5 * Revision 1.1.1.2 1996/10/30 08:27:48 cernlib
8 * Revision 1.1.1.1 1996/04/12 15:29:10 plothow
12 #include "pdf/pilot.h"
13 C Version 2 CTEQ distribution function in a parametrized form.
15 C By: J. Botts, H.L. Lai, J.G. Morfin, J.F. Owens, J. Qiu, W.K. Tung
18 C To avoid the proliferation of parton distribution functions, we recommend
19 C that these distributions should replace Version 1 CTEQ distributions for
20 C general usage. The differences between the two sets of distributions, as
21 C briefly described below, do not significantly affect most applications for
22 C fixed-target and hadron-collider applications.
24 C Both CTEQ1 and CTEQ2 distributions fit existing DIS, Drell-Yan and Direct
25 C phton data with excellent chi-squares. They represent two distinct ways to
26 C resolve the inconsistency between CCFR and NMC measurements on F2 at small-x
27 C and the neutrino dimuon measurements of s(x), as discovered by the CTEQ1
28 C analysis: in the CTEQ1 analysis, the F2 measurements of CCFR and NMC are
29 C taken seriously, leaving out the dimuon information on s(x); whereas in the
30 C CTEQ2 analysis, thelatest CCFR NLO dimuon analysis of s(x) is used (within
31 C errors) as input butleaving out the small-x F2 data which conflict with this
32 C input. The small-xbehavior of the parton distributions are contrained in the
33 C latter case by thenewly released HERA data. For details, see our
36 C This file contains three versions of the same CTEQ2 parton distributions:
38 C Two "front-end" subprograms:
39 C FUNCTION Ctq2pPf (Iset, Iparton, X, Q, Irt)
40 C returns the PROBABILITY density for a GIVEN flavor;
41 C SUBROUTINE Ctq2pPs(Iset, Pdf, XX, QQ, Irt)
42 C returns an array of MOMENTUM densities for ALL flavors;
43 C One lower-level subprogram:
44 C FUNCTION Ctq2pPd (Iset, Iprtn, XX, QQ, Irt)
45 C returns the MOMENTUM density of a GIVEN valence or sea distribution.
46 C Supplementary functions to return the relevant QCD parameters and other
47 C information concerning these distributions are also included (see below).
49 C Since this is an initial distribution of version 2, it is
50 C useful for the authors to maintain a record of the distribution list in
51 C case there are revisions or corrections.
52 C In the interest of maintaining the integrity of this package,
53 C please do not freely distribute this program package; instead, refer any
54 C interested colleagues to direct their request for a copy to:
55 C Botts@hades.ifh.de or Lai@cteq11.pa.msu.edu
57 C If you have detailed questions concerning these CTEQ2 distributions, direct
58 C inquires to Botts, Lai (see above) or Wu-Ki Tung (Tung@msupa.pa.msu.edu).
60 C -------------------------------------------
61 C Detailed instructions follow.
63 C Name convention for CTEQ distributions: CTEQnSx where
64 C n : version number (currently n = 2)
65 C S : factorization scheme label: = [M D L] for [MS-bar DIS LO]
67 C x : special characteristics, if any
68 C (e.g. S(F) for singular (flat) small-x, L for "LEP lambda value")
70 C Explanation of functional arguments:
72 C Iset is the set label; in this version, Iset = 1, 2, 3, 4, 5, 6
73 C correspond to the following CTEQ global fits:
75 C cteq2M : best fit in the MS-bar scheme
76 C cteq2MS : singular small-x
77 C cteq2MF : flat small-x
78 C cteq2ML : large lambda (Lambda(5) = 220 MeV)
80 C cteq2L : best fit in Leading order QCD
82 C cteq2D : best fit in the DIS scheme
84 C Iprtn is the parton label (6, 5, 4, 3, 2, 1, 0, -1, ......, -6)
85 C for (t, b, c, s, d, u, g, u_bar, ..., t_bar)
87 C X, Q are the usual x, Q;
88 C Irt is a return error code (see individual modules for explanation).
90 C ---------------------------------------------
91 C --> QCD parameters for parton distribution set Iset can be obtained inside
92 C the user's program by:
94 C > (Iset, Iord, Ischeme, MxFlv,
95 C > Alam4, Alam5, Alam6, Amas4, Amas5, Amas6,
96 C > Xmin, Qini, Qmax, ExpNor)
97 C where all but the first argument are output parameters.
98 C They should be self-explanatory -- see details under ENTRY PrCtq2p.
100 C Since the QCD Lambda value for the various sets are needed more often than
101 C the other parameters in most applications, a special function
102 C Wlamd2p (Iset, Iorder, Neff) is provided
103 C which returns the lambda value for Neff = 4,5,6 effective flavors as well as
104 C the order these values pertain to.
106 C ----------------------------------------------
107 C The range of (x, Q) used in this round of global analysis is, approxi-
108 C mately, 0.01 < x < 0.75 ; and 4 GeV^2 < Q^2 < 400 GeV^2 for fixed target
109 C experiments and 0.0001 < x < 0.01 from first official data of HERA.
111 C The range of (x, Q) used in the reparametrization of the QCD evolved
112 C parton distributions is 10E-5 < x < 1 ; 1.6 GeV < Q < 1 TeV. The
113 C functional form of this parametrization is:
115 C A0 * x^A1 * (1-x)^A2 * (1 + A3 * x^A4) * [log(1+1/x)]^A5
117 C with the A'coefficients being smooth functions of Q. For heavy quarks,
118 C a threshold factor is applied to A0 which simulates the proper Q-dependence
119 C of the QCD evolution in that region according to the renormalization
120 C scheme defined in Collins-Tung, Nucl. Phys. B278, 934 (1986).
122 C Since this function is positive definite and smooth, it provides sensible
123 C extrapolations of the parton distributions if they are called beyond
124 C the original range in an application. There is no artificial boundaries
126 C ------------------------------------------------
128 FUNCTION Ctq2pPf (Iset, Iparton, X, Q, Irt)
130 C This function returns the CTEQ parton distributions f^Iset_Iprtn/proton
131 C --- the PROBABILITY density
133 C (Iset, Iparton, X, Q): explained above;
135 C Irt : return error code: see module Ctq2pPd for explanation.
137 C IMPLICIT DOUBLE PRECISION (A-H, O-Z)
143 IF (Ifl.Eq.1 .or. Ifl.Eq.2) THEN
144 VL = Ctq2pPd (Iset, Ifl, X, Q, Irt)
149 SEA = Ctq2pPd (Iset, -JFL, X, Q, Irt)
150 C Full (probability) Distribution
151 Ctq2pPf = (VL + SEA) / X
154 C *************************