2 C*********************************************************************
4 SUBROUTINE LURADK(ECM,MK,PAK,THEK,PHIK,ALPK)
6 C...Purpose: to generate initial state photon radiation.
7 COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
10 C...Function: cumulative hard photon spectrum in QFD case.
11 FXK(XX)=2.*LOG(XX)+PARJ(161)*LOG(1.-XX)+PARJ(162)*XX+
12 &PARJ(163)*LOG((XX-SZM)**2+SZW**2)+PARJ(164)*ATAN((XX-SZM)/SZW)
14 C...Determine whether radiative photon or not.
17 IF(PARJ(160).LT.RLU(0)) RETURN
20 C...Photon energy range. Find photon momentum in QED case.
22 XKU=MIN(PARJ(136),1.-(2.*PARJ(127)/ECM)**2)
23 IF(MSTJ(102).LE.1) THEN
24 100 XK=1./(1.+(1./XKL-1.)*((1./XKU-1.)/(1./XKL-1.))**RLU(0))
25 IF(1.+(1.-XK)**2.LT.2.*RLU(0)) GOTO 100
27 C...Ditto in QFD case, by numerical inversion of integrated spectrum.
29 SZM=1.-(PARJ(123)/ECM)**2
30 SZW=PARJ(123)*PARJ(124)/ECM**2
34 FXKR=FXKL+RLU(0)*(FXKU-FXKL)
46 IF(NXK.LT.15.AND.FXKU-FXKL.GT.FXKD) GOTO 110
47 XK=XKL+(XKU-XKL)*(FXKR-FXKL)/(FXKU-FXKL)
51 C...Photon polar and azimuthal angle.
52 PME=2.*(ULMASS(11)/ECM)**2
53 120 CTHM=PME*(2./PME)**RLU(0)
54 IF(1.-(XK**2*CTHM*(1.-0.5*CTHM)+2.*(1.-XK)*PME/MAX(PME,
55 &CTHM*(1.-0.5*CTHM)))/(1.+(1.-XK)**2).LT.RLU(0)) GOTO 120
57 IF(RLU(0).GT.0.5) CTHE=-CTHE
58 STHE=SQRT(MAX(0.,(CTHM-PME)*(2.-CTHM)))
59 THEK=ULANGL(CTHE,STHE)
62 C...Rotation angle for hadronic system.
64 IF(0.5*(2.-XK*(1.-CTHE))**2/((2.-XK)**2+(XK*CTHE)**2).GT.
66 ALPK=ASIN(SGN*STHE*(XK-SGN*(2.*SQRT(1.-XK)-2.+XK)*CTHE)/
67 &(2.-XK*(1.-SGN*CTHE)))