PDF/spdf/alphas2.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.3  1996/10/30 11:05:22  cernlib
   6 * Conflicts resolved
   7 *
   8 * Revision 1.1.1.2  1996/10/30 08:32:07  cernlib
   9 * Version 7.04
  10 *
  11 * Revision 1.2  1996/05/31 13:57:48  pdflib
  12 * replace # by +
  13 *
  14 * Revision 1.1.1.1  1996/04/12 15:29:01  plothow
  15 * Version 7.01
  16 *
  17 *
  18 #include "pdf/pilot.h"
  19 C-----------------------------------------------------------------------
  20 #if defined(CERNLIB_SINGLE)
  21       FUNCTION ALPHAS2(SCALE)
  22 #endif
  23 #if defined(CERNLIB_DOUBLE)
  24       DOUBLE PRECISION FUNCTION ALPHAS2(SCALE)
  25
  26 #endif
  27 C
  28 C **********************************************************************
  29 C *                                                                    *
  30 C *   Program to calculate alfa strong to second order                 *
  31 C *   as a function of lambda of 5 flavours                            *
  32 C *   and the desired number of flavours (NFL)                         *
  33 C *   for the selected set of structure functions which fixes lambda.  *
  34 C *   NFL is limited to max. of 6 flavours.                            *
  35 C *   The value of alfa is matched at the thresholds q = mq.           *
  36 C *   When invoked with NFL < 0, it chooses NFL                        *
  37 C *   as the number of flavours with mass less then q.                 *
  38 C *   (mc = 1.5 GeV, mb = 4.75 GeV, mt = 100 GeV)                      *
  39 C *                                                                    *
  40 C *   Input:   SCALE   = QCD scale in GeV                              *
  41 C *                                                                    *
  42 C *   Output:  ALPHAS2 = alpha strong to second order,                 *
  43 C *                      if not LO = 1                                 *
  44 C *                                                                    *
  45 C *   The variables NPTYPE,NGROUP,NSET,NFL,LO,TMAS,QCDL4,QCDL5         *
  46 C *   should be provided by the user via a call to the                 *
  47 C *   subroutine PDFSET at the initialization phase.                   *
  48 C *                                                                    *
  49 C *   Author:   H. Plothow-Besch (CERN-PPE)                            *
  50 C *                                                                    *
  51 C **********************************************************************
  52 C
  53 #include "pdf/impdp.inc"
  54 C
  55 #include "pdf/w5051p1.inc"
  56 #include "pdf/w5051p2.inc"
  57 #include "pdf/w5051p7.inc"
  58 #include "pdf/w50510.inc"
  59 #include "pdf/w50511.inc"
  60 #include "pdf/w50512.inc"
  61 #include "pdf/w50513.inc"
  62 #include "pdf/w50515.inc"
  63 #include "pdf/w50516.inc"
  64 #include "pdf/w50517.inc"
  65 #include "pdf/w50519.inc"
  66 #include "pdf/w505120.inc"
  67 #include "pdf/w505121.inc"
  68 C
  69 #include "pdf/expdp.inc"
  70      +    NF,KNF
  71       CHARACTER*20 PARM(NCHDIM)
  72 #include "pdf/expdp.inc"
  73      +       VAL(NCHDIM)
  74       DATA XMC/1.5D0/,XMB/4.75D0/,XMT/100.D0/
  75       DATA ZEROD/0.D0/,PONED/0.001D0/,ONED/1.D0/,TWOD/2.D0/
  76 C.
  77 C.    initialization of the parameters for the coupling constant
  78 C.
  79 C.    QCDL4  : QCD scale, which is matched to the scale used in the
  80 C.             parton distribution function chosen above for 4 flavours.
  81 C.
  82 C.    QCDL5  : QCD scale, which is matched to the scale used in the
  83 C.              parton distribution function chosen above.
  84 C.
  85 C. be aware, this lambda is given for 5 flavours (mb = 4.75 GeV/c**2) !!
  86 C.
  87 C
  88 C   set the default values
  89 C
  90       ALPHAS2 = ZEROD
  91 C
  92       IF(N6.LE.0) N6 = L6
  93 C.
  94 #include "pdf/w50511c.inc"
  95 C.
  96 C User wants new version (4.0 or bigger) of PDFLIB format
  97       IF (IFLSET.NE.1) THEN
  98          IF(FIRST) THEN
  99          WRITE(N6,*) ' Warning : NO initialisation via PDFSET made !!'
 100          WRITE(N6,*)
 101      +   '           ALL Parameters set to default (Nucleon PDFs) !!'
 102          ENDIF
 103          NPTYPE = LPTYPE
 104          NGROUP = LGROUP
 105          NSET   = LNSET
 106 C
 107          PARM(1) = 'NPTYPE'
 108          VAL(1)  = NPTYPE
 109          PARM(2) = 'NGROUP'
 110          VAL(2)  = NGROUP
 111          PARM(3) = 'NSET'
 112          VAL(3)  = NSET
 113 C
 114          CALL PDFSET(PARM,VAL)
 115       ENDIF
 116 C.
 117 C User wants old version (3.0 or less) of PDFLIB format
 118       IF(.NOT.NEWVER) THEN
 119         IF (MODE .GE.0 .AND. MODE .LE.MODEMX) THEN
 120            IF(MODE.EQ.0) THEN
 121              NPTYPE = LPTYPO
 122              NGROUP = LGROPO
 123              NSET   = LNSETO
 124            ELSE
 125              NPTYPE = NPTYCR(MODE)
 126              NGROUP = NGROCR(MODE)
 127              NSET   = NSETCR(MODE)
 128 C   Check on validity of parameter values
 129              IF (NPTYPE.LT.0 .OR. NGROUP.LT.0 .OR. NSET.LT.0) THEN
 130                 IF(FIRST) THEN
 131                 WRITE(N6,*) ' PDFLIB  : MODE value INCORRECT, MODE = ',
 132      +          MODE
 133                WRITE(N6,*) ' Warning : MODE value set to OLD default !!'
 134                 ENDIF
 135                 NPTYPE = LPTYPO
 136                 NGROUP = LGROPO
 137                 NSET   = LNSETO
 138              ENDIF
 139            ENDIF
 140         ENDIF
 141       ENDIF
 142 C.
 143          IF (QCDL5 .LE. PONED) THEN
 144             IF(FIRST) THEN
 145             WRITE (N6,*) ' PDFLIB: QCD-Lambda5 is not defined !! '
 146             ENDIF
 147             ALPHAS2 = ZEROD
 148             RETURN
 149          ENDIF
 150 C.
 151         PI=4.0D0*ATAN(ONED)
 152         B6  = (33.D0-2.D0*6.D0)/PI/12.D0
 153         BP6 = (153.D0 - 19.D0*6.D0) / PI / TWOD / (33.D0 - 2.D0*6.D0)
 154         B5  = (33.D0-2.D0*5.D0)/PI/12.D0
 155         BP5 = (153.D0 - 19.D0*5.D0) / PI / TWOD / (33.D0 - 2.D0*5.D0)
 156         B4  = (33.D0-2.D0*4.D0)/PI/12.D0
 157         BP4 = (153.D0 - 19.D0*4.D0) / PI / TWOD / (33.D0 - 2.D0*4.D0)
 158         B3  = (33.D0-2.D0*3.D0)/PI/12.D0
 159         BP3 = (153.D0 - 19.D0*3.D0) / PI / TWOD / (33.D0 - 2.D0*3.D0)
 160         XLC = TWOD * LOG( XMC/QCDL5)
 161         XLB = TWOD * LOG( XMB/QCDL5)
 162         XLT = TWOD * LOG( XMT/QCDL5 * TMAS/XMT)
 163         XLLC = LOG( XLC)
 164         XLLB = LOG( XLB)
 165         XLLT = LOG( XLT)
 166         C65  =  ONED/( ONED/(B5 * XLT) - XLLT*BP5/(B5 * XLT)**2 )
 167      +        - ONED/( ONED/(B6 * XLT) - XLLT*BP6/(B6 * XLT)**2 )
 168         C45  =  ONED/( ONED/(B5 * XLB) - XLLB*BP5/(B5 * XLB)**2 )
 169      +        - ONED/( ONED/(B4 * XLB) - XLLB*BP4/(B4 * XLB)**2 )
 170         C35  =  ONED/( ONED/(B4 * XLC) - XLLC*BP4/(B4 * XLC)**2 )
 171      +        - ONED/( ONED/(B3 * XLC) - XLLC*BP3/(B3 * XLC)**2 ) + C45
 172 C
 173       Q   = SCALE
 174       XLQ = TWOD *  LOG( Q/QCDL5 )
 175       XLLQ =  LOG( XLQ )
 176       KNF = NFL
 177       NF = KNF
 178       IF  ( NF .LT. ZEROD) THEN
 179         IF      ( Q .GT. XMT * TMAS/XMT) THEN
 180           NF = 6.D0
 181         ELSEIF  ( Q .GT. XMB ) THEN
 182           NF = 5.D0
 183         ELSEIF  ( Q .GT. XMC ) THEN
 184           NF = 4.D0
 185         ELSE
 186           NF = 3.D0
 187         ENDIF
 188       ENDIF
 189       IF(NF .GT. 6.D0) NF = 6.D0
 190       IF      ( NF .EQ. 6.D0 ) THEN
 191        ALF = ONED/(ONED/(ONED/(B6*XLQ)- BP6/(B6*XLQ)**2*XLLQ) + C65)
 192        IF (LO.EQ.1) ALF = ONED/B6/XLQ
 193       ELSEIF  ( NF .EQ. 5.D0 ) THEN
 194        ALF = ONED/(B5 * XLQ) -  BP5/(B5 * XLQ)**2 * XLLQ
 195        IF (LO.EQ.1) ALF = ONED/B5/XLQ
 196       ELSEIF  ( NF .EQ. 4.D0 ) THEN
 197        ALF = ONED/(ONED/(ONED/(B4*XLQ)- BP4/(B4*XLQ)**2*XLLQ) + C45)
 198        IF (LO.EQ.1) ALF = ONED/B4/XLQ
 199       ELSEIF  ( NF .EQ. 3.D0 ) THEN
 200        ALF = ONED/(ONED/(ONED/(B3*XLQ)- BP3/(B3*XLQ)**2*XLLQ) + C35)
 201        IF (LO.EQ.1) ALF = ONED/B3/XLQ
 202       ELSE
 203        WRITE(N6,*)'Error in Alphas2: unimplemented # of light flavours',
 204      +             NFL
 205        STOP
 206       ENDIF
 207       ALPHAS2 = ALF
 208       RETURN
 209       END