Use tgt_ prefix for binary target directories

[u/mrichter/AliRoot.git] / PYTHIA / jetset / lu4ent.F

 
C********************************************************************* 
 
      SUBROUTINE LU4ENT(IP,KF1,KF2,KF3,KF4,PECM,X1,X2,X4,X12,X14) 
 
C...Purpose: to store four partons or particles in their CM frame, with 
C...the first along the +z axis, the last in the xz plane with x > 0 
C...and the second having y < 0 and y > 0 with equal probability. 
      COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5) 
      COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200) 
      COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4) 
      SAVE /LUJETS/,/LUDAT1/,/LUDAT2/ 
 
C...Standard checks. 
      MSTU(28)=0 
      IF(MSTU(12).GE.1) CALL LULIST(0) 
      IPA=MAX(1,IABS(IP)) 
      IF(IPA.GT.MSTU(4)-3) CALL LUERRM(21, 
     &'(LU4ENT:) writing outside LUJETS momory') 
      KC1=LUCOMP(KF1) 
      KC2=LUCOMP(KF2) 
      KC3=LUCOMP(KF3) 
      KC4=LUCOMP(KF4) 
      IF(KC1.EQ.0.OR.KC2.EQ.0.OR.KC3.EQ.0.OR.KC4.EQ.0) CALL LUERRM(12, 
     &'(LU4ENT:) unknown flavour code') 
 
C...Find masses. Reset K, P and V vectors. 
      PM1=0. 
      IF(MSTU(10).EQ.1) PM1=P(IPA,5) 
      IF(MSTU(10).GE.2) PM1=ULMASS(KF1) 
      PM2=0. 
      IF(MSTU(10).EQ.1) PM2=P(IPA+1,5) 
      IF(MSTU(10).GE.2) PM2=ULMASS(KF2) 
      PM3=0. 
      IF(MSTU(10).EQ.1) PM3=P(IPA+2,5) 
      IF(MSTU(10).GE.2) PM3=ULMASS(KF3) 
      PM4=0. 
      IF(MSTU(10).EQ.1) PM4=P(IPA+3,5) 
      IF(MSTU(10).GE.2) PM4=ULMASS(KF4) 
      DO 110 I=IPA,IPA+3 
      DO 100 J=1,5 
      K(I,J)=0 
      P(I,J)=0. 
      V(I,J)=0. 
  100 CONTINUE 
  110 CONTINUE 
 
C...Check flavours. 
      KQ1=KCHG(KC1,2)*ISIGN(1,KF1) 
      KQ2=KCHG(KC2,2)*ISIGN(1,KF2) 
      KQ3=KCHG(KC3,2)*ISIGN(1,KF3) 
      KQ4=KCHG(KC4,2)*ISIGN(1,KF4) 
      IF(MSTU(19).EQ.1) THEN 
        MSTU(19)=0 
      ELSEIF(KQ1.EQ.0.AND.KQ2.EQ.0.AND.KQ3.EQ.0.AND.KQ4.EQ.0) THEN 
      ELSEIF(KQ1.NE.0.AND.KQ2.EQ.2.AND.KQ3.EQ.2.AND.(KQ1+KQ4.EQ.0.OR. 
     &KQ1+KQ4.EQ.4)) THEN 
      ELSEIF(KQ1.NE.0.AND.KQ1+KQ2.EQ.0.AND.KQ3.NE.0.AND.KQ3+KQ4.EQ.0.) 
     &THEN 
      ELSE 
        CALL LUERRM(2,'(LU4ENT:) unphysical flavour combination') 
      ENDIF 
      K(IPA,2)=KF1 
      K(IPA+1,2)=KF2 
      K(IPA+2,2)=KF3 
      K(IPA+3,2)=KF4 
 
C...Store partons/particles in K vectors for normal case. 
      IF(IP.GE.0) THEN 
        K(IPA,1)=1 
        IF(KQ1.NE.0.AND.(KQ2.NE.0.OR.KQ3.NE.0.OR.KQ4.NE.0)) K(IPA,1)=2 
        K(IPA+1,1)=1 
        IF(KQ2.NE.0.AND.KQ1+KQ2.NE.0.AND.(KQ3.NE.0.OR.KQ4.NE.0)) 
     &  K(IPA+1,1)=2 
        K(IPA+2,1)=1 
        IF(KQ3.NE.0.AND.KQ4.NE.0) K(IPA+2,1)=2 
        K(IPA+3,1)=1 
 
C...Store partons for parton shower evolution from q-g-g-qbar or 
C...g-g-g-g event. 
      ELSEIF(KQ1+KQ2.NE.0) THEN 
        K(IPA,1)=3 
        K(IPA+1,1)=3 
        K(IPA+2,1)=3 
        K(IPA+3,1)=3 
        KCS=4 
        IF(KQ1.EQ.-1) KCS=5 
        K(IPA,KCS)=MSTU(5)*(IPA+1) 
        K(IPA,9-KCS)=MSTU(5)*(IPA+3) 
        K(IPA+1,KCS)=MSTU(5)*(IPA+2) 
        K(IPA+1,9-KCS)=MSTU(5)*IPA 
        K(IPA+2,KCS)=MSTU(5)*(IPA+3) 
        K(IPA+2,9-KCS)=MSTU(5)*(IPA+1) 
        K(IPA+3,KCS)=MSTU(5)*IPA 
        K(IPA+3,9-KCS)=MSTU(5)*(IPA+2) 
 
C...Store partons for parton shower evolution from q-qbar-q-qbar event. 
      ELSE 
        K(IPA,1)=3 
        K(IPA+1,1)=3 
        K(IPA+2,1)=3 
        K(IPA+3,1)=3 
        K(IPA,4)=MSTU(5)*(IPA+1) 
        K(IPA,5)=K(IPA,4) 
        K(IPA+1,4)=MSTU(5)*IPA 
        K(IPA+1,5)=K(IPA+1,4) 
        K(IPA+2,4)=MSTU(5)*(IPA+3) 
        K(IPA+2,5)=K(IPA+2,4) 
        K(IPA+3,4)=MSTU(5)*(IPA+2) 
        K(IPA+3,5)=K(IPA+3,4) 
      ENDIF 
 
C...Check kinematics. 
      MKERR=0 
      IF(0.5*X1*PECM.LE.PM1.OR.0.5*X2*PECM.LE.PM2.OR.0.5*(2.-X1-X2-X4)* 
     &PECM.LE.PM3.OR.0.5*X4*PECM.LE.PM4) MKERR=1 
      PA1=SQRT(MAX(1E-10,(0.5*X1*PECM)**2-PM1**2)) 
      PA2=SQRT(MAX(1E-10,(0.5*X2*PECM)**2-PM2**2)) 
      PA4=SQRT(MAX(1E-10,(0.5*X4*PECM)**2-PM4**2)) 
      X24=X1+X2+X4-1.-X12-X14+(PM3**2-PM1**2-PM2**2-PM4**2)/PECM**2 
      CTHE4=(X1*X4-2.*X14)*PECM**2/(4.*PA1*PA4) 
      IF(ABS(CTHE4).GE.1.002) MKERR=1 
      CTHE4=MAX(-1.,MIN(1.,CTHE4)) 
      STHE4=SQRT(1.-CTHE4**2) 
      CTHE2=(X1*X2-2.*X12)*PECM**2/(4.*PA1*PA2) 
      IF(ABS(CTHE2).GE.1.002) MKERR=1 
      CTHE2=MAX(-1.,MIN(1.,CTHE2)) 
      STHE2=SQRT(1.-CTHE2**2) 
      CPHI2=((X2*X4-2.*X24)*PECM**2-4.*PA2*CTHE2*PA4*CTHE4)/ 
     &MAX(1E-8*PECM**2,4.*PA2*STHE2*PA4*STHE4) 
      IF(ABS(CPHI2).GE.1.05) MKERR=1 
      CPHI2=MAX(-1.,MIN(1.,CPHI2)) 
      IF(MKERR.EQ.1) CALL LUERRM(13, 
     &'(LU4ENT:) unphysical kinematical variable setup') 
 
C...Store partons/particles in P vectors. 
      P(IPA,3)=PA1 
      P(IPA,4)=SQRT(PA1**2+PM1**2) 
      P(IPA,5)=PM1 
      P(IPA+3,1)=PA4*STHE4 
      P(IPA+3,3)=PA4*CTHE4 
      P(IPA+3,4)=SQRT(PA4**2+PM4**2) 
      P(IPA+3,5)=PM4 
      P(IPA+1,1)=PA2*STHE2*CPHI2 
      P(IPA+1,2)=PA2*STHE2*SQRT(1.-CPHI2**2)*(-1.)**INT(RLU(0)+0.5) 
      P(IPA+1,3)=PA2*CTHE2 
      P(IPA+1,4)=SQRT(PA2**2+PM2**2) 
      P(IPA+1,5)=PM2 
      P(IPA+2,1)=-P(IPA+1,1)-P(IPA+3,1) 
      P(IPA+2,2)=-P(IPA+1,2) 
      P(IPA+2,3)=-P(IPA,3)-P(IPA+1,3)-P(IPA+3,3) 
      P(IPA+2,4)=SQRT(P(IPA+2,1)**2+P(IPA+2,2)**2+P(IPA+2,3)**2+PM3**2) 
      P(IPA+2,5)=PM3 
 
C...Set N. Optionally fragment/decay. 
      N=IPA+3 
      IF(IP.EQ.0) CALL LUEXEC 
 
      RETURN 
      END