This code allows public access to the diffractive parton distribution functions
(DPDFs) and diffractive structure functions (DSFs) corresponding to the pQCD
fit to H1 LRG data (hep-ex/0606004) published in:

  A. D. Martin, M. G. Ryskin and G. Watt,
  "Diffractive parton distributions from H1 data",
  Phys. Lett. B 644 (2007) 131 [arXiv:hep-ph/0609273].

Please reference this paper if you use the code for a publication.

IMPORTANT: Both the DPDFs and DSFs have been corrected to M_Y = m_p by an
overall factor of 0.813 (= 1/1.23) relative to the H1 LRG data which have
M_Y < 1.6 GeV.  Therefore, for comparison with the H1 LRG data or the
H1 2006 DPDFs, a multiplicative factor of 1.23 should be applied.

The parameterisations for the DPDFs and DSFs are provided as large
three-dimensional grids in (xPom,z,Qsq) for the DPDFs or (xPom,beta,Qsq) for
the DSFs.  Fortran code is provided to interpolate from these grids.  An
example program is provided to demonstrate the usage.  To run this example
program, check the location of CERNLIB (default: /cern/pro/lib) is set
correctly in the Makefile then type:

  make
  ./example

Note that use of the Makefile is completely optional and the example program
could also be compiled manually using e.g.:

  g77 example.f mrw2006.f -L/cern/pro/lib -lpdflib804 -lmathlib -lkernlib

During the fit, the Pomeron contributions to the DSFs were calculated in the
fixed flavour number scheme (FFNS), where there are no heavy quark DPDFs.  The
NLO alpha_S routine from QCDNUM was used with three fixed flavours and
Lambda_{QCD}^{n_f=3} = 407 MeV corresponding to alpha_S(M_Z,n_f=3) = 0.106340.
[For calculations of jet production, where the coefficient functions are
usually calculated using a variable-flavour alpha_S, the corresponding value of
alpha_S(M_Z,n_f=5) = 0.118533 with flavour thresholds at m_c = 1.43 GeV and 
m_b = 4.3 GeV.]
Heavy quark contributions (h=c,b) were generated from photon-gluon fusion at 
NLO (using QCDNUM with factorisation and renormalisation scales set to
Q^2+4*m_h^2) and photon-Pomeron fusion at LO (calculations from
hep-ph/0504132), with m_c = 1.43 GeV and m_b = 4.3 GeV.  The secondary
Reggeon contributions to the DSFs were calculated in the zero-mass variable
flavour number scheme (ZMVFNS) at NLO using the GRV-P-HO pion PDFs
(from PDFLIB), with the NLO alpha_S routine also taken from PDFLIB using
m_{c,b,t} = 1.5, 4.75, 180 GeV.  It would make sense to use the same settings
in the calculation of any final state observables.

Comments to watt(at)hep.ucl.ac.uk