HERWIG/src/hwsdgq.f

   1
   2 CDECK  ID>, HWSDGQ.
   3
   4 *CMZ :-        -26/04/91  13.04.45  by  Federico Carminati
   5
   6 *-- Author :    Drees, Grassie, Charchula, modified by Bryan Webber
   7
   8 C --------------------------------------
   9
  10 C  QUARK PART OF THE PHOTON SF
  11
  12 C --------------------------------------
  13
  14       FUNCTION HWSDGQ(X,Q2,NFL,NCH)
  15
  16       IMPLICIT REAL (A-H,P-Z)
  17
  18       INTEGER NFL,NCH
  19
  20       DIMENSION A(5,4,2,3),AT(5,2),XQPOM(2),E(2)
  21
  22       COMMON/DG/F2
  23
  24 C SQUARE OF LAMBDA=0.4 GEV
  25
  26       ALAM2=0.160
  27
  28       T=LOG(Q2/ALAM2)
  29
  30 C
  31
  32 C  CHECK WHETHER NFL AND NCH HAVE RIGHT VALUES
  33
  34 C
  35
  36       IF(.NOT.((NFL.EQ.3).OR.(NFL.EQ.4).OR.(NFL.EQ.5))) THEN
  37
  38  110   WRITE(6,111)
  39
  40  111   FORMAT('NUMBER OF FLAVOURS (NFL) HAS NOT BEEN SET TO: 3,4 OR 5'/
  41
  42      *'          NFL=3 IS ASSUMED')
  43
  44        NFL=3
  45
  46       ELSEIF (T.LE.0) THEN
  47
  48        WRITE(6,132)
  49
  50  132   FORMAT(' HWSDGQ CALLED WITH SCALE < LAMBDA. RETURNING ZERO.')
  51
  52        HWSDGQ=0
  53
  54        RETURN
  55
  56       ENDIF
  57
  58       IF (.NOT.((NCH.EQ.1).OR.(NCH.EQ.2))) THEN
  59
  60  120     WRITE(6,121)
  61
  62  121     FORMAT(' QUARK CHARGE NUMBER (NCH) HAS NOT BEEN SET',
  63
  64      *'           TO 1 OR 2;'/
  65
  66      *'           NCH=1 IS ASSUMED')
  67
  68          NCH=1
  69
  70       ENDIF
  71
  72 C ------ INITIALIZATION ------
  73
  74       DATA(((A(I,J,K,1),I=1,5),J=1,4),K=1,2)/
  75
  76      + 2.28500,  6.07300, -0.42020,-0.08080, 0.05530,
  77
  78      +-0.01530, -0.81320,  0.01780, 0.63460, 1.13600,
  79
  80      + 1.3300E3,-41.3100,   0.92160, 1.20800, 0.95120,
  81
  82      + 4.21900,  3.16500,  0.18000, 0.20300, 0.01160,
  83
  84      +16.6900,   0.17600, -0.02080,-0.01680,-0.19860,
  85
  86      +-0.79160,  0.04790,  0.3386E-2,1.35300, 1.10000,
  87
  88      + 1.0990E3,  1.04700,  4.85300, 1.42600, 1.13600,
  89
  90      + 4.42800,  0.02500,  0.84040, 1.23900,-0.27790/
  91
  92         DATA(((A(I,J,K,2),I=1,5),J=1,4),K=1,2)/
  93
  94      +-0.37110,-0.17170, 0.087660,-0.89150,-0.18160,
  95
  96      + 1.06100, 0.78150, 0.021970, 0.28570, 0.58660,
  97
  98      + 4.75800, 1.53500, 0.109600, 2.97300, 2.42100,
  99
 100      +-0.01500, 0.7067E-2,0.204000, 0.11850, 0.40590,
 101
 102      +-0.12070,25.00000,-0.012300,-0.09190, 0.020150,
 103
 104      + 1.07100,-1.64800, 1.162000, 0.79120, 0.98690,
 105
 106      + 1.97700,-0.015630,0.482400, 0.63970,-0.070360,
 107
 108      +-0.8625E-2,6.43800,-0.011000, 2.32700, 0.016940/
 109
 110         DATA(((A(I,J,K,3),I=1,5),J=1,4),K=1,2)/
 111
 112      +15.80,     2.7420,  0.029170,-0.03420, -0.023020,
 113
 114      +-0.94640, -0.73320, 0.046570, 0.71960,  0.92290,
 115
 116      +-0.50,     0.71480, 0.17850,  0.73380,  0.58730,
 117
 118      +-0.21180,  3.2870,  0.048110, 0.081390,-0.79E-4,
 119
 120      + 6.7340,  59.880,  -0.3226E-2,-0.03321,   0.10590,
 121
 122      +-1.0080,  -2.9830,  0.84320,  0.94750,  0.69540,
 123
 124      +-0.085940, 4.480,   0.36160, -0.31980, -0.66630,
 125
 126      + 0.076250, 0.96860, 0.1383E-2, 0.021320, 0.36830/
 127
 128       CF=10.0
 129
 130 C ------- EVALUATION OF PARAMETERS IN Q2 ---------
 131
 132       E(1)=1.0
 133
 134       IF (NFL.EQ.3) THEN
 135
 136         E(2)=9.0
 137
 138         LF=1
 139
 140       ELSEIF (NFL.EQ.4) THEN
 141
 142         E(2)=10.0
 143
 144         LF=2
 145
 146       ELSEIF (NFL.EQ.5) THEN
 147
 148         E(2)=55.0/6.0
 149
 150         LF=3
 151
 152       ENDIF
 153
 154       DO 10 J=1,2
 155
 156         DO 20 I=1,5
 157
 158            ATP=A(I,1,J,LF)*T**A(I,2,J,LF)
 159
 160            AT(I,J)=ATP+A(I,3,J,LF)*T**(-A(I,4,J,LF))
 161
 162  20     CONTINUE
 163
 164  10   CONTINUE
 165
 166       DO 30 J=1,2
 167
 168        POM1=X*(X*X+(1.0-X)**2)/(AT(1,J)-AT(2,J)*ALOG(1.0-X))
 169
 170        POM2=AT(3,J)*X**AT(4,J)*(1.0-X)**AT(5,J)
 171
 172        XQPOM(J)=E(J)*POM1+POM2
 173
 174  30   CONTINUE
 175
 176 C -------  QUARK DISTRIBUTIONS ----------
 177
 178       IF (NFL.EQ.3) THEN
 179
 180          IF (NCH.EQ.2) THEN
 181
 182            HWSDGQ=1.0/6.0*(XQPOM(2)+9.0*XQPOM(1))
 183
 184          ELSEIF(NCH.EQ.1) THEN
 185
 186            HWSDGQ=1.0/6.0*(XQPOM(2)-9.0/2.0*XQPOM(1))
 187
 188          ENDIF
 189
 190         F2=2.0/9.0*XQPOM(2)+XQPOM(1)
 191
 192       ELSEIF (NFL.EQ.4) THEN
 193
 194          IF (NCH.EQ.2) THEN
 195
 196            HWSDGQ=1.0/8.0*(XQPOM(2)+6.0*XQPOM(1))
 197
 198          ELSEIF(NCH.EQ.1) THEN
 199
 200            HWSDGQ=1.0/8.0*(XQPOM(2)-6.0*XQPOM(1))
 201
 202          ENDIF
 203
 204         F2=5.0/18.0*XQPOM(2)+XQPOM(1)
 205
 206       ELSEIF (NFL.EQ.5) THEN
 207
 208          IF (NCH.EQ.2) THEN
 209
 210            HWSDGQ=1.0/10.0*(XQPOM(2)+15.0/2.0*XQPOM(1))
 211
 212          ELSEIF(NCH.EQ.1) THEN
 213
 214            HWSDGQ=1.0/10.0*(XQPOM(2)-5.0*XQPOM(1))
 215
 216          ENDIF
 217
 218         F2=11.0/45.0*XQPOM(2)+XQPOM(1)
 219
 220       ENDIF
 221
 222       HWSDGQ=HWSDGQ/137.
 223
 224       RETURN
 225
 226       END