SUSY examples

The SUSY routines and common block variables are described in section . To illustrate the usage of the switches and parameters, we give five simple examples.

Example 1: Light Stop
The first example is an MSSM model with a light neutralino $\tilde{\chi}_1$ and a light stop $\tilde{\mathrm t}_1$, so that $\t\to \tilde{\mathrm t}_1\tilde{\chi}_1$ can occur. The input parameters are
IMSS(1)=1, RMSS(1)=70., RMSS(2)=70., RMSS(3)=225., RMSS(4)=-40., RMSS(5)=1.5,
RMSS(6)=100., RMSS(7)=125., RMSS(8)=250., RMSS(9)=250., RMSS(10)=1500.,
RMSS(11)=1500., RMSS(12)=-128., RMSS(13)=100., RMSS(14)=125., RMSS(15)=800.,
RMSS(16)=800., RMSS(17)=0., and RMSS(19)=400.0.
The top mass is fixed at 175 GeV, PMAS(6,1)=175.0. The resulting model has $M_{\tilde{\mathrm t}_1}=55$ GeV and $M_{\tilde{\chi}_1}=38$ GeV. IMSS(1)=1 turns on the MSSM simulation. By default, there are no intrinsic relations between the gaugino masses, so $M_1=70$ GeV, $M_2=70$ GeV, and $M_3=225$ GeV. The pole mass of the gluino is slightly higher than the parameter $M_3$, and the decay $\tilde{\mathrm g}\to\tilde{\mathrm t}_1^*\t +\tilde{\mathrm t}_1\overline{\mathrm{t}}$ occurs almost 100% of the time.

Example 2: SUSY Les Houches Accord spectrum
The second example shows how to input a spectrum file in the SUSY Les Houches Accord format [Ska03] to PYTHIA. First, you should set IMSS(1)=11 and open the spectrum file you want to use on some unused Logical Unit Number. Then, set IMSS(21) equal to that number, to tell PYTHIA where to read the spectrum file from. This should be done somewhere in your main program before calling PYINIT. During the call to PYINIT, PYTHIA will read the spectrum file, perform a number of consistency checks and issue warning messages if it finds something it does not understand or which seems inconsistent. E.g. BLOCK GAUGE will normally be present in the spectrum file, but since PYTHIA currently cannot use the information in that block, it will issue a warning that the block will be ignored. In case a decay table is also desired to be read in, the Logical Unit Number on which the decay table is opened should be put in IMSS(22). To avoid inconsistencies, the spectrum and the decay table should normally go together, so IMSS(22) should normally be equal to IMSS(21).

Example 3: Calling ISASUSY 7.67 at runtime
The third example shows how to use the built-in interface to ISASUSY. First, the PYTHIA source code needs to be changed. Rename the function VISAJE to, for example, FDUMMY, rename the subroutine SUGRA to e.g. SDUMMY, and recompile. In the calling program, set IMSS(1)=12 and the RMSS input parameters exactly as in example 4, and compile the executable while linked to both ISAJET and the modified PYTHIA. The resulting mass and mixing spectrum is printed in the PYTHIA output.

Example 4: Approximate SUGRA
This example shows you how to get a (very) approximate SUGRA model. Note that this way of obtaining the SUSY spectrum should never be used for serious studies. The input parameters are
IMSS(1)=2, RMSS(1)=200., RMSS(4)=1., RMSS(5)=10., RMSS(8)=800., and
RMSS(16)=0.0.
The resulting model has $M_{\tilde{\mathrm d}_L}=901$ GeV, $M_{\tilde{\mathrm u}_R}=890$ GeV, $M_{\tilde{\mathrm t}_1}=538$ GeV, $M_{\tilde{\mathrm e}_L}=814$ GeV, $M_{\tilde{\mathrm g}}=560$ GeV, $M_{\tilde{\chi}_1}=80$ GeV, $M_{\tilde{\chi}^{\pm}_1}=151$ GeV, $M_{\mathrm{h}}=110$ GeV, and $M_{A}=883$ GeV. It corresponds to the choice $M_0$=800 GeV, $M_{1/2}=$200 GeV, $\tan\beta=10$, $A_0=0$, and sign($\mu$)$>0$. The output is similar to an ISASUSY run, but there is not exact agreement.

Example 5: ISASUSY 7.61 Model
The final example demonstrates how to convert the output of an ISASUSY run directly into the PYTHIA format, i.e. if SUSY Les Houches Accord output is not available. This assumes that you already made an ISASUSY run, e.g. with the equivalents of the input parameters above. From the output of this run you can now extract those physical parameters that need to be handed to PYTHIA, in the above example
IMSS(1)=1, IMSS(3)=1, IMSS(8)=0, IMSS(9)=1, RMSS(1)=79.61, RMSS(2)=155.51,
RMSS(3)=533.1, RMSS(4)=241.30, RMSS(5)=10., RMSS(6)=808.0, RMSS(7)=802.8,
RMSS(8)=878.4, RMSS(9)=877.1, RMSS(10)=743.81, RMSS(11)=871.26,
RMSS(12)=569.87, RMSS(13)=803.20, RMSS(14)=794.71, RMSS(15)=-554.96,
RMSS(16)=-383.23, RMSS(17)=-126.11, RMSS(19)=829.94 and RMSS(22)=878.5.