Bornzerodamp.f

      subroutine bornzerodamp(alr,r0,rc,rs,rcs,dampfac)
c given the R_alpha region (i.e. the alr) and the associated
c real contribution r (without pdf factor),
c returns in dampfac the damping factor to be applied to
c the real contribution to implement Born zero suppression
      implicit none
      include 'nlegborn.h'
      include 'pwhg_flst.h'
      include 'pwhg_kn.h'
      include 'pwhg_flg.h'
      include 'pwhg_math.h'
      integer alr
      real * 8 r0,rc,rs,rcs,dampfac,h,pwhg_pt2,pt2,powheginput
      logical ini
      data ini/.true./
      save ini,h
      external pwhg_pt2,powheginput
      if(ini) then
         h=powheginput("#hdamp")
         if(h.lt.0) then
            h=powheginput("#hfact")
            if(h.gt.0) then
               write(*,*)'***************************************'
               write(*,*)' Warning: hfact is here for backward'
               write(*,*)' compatibility with older inplementations'
               write(*,*)' New implementations will use hdamp and'
               write(*,*)' bornzerodamp independently.'
               write(*,*)'***************************************'
            endif
         endif
         if(h.gt.0) then
            write(*,*)'***************************************'
            write(*,*)' Using a damping factor h**2/(pt2+h**2)'
            write(*,*)' to separate real contributions between'
            write(*,*)' Sudakov and remnants    h=',h,' GeV   ' 
            write(*,*)'***************************************'
         endif
         ini=.false.
      endif
c local variables
      if(h.gt.0) then
         pt2=pwhg_pt2()
         dampfac=h**2/(pt2+h**2)
      else
         dampfac=1
      endif

      if(flg_bornzerodamp.and.r0.gt.5*rc.and.r0.gt.5*rs) then
         dampfac=0
      endif
c      write(*,*) ' bornzerodamp: r0=',r0,'  rc=',rc,'  rs=',rs,
c     # ' dampfac=',dampfac
      end