AliDecayer realisation for the EvtGen code and EvtGen itself.

[u/mrichter/AliRoot.git] / TEvtGen / PHOTOS / phoene.F

diff --git a/TEvtGen/PHOTOS/phoene.F b/TEvtGen/PHOTOS/phoene.F
new file mode 100644 (file)
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+++ b/TEvtGen/PHOTOS/phoene.F
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+      SUBROUTINE PHOENE(MPASQR,MCHREN,BETA,IDENT)
+C.----------------------------------------------------------------------
+C.
+C.    PHOTOS:   PHOton radiation in decays calculation  of photon ENErgy
+C.              fraction
+C.
+C.    Purpose:  Subroutine  returns  photon  energy fraction (in (parent
+C.              mass)/2 units) for the decay bremsstrahlung.
+C.
+C.    Input Parameters:  MPASQR:  Mass of decaying system squared,
+C.                       XPHCUT:  Minimum energy fraction of photon,
+C.                       XPHMAX:  Maximum energy fraction of photon.
+C.
+C.    Output Parameter:  MCHREN:  Renormalised mass squared,
+C.                       BETA:    Beta factor due to renormalisation,
+C.                       XPHOTO:  Photon energy fraction,
+C.                       XF:      Correction factor for PHOFAC.
+C.
+C.    Author(s):  S. Jadach, Z. Was               Created at:  01/01/89
+C.                B. van Eijk                     Last Update: 26/03/93
+C.
+C.----------------------------------------------------------------------
+      IMPLICIT NONE
+      DOUBLE PRECISION MPASQR,MCHREN,BIGLOG,BETA,DATA
+      INTEGER IWT1,IRN,IWT2
+      REAL*8 PRSOFT,PRHARD,PHORAN,PHOFAC
+      DOUBLE PRECISION MCHSQR,MNESQR
+      REAL*8 PNEUTR
+      INTEGER IDENT
+      REAL*8 PHOCHA
+      COMMON/PHOMOM/MCHSQR,MNESQR,PNEUTR(5)
+      DOUBLE PRECISION COSTHG,SINTHG
+      REAL*8 XPHMAX,XPHOTO
+      COMMON/PHOPHS/XPHMAX,XPHOTO,COSTHG,SINTHG
+      REAL*8 ALPHA,XPHCUT
+      COMMON/PHOCOP/ALPHA,XPHCUT
+      REAL*8 PI,TWOPI
+      COMMON/PHPICO/PI,TWOPI
+      INTEGER IREP
+      REAL*8 PROBH,CORWT,XF
+      COMMON/PHOPRO/PROBH,CORWT,XF,IREP
+      LOGICAL INTERF,ISEC,IFTOP
+      REAL*8 FINT,FSEC
+      COMMON /PHOKEY/ FSEC,FINT,INTERF,ISEC,IFTOP
+C--
+      IF (XPHMAX.LE.XPHCUT) THEN
+        XPHOTO=0.0D0
+        RETURN
+      ENDIF
+C--   Probabilities for hard and soft bremstrahlung...
+      MCHREN=4.D0*MCHSQR/MPASQR/(1.D0+MCHSQR/MPASQR)**2
+      BETA=SQRT(1.D0-MCHREN)
+      BIGLOG=LOG(MPASQR/MCHSQR*(1.D0+BETA)**2/4.D0*
+     &          (1.D0+MCHSQR/MPASQR)**2)
+      PRHARD=ALPHA/PI/BETA*BIGLOG*(LOG(XPHMAX/XPHCUT)-.75D0+XPHCUT/
+     &XPHMAX-.25D0*XPHCUT**2/XPHMAX**2)
+      PRHARD=PRHARD*PHOCHA(IDENT)**2*FINT*FSEC
+      IF (IREP.EQ.0) PROBH=0.D0
+      PRHARD=PRHARD*PHOFAC(0)
+      PROBH=PRHARD
+      PRSOFT=1.D0-PRHARD
+C--
+C--   Check on kinematical bounds
+      IF (PRSOFT.LT.0.1D0) THEN
+        DATA=PRSOFT
+        CALL PHOERR(2,'PHOENE',DATA)
+      ENDIF
+      IF (PHORAN(IWT1).LT.PRSOFT) THEN
+C--
+C--   No photon... (ie. photon too soft)
+        XPHOTO=0.D0
+      ELSE
+C--
+C--   Hard  photon... (ie.  photon  hard enough).
+C--   Calculate  Altarelli-Parisi Kernel
+   10   XPHOTO=EXP(PHORAN(IRN)*LOG(XPHCUT/XPHMAX))
+        XPHOTO=XPHOTO*XPHMAX
+        IF (PHORAN(IWT2).GT.((1.D0+(1.D0-XPHOTO/XPHMAX)**2)/2.D0)) 
+     &                            GOTO 10
+      ENDIF
+C--
+C--   Calculate parameter for PHOFAC function
+      XF=4.D0*MCHSQR*MPASQR/(MPASQR+MCHSQR-MNESQR)**2
+      RETURN
+      END