Experience with CalcHEP H. S. Goh Univ. of Arizona very little West Coast LHC Theory Network -- UC Irvine May

An overview Author’s web site 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. 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 are models results ….. Run CalcHEP from your working directory :./calchep Root directory

Model Implementation A 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->2,3,4,5 No phase space integration for two body decay, so the numeric part in trivial. Example … Production : 2->2,3,4 Example…….Interactive mode

CalcHEP User interface Theorist Parameters, cut, … Request input Receive input Graduate student clone C-code By user, author 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 !!