HIJING/hipyset1_35/lu2ent_hijing.F

   1 * $Id$
   2
   3 C*********************************************************************
   4
   5       SUBROUTINE LU2ENT_HIJING(IP,KF1,KF2,PECM)
   6
   7 C...Purpose: to store two partons/particles in their CM frame,
   8 C...with the first along the +z axis.
   9 #include "lujets_hijing.inc"
  10 #include "ludat1_hijing.inc"
  11 #include "ludat2_hijing.inc"
  12
  13 C...Standard checks.
  14       MSTU(28)=0
  15       IF(MSTU(12).GE.1) CALL LULIST_HIJING(0)
  16       IPA=MAX(1,IABS(IP))
  17       IF(IPA.GT.MSTU(4)-1) CALL LUERRM_HIJING(21,
  18      &'(LU2ENT_HIJING:) writing outside LUJETS_HIJING memory')
  19       KC1=LUCOMP_HIJING(KF1)
  20       KC2=LUCOMP_HIJING(KF2)
  21       IF(KC1.EQ.0.OR.KC2.EQ.0) CALL LUERRM_HIJING(12,
  22      &'(LU2ENT_HIJING:) unknown flavour code')
  23
  24 C...Find masses. Reset K, P and V vectors.
  25       PM1=0.
  26       IF(MSTU(10).EQ.1) PM1=P(IPA,5)
  27       IF(MSTU(10).GE.2) PM1=ULMASS_HIJING(KF1)
  28       PM2=0.
  29       IF(MSTU(10).EQ.1) PM2=P(IPA+1,5)
  30       IF(MSTU(10).GE.2) PM2=ULMASS_HIJING(KF2)
  31       DO 100 I=IPA,IPA+1
  32       DO 100 J=1,5
  33       K(I,J)=0
  34       P(I,J)=0.
  35   100 V(I,J)=0.
  36
  37 C...Check flavours.
  38       KQ1=KCHG(KC1,2)*ISIGN(1,KF1)
  39       KQ2=KCHG(KC2,2)*ISIGN(1,KF2)
  40       IF(KQ1+KQ2.NE.0.AND.KQ1+KQ2.NE.4) CALL LUERRM_HIJING(2,
  41      &'(LU2ENT_HIJING:) unphysical flavour combination')
  42       K(IPA,2)=KF1
  43       K(IPA+1,2)=KF2
  44
  45 C...Store partons/particles in K vectors for normal case.
  46       IF(IP.GE.0) THEN
  47         K(IPA,1)=1
  48         IF(KQ1.NE.0.AND.KQ2.NE.0) K(IPA,1)=2
  49         K(IPA+1,1)=1
  50
  51 C...Store partons in K vectors for parton shower evolution.
  52       ELSE
  53          IF(KQ1.EQ.0.OR.KQ2.EQ.0) CALL LUERRM_HIJING(2,
  54      &        '(LU2ENT_HIJING:) requested flavours can not develop'//
  55      $        'parton shower')
  56         K(IPA,1)=3
  57         K(IPA+1,1)=3
  58         K(IPA,4)=MSTU(5)*(IPA+1)
  59         K(IPA,5)=K(IPA,4)
  60         K(IPA+1,4)=MSTU(5)*IPA
  61         K(IPA+1,5)=K(IPA+1,4)
  62       ENDIF
  63
  64 C...Check kinematics and store partons/particles in P vectors.
  65       IF(PECM.LE.PM1+PM2) CALL LUERRM_HIJING(13,
  66      &'(LU2ENT_HIJING:) energy smaller than sum of masses')
  67       PA=SQRT(MAX(0.,(PECM**2-PM1**2-PM2**2)**2-(2.*PM1*PM2)**2))/
  68      &(2.*PECM)
  69       P(IPA,3)=PA
  70       P(IPA,4)=SQRT(PM1**2+PA**2)
  71       P(IPA,5)=PM1
  72       P(IPA+1,3)=-PA
  73       P(IPA+1,4)=SQRT(PM2**2+PA**2)
  74       P(IPA+1,5)=PM2
  75
  76 C...Set N. Optionally fragment/decay.
  77       N=IPA+1
  78       IF(IP.EQ.0) CALL LUEXEC_HIJING
  79
  80       RETURN
  81       END