Particle Physics Tour with CalcHEPParticle Physics Tour with CalcHEP

by by

Shymaa M. SeifShymaa M. Seif

Assistant lecturer in Physics Department Assistant lecturer in Physics Department

Cairo University, EgyptCairo University, Egypt

Supervision:Supervision:

Dr. A. GlayshevDr. A. Glayshev

A. BednyakovA. Bednyakov

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CalcHEP

• CalcHEP package is created for calculation of decay and high energy collision processes of elementary particle in tree approximation.

• The mean idea of CalcHEP is to make available passing from the Lagrangian to the final distribution effectively, with high level of automatization.

Some useful features CalcHEP

• You can restrict/specify the particle that enter the intermediate state.

• CalcHEP provides a menu of structure functions, including CTEQ6 series which can be used to help compute pp scattering

processes.

• You can apply cuts before computing cross sections, sometimes this is necessary to remove divergences.

• CalcHEP can perform calculations in various SUSY models; this is

require CERNLIB

• Limit on number of external legs (involved particles) and number of diagrams

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CalcHEP SM Particles

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CalcHEP SM Parameters

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CalcHEP SM Constraints

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CalcHEP SM Vertices

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Switch on External Libraries

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Particle content of CalcHEP

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CalcHEP limitations

• No Hadronic bound state.

• No loop o box diagrams.

• All processes are averaged over allowed initial-state spin polarizations and summed over final-state polarization.

• No neutrino oscillations.

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Procedure for computing results 1. Specify decay or scattering process

2. View diagrams; can be written in latex, can delet selected diagrams

3. Square diagrams (can view)

4. Symbolic calculations

5. Write results

6. C code

7. C-compiler

8. Go to new window for numerical calculations

9. Select subprocess if applicable

10. Define cuts if desired

11. Vegas (Simpson if applicable)

12. Set distributions and ranges if desired

13. Integrate (2 < 1 for numerically consistent result)

14. View distribution

15. Generate events if desired 11

Setting Model Parameters

• I have studied the dependence of the total cross section on the mass of light Higgs mass for the tree level process

in mSUGRA.

• The model parameters were set:

tanβ=10, μ >1, m0 = –A0 =100 GeV and m1/2 =250 GeV.

and the SM parameters had taken as

ew(MZ)-1 =127.918, mW =80.423 GeV, mZ = 91.18 GeV,

mt =175 GeV, mb =4.62 GeV

11~~tthpp

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control of the initial states and parton densityfunctions

• The structure function (PDF) for the proton is CTEQ6l

• The momenta for both protons = 7000 GeVq~

The cuts

• M0 30 GeV, m >176 GeV, m >173GeV,

• The momenta for both protons = 7000 GeV such that s =14 TeV

g~

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LO Feynman Diagrams for 11~~tthqq

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LO Feynman Diagrams for 11~~tthgg

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Comparison between cross-sections

Mh (GeV)σ (fb)

μ = μ0 μ = 4μ0

95 0.3482 0.2363

100 0.3314 0.2163

105 0.3117 0.2035

110 0.2961 0.1943

115 0.2755 0.1826

120 0.2594 0.1746

125 0.2466 0.1625

130 0.2337 0.1484

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Table 1 Table 2

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