hijing/src/luradk.f

0001
0002 C*********************************************************************
0003
0004       SUBROUTINE LURADK(ECM,MK,PAK,THEK,PHIK,ALPK)
0005
0006 C...Purpose: to generate initial state photon radiation.
0007       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
0008       SAVE /LUDAT1/
0009
0010 C...Function: cumulative hard photon spectrum in QFD case.
0011       FXK(XX)=2.*LOG(XX)+PARJ(161)*LOG(1.-XX)+PARJ(162)*XX+
0012      &PARJ(163)*LOG((XX-SZM)**2+SZW**2)+PARJ(164)*ATAN((XX-SZM)/SZW)
0013
0014 C...Determine whether radiative photon or not.
0015       MK=0
0016       PAK=0.
0017       IF(PARJ(160).LT.RLU(0)) RETURN
0018       MK=1
0019
0020 C...Photon energy range. Find photon momentum in QED case.
0021       XKL=PARJ(135)
0022       XKU=MIN(PARJ(136),1.-(2.*PARJ(127)/ECM)**2)
0023       IF(MSTJ(102).LE.1) THEN
0024   100   XK=1./(1.+(1./XKL-1.)*((1./XKU-1.)/(1./XKL-1.))**RLU(0))
0025         IF(1.+(1.-XK)**2.LT.2.*RLU(0)) GOTO 100
0026
0027 C...Ditto in QFD case, by numerical inversion of integrated spectrum.
0028       ELSE
0029         SZM=1.-(PARJ(123)/ECM)**2
0030         SZW=PARJ(123)*PARJ(124)/ECM**2
0031         FXKL=FXK(XKL)
0032         FXKU=FXK(XKU)
0033         FXKD=1E-4*(FXKU-FXKL)
0034         FXKR=FXKL+RLU(0)*(FXKU-FXKL)
0035         NXK=0
0036   110   NXK=NXK+1
0037         XK=0.5*(XKL+XKU)
0038         FXKV=FXK(XK)
0039         IF(FXKV.GT.FXKR) THEN
0040           XKU=XK
0041           FXKU=FXKV
0042         ELSE
0043           XKL=XK
0044           FXKL=FXKV
0045         ENDIF
0046         IF(NXK.LT.15.AND.FXKU-FXKL.GT.FXKD) GOTO 110
0047         XK=XKL+(XKU-XKL)*(FXKR-FXKL)/(FXKU-FXKL)
0048       ENDIF
0049       PAK=0.5*ECM*XK
0050
0051 C...Photon polar and azimuthal angle.
0052       PME=2.*(ULMASS(11)/ECM)**2
0053   120 CTHM=PME*(2./PME)**RLU(0)
0054       IF(1.-(XK**2*CTHM*(1.-0.5*CTHM)+2.*(1.-XK)*PME/MAX(PME,
0055      &CTHM*(1.-0.5*CTHM)))/(1.+(1.-XK)**2).LT.RLU(0)) GOTO 120
0056       CTHE=1.-CTHM
0057       IF(RLU(0).GT.0.5) CTHE=-CTHE
0058       STHE=SQRT(MAX(0.,(CTHM-PME)*(2.-CTHM)))
0059       THEK=ULANGL(CTHE,STHE)
0060       PHIK=PARU(2)*RLU(0)
0061
0062 C...Rotation angle for hadronic system.
0063       SGN=1.
0064       IF(0.5*(2.-XK*(1.-CTHE))**2/((2.-XK)**2+(XK*CTHE)**2).GT.
0065      &RLU(0)) SGN=-1.
0066       ALPK=ASIN(SGN*STHE*(XK-SGN*(2.*SQRT(1.-XK)-2.+XK)*CTHE)/
0067      &(2.-XK*(1.-SGN*CTHE)))
0068
0069       RETURN
0070       END