5 * Revision 1.1.1.2 1996/10/30 08:27:44 cernlib
8 * Revision 1.1.1.1 1996/04/12 15:29:09 plothow
12 #include "pdf/pilot.h"
13 C Version 2 CTEQ distribution function in a parametrized form.
14 C By: J. Botts, H.L. Lai, J.G. Morfin, J.F. Owens, J. Qiu, W.K. Tung & H. Weerts
16 C To avoid the proliferation of parton distribution functions, we recommend
18 C these distributions should replace Version 1 CTEQ distributions for all
20 C usage. The differences between the two sets of distributions, as briefly
21 C described below, do not significantly affect most applications for
23 C and hadron-collider applications.
25 C Both CTEQ1 and CTEQ2 distributions fit existing DIS, Drell-Yan and Direct
27 C data with excellent chi-squares. They represent two distinct ways to resolve
28 C the inconsistency between CCFR and NMC measurements on F2 at small-x and the
29 C neutrino dimuon measurements of s(x), as discovered by the CTEQ1 analysis:
30 C in the CTEQ1 analysis, the F2 measurements of CCFR and NMC are taken
32 C leaving out the dimuon information on s(x); whereas in the CTEQ2 analysis,
34 C latest CCFR NLO dimuon analysis of s(x) is used (within errors) as input
36 C leaving out the small-x F2 data which conflict with this input. The small-x
37 C behavior of the parton distributions are contrained in the latter case by the
38 C newly released HERA data. For details, see our forthcoming paper.
40 C This file contains three versions of the same CTEQ2 parton distributions:
42 C Two "front-end" subprograms:
43 C FUNCTION Ctq2OPf (Iset, Iparton, X, Q, Irt)
44 C returns the PROBABILITY density for a GIVEN flavor;
45 C SUBROUTINE Ctq2OPs (Iset, Pdf, XX, QQ, Irt)
46 C returns an array of MOMENTUM densities for ALL flavors;
47 C One lower-level subprogram:
48 C FUNCTION Ctq2OPd (Iset, Iprtn, XX, QQ, Irt)
49 C returns the MOMENTUM density of a GIVEN valence or sea distribution.
50 C Supplementary functions to return the relevant QCD parameters and other
51 C information concerning these distributions are also included (see below).
53 C Since this is an initial distribution of version 2, it is
54 C useful for the authors to maintain a record of the distribution list in
55 C case there are revisions or corrections.
56 C In the interest of maintaining the integrity of this package,
57 C please do not freely distribute this program package; instead, refer any
58 C interested colleagues to direct their request for a copy to:
59 C Botts@hades.ifh.de or Lai@cteq11.pa.msu.edu
61 C If you have detailed questions concerning these CTEQ2 distributions, direct
62 C inquires to Botts, Lai (see above) or Wu-Ki Tung (Tung@msupa.pa.msu.edu).
64 C -------------------------------------------
65 C Detailed instructions follow.
67 C Name convention for CTEQ distributions: CTEQnSx where
68 C n : version number (currently n = 2)
69 C S : factorization scheme label: = [M D L] for [MS-bar DIS LO]
71 C x : special characteristics, if any
72 C (e.g. S(F) for singular (flat) small-x, L for "LEP lambda value")
74 C Explanation of functional arguments:
76 C Iset is the set label; in this version, Iset = 1, 2, 3, 4, 5, 6
77 C correspond to the following CTEQ global fits:
79 C cteq2M : best fit in the MS-bar scheme
80 C cteq2MS : singular small-x
81 C cteq2MF : flat small-x
82 C cteq2ML : large lambda (Lambda(5) = 220 MeV)
84 C cteq2L : best fit in Leading order QCD
86 C cteq2D : best fit in the DIS scheme
88 C Iprtn is the parton label (6, 5, 4, 3, 2, 1, 0, -1, ......, -6)
89 C for (t, b, c, s, d, u, g, u_bar, ..., t_bar)
91 C X, Q are the usual x, Q;
92 C Irt is a return error code (see individual modules for explanation).
94 C ---------------------------------------------
95 C --> QCD parameters for parton distribution set Iset can be obtained inside
96 C the user's program by:
98 C > (Iset, Iord, Ischeme, MxFlv,
99 C > Alam4, Alam5, Alam6, Amas4, Amas5, Amas6,
100 C > Xmin, Qini, Qmax, ExpNor)
101 C where all but the first argument are output parameters.
102 C They should be self-explanatory -- see details under ENTRY PrCtq2O.
104 C Since the QCD Lambda value for the various sets are needed more often than
105 C the other parameters in most applications, a special function
106 C Wlamd2O (Iset, Iorder, Neff) is provided
107 C which returns the lambda value for Neff = 4,5,6 effective flavors as well as
108 C the order these values pertain to.
110 C ----------------------------------------------
111 C The range of (x, Q) used in this round of global analysis is, approxi-
112 C mately, 0.01 < x < 0.75 ; and 4 GeV^2 < Q^2 < 400 GeV^2 for fixed target
113 C experiments and 0.0001 < x < 0.01 from first official data of HERA.
115 C The range of (x, Q) used in the reparametrization of the QCD evolved
116 C parton distributions is 10E-5 < x < 1 ; 1.6 GeV < Q < 1 TeV. The
117 C functional form of this parametrization is:
119 C A0 * x^A1 * (1-x)^A2 * (1 + A3 * x^A4) * [log(1+1/x)]^A5
121 C with the A'coefficients being smooth functions of Q. For heavy quarks,
122 C a threshold factor is applied to A0 which simulates the proper Q-dependence
123 C of the QCD evolution in that region according to the renormalization
124 C scheme defined in Collins-Tung, Nucl. Phys. B278, 934 (1986).
126 C Since this function is positive definite and smooth, it provides sensible
127 C extrapolations of the parton distributions if they are called beyond
128 C the original range in an application. There is no artificial boundaries
130 C ------------------------------------------------
132 FUNCTION Ctq2OPf (Iset, Iparton, X, Q, Irt)
134 C This function returns the CTEQ parton distributions f^Iset_Iprtn/proton
135 C --- the PROBABILITY density
137 C (Iset, Iparton, X, Q): explained above;
139 C Irt : return error code: see module Ctq2OPd for explanation.
141 C IMPLICIT DOUBLE PRECISION (A-H, O-Z)
147 IF (Ifl.Eq.1 .or. Ifl.Eq.2) THEN
148 VL = Ctq2OPd (Iset, Ifl, X, Q, Irt)
153 SEA = Ctq2OPd (Iset, -JFL, X, Q, Irt)
154 C Full (probability) Distribution
155 Ctq2OPf = (VL + SEA) / X
158 C *************************