TEvtGen/PHOTOS/phocor.F

   1       FUNCTION PHOCOR(MPASQR,MCHREN,ME)
   2 C.----------------------------------------------------------------------
   3 C.
   4 C.    PHOTOS:   PHOton radiation in decays CORrection weight from
   5 C.              matrix elements
   6 C.
   7 C.    Purpose:  Calculate  photon  angle.  The reshaping functions  will
   8 C.              have  to  depend  on the spin S of the charged particle.
   9 C.              We define:  ME = 2 * S + 1 !
  10 C.
  11 C.    Input Parameters:  MPASQR:  Parent mass squared,
  12 C.                       MCHREN:  Renormalised mass of charged system,
  13 C.                       ME:      2 * spin + 1 determines matrix element
  14 C.
  15 C.    Output Parameter:  Function value.
  16 C.
  17 C.    Author(s):  Z. Was, B. van Eijk             Created at:  26/11/89
  18 C.                                                Last Update: 21/03/93
  19 C.
  20 C.----------------------------------------------------------------------
  21       IMPLICIT NONE
  22       DOUBLE PRECISION MPASQR,MCHREN,BETA,XX,YY,DATA
  23       INTEGER ME
  24       REAL*8 PHOCOR,PHOFAC,WT1,WT2,WT3
  25       DOUBLE PRECISION MCHSQR,MNESQR
  26       REAL*8 PNEUTR
  27       COMMON/PHOMOM/MCHSQR,MNESQR,PNEUTR(5)
  28       DOUBLE PRECISION COSTHG,SINTHG
  29       REAL*8 XPHMAX,XPHOTO
  30       COMMON/PHOPHS/XPHMAX,XPHOTO,COSTHG,SINTHG
  31       INTEGER IREP
  32       REAL*8 PROBH,CORWT,XF
  33       COMMON/PHOPRO/PROBH,CORWT,XF,IREP
  34 C--
  35 C--   Shaping (modified by ZW)...
  36       XX=4.D0*MCHSQR/MPASQR*(1.D0-XPHOTO)/(1.D0-XPHOTO+(MCHSQR-MNESQR)/
  37      &MPASQR)**2
  38       IF (ME.EQ.1) THEN
  39         YY=1.D0
  40         WT3=(1.D0-XPHOTO/XPHMAX)/((1.D0+(1.D0-XPHOTO/XPHMAX)**2)/2.D0)
  41       ELSEIF (ME.EQ.2) THEN
  42         YY=0.5D0*(1.D0-XPHOTO/XPHMAX+1.D0/(1.D0-XPHOTO/XPHMAX))
  43         WT3=1.D0
  44       ELSEIF ((ME.EQ.3).OR.(ME.EQ.4).OR.(ME.EQ.5)) THEN
  45         YY=1.D0
  46         WT3=(1.D0+(1.D0-XPHOTO/XPHMAX)**2-(XPHOTO/XPHMAX)**3)/
  47      &  (1.D0+(1.D0-XPHOTO/XPHMAX)** 2)
  48       ELSE
  49         DATA=(ME-1.D0)/2.D0
  50         CALL PHOERR(6,'PHOCOR',DATA)
  51         YY=1.D0
  52         WT3=1.D0
  53       ENDIF
  54       BETA=SQRT(1.D0-XX)
  55       WT1=(1.D0-COSTHG*SQRT(1.D0-MCHREN))/(1.D0-COSTHG*BETA)
  56       WT2=(1.D0-XX/YY/(1.D0-BETA**2*COSTHG**2))*(1.D0+COSTHG*BETA)/2.D0
  57       WT2=WT2*PHOFAC(1)
  58       PHOCOR=WT1*WT2*WT3
  59       CORWT=PHOCOR
  60       IF (PHOCOR.GT.1.D0) THEN
  61         DATA=PHOCOR
  62         CALL PHOERR(3,'PHOCOR',DATA)
  63       ENDIF
  64       RETURN
  65       END