ISAJET/code/alqcd.F

   1 #include "isajet/pilot.h"
   2       FUNCTION ALQCD(Q2)
   3 C-----------------------------------------------------------------------
   4 C     Strong coupling formula from page 201 of Barger and Phillips:
   5 C     (using ALQCD4 for 4 flavor Lambda)
   6 C-----------------------------------------------------------------------
   7       REAL Q2,AS,TH5,TH6,PI,ALQCD4
   8       LOGICAL FIRST
   9       SAVE FIRST,PI,TH5,TH6,ALQCD4
  10       DATA FIRST/.TRUE./
  11 C
  12       IF(FIRST) THEN
  13         PI=4.*ATAN(1.)
  14         TH5=4*AMASS(5)**2
  15         TH6=4*AMASS(6)**2
  16         ALQCD4=0.177
  17         FIRST=.FALSE.
  18       ENDIF
  19       IF (Q2.LE.TH5)THEN
  20         AS=12*PI/(25*LOG(Q2/ALQCD4**2))
  21       ELSE IF(Q2.GT.TH5.AND.Q2.LE.TH6) THEN
  22         AS=25*LOG(Q2/ALQCD4**2)-2*LOG(Q2/TH5)
  23         AS=12*PI/AS
  24       ELSEIF(Q2.GT.TH6)THEN
  25         AS=25*LOG(Q2/ALQCD4**2)
  26         AS=AS-2*(LOG(Q2/TH5)+LOG(Q2/TH6))
  27         AS=12*PI/AS
  28       ENDIF
  29       ALQCD=AS
  30       RETURN
  31       END