CalcHEP reference
Here is the CalcHEP batch mode reference. You should find description for every possible parameters the batch mode accepts except if it is redondant with some HEPMDB function.
We tried to organize this document this way: entries concerning similar or close information are gathered together. Each subsection is directly the parameter name. Sometimes only the main parameter is in the subsection title but the other subparameters should be decribed anyway.
Contents
Model information
Model
This line corresponds to the model used. When using HEPMDB, each batch file is associated with a specific model. As a consequence, the default value of this line should not be changed.
Gauge
CalcHEP is able to use two different gauges for computation: Feynman gauge and unitary gauge. Some models require a specific gauge. We recommand leaving the default value for this.
Model changed
Each time the batch interface is run, it checks initially whether or not the subprocess numerical code exists. If it does, CalcHEP reuses the code and skips the often long process of code generation. If the code does not already exist, the numerical code is then generated and added to the library. If the model changed, the numerical codes are regenerated as appropriate.
Process description
Process
Using the process keyword, it is possible to specify which process to compute. Multiple processes can be required. The general syntax is:
Incoming and outgoing particles are separated by ->. Particles can be particles from the model you are using or composite particles. It is recommended that the number of outgoing particles not exceed 6.
Decay
It is possible to specify decays for the outgoing particles. Each decay will be written as follow:
Decays will automatically be connected to outgoing particles if possible. Decays will even be connected with one another.
Important note: make sure the same decay does not appear twice.
Composite
When specifying processes and decays, you can use composite particles, i.e. labels that refer to various possible particles. This is particularly useful when colliding protons or when studying jets.
The syntax is:
Remove
Sometimes, you'll be only interested in specific processes. It is possible to tell CalcHEP which particle you don't want as virtual particles in the processes. The syntax is:
Beam description
pdf1/pdf2
p1/p2
These two parameters defines the energy of the beams. When using pdf, it can also be used as an input parameter for the pdf. For instance, when using proton photon, this would corresponds to the energy of the initial proton.
Model parameters
Parameter
It is possible to change some parameters of a model using Parameter keyword. The parameters are model specific. Here's an example for selecting the elementary charge in the standard model:
Run parameter
It is usual for a model to have some free parameters not completely fixed by experiment. For that kind of situation, you have the possibility to run several times the same computation with a different value for a specific parameter.
In order to use this possibility, you have to write four consecutive lines. The first one specifies what parameter to study. To study the higgs mass using the standard model, you'll write:
Then you must specify the initial value and the increase of the value between each run:
Finally, the number of steps is defined by:
So with these specific lines, you'll get 6 runs using the following value for the Higgs mass: 100, 110, 120, 130, 140, 150.
It is possible to mark several parameters for running. But it is only possible to explore hyperrectangle in the parameter space.
