5 * Revision 1.1.1.2 1996/10/30 08:27:51 cernlib
8 * Revision 1.1.1.1 1996/04/12 15:29:15 plothow
12 #include "pdf/pilot.h"
13 C Version 3 CTEQ distribution function in a parametrized form.
15 C By: H.L. Lai, J. Botts, J. Huston, J.G. Morfin, J.F. Owens, J. Qiu,
16 C W.K. Tung & H. Weerts; Preprint MSU-HEP/41024, CTEQ 404
18 C This file contains three versions of the same CTEQ3 parton distributions:
20 C Two "front-end" subprograms:
21 C FUNCTION Ctq3Pf (Iset, Iparton, X, Q, Irt)
22 C returns the PROBABILITY density for a GIVEN flavor;
23 C SUBROUTINE Ctq3Pds(Iset, Pdf, XX, QQ, Irt)
24 C returns an array of MOMENTUM densities for ALL flavors;
25 C One lower-level subprogram:
26 C FUNCTION Ctq3Pd (Iset, Iprtn, XX, QQ, Irt)
27 C returns the MOMENTUM density of a GIVEN valence or sea distribution.
29 C One supplementary function to return the QCD lambda parameter
30 C concerning these distributions is also included (see below).
32 C Although DOUBLE PRECISION is used, conversion to SINGLE PRECISION
33 C is straightforward by removing the
34 C Implicit Double Precision statements.
36 C Since this is an initial distribution of version 3, it is
37 C useful for the authors to maintain a record of the distribution
38 C list in case there are revisions or corrections.
39 C In the interest of maintaining the integrity of this package,
40 C please do not freely distribute this program package; instead, refer
41 C any interested colleagues to direct their request for a copy to:
42 C Lai@cteq11.pa.msu.edu or Tung@msupa.pa.msu.edu.
44 C If you have detailed questions concerning these CTEQ3 distributions,
45 C or if you find problems/bugs using this initial distribution, direct
46 C inquires to Hung-Liang Lai or Wu-Ki Tung.
48 C -------------------------------------------
49 C Detailed instructions follow.
51 C Name convention for CTEQ distributions: CTEQnSx where
52 C n : version number (currently n = 3)
53 C S : factorization scheme label: = [M L D] for [MS-bar LO DIS]
55 C x : special characteristics, if any
56 C (e.g. S(F) for singular (flat) small-x, L for "LEP lambda value")
57 C (not applicable to CTEQ3 since only three standard sets are given.)
59 C Explanation of functional arguments:
61 C Iset is the set label; in this version, Iset = 1, 2, 3
62 C correspond to the following CTEQ global fits:
64 C cteq3M : best fit in the MS-bar scheme
65 C cteq3L : best fit in Leading order QCD
66 C cteq3D : best fit in the DIS scheme
68 C Iprtn is the parton label (6, 5, 4, 3, 2, 1, 0, -1, ......, -6)
69 C for (t, b, c, s, d, u, g, u_bar, ..., t_bar)
70 C *** WARNING: We use the parton label 2 as D-quark, and 1 as U-quark which
71 C might be different with your labels.
73 C X, Q are the usual x, Q;
74 C Irt is a return error code (see individual modules for explanation).
76 C ---------------------------------------------
78 C Since the QCD Lambda value for the various sets are needed more often than
79 C the other parameters in most applications, a special function
80 C Wlamd3 (Iset, Iorder, Neff) is provided
81 C which returns the lambda value for Neff = 4,5,6 effective flavors as well as
82 C the order these values pertain to.
84 C ----------------------------------------------
85 C The range of (x, Q) used in this round of global analysis is, approxi-
86 C mately, 0.01 < x < 0.75 ; and 4 GeV^2 < Q^2 < 400 GeV^2 for fixed target
87 C experiments and 0.0001 < x < 0.1 from HERA data.
89 C The range of (x, Q) used in the reparametrization of the QCD evolved
90 C parton distributions is 10E-6 < x < 1 ; 1.6 GeV < Q < 10 TeV. The
91 C functional form of this parametrization is:
93 C A0 * x^A1 * (1-x)^A2 * (1 + A3 * x^A4) * [log(1+1/x)]^A5
95 C with the A'coefficients being smooth functions of Q. For heavy quarks,
96 C a threshold factor is applied to A0 which simulates the proper Q-dependence
97 C of the QCD evolution in that region according to the renormalization
98 C scheme defined in Collins-Tung, Nucl. Phys. B278, 934 (1986).
100 C Since this function is positive definite and smooth, it provides sensible
101 C extrapolations of the parton distributions if they are called beyond
102 C the original range in an application. There is no artificial boundaries
104 C ------------------------------------------------
106 FUNCTION Ctq3Pf (Iset, Iparton, X, Q, Irt)
108 C This function returns the CTEQ parton distributions f^Iset_Iprtn/proton
109 C --- the PROBABILITY density
111 C (Iset, Iparton, X, Q): explained above;
113 C Irt : return error code: see module Ctq3Pd for explanation.
115 C IMPLICIT DOUBLE PRECISION (A-H, O-Z)
121 IF (Ifl.Eq.1 .or. Ifl.Eq.2) THEN
122 VL = Ctq3Pd(Iset, Ifl, X, Q, Irt)
127 SEA = Ctq3Pd (Iset, -JFL, X, Q, Irt)
128 C Full (probability) Distribution
129 Ctq3Pf = (VL + SEA) / X
132 C *************************