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1 | #include "isajet/pilot.h" | |
2 | SUBROUTINE TWOKIN(AMI1,AMI2,AM1,AM2) | |
3 | C | |
4 | C Given P,PT,TH,PHI, and initial and final masses AMI1, AMI2, | |
5 | C AM1,AM2, set X1, X2, SHAT, etc. | |
6 | C | |
7 | #if defined(CERNLIB_IMPNONE) | |
8 | IMPLICIT NONE | |
9 | #endif | |
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" | |
15 | C | |
16 | REAL AMI1,AMI2,AM1,AM2,P1PL,P1MN,P2PL,P2MN,E1,E2,PPL,PMN, | |
17 | $ PI1PL,PI1MN,PI2PL,PI2MN,ANEFF,AMASS,ALAMFN | |
18 | C | |
19 | E1=SQRT(P(1)**2+AM1**2) | |
20 | E2=SQRT(P(2)**2+AM2**2) | |
21 | C | |
22 | C For 32-bit machines must use large and small components | |
23 | C carefully, with pbig*psmall = pt**2+am**2. | |
24 | C | |
25 | IF(CTH(1).GT.0.) THEN | |
26 | P1PL=E1+P(1)*CTH(1) | |
27 | P1MN=(PT(1)**2+AM1**2)/P1PL | |
28 | ELSE | |
29 | P1MN=E1-P(1)*CTH(1) | |
30 | P1PL=(PT(1)**2+AM1**2)/P1MN | |
31 | ENDIF | |
32 | IF(CTH(2).GT.0.) THEN | |
33 | P2PL=E2+P(2)*CTH(2) | |
34 | P2MN=(PT(2)**2+AM2**2)/P2PL | |
35 | ELSE | |
36 | P2MN=E2-P(2)*CTH(2) | |
37 | P2PL=(PT(2)**2+AM2**2)/P2MN | |
38 | ENDIF | |
39 | C | |
40 | C Initial light cone momenta. Not symmetric if AMI1 /= AMI2. | |
41 | C | |
42 | PPL=P1PL+P2PL | |
43 | PMN=P1MN+P2MN | |
44 | SHAT=PPL*PMN | |
45 | ALAMFN=SQRT((SHAT-AMI1**2-AMI2**2)**2-4.*(AMI1*AMI2)**2) | |
46 | PI1PL=(SHAT+AMI1**2-AMI2**2+ALAMFN)/(2.*PMN) | |
47 | PI1MN=AMI1**2/PI1PL | |
48 | PI2MN=(SHAT+AMI2**2-AMI1**2+ALAMFN)/(2.*PPL) | |
49 | PI2PL=AMI2**2/PI2MN | |
50 | X1=PI1PL/ECM | |
51 | X2=PI2MN/ECM | |
52 | C | |
53 | C t=(p1-pi1)**2, u=(p1-pi2)**2 | |
54 | C | |
55 | THAT=AM1**2+AMI1**2-P1PL*PI1MN-P1MN*PI1PL | |
56 | UHAT=AM1**2+AMI2**2-P1PL*PI2MN-P1MN*PI2PL | |
57 | C | |
58 | C Q**2 variable from Field, Fox, Wolfram | |
59 | C | |
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)) | |
64 | RETURN | |
65 | END |