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gdecay.F
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*
* $Id: gdecay.F,v 1.2 2003/11/28 11:23:56 brun Exp $
*
* $Log: gdecay.F,v $
* Revision 1.2 2003/11/28 11:23:56 brun
* New version of geant321 with all geant3 routines renamed from G to G3
*
* Revision 1.1.1.1 2002/07/24 15:56:25 rdm
* initial import into CVS
*
* Revision 1.1.1.1 2002/06/16 15:18:40 hristov
* Separate distribution of Geant3
*
* Revision 1.1.1.1 1999/05/18 15:55:20 fca
* AliRoot sources
*
* Revision 1.1.1.1 1995/10/24 10:21:23 cernlib
* Geant
*
*
#include "geant321/pilot.h"
*CMZ : 3.21/02 29/03/94 15.41.21 by S.Giani
*-- Author :
SUBROUTINE G3DECAY
C.
C. ******************************************************************
C. * *
C. * Control routine for generation of particle decays. *
C. * *
C. * MODE(I) I'th decay mode of current particle *
C. * BRATIO(I) branching ratio for I'th decay mode of *
C. * current particle. *
C. * *
C. * ==>Called by : G3HSTOP,G3THADR,G3TNEUT,G3TMUON *
C. * Author G.Patrick ********* *
C. * *
C. ******************************************************************
C.
#include "geant321/gcbank.inc"
#include "geant321/gctrak.inc"
#include "geant321/gconsp.inc"
#include "geant321/gcking.inc"
#include "geant321/gckine.inc"
#include "geant321/gcunit.inc"
#include "geant321/gcphys.inc"
#if defined(CERNLIB_USRJMP)
#include "geant321/gcjump.inc"
#endif
DIMENSION BAREA(7)
DIMENSION BETA(4)
DIMENSION BRATIO(6)
DIMENSION MODE(6)
DIMENSION NTYPE(3)
DIMENSION PCM(4,3)
DIMENSION XM(3)
DIMENSION RNDM(1)
LOGICAL ROTATE
C.
C. ------------------------------------------------------------------
C.
C Search for parent particle in decay list.
C
C
KCASE = NAMEC(5)
NGKINE = 0
IF(IDCAY.EQ.2) THEN
DESTEP = DESTEP+GETOT
ISTOP = 2
GO TO 99
ENDIF
DMASS = AMASS
JPA = LQ(JPART-IPART)
JDK1 = LQ(JPA-1)
JDK2 = LQ(JPA-2)
IF (JDK1.LE.0) GO TO 90
IF (JDK2.LE.0) GO TO 90
DO 5 I=1,6
BRATIO(I)=Q(JDK1+I)
MODE(I)=IQ(JDK2+I)
5 CONTINUE
C
C Generate branching ratio and select decay mode.
C
NBR = 1
BAREA(1) = 0.
DO 10 I=2,7
BRADD = BRATIO(I-1)
IF (BRADD.EQ.0.) GO TO 20
NBR = NBR+1
BAREA(I) = BAREA(I-1)+BRADD
10 CONTINUE
C
20 CALL GRNDM(RNDM,1)
BRAND = 100.*RNDM(1)
IF (BRAND.GE.BAREA(NBR)) GO TO 99
ID = IABS((LOCATF(BAREA,NBR,BRAND)))
C
C Unpack decay mode.
C
MXX = MODE(ID)
NTYPE(1) = MOD(MXX,100)
NTYPE(2) = MOD(MXX/100,100)
JP1 = LQ(JPART-NTYPE(1))
JP2 = LQ(JPART-NTYPE(2))
XM(1) = Q(JP1+7)
XM(2) = Q(JP2+7)
IF (MXX.LT.10000)THEN
C
C Two body decay.
C
NGKINE = 2
IF (TLIFE.LT.1.E-15) THEN
XMTOT = XM(1)+XM(2)
DO 30 I=1,1000
C-- Create Lorentz distributed energy with FWHM HBAR/TLIFE.
C-- (via integral-transformation of Lorentz-distribution)
C-- (M.Guckes)
CALL GRNDM(RNDM,1)
RMASS = DMASS
1 + 3.291086E-25/TLIFE * TAN(PI*(RNDM(1)-0.5))
IF (RMASS.GE.XMTOT) GO TO 40
30 CONTINUE
WRITE(CHMAIL,1000) IPART, NTYPE(1), NTYPE(2)
CALL GMAIL(0,0)
NGKINE=0
GO TO 99
40 DMASS = RMASS
END IF
CALL G3DECA2(DMASS,XM(1),XM(2),PCM)
ELSE
C
C Three body decay.
C
NTYPE(3) = MXX/10000
NGKINE = 3
JP3 = LQ(JPART-NTYPE(3))
XM(3) = Q(JP3+7)
IF (TLIFE.LT.1.E-15) THEN
XMTOT = XM(1)+XM(2)+XM(3)
DO 31 I=1,1000
C-- Create Lorentz distributed energy with FWHM HBAR/TLIFE.
C-- (via integral-transformation of Lorentz-distribution)
CALL GRNDM(RNDM,1)
RMASS = DMASS
1 + 3.291086E-25/TLIFE * TAN(PI*(RNDM(1)-0.5))
IF (RMASS.GE.XMTOT) GO TO 41
31 CONTINUE
WRITE(CHMAIL,1000) IPART, NTYPE(1), NTYPE(2), NTYPE(3)
CALL GMAIL(0,0)
NGKINE=0
GO TO 99
41 DMASS = RMASS
END IF
IF (IPART.EQ.7) THEN
IF (MXX.EQ.30201) THEN ! pi0 -> gamma e+e- (=30201)
CALL GDALET(DMASS,XM(1),XM(2),XM(3),PCM,1)
ELSE
CALL G3DECA3(DMASS,XM(1),XM(2),XM(3),PCM)
ENDIF
ENDIF
IF (IPART.EQ.17) THEN ! eta
IF(MXX.EQ.30201) THEN ! -> gamma e+e-
CALL GDALET(DMASS,XM(1),XM(2),XM(3),PCM,2)
ELSE ! phase space
CALL G3DECA3(DMASS,XM(1),XM(2),XM(3),PCM)
ENDIF
ENDIF
IF (IPART.EQ.33) THEN ! omega
IF(MXX.EQ.30207) THEN ! -> pi0 e+e-
CALL GDALET(DMASS,XM(1),XM(2),XM(3),PCM,3)
ELSE
CALL G3DECA3(DMASS,XM(1),XM(2),XM(3),PCM)
ENDIF
ENDIF
IF (IPART.NE.7.AND.IPART.NE.17.AND.IPART.NE.33) THEN ! other particle
CALL G3DECA3(DMASS,XM(1),XM(2),XM(3),PCM)
ENDIF
c CALL G3DECA3(DMASS,XM(1),XM(2),XM(3),PCM)
ENDIF
C
C LORENTZ boost into LAB system defined along parent vector
C followed by rotation back into GEANT system.
C
P0 = VECT(7)
E0 = SQRT(P0*P0+DMASS*DMASS)
BETA(1) = 0.
BETA(2) = 0.
BETA(3) = -P0/E0
BETA(4) = E0/DMASS
CALL G3FANG(VECT(4),COSTH,SINTH,COSPH,SINPH,ROTATE)
C
DO 60 K=1,NGKINE
IF (P0.LE.0.) THEN
DO 59 I = 1,3
59 GKIN(I,K) = PCM(I,K)
ELSE
CALL G3LOREN (BETA, PCM(1,K), GKIN(1,K))
ENDIF
IF(ROTATE) CALL G3DROT (GKIN(1,K),COSTH,SINTH,COSPH,SINPH)
GKIN(4,K)=SQRT(GKIN(1,K)**2+GKIN(2,K)**2+GKIN(3,K)**2+XM(K)**2)
GKIN(5,K)=NTYPE(K)
TOFD(K)=0.
GPOS(1,K) = VECT(1)
GPOS(2,K) = VECT(2)
GPOS(3,K) = VECT(3)
60 CONTINUE
GO TO 99
C
C No branching ratio defined. Call user routine
C
#if !defined(CERNLIB_USRJMP)
90 CALL GUDCAY
#endif
#if defined(CERNLIB_USRJMP)
90 CALL JUMPT0(JUDCAY)
#endif
C
99 RETURN
1000 FORMAT(' ***** GDECAY ERROR : Not enough energy available for ',
+ 'decay of resonance',I3,' to',3I3,'; no decay.')
END