lremh.F

Go to the documentation of this file. Or view the newest version in sPHENIX GitHub for file lremh.F

C **********************************************************************

      SUBROUTINE lremh(IFLRO,PT,IFLR,K2,Z)

      IMPLICIT NONE

C...Gives flavour and energy-momentum fraction Z for the particle
C...to be produced out of the target remnant when that is not a
C...simple diquark.

*
* to avoid variable conflictions, a second keep element is necessary
* with the same common block name (see LPTOU2)
*
      COMMON /leptou/ cut(14),lst(40),parl(30),
     &                x,y,w2,q2,u
      REAL cut,parl,x,y,w2,q2,u
      INTEGER lst
      SAVE /leptou/

      common/ludat1/mstu(200),paru(200),mstj(200),parj(200)
      INTEGER  mstu,mstj
      REAL  paru,parj
      SAVE /ludat1/

      COMMON /linter/ pari(50),ewqc(2,2,8),qc(8),zl(2,4),zq(2,8),pq(17)
      REAL  pari,ewqc,qc,zl,zq,pq
      SAVE /linter/

      INTEGER iflro,iflr,k2,idum,ksp,kc2,k2a
      INTEGER iflq,iflqq,lucomp
      REAL rlu,ulmass,tm2,pt
      REAL z,amsp,amk2,a,fc

C...Flavours fixed when calling from LQQBEV OR LYREMN
      IF(iflro.EQ.0) goto 200

C...Split target remnant qqqQ -> qqQ + q or qqqQbar -> qQbar + qq
C...Q (Qbar) is the partner to the struck sea quark
C...qqq are the nucleon valence quarks from which a quark q or a
C...diquark qq is chosen at random to form a jet system with the
C...scattered sea antiquark or quark, respectively, the other parton
C...forms a baryon qqQ or meson qQbar, respectively.
  100 iflq=int(1.+lst(22)/3.+rlu(0))
      IF(iflq.EQ.lst(22)) THEN
        iflqq=2101
        IF(rlu(0).GT.parl(4)) iflqq =2103
      ELSE
        iflqq=1000*iflq+100*iflq+3
      ENDIF
      iflq=3-iflq

C...Choose flavour of hadron and parton for jet system
      IF(iflro.GT.0) THEN
        CALL lukfdi(iflqq,iflro,idum,k2)
        IF(k2.EQ.0) goto 100
        iflr=iflq
      ELSE
        CALL lukfdi(iflq,iflro,idum,k2)
        IF(k2.EQ.0) goto 100
        iflr=iflqq
      ENDIF

C...Entry from LQQBEV & LYREMN with flavours given, choose E-p fraction
  200 ksp=iflr
C...Split energy-momentum of target remnant according to functions P(z)
C...z=E-pz fraction for qq (q) forming jet-system with struck Q (Qbar)
C...1-z=E-pz fraction for qQbar (qqQ) hadron
C...mq=mass of (light) parton remnant q (qq) in jet system
C...mQ=mass of produced (heavy flavour) hadron
      mstj(93)=1
      amsp=ulmass(ksp)
      mstj(93)=1
      amk2=ulmass(k2)
      IF(lst(14).EQ.1) THEN
C...P(z)=(a+1)(1-z)**a with <z>=1/(a+2)=1/3 since a=1 fixed
        z=1.-sqrt(rlu(0))
C...Flip if baryon produced
        kc2=iabs(lucomp(k2))
        IF(kc2.GE.301.AND.kc2.LE.400) z=1.-z
      ELSEIF(lst(14).EQ.2) THEN
C...P(z)=(a+1)(1-z)**a with <z>=1/(a+2)=mq/(mq+mQ) --> a=a(mq,mQ)
        a=(amsp+amk2)/amsp - 2.
        z=rlu(0)**(1./(a+1.))
      ELSEIF(lst(14).EQ.3) THEN
C...Using Peterson fragmentation function
C...P(z)=N/(z(1-1/z-c/(1-z))**2)  where c=(mq/mQ)**2  (FC=-c)
        fc=-(amsp/amk2)**2
  300   z=rlu(0)
        IF(-4.*fc*z*(1.-z)**2.LT.rlu(0)*((1.-z)**2-fc*z)**2) goto 300
      ELSEIF(lst(14).EQ.4) THEN
C...Using chosen fragmentation function in JETSET
        tm2=amk2**2+pt**2
        CALL luzdis(1,0,tm2,z)
      ENDIF
      lst(27)=1
      k2a=iabs(k2)
      IF((k2a.GE.1.AND.k2a.LE.8).OR.k2a.EQ.21.OR.lucomp(k2a).EQ.90)
     &lst(27)=2

      RETURN
      END