Description of the

make_param

Program

So you would like to make parameterisations on your own? Then this is the page for you.

There are an infinite number of ways to make a parameterisation. The method adopted in ALEPH is to describe the expectation values and errors of the fit parameter as functions of energy and cosinus theta of the input particles. An additional complication is the choice of reference system: Use the particles TRUE or MEASURED values for binning.

Once the choices have been made the actual making of parameterisations requires the fitting of 100 or more histograms -- each with it own fitting range to get the correct estimation of the gaussian nature of the parameters. Afterwards the results of the individual fits has to be smoothed or interpolated to give a final continuous functional description of the fit parameter value AND its error.

THIS IS NOT AN EASY TASK. Even if everything is automated it is still necessary to look through all the histograms and check the results. To ease the construction of parameterisation a general fairly easy-to-use parameterisation tool has been written. The package include:

A general routine to book, fill and output a CW-ntuple from any program, with the information needed for parameterisation making
A highly configurable automatic range detection algorithm: "If you have almost anything with a peak - it will find it!"
Many different methods to fit and extract the gaussian information from the histograms
Different types of matching of particles to TRUE-level, with the possibility to construct sum-particles (e.g. jet+jet from W)
Many different parameterisations and each group of particles can have different parameterisations
Several kumac files to plot and check histograms and the final smoothing output

It is the hope that this tool will allow anybody to produce parameterisations with a minimum of baby-sitting and with satisfactory results.

Availability
The source code of the make_param package is organised in two separate files each related to a specific part of the package. The present version consists of the fortran files:

make_param.F contains the actual fitting program which makes the parameterisation data from suitable input ntuples
ntparam.F holds the routine to generate the ntuples used by the make_param program

and the include files:

The main package requires CERNLIB and several routines from abcfit_bmatrix.F as well as the corresponding include file: abcfit_bmatrix.inc.

Usage
The high degree of freedom for the user and generality of the make_param program, implies that a simple "press the key and wait for the result" approach is not recommendable. Although the examples given here will be sufficient for many users, any user should at least be aware of the tools he can use and make sure that he checks the output before using it.

Rather than trying to explain the usage in great detail (tedious) a set of illustrative examples will be given.

The making of a parameterisation proceeds in two steps

Making the ntuples using the ntparam subroutine. Examples on its use can be found here.
Producing the parameterisation data with the make_param program. The running of the program is controlled by a steering file. The content of the steering file, hence, the controlling of the program, is described here.

If these examples do not give you the information you need to make your type of parameterisation, don't hesitate to contact O.Buchmuller.

History

October 1998: First release of program.

Comments/suggestions to O.Buchmuller or J.B.Hansen
#5 10-10-1998