Experience with CalcHEP

H. S. GohUniv. of Arizona

very little

West Coast LHC Theory Network -- UC Irvine

May 4 2007

An overview

• Author’s web sitehttp://www.ifh.de/~pukhov/calchep.html

• Simple tool – user friendly, or theorist friendly

• For simple task : – tree level, – 6 fundamental particles, – no polarization

• Technical requirement : typing, no programming needed

Detector Simulation

Parton Shower

Matrix Element

Herwig, Pythia

Madgraph, CompHEP/CalcHEP

Something too advanced for theorist (like me)

Models

You and me

Real World

LanHEP

Basic Structure of CalcHEP

Model Implementation

Symbolic calculation

Numeric calculation

Non-interactive (Batch mode)Interactive

Feynman diagram, square amplitude, sum over index, generate C-code

Phase space integration. Cross section, distribution, event generation,…

Step –0 : Installation

• Download, unzip – root directory generated with all needed files. http://www.ifh.de/~pukhov/calchep.html

tar -xzf calchep_2.4.5.tgz

• Compile inside the root directory:

./gmake

• Make user directory(working directory) from root directory : ./mkUsrDir ~/my_model

• Inside the working directory “my_model”, there aremodels results …..

• Run CalcHEP from your working directory : ./calchep

Root directory

Model ImplementationA model is defined by 4 (tables) files in the directory “models” :

• prtcls# : list of particles with properties, i.e. mass, spin, identity,..

• vars# : list of free parameters and their values

• func# : list of variables written as function of free parameters above

• lgrng# : interactions – Feynman rules

To implement a new model = create these 4 files, one can either

• Copy the existing files to the directory “models”

• Use the “import model” function after launching CalcHEP

• Modify the SM model files

--these files are simple text files that can be edited by other editor

or within CalcHEP

Ready to go

• Decay : 1->2,3,4,5No phase space integration for two body decay, so the numeric part in trivial.

Example …

• Production : 2->2,3,4Example…….Interactive mode

CalcHEP

User interface

Theorist

Parameters, cut, …

Request input

Receive input

Graduate studentclone

C-code By

user, author

Batch

mode

Batch mode

[ : Down] : Up{ : Enter} : Escape

and number are most commonly used

use a series of these characters to simulate the key board entry as if you are in the interactive mode.

you can write a routine to repeat the same operation with different input parameters

n_calchep -blind “[[[[[[{{]]]”

– Go through the symbolic part in the interactive mode and get the c-code for a certain process. (Although you can use the batch mode for the symbolic calculation as well)

– Now do N cycles of numerical calculation with automatically changing the parameters

– Extract the final result from output files

Some useful build-in scripts

s_blind

set_param

name_cycle

subproc_cycle

And you can make your own !

Or combine the existing scripts to build a larger one

END

Have fun !!