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21886bb6 | 1 | * |
2 | * $Id$ | |
3 | * | |
4 | * $Log$ | |
5 | * Revision 1.1.1.2 1996/10/30 08:27:51 cernlib | |
6 | * Version 7.04 | |
7 | * | |
8 | * Revision 1.1.1.1 1996/04/12 15:29:15 plothow | |
9 | * Version 7.01 | |
10 | * | |
11 | * | |
12 | #include "pdf/pilot.h" | |
13 | C Version 3 CTEQ distribution function in a parametrized form. | |
14 | ||
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 | |
17 | ||
18 | C This file contains three versions of the same CTEQ3 parton distributions: | |
19 | C | |
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. | |
28 | ||
29 | C One supplementary function to return the QCD lambda parameter | |
30 | C concerning these distributions is also included (see below). | |
31 | ||
32 | C Although DOUBLE PRECISION is used, conversion to SINGLE PRECISION | |
33 | C is straightforward by removing the | |
34 | C Implicit Double Precision statements. | |
35 | ||
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. | |
43 | ||
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. | |
47 | ||
48 | C ------------------------------------------- | |
49 | C Detailed instructions follow. | |
50 | ||
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] | |
54 | c resp. | |
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.) | |
58 | ||
59 | C Explanation of functional arguments: | |
60 | ||
61 | C Iset is the set label; in this version, Iset = 1, 2, 3 | |
62 | C correspond to the following CTEQ global fits: | |
63 | ||
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 | |
67 | ||
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. | |
72 | ||
73 | C X, Q are the usual x, Q; | |
74 | C Irt is a return error code (see individual modules for explanation). | |
75 | C | |
76 | C --------------------------------------------- | |
77 | ||
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. | |
83 | ||
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. | |
88 | ||
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: | |
92 | ||
93 | C A0 * x^A1 * (1-x)^A2 * (1 + A3 * x^A4) * [log(1+1/x)]^A5 | |
94 | ||
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). | |
99 | ||
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 | |
103 | C or sharp cutoff's. | |
104 | C ------------------------------------------------ | |
105 | ||
106 | FUNCTION Ctq3Pf (Iset, Iparton, X, Q, Irt) | |
107 | ||
108 | C This function returns the CTEQ parton distributions f^Iset_Iprtn/proton | |
109 | C --- the PROBABILITY density | |
110 | ||
111 | C (Iset, Iparton, X, Q): explained above; | |
112 | ||
113 | C Irt : return error code: see module Ctq3Pd for explanation. | |
114 | ||
115 | C IMPLICIT DOUBLE PRECISION (A-H, O-Z) | |
116 | C+SEQ, IMPDP. | |
117 | ||
118 | Ifl = Iparton | |
119 | JFL = ABS(Ifl) | |
120 | C Valence | |
121 | IF (Ifl.Eq.1 .or. Ifl.Eq.2) THEN | |
122 | VL = Ctq3Pd(Iset, Ifl, X, Q, Irt) | |
123 | ELSE | |
124 | VL = 0. | |
125 | ENDIF | |
126 | C Sea | |
127 | SEA = Ctq3Pd (Iset, -JFL, X, Q, Irt) | |
128 | C Full (probability) Distribution | |
129 | Ctq3Pf = (VL + SEA) / X | |
130 | ||
131 | Return | |
132 | C ************************* | |
133 | END |