (SM decay)
pp ttH +X tt bb + X (pp collider)

13. γ + e- γ + e- (Compton scattering)
Thomson
(α=1/137)
Klein-Nishina limit
x << 1 (nonrelat.)
Thomson scattering
x >> 1 (relat.)
Klein-Nishina limit

14. e+ + e μ+μ-
σCompHEP= nb
σLEP= nb

15. Higgs decay, H 2*x
decay width
lifetime

16. pp ttH +X tt bb + X Proton structure functions fi(x,q2) u u p d t g b

18. pp ttH +X tt bb + X Signal gg ttH σ = 0.729 pb uu ttH σ = 0.075 pb
dd ttH σ = pb
Background
gg ttgg σ = 400 pb
gg ttbb σ = 6 pb

19. Research with CompHEP Add your own model with OneHEP
Send events to PYTHIA or HERWIG

20. Future developments Loops Polarized cross-sections
Grid and new algorithm