4 *CMZ :- -23/08/94 13.22.29 by Mike Seymour
6 *-- Author : Ulrich Baur & Nigel Glover, adapted by Ian Knowles
8 C-----------------------------------------------------------------------
10 SUBROUTINE HWHIGA(S,T,U,EMH2,WTQQ,WTQG,WTGQ,WTGG)
12 C-----------------------------------------------------------------------
14 C Gives amplitudes squared for q-qbar, q(bar)-g and gg -> Higgs +jet
16 C IAPHIG (set in HWIGIN)=0: zero mass approximation =1: exact result
18 C =2: infinite mass limit.
20 C Only top loop included. A factor (alpha_s**3*alpha_W) is extracted
22 C-----------------------------------------------------------------------
24 INCLUDE 'HERWIG61.INC'
26 DOUBLE COMPLEX HWHIGB,HWHIGC,HWHIGD,HWHIG5,HWHIG1,HWHIG2,BI(4),
28 & CI(7),DI(3),EPSI,TAMP(7)
30 DOUBLE PRECISION S,T,U,EMH2,WTQQ,WTQG,WTGQ,WTGG,EMW2,RNGLU,RNQRK,
32 & FLUXGG,FLUXGQ,FLUXQQ,EMQ2,TAMPI(7),TAMPR(7)
38 EXTERNAL HWHIGB,HWHIGC,HWHIGD,HWHIG5,HWHIG1,HWHIG2
44 EPSI=CMPLX(ZERO,-1.D-10)
48 C Spin and colour flux factors plus enhancement factor
50 RNGLU=1./FLOAT(NCOLO**2-1)
54 FLUXGG=.25*RNGLU**2*ENHANC(6)**2
56 FLUXGQ=.25*RNGLU*RNQRK*ENHANC(6)**2
58 FLUXQQ=.25*RNQRK**2*ENHANC(6)**2
62 C Infinite mass limit in loops
64 WTGG=2./3.*FLOAT(NCOLO*(NCOLO**2-1))
66 & *(EMH2**4+S**4+T**4+U**4)/(S*T*U*EMW2)*FLUXGG
68 WTQQ= 16./9.*(U**2+T**2)/(S*EMW2)*FLUXQQ
70 WTQG=-16./9.*(U**2+S**2)/(T*EMW2)*FLUXGQ
72 WTGQ=-16./9.*(S**2+T**2)/(U*EMW2)*FLUXGQ
76 ELSEIF (IAPHIG.EQ.1) THEN
78 C Exact result for loops
82 ELSEIF (IAPHIG.EQ.0) THEN
84 C Small mass approximation in loops
90 CALL HWWARN('HWHIGA',500,*999)
94 C Include only top quark contribution
98 BI(1)=HWHIGB(NOMASS,S,ZERO,ZERO,EMQ2)
100 BI(2)=HWHIGB(NOMASS,T,ZERO,ZERO,EMQ2)
102 BI(3)=HWHIGB(NOMASS,U,ZERO,ZERO,EMQ2)
104 BI(4)=HWHIGB(NOMASS,EMH2,ZERO,ZERO,EMQ2)
112 CI(1)=HWHIGC(NOMASS,S,ZERO,ZERO,EMQ2)
114 CI(2)=HWHIGC(NOMASS,T,ZERO,ZERO,EMQ2)
116 CI(3)=HWHIGC(NOMASS,U,ZERO,ZERO,EMQ2)
118 CI(7)=HWHIGC(NOMASS,EMH2,ZERO,ZERO,EMQ2)
120 CI(4)=(S*CI(1)-EMH2*CI(7))/(S-EMH2)
122 CI(5)=(T*CI(2)-EMH2*CI(7))/(T-EMH2)
124 CI(6)=(U*CI(3)-EMH2*CI(7))/(U-EMH2)
126 DI(1)=HWHIGD(NOMASS,U,T,EMH2,EMQ2)
128 DI(2)=HWHIGD(NOMASS,S,U,EMH2,EMQ2)
130 DI(3)=HWHIGD(NOMASS,S,T,EMH2,EMQ2)
132 C Compute complex amplitudes
134 TAMP(1)=HWHIG1(S,T,U,EMH2,EMQ2,1,2,3,4,5,6)
136 TAMP(2)=HWHIG2(S,T,U,EMH2,EMQ2,1,2,3,0,0,0)
138 TAMP(3)=HWHIG1(T,S,U,EMH2,EMQ2,2,1,3,5,4,6)
140 TAMP(4)=HWHIG1(U,T,S,EMH2,EMQ2,3,2,1,6,5,4)
142 TAMP(5)=HWHIG5(S,T,U,EMH2,EMQ2,1,0,4,0,0,0)
144 TAMP(6)=HWHIG5(T,S,U,EMH2,EMQ2,2,0,5,0,0,0)
146 TAMP(7)=HWHIG5(U,T,S,EMH2,EMQ2,3,0,6,0,0,0)
150 TAMPI(I)= DBLE(TAMP(I))
152 20 TAMPR(I)=-IMAG(TAMP(I))
154 C Square and add prefactors
156 WTGG=0.03125*FLOAT(NCOLO*(NCOLO**2-1))
158 & *(TAMPR(1)**2+TAMPI(1)**2+TAMPR(2)**2+TAMPI(2)**2
160 & +TAMPR(3)**2+TAMPI(3)**2+TAMPR(4)**2+TAMPI(4)**2)*FLUXGG
162 WTQQ= 16.*(U**2+T**2)/(U+T)**2*EMQ2**2/(S*EMW2)
164 & *(TAMPR(5)**2+TAMPI(5)**2)*FLUXQQ
166 WTQG=-16.*(U**2+S**2)/(U+S)**2*EMQ2**2/(T*EMW2)
168 & *(TAMPR(6)**2+TAMPI(6)**2)*FLUXGQ
170 WTGQ=-16.*(S**2+T**2)/(S+T)**2*EMQ2**2/(U*EMW2)
172 & *(TAMPR(7)**2+TAMPI(7)**2)*FLUXGQ