               ------------------------------------------------
                                FONLL interface 
               ------------------------------------------------

The FONLL structure functions are provided by the APFEL program which
can be interfaced to xFitter by configuring it with the --enable-apfel
flag.

REFERENCE:

"APFEL: A PDF Evolution Library with QED corrections"
V. Bertone, S. Carrazza and J. Rojo,
Published in Comput. Phys. Commun.  185 (2014) 1647,
e-Print: arXiv:1310.1394 [hep-ph].

For a detailed discussion of the FONLL GM-VFNS, the reader can refer
to the following paper.

REFERENCE: 


"Heavy quarks in deep-inelastic scattering"
S. Forte, E. Laenen, P. Nason and J. Rojo,
Published in Nucl. Phys. B 834 (2010) 116,
e-Print: arXiv:1001.2312 [hep-ph].

For support and information, please contact: 
Valerio Bertone: valerio.bertone@cern.ch

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

                 Running FONLL in xFitter

In order to use one of the possible variants of the FONLL scheme the user should
set in the steering.txt card one of the following options:

 ! ---  HF_SCHEME = 'FONLL-A'          : FONLL-A mass scheme provided by APFEL with pole masses (available only at NLO)
 ! ---  HF_SCHEME = 'FONLL-A RUNM OFF' : FONLL-A mass scheme provided by APFEL with MSbar masses running OFF (available only at NLO)
 ! ---  HF_SCHEME = 'FONLL-A RUNM ON'  : FONLL-A mass scheme provided by APFEL with MSbar masses running ON (available only at NLO)
 ! ---  HF_SCHEME = 'FONLL-B'          : FONLL-B mass scheme provided by APFEL with pole masses (available only at NLO)
 ! ---  HF_SCHEME = 'FONLL-B RUNM OFF' : FONLL-B mass scheme provided by APFEL with MSbar masses running OFF (available only at NLO)
 ! ---  HF_SCHEME = 'FONLL-B RUNM ON'  : FONLL-B mass scheme provided by APFEL with MSbar masses running ON (available only at NLO)
 ! ---  HF_SCHEME = 'FONLL-C'          : FONLL-C mass scheme provided by APFEL with pole masses (available only at NNLO)
 ! ---  HF_SCHEME = 'FONLL-C RUNM OFF' : FONLL-C mass scheme provided by APFEL with MSbar masses running OFF (available only at NNLO)
 ! ---  HF_SCHEME = 'FONLL-C RUNM ON'  : FONLL-C mass scheme provided by APFEL with MSbar masses running ON (available only at NNLO)

There are three main variants: FONLL-A, -B ans -C. The FONLL-A scheme is a 
NLO GM-VFNS that matches O(alphas) massless coefficient functions with O(alphas)
massive coefficient functions. The FONLL-B scheme is also a NLO GM-VFNS but in
this case the matching is done between the O(alphas) massless coefficient functions 
with O(alphas^2) massive coefficient functions. Finally the FONLL-C scheme is a
NNLO GM-VFNS scheme that matches O(alphas^2) massless coefficient functions with 
the O(alphas^2) massive	coefficient functions.

By default, the FONLL schemes use the pole mass definition for the heavy quark
masses. If the "RUNM" string is present in the option chosen, the MSbar definition
for the heavy quark masses will instead be used. Finally, the strings "OFF" and
"ON" indicate that the running of the masses as functions of the renormalization
scale is consistently disabled or enabled, respactively.
