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ubprojections.f
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c Find the underlying Born momenta from the real momenta and the
c emitter-readiated pair
subroutine compuborn(em,rad,reslist,cmppborn)
implicit none
include 'nlegborn.h'
integer em,rad,reslist(nlegreal)
include 'pwhg_flst.h'
real * 8 cmppborn(0:3,nlegreal)
if(em.lt.3) then
call findubisr(rad,cmppborn)
else
call findubfsr(em,rad,reslist,cmppborn)
endif
end
subroutine findubfsr(em,rad,reslist,cmppborn)
implicit none
include 'nlegborn.h'
include 'pwhg_flst.h'
integer em,rad,reslist(nlegreal)
real * 8 cmppborn(0:3,nlegreal)
include 'pwhg_kn.h'
real * 8 krecv(3),q0,q2,krec,beta,
1 k0rec,k,vec(3)
integer res,j
res=reslist(em)
if(res.ne.reslist(rad)) then
write(*,*) ' findubfsr: error'
call pwhg_exit(-1)
endif
cmppborn=kn_cmpreal
if(res.ne.0) then
call boost2reson(kn_cmpreal(:,res),nlegreal,
1 kn_cmpreal,cmppborn)
q0=cmppborn(0,res)
else
q0=2*cmppborn(0,1)
endif
q2=q0**2
c recoil system momentum
k0rec=q0-cmppborn(0,em)-cmppborn(0,rad)
krecv=-cmppborn(1:3,em)-cmppborn(1:3,rad)
krec=sqrt(krecv(1)**2+krecv(2)**2+krecv(3)**2)
beta=(q2-(k0rec+krec)**2)/(q2+(k0rec+krec)**2)
vec=krecv/krec
if(res.eq.0) then
call mboost(nlegreal-2,vec,beta,
1 cmppborn(:,3:nlegreal),cmppborn(:,3:nlegreal))
else
do j=3,nlegreal
if(reslist(j).eq.res) then
call mboost(1,vec,beta,
1 cmppborn(:,j:j),cmppborn(:,j:j))
endif
enddo
endif
k=(q2-(k0rec**2-krec**2))/(2*q0)
cmppborn(0,em)=k
cmppborn(1:3,em)=-vec*k
cmppborn(:,rad)=0
end
subroutine findubisr(j,cmppborn)
implicit none
integer j
include 'nlegborn.h'
include 'pwhg_flst.h'
real * 8 cmppborn(0:3,nlegreal)
include 'pwhg_kn.h'
real * 8 krecv(3),q0,q2,krec,k0rec,
1 krecperp,mrec2,beta,vec(3)
cmppborn(0:3,1)=kn_cmpreal(0:3,1)
cmppborn(0:3,2)=kn_cmpreal(0:3,2)
q0=2*cmppborn(0,1)
q2=q0**2
c recoil system momentum
k0rec=q0-kn_cmpreal(0,j)
krecv=-kn_cmpreal(1:3,j)
krec=sqrt(krecv(1)**2+krecv(2)**2+krecv(3)**2)
mrec2=(k0rec**2-krec**2)
beta=-krecv(3)/k0rec
vec(1)=0
vec(2)=0
vec(3)=1
call mboost(nlegreal-2,vec,beta,
1 kn_cmpreal(:,3:nlegreal),cmppborn(:,3:nlegreal))
c Now the transverse boost
krecperp=sqrt(krecv(1)**2+krecv(2)**2)
vec(3)=0
vec(1:2)=krecv(1:2)/krecperp
beta=-krecperp/sqrt(mrec2+krecperp**2)
call mboost(nlegreal-2,vec,beta,
1 cmppborn(:,3:nlegreal),cmppborn(:,3:nlegreal))
cmppborn(:,j)=0
end
function dijterm(em,rad,alr)
implicit none
real * 8 dijterm
integer em,rad,alr
include 'nlegborn.h'
include 'pwhg_flst.h'
include 'pwhg_kn.h'
include 'pwhg_par.h'
integer rflav(nlegreal),reslist(nlegreal),res
real * 8 cmppborn(0:3,nlegreal)
real * 8 avub,getdistance,dalr,tmp
integer nub,mergeisr,mergefsr,i,j,k,ifl1,ifl2,onem
parameter (onem=1000000)
logical ini,olddij
data ini/.true./
save ini,olddij
real * 8 powheginput
external powheginput
if(ini) then
if(powheginput("#olddij").eq.1) then
olddij=.true.
else
olddij=.false.
endif
ini=.false.
endif
if(olddij) then
dijterm=kn_dijterm(em,rad)
return
endif
rflav(:)=flst_alr(:,alr)
c we only consider singularities within the same
c resonance decay (or in production)
reslist(:)=flst_alrres(:,alr)
res=reslist(nlegreal)
c find UB flavour
if(em.eq.0) then
continue
elseif(em.eq.1) then
rflav(1)=mergeisr(rflav(1),rflav(rad))
elseif(em.eq.2) then
rflav(2)=mergeisr(rflav(2),rflav(rad))
else
rflav(em)=mergefsr(rflav(em),rflav(rad))
endif
c invalidater rad parton with impossible pdg code
rflav(rad)=onem
call compuborn(em,rad,reslist,cmppborn)
c looop over all possible singularities
dalr=getdistance(em,rad,res,kn_cmpreal)
if(abs(dalr/kn_dijterm(em,rad)-1).gt.1d-6) then
write(*,*) 'dalr', dalr/kn_dijterm(em,rad)
write(*,*) 'This may imply that running the program ',
1 'with olddij is wrong; it may also imply ',
2 'that kn_dijterm_soft() are incorrect.',
3 'A dijterm_soft() function should be built instead'
call pwhg_exit(-1)
endif
c get average singularity from underlying Born
avub=1
nub=0
do j=3,nlegreal
if(reslist(j).ne.res) cycle
if(res.eq.0) then
ifl1=mergeisr(rflav(1),rflav(j))
ifl2=mergeisr(rflav(2),rflav(j))
if(ifl1.eq.rflav(1).and.ifl2.eq.rflav(2)) then
tmp = getdistance(0,j,res,cmppborn)
if(tmp.eq.0) goto 999
avub=avub*(1+dalr/tmp)
nub=nub+1
else
if(ifl1.ne.onem) then
tmp = getdistance(1,j,res,cmppborn)
if(tmp.eq.0) goto 999
avub=avub*(1+dalr/tmp)
nub=nub+1
endif
if(ifl2.ne.onem) then
tmp = getdistance(2,j,res,cmppborn)
if(tmp.eq.0) goto 999
avub=avub*(1+dalr/tmp)
nub=nub+1
endif
endif
endif
do k=j+1,nlegreal
if(reslist(k).ne.res) cycle
if(mergefsr(rflav(j),rflav(k)).ne.onem) then
tmp = getdistance(j,k,res,cmppborn)
if(tmp.eq.0) goto 999
avub=avub*(1+dalr/tmp)
nub=nub+1
endif
enddo
enddo
dijterm=dalr*avub
return
999 continue
dijterm = 1d200
if(dalr.eq.0) then
call increasecnt("dalr and ub distance = 0 in ubprojections")
else
call increasecnt("ub distance = 0 in ubprojections")
endif
end
function getdistance(em,rad,res,cmp)
implicit none
include 'nlegborn.h'
include 'pwhg_par.h'
include 'pwhg_kn.h'
real * 8 getdistance
integer em,rad,res
real * 8 cmp(0:3,nlegreal),y,e_em,e_rad
real * 8 dotp
external dotp
if(em.lt.3) then
y=1-dotp(cmp(:,1),cmp(:,rad))/(cmp(0,1)*cmp(0,rad))
if(em.eq.0) then
getdistance=(cmp(0,rad)**2*(1-y**2))**par_diexp
elseif(em.eq.1) then
getdistance=(cmp(0,rad)**2*2*(1-y))**par_diexp
elseif(em.eq.2) then
getdistance=(cmp(0,rad)**2*2*(1+y))**par_diexp
endif
else
if(res.eq.0) then
e_em=cmp(0,em)
e_rad=cmp(0,rad)
else
e_em=dotp(cmp(:,res),cmp(:,em))
e_rad=dotp(cmp(:,res),cmp(:,rad))
endif
if(kn_masses(em).gt.0.and.kn_masses(rad).eq.0) then
getdistance=(2*dotp(cmp(:,em),cmp(:,rad))*
1 e_rad/e_em
2 )**par_dijexp
else
getdistance=(2*dotp(cmp(:,em),cmp(:,rad))*
1 e_em*e_rad/(e_em+e_rad)**2
2 )**par_dijexp
endif
endif
end
function mergeisr(i,j)
implicit none
integer mergeisr,i,j,onem
parameter (onem = 1000000)
if(abs(i).gt.5.or.abs(j).gt.5) then
mergeisr = onem
elseif(j.eq.0) then
mergeisr = i
elseif(i.eq.0) then
mergeisr = -j
elseif(i.eq.j) then
mergeisr = 0
else
mergeisr = onem
endif
end
function mergefsr(i,j)
implicit none
integer mergefsr,i,j,onem
parameter (onem = 1000000)
if(abs(i).gt.5.or.abs(j).gt.5) then
mergefsr = onem
elseif(j.eq.0) then
mergefsr = i
elseif(i.eq.0) then
mergefsr = j
elseif(i.eq.-j) then
mergefsr = 0
else
mergefsr = onem
endif
end