1 #include "isajet/pilot.h"
2 C----------------------------------------------------------------------
3 FUNCTION SUALFS(QSQ,ALAM4,TMASS,LOOP)
4 C----------------------------------------------------------------------
6 C This function returns the 1, 2, or 3-loop value of alpha_s
9 C ALAM4 = Lambda for 4 active quark flavors (real)
10 C TMASS = top quark mass to determine lambda-6 (real)
11 C LOOP = number of loops for alpha_s (= 1, 2 or 3)
12 C Parametrization of the strong coupling constant according to
13 C LOOP = 1, 2 : from the book;
14 C LOOP = 3: W. J. Marciano, Phys. Rev. D 29 (1984) 580.
15 C Note : threshold at 2*Mq
17 #if defined(CERNLIB_IMPNONE)
20 #include "isajet/sslun.inc"
21 REAL SUALFS, QSQ, ALAM4, TMASS
24 REAL ANF, ALAM, ALAMSQ, ALAM5, T, TT, B0, B1, B2, X, ALPHAS
25 DATA PI/3.1415927/, BMASS/5.0/
27 IF (QSQ .LT. 4.0*BMASS**2) THEN
30 ELSE IF (QSQ .LT. 4.0*TMASS**2) THEN
32 ALAM = ALAM4*(ALAM4/(2.0*BMASS))**(2.0/23.0)
33 1 *(ALOG(4.0*BMASS**2/ALAM4**2))**(-963.0/13225.0)
36 ALAM5 = ALAM4*(ALAM4/(2.0*BMASS))**(2.0/23.0)
37 1 *(ALOG(4.0*BMASS**2/ALAM4**2))**(-963.0/13225.0)
38 ALAM = ALAM5*(ALAM5/(2.0*TMASS))**(2.0/21.0)
39 1 *(ALOG(4.0*TMASS**2/ALAM5**2))**(-107.0/1127.0)
44 IF (T .LE. 1.0) T = ALOG(4.0/ALAMSQ)
48 ELSE IF (LOOP .EQ. 2) THEN
49 B1 = 102.0-38.0/3.0*ANF
52 SUALFS = ALPHAS*(1.0-X*TT)
53 ELSE IF (LOOP .EQ. 3) THEN
54 B1 = 102.0-38.0/3.0*ANF
55 B2 = 0.5*(2857.0-5033.0/9.0*ANF+325.0/27.0*ANF**2)
58 SUALFS = ALPHAS*(1.0-X*TT+X**2*((TT-0.5)**2
61 WRITE(LOUT,*) ' WRONG LOOP NUMBER IN ALPHA-S EVALUATION!'