I. Introduction

The supersymmetric (SUSY) standard model is the most promising extension of the standard model as it could naturally give a solution to the gauge hierarchy problem. In SUSY models, thanks to the symmetry between boson and fermion, the quadratic divergences are genuinely canceled out from the contributions of boson and fermion loops.
In addition, all SUSY partner (sparticle) masses must be less than about 1 TeV in order to solve the hierarchy problem. The price to pay is the prediction of the existence of a wealth of new particles yet undiscovered. However, the sparticles play an essential role in some phenomenologically favorable properties in the model. That is, the most impressive evidence in favor of SUSY may be the unification of gauge couplings in SUSY Grand Unified Theories (GUTs). The dark matter issue in astrophysics also encourages SUSY proponents. Many peoples consider the "SUSY world" as a plausible scenario for future particle physics.

Although the existence of the mass upper bounds is the most phenomenologically interesting property of the model, it should be noted that lighter sparticles give us a more natural solution of the gauge hierarchy problem. So there is a possibility that the sparticles could be discovered at the LEP1.5 or LEP2 energy regions in electron-positron scattering. While the hadron colliders such as FNAL Tevatron and DESY HERA have already covered larger scattering energies, LEP2, the electron-positron collider in the energy frontier, could be the first machine discovering "light" sparticles (the chargino, the slepton or the stop) as the background conditions are far better in electron-positron than in hadron colliders.

II. What do you get using "susy23"?

"SUSY23" is an event generator for SUSY processes.
Users will get (a) total cross sections, (b) differential cross sections (physical distributions) and (c) generated events. Available processes in the present version are :


name of dir


chargino1+ chargino1-



neutralino1 neutralino2



neutralino2 neutralino2



gamma neutralino1 neutralino1



selectronR+ selectronR-



selectronL+ selectronL-



selectronR+ selectronL-



selectronL+ selectronR-



smuonR+ smuonR-



smuonL+ smuonL-



stau1+ stau1-



stau2+ stau2-



stau1+ stau2-



stau2+ stau1-



snuetrino(e) anti-sneutrino(e)



snuetrino(mu) anti-sneutrino(mu)



snuetrino(tau) anti-sneutrino(tau)



positron selectronR- neutralino1



positron selectronL- neutralino1



positron sneutrino(e) chargino1-



neutrino(e) selectronL+ chargino1-



stop1 anti-stop1



sbottom1 anti-sbottom1


Final sparticle decays are generated for all processes (for detail, see (V)).
Initial state radiation (ISR) using the structure function is available for all processes as well as ISR using the QEDPS generator except for the process (4) in this version.

reference :
Y. Kurihara, J. Fujimoto, T. Munehisa, Y. Shimizu, "QEDPS" in this
LEP2 Report :
KEK CP-035, KEK Preprint 95-126, 1995

III. How does it work?

For each process, the FORTRAN source code is generated by the "GRACE" system : a general package for the automatic computation of the Feynman amplitudes. Largely exercised on standard model processes, this package is used in the SUSY framework thanks to the addition of a dedicated vertex and propagator library. The package is based on the minimal supersymmetric standard model (MSSM) and the notation of SUSY parameters described in "JLC Supersymmetry Manual" by K.Hikasa (unpublished) is adopted. Tools have been developed to build automatically the SUSY23 event generator from the various processes thus prepared. Based on an open architecture, the generator can easily accommodate the addition of foreseen more complex processes (2->4).

The numerical integration of the differential cross section over the phase space is carried out by the program BASES. All kinematics information and the phase space hyper-cell weight map are then used by the event generation program SPRING to produce weight=1 events. Helicity information are available at the parton level.
The hadronization is performed through the interface to the JETSET package which has been extended to incorporate SUSY particle codes.

In this version (V2.0), the user may generate only one process per run, in future releases, the possibility will be given to produce events from a selected set of processes accordingly to their respective probability.

reference :
Minami-Tateya collaboration, "GRACE manual ver 1.0", KEK Report
92-19, 1993,
T. Sjostrand, M. Bengtsson, Comp. Phys. Comm., 82 (1994) 74
S. Kawabata, Comp. Phys. Comm., 88 (1995) 309
K. Hikasa, "JLC Supersymmetry Manual", unpublished

IV. Input parameters

The following parameters can be set by the user:
(1) Selection of SUSY process
(2) Center of mass energy
(3) SUSY parameters

* gaugino parameters: tan(beta), M_2, mu
* 1st and 2nd generation sfermion masses
* 3rd generation sfermion masses and mixing angles

In addition, following physical option switches are prepared.

(1) ISR (SF or QEDPS ; ON or OFF)
(2) QCD correction for squark production (ON or OFF)
(3) unstable sparticle decays (YES or NO)
(4) interface to JETSET (ON or OFF)
(5) set gaugino masses, mixing angles and charged Higgs mass
(YES or NO(determined by MSSM))
(6) maintain spin information in 2-body and 3-body decays of gauginos (YES or NO)

V. Sparticle decays

Particle widths and decay branching ratios for possible modes are calculated. Each event final state is then generated according to these probabilities. In the present version, we have included some possible cascade decays of sparticles as well as 2-body and 3-body direct decays as follows ;

(1) chargino1

--> lepton neutrino neutralino1
--> quark quark' neutralino1
--> lepton sneutrino
--> neutrino slepton
--> b-quark stop1

(2) neutralino2

--> lepton lepton neutralino1
--> neutrino neutrino neutralino1
--> quark quark neutralino1
--> lepton slepton
--> neutrino sneutrino

(3) sleptonR

--> lepton neutralino1
--> lepton neutralino2

(4) sleptonL

--> lepton neutralino1
--> lepton neutralino2
--> neutrino chargino1

(5) stau1

--> tau neutralino1
--> tau neutralino2
--> neutrino(tau) chargino1

(6) stau2

--> tau neutralino1
--> tau neutralino2
--> neutrino(tau) chargino1

(7) sneutrino

--> neutrino neutralino1
--> neutrino neutralino2
--> lepton chargino1

(8) stop1

--> c-quark neutralino1
--> c-quark neutralino2
--> b-quark chargino1

(9) sbottom1

--> b-quark neutralino1
--> b-quark neutralino2

In particular, helicity information of matrix elements in the fermionic
2-body and 3-body decays of the chargino1 and neutralino2 are reflected
in the event generation of their decay products.

VI. File Structure of susy23 v2.0 System

+--- Makefile .............. Makefile
+--- README ................ This file
+--* bin (#)................ Executables
+--* lib (#)................ Libraries
+--* prc-* SW1sw1 ........ A set of FORTRAN program for SW1sw1.
| |...
| |...
| |...
| +--* Esersz1
+--* src0 .................. Interface program
+--* basesv5.1 ............. BASES/SPRING 5.1
+--* chanel ................ CHANEL version 2.0
+--* kinemlib .............. Kinematics FORTRAN Library
+--* doc ................... susy23 Manual (in preparation)

VII. How to install the program

1. make clean

2. vi Makefile

In Makefile, following Marco variables should be

SU23DIR = directory where susy23 are installed.
PDIR = directory where susy23/process are installed.
LIBDIR = directory where libraries are installed.
BINDIR = directory where an executable is installed.

MACHINE = [hpux|hiux|sgi|dec] ...... machine type
hpux : HP-UX A.09.05
hiux : HI-UX
dec : OSF1 V3.0
sgi : IRIX 5.3

FC = FORTRAN compiler command name
FOPT = FORTRAN compiler options

3. make

4. make install

5. cd src0;lgen.sh
(Local Generation for all process in default values.)

USE BASES/SPRING and CHANEL in this file.

VIII. How to get program and support

you can get susy23 via anonymous ftp :


If you have some question, please send e-mail to