d2/d83/ctq6pdf_8F_source.html

C============================================================================

C                CTEQ Parton Distribution Functions: Version 6.0

C                             January 24, 2002

C

C   Ref: "New Generation of Parton Distributions with

C         Uncertainties from Global QCD Analysis"

C   By: J. Pumplin, D.R. Stump, J.Huston, H.L. Lai, P. Nadolsky, W.K. Tung

C       hep-ph/0201195

C

C   This package contains 3 standard sets of CTEQ6 PDF's and 40 up/down sets

C   with respect to CTEQ6M PDF's. Details are:

C ---------------------------------------------------------------------------

C  Iset   PDF        Description       Alpha_s(Mz)**Lam4  Lam5   Table_File

C ---------------------------------------------------------------------------

C   1    CTEQ6M   Standard MSbar scheme   0.118     326   226    cteq6m.tbl

C   2    CTEQ6D   Standard DIS scheme     0.118     326   226    cteq6d.tbl

C   3    CTEQ6L   Leading Order           0.118**   326** 226    cteq6l.tbl

C     ------------------------------

C   1xx  CTEQ6M1xx  +/- w.r.t. CTEQ6M     0.118     326   226    cteq6m1xx.tbl

C    (where xx=01--40)

C ---------------------------------------------------------------------------

C   ** ALL fits are obtained by using the same coupling strength \alpha_s(Mz)=0.118;

C   and the NLO running \alpha_s formula.  For the LO fit, the evolution of the PDF

C   and the hard cross sections are calculated at LO.  More detailed discussions are

C   given in hep-ph/0201195.

C

C   The table grids are generated for 10^-6 < x < 1 and 1.3 < Q < 10,000 (GeV).

C   PDF values outside of the above range are returned using extrapolation.

C   Lam5 (Lam4) represents Lambda value (in MeV) for 5 (4) flavors.

C   The matching alpha_s between 4 and 5 flavors takes place at Q=4.5 GeV,

C   which is defined as the bottom quark mass, whenever it can be applied.

C

C   The Table_Files are assumed to be in the working directory.

C

C   Before using the PDF, it is necessary to do the initialization by

C       Call SetCtq6(Iset)

C   where Iset is the desired PDF specified in the above table.

C

C   The function Ctq6Pdf (Iparton, X, Q)

C   returns the parton distribution inside the proton for parton [Iparton]

C   at [X] Bjorken_X and scale [Q] (GeV) in PDF set [Iset].

C   Iparton  is the parton label (5, 4, 3, 2, 1, 0, -1, ......, -5)

C                            for (b, c, s, d, u, g, u_bar, ..., b_bar),

C

C   For detailed information on the parameters used, e.q. quark masses,

C   QCD Lambda, ... etc.,  see info lines at the beginning of the

C   Table_Files.

C

C   These programs, as provided, are in double precision.  By removing the

C   "Implicit Double Precision" lines, they can also be run in single

C   precision.

C

C   If you have detailed questions concerning these CTEQ6 distributions,

C   or if you find problems/bugs using this package, direct inquires to

C   Pumplin@pa.msu.edu or Tung@pa.msu.edu.

C

C===========================================================================


      Function ctq6pdf (Iparton, X, Q)

      Implicit Double Precision (a-h,o-z)

      Logical warn

      Common

     > / ctqpar2 / nx, nt, nfmx

     > / qcdtable /  alambda, nfl, iorder


      Data warn /.true./

      save warn


      If (x .lt. 0d0 .or. x .gt. 1d0) Then

        print *, 'X out of range in Ctq6Pdf: ', x

        stop

      Endif

      If (q .lt. alambda) Then

        print *, 'Q out of range in Ctq6Pdf: ', q

        stop

      Endif

      If ((iparton .lt. -nfmx .or. iparton .gt. nfmx)) Then

         If (warn) Then

C        put a warning for calling extra flavor.

             warn = .false.

             print *, 'Warning: Iparton out of range in Ctq6Pdf: '

     >              , iparton

         Endif

         ctq6pdf = 0d0

         Return

      Endif


      ctq6pdf = partonx6(iparton, x, q)

      if(ctq6pdf.lt.0.d0)  ctq6pdf = 0.d0


      Return


C                             ********************

      End