1 #include "isajet/pilot.h"
2 SUBROUTINE TWOKIN(AMI1,AMI2,AM1,AM2)
4 C Given P,PT,TH,PHI, and initial and final masses AMI1, AMI2,
5 C AM1,AM2, set X1, X2, SHAT, etc.
7 #if defined(CERNLIB_IMPNONE)
10 #include "isajet/itapes.inc"
11 #include "isajet/primar.inc"
12 #include "isajet/jetpar.inc"
13 #include "isajet/qcdpar.inc"
14 #include "isajet/const.inc"
16 REAL AMI1,AMI2,AM1,AM2,P1PL,P1MN,P2PL,P2MN,E1,E2,PPL,PMN,
17 $ PI1PL,PI1MN,PI2PL,PI2MN,ANEFF,AMASS,ALAMFN
19 E1=SQRT(P(1)**2+AM1**2)
20 E2=SQRT(P(2)**2+AM2**2)
22 C For 32-bit machines must use large and small components
23 C carefully, with pbig*psmall = pt**2+am**2.
27 P1MN=(PT(1)**2+AM1**2)/P1PL
30 P1PL=(PT(1)**2+AM1**2)/P1MN
34 P2MN=(PT(2)**2+AM2**2)/P2PL
37 P2PL=(PT(2)**2+AM2**2)/P2MN
40 C Initial light cone momenta. Not symmetric if AMI1 /= AMI2.
45 ALAMFN=SQRT((SHAT-AMI1**2-AMI2**2)**2-4.*(AMI1*AMI2)**2)
46 PI1PL=(SHAT+AMI1**2-AMI2**2+ALAMFN)/(2.*PMN)
48 PI2MN=(SHAT+AMI2**2-AMI1**2+ALAMFN)/(2.*PPL)
53 C t=(p1-pi1)**2, u=(p1-pi2)**2
55 THAT=AM1**2+AMI1**2-P1PL*PI1MN-P1MN*PI1PL
56 UHAT=AM1**2+AMI2**2-P1PL*PI2MN-P1MN*PI2PL
58 C Q**2 variable from Field, Fox, Wolfram
60 QSQ=2.*SHAT*THAT*UHAT/(SHAT**2+THAT**2+UHAT**2)
61 QSQ=AMAX1(QSQ,(AM1+AM2)**2)
62 ANEFF=4.+QSQ/(QSQ+AMASS(5)**2)+QSQ/(QSQ+AMASS(6)**2)
63 ALFQSQ=12.*PI/((33.-2.*ANEFF)*ALOG(QSQ/ALAM2))