4 *CMZ :- -26/04/91 11.11.54 by Bryan Webber
6 *-- Author : Ian Knowles
8 C-----------------------------------------------------------------------
12 C-----------------------------------------------------------------------
14 C Constructs appropriate spin density/decay matrix for parton
16 C in hard subprocess, othwise zero. Assignments based upon
18 C Comp. Phys. Comm. 58 (1990) 271.
20 C-----------------------------------------------------------------------
22 INCLUDE 'HERWIG61.INC'
24 DOUBLE PRECISION C,V12,V23,V13,TR,C1,C2,C3,R1(2),R2(2)
30 IF (IERROR.NE.0) RETURN
32 IST=MOD(ISTHEP(NEVPAR),10)
34 C Assumed partons processed in the order IST=1,2,3,4
36 IF (IPROC.GE.100.AND.IPROC.LE.116) THEN
38 C An e+e- ---> qqbar g event
40 IF (IDPAR(2).EQ.13) THEN
50 ELSEIF (IPRO.EQ.15.OR.IPRO.EQ.17) THEN
52 IF (IHPRO.EQ. 7.OR.IHPRO.EQ. 8.OR.
54 & IHPRO.EQ.10.OR.IHPRO.EQ.11.OR.
56 & IHPRO.EQ.15.OR.IHPRO.EQ.16.OR.
58 & (IHPRO.GE.21.AND.IHPRO.LE.31)) THEN
60 C A hard 2 --- > 2 QCD subprocess involving gluons
64 CALL HWVEQU(2,RHOPAR(1,2),R1(1))
74 ELSEIF (IST.EQ.3) THEN
76 CALL HWVEQU(2,RHOPAR(1,2),R2(1))
78 V12=R1(1)*R2(1)+R1(2)*R2(2)
80 TR=1./(GCOEF(1)+GCOEF(2)*V12)
82 RHOPAR(1,2)= (GCOEF(3)*R1(1)+GCOEF(4)*R2(1))*TR
84 RHOPAR(2,2)=-(GCOEF(3)*R1(2)+GCOEF(4)*R2(2))*TR
88 ELSEIF (IST.EQ.4) THEN
90 V13=R1(1)*DECPAR(1,2)+R1(2)*DECPAR(2,2)
92 V23=R2(1)*DECPAR(1,2)+R2(2)*DECPAR(2,2)
94 TR=1./(GCOEF(1)+GCOEF(2)*V12+GCOEF(3)*V13+GCOEF(4)*V23)
96 C1=(GCOEF(2)+GCOEF(5))*TR
98 C2=(GCOEF(3)+GCOEF(6))*TR
100 C3=(GCOEF(4)+GCOEF(6))*TR
102 RHOPAR(1,2)=C1*DECPAR(1,2)+C2*R2(1)+C3*R1(1)
104 RHOPAR(2,2)=C1*DECPAR(2,2)-C2*R1(2)-C3*R2(2)
112 ELSEIF (IPRO.EQ.16) THEN
114 C A gluon fusion ---> Higgs event
118 DECPAR(1,2)=RHOPAR(1,2)
120 DECPAR(2,2)=-RHOPAR(2,2)
128 CALL HWVZRO(2,RHOPAR(1,2))
130 CALL HWVZRO(2,DECPAR(1,2))