DIS: IC in F3charm in NC

[felixhekhorn]

• we believe the IC contributions for F3charm in the NC case are not present
• it is discussed in the documentation but not implemented in the code:
  

  apfel/src/DIS/IncludeIntrinsicCharm.f

  Lines 92 to 150 in fdfd068

  	SC2mNC(igrid,ixi,3,0,beta,alpha) = ( 2d0 - eta ) * fL
  	SCLmNC(igrid,ixi,3,0,beta,alpha) = 4d0 * ( 1d0 - eta )
  	1 / ( 2d0 - eta ) / factL * fL
  	*
  	* NLO
  	*
  	if(ipt.ge.1)then
  	*
  	bound = alpha-inter_degree(igrid)
  	if(alpha.lt.inter_degree(igrid)) bound = 0
  	*
  	c = max(xg(igrid,beta),
  	1 xg(igrid,beta)/xg(igrid,alpha+1)) / eta
  	d = min(eta,xg(igrid,beta)/xg(igrid,bound)) / eta
  	*
  	if(c.ge.1d0) cycle
  	*
  	walpha = alpha
  	wbeta = beta
  	*
  	k = 3
  	wl = 1
  	*
  	sf = 1
  	C2RS = fact2 * eta * dgauss(integrandsICm,c,d,eps)
  	C2L = fact2 * eta * c21ICL(c)
  	*
  	sf = 2
  	CLRS = eta * dgauss(integrandsICm,c,d,eps)
  	CLL = eta * cL1ICL(c)
  	*
  	if(MassScheme(1:5).eq."FONLL")then
  	sf = 2
  	* Gluon
  	k = 1
  	gDIC = dgauss(integrandsICm,c,d,eps)
  	* Put these terms in the LO gluon slot (e.g. SC2mNC(igrid,ixi,1,0,beta,alpha))
  	* which is empty.
  	SC2mNC(igrid,ixi,1,0,beta,alpha) =
  	1 - ( 2d0 - eta ) * lnF * gDIC
  	SCLmNC(igrid,ixi,1,0,beta,alpha) =
  	1 - 4d0 * ( 1d0 - eta ) / ( 2d0 - eta ) / factL
  	2 * lnF * gDIC
  	* Non-singlet
  	k = 3
  	wl = 2
  	nsDIC = dgauss(integrandsICm,c,d,eps)
  	*
  	C2RS = C2RS - ( 2d0 - eta ) * nsDIC
  	C2L = C2L - ( 2d0 - eta ) * DICc(xi,c)
  	*
  	CLRS = CLRS - 4d0 * ( 1d0 - eta ) / ( 2d0 - eta )
  	1 * nsDIC
  	CLL = CLL - 4d0 * ( 1d0 - eta ) / ( 2d0 - eta )
  	1 * DICc(xi,c)
  	endif
  	*
  	SC2mNC(igrid,ixi,3,1,beta,alpha) = C2RS + C2L * fL
  	SCLmNC(igrid,ixi,3,1,beta,alpha) = CLRS + CLL * fL

  
  

  apfel/src/DIS/ComputeDISOperators.f

  Lines 469 to 488 in fdfd068

  	if(IntrinsicCharm)then
  	if(Nf_FF.lt.4)then
  	do pt=0,ipt_max_IC
  	CLnsp(4) = CLnsp(4) + as(pt)
  	1 * ( c0(4)
  	2 * SCLm0NC(jgrid,ixi(4),
  	3 3,pt,alpha,beta)
  	4 + c1(4)
  	5 * SCLm0NC(jgrid,ixi(4)+1,
  	6 3,pt,alpha,beta) )
  	C2nsp(4) = C2nsp(4) + as(pt)
  	1 * ( c0(4)
  	2 * SC2m0NC(jgrid,ixi(4),
  	3 3,pt,alpha,beta)
  	4 + c1(4)
  	5 * SC2m0NC(jgrid,ixi(4)+1,
  	6 3,pt,alpha,beta) )
  	enddo
  	endif
  	endif

[vbertone]

This is correct. The reason is that F3 in NC scattering is relevant only for large values of Q because the couplings are suppressed by the Z propagator. Therefore IC effects (and heavy-quark mass effects in general) are expected to be negligible in the region where F3 becomes relevant.