HIJING/hipyset1_35/pydiff_hijing.F

   1 * $Id$
   2
   3 C*********************************************************************
   4
   5       SUBROUTINE PYDIFF_HIJING
   6
   7 C...Handles diffractive and elastic scattering.
   8 #include "lujets_hijing.inc"
   9 #include "ludat1_hijing.inc"
  10 #include "pypars_hijing.inc"
  11 #include "pyint1_hijing.inc"
  12
  13 C...Reset K, P and V vectors. Store incoming particles.
  14       DO 100 JT=1,MSTP(126)+10
  15       I=MINT(83)+JT
  16       DO 100 J=1,5
  17       K(I,J)=0
  18       P(I,J)=0.
  19   100 V(I,J)=0.
  20       N=MINT(84)
  21       MINT(3)=0
  22       MINT(21)=0
  23       MINT(22)=0
  24       MINT(23)=0
  25       MINT(24)=0
  26       MINT(4)=4
  27       DO 110 JT=1,2
  28       I=MINT(83)+JT
  29       K(I,1)=21
  30       K(I,2)=MINT(10+JT)
  31       P(I,5)=VINT(2+JT)
  32       P(I,3)=VINT(5)*(-1)**(JT+1)
  33   110 P(I,4)=SQRT(P(I,3)**2+P(I,5)**2)
  34       MINT(6)=2
  35
  36 C...Subprocess; kinematics.
  37       ISUB=MINT(1)
  38       SQLAM=(VINT(2)-VINT(63)-VINT(64))**2-4.*VINT(63)*VINT(64)
  39       PZ=SQRT(SQLAM)/(2.*VINT(1))
  40       DO 150 JT=1,2
  41       I=MINT(83)+JT
  42       PE=(VINT(2)+VINT(62+JT)-VINT(65-JT))/(2.*VINT(1))
  43
  44 C...Elastically scattered particle.
  45       IF(MINT(16+JT).LE.0) THEN
  46         N=N+1
  47         K(N,1)=1
  48         K(N,2)=K(I,2)
  49         K(N,3)=I+2
  50         P(N,3)=PZ*(-1)**(JT+1)
  51         P(N,4)=PE
  52         P(N,5)=P(I,5)
  53
  54 C...Diffracted particle: valence quark kicked out.
  55       ELSEIF(MSTP(101).EQ.1) THEN
  56         N=N+2
  57         K(N-1,1)=2
  58         K(N,1)=1
  59         K(N-1,3)=I+2
  60         K(N,3)=I+2
  61         CALL PYSPLI_HIJING(K(I,2),21,K(N,2),K(N-1,2))
  62         P(N-1,5)=ULMASS_HIJING(K(N-1,2))
  63         P(N,5)=ULMASS_HIJING(K(N,2))
  64         SQLAM=(VINT(62+JT)-P(N-1,5)**2-P(N,5)**2)**2-
  65      &  4.*P(N-1,5)**2*P(N,5)**2
  66         P(N-1,3)=(PE*SQRT(SQLAM)+PZ*(VINT(62+JT)+P(N-1,5)**2-
  67      &  P(N,5)**2))/(2.*VINT(62+JT))*(-1)**(JT+1)
  68         P(N-1,4)=SQRT(P(N-1,3)**2+P(N-1,5)**2)
  69         P(N,3)=PZ*(-1)**(JT+1)-P(N-1,3)
  70         P(N,4)=SQRT(P(N,3)**2+P(N,5)**2)
  71
  72 C...Diffracted particle: gluon kicked out.
  73       ELSE
  74         N=N+3
  75         K(N-2,1)=2
  76         K(N-1,1)=2
  77         K(N,1)=1
  78         K(N-2,3)=I+2
  79         K(N-1,3)=I+2
  80         K(N,3)=I+2
  81         CALL PYSPLI_HIJING(K(I,2),21,K(N,2),K(N-2,2))
  82         K(N-1,2)=21
  83         P(N-2,5)=ULMASS_HIJING(K(N-2,2))
  84         P(N-1,5)=0.
  85         P(N,5)=ULMASS_HIJING(K(N,2))
  86 C...Energy distribution for particle into two jets.
  87   120   IMB=1
  88         IF(MOD(K(I,2)/1000,10).NE.0) IMB=2
  89         CHIK=PARP(92+2*IMB)
  90         IF(MSTP(92).LE.1) THEN
  91           IF(IMB.EQ.1) CHI=RLU_HIJING(0)
  92           IF(IMB.EQ.2) CHI=1.-SQRT(RLU_HIJING(0))
  93         ELSEIF(MSTP(92).EQ.2) THEN
  94           CHI=1.-RLU_HIJING(0)**(1./(1.+CHIK))
  95         ELSEIF(MSTP(92).EQ.3) THEN
  96           CUT=2.*0.3/VINT(1)
  97   130     CHI=RLU_HIJING(0)**2
  98           IF((CHI**2/(CHI**2+CUT**2))**0.25*(1.-CHI)**CHIK.LT.
  99      &    RLU_HIJING(0)) GOTO 130
 100         ELSE
 101           CUT=2.*0.3/VINT(1)
 102           CUTR=(1.+SQRT(1.+CUT**2))/CUT
 103   140     CHIR=CUT*CUTR**RLU_HIJING(0)
 104           CHI=(CHIR**2-CUT**2)/(2.*CHIR)
 105           IF((1.-CHI)**CHIK.LT.RLU_HIJING(0)) GOTO 140
 106         ENDIF
 107         IF(CHI.LT.P(N,5)**2/VINT(62+JT).OR.CHI.GT.1.-P(N-2,5)**2/
 108      &  VINT(62+JT)) GOTO 120
 109         SQM=P(N-2,5)**2/(1.-CHI)+P(N,5)**2/CHI
 110         IF((SQRT(SQM)+PARJ(32))**2.GE.VINT(62+JT)) GOTO 120
 111         PZI=(PE*(VINT(62+JT)-SQM)+PZ*(VINT(62+JT)+SQM))/
 112      &  (2.*VINT(62+JT))
 113         PEI=SQRT(PZI**2+SQM)
 114         PQQP=(1.-CHI)*(PEI+PZI)
 115         P(N-2,3)=0.5*(PQQP-P(N-2,5)**2/PQQP)*(-1)**(JT+1)
 116         P(N-2,4)=SQRT(P(N-2,3)**2+P(N-2,5)**2)
 117         P(N-1,3)=(PZ-PZI)*(-1)**(JT+1)
 118         P(N-1,4)=ABS(P(N-1,3))
 119         P(N,3)=PZI*(-1)**(JT+1)-P(N-2,3)
 120         P(N,4)=SQRT(P(N,3)**2+P(N,5)**2)
 121       ENDIF
 122
 123 C...Documentation lines.
 124       K(I+2,1)=21
 125       IF(MINT(16+JT).EQ.0) K(I+2,2)=MINT(10+JT)
 126       IF(MINT(16+JT).NE.0) K(I+2,2)=10*(MINT(10+JT)/10)
 127       K(I+2,3)=I
 128       P(I+2,3)=PZ*(-1)**(JT+1)
 129       P(I+2,4)=PE
 130       P(I+2,5)=SQRT(VINT(62+JT))
 131   150 CONTINUE
 132
 133 C...Rotate outgoing partons/particles using cos(theta).
 134       CALL LUDBRB_HIJING(MINT(83)+3,N,ACOS(VINT(23)),VINT(24),0D0,0D0
 135      $     ,0D0)
 136
 137       RETURN
 138       END