1 #include "isajet/pilot.h"
3 C***********************************************************************
4 C* Modified from contributed subroutine by M. Drees (1/8/99)
5 C* Computes the effective single elctrn spectrum from beamstrahlung at *
6 C* e+e- colliders, using Chen's approximate expressions, for a given *
7 C* beamstrahlung parameter Y; is supposed to work for Y <= 10 or so. *
8 C* The quantities in the COMMON block are the beamstrahlungs parameter *
9 C* Y, the bunch length XL in GeV, the number of photons NGAM, and the *
10 C* parameters NUCL, NUGAM, W, XKAPPA defined by Chen, as well as the *
11 C* pre-factor FAC. Y, E and XLMM are read in by BEAM when it is called *
12 C* for the first time, with INIT=1; in this first run the other para- *
13 C* meters are then computed, and simply used in later calls with *
14 C* INIT = 0. This COMMON block should be present in the main program *
15 C* in order to guarantee the survival of these parameters. Finally, X *
16 C* is the electron energy in units of the nominal beam energy. Notice *
17 C* that BEAMEL is only the part which is NOT proportional to *
18 C* delta(1-X); the coefficient of the delta-function is simply *
19 C* (1-exp(-NGAM))/NGAM. *
20 C***********************************************************************
21 #if defined(CERNLIB_IMPNONE)
24 #include "isajet/eepar.inc"
26 REAL XLMM,XL,GAM,RE,XKAPPA,NUCL,NUGAM,NGAM,X,NUBAR,
27 $ETA,EPS,HFAC,RAT,MTERM,TERM,HBAR,XN,EBEAM,Y,E,GAMMA
28 DOUBLE PRECISION DINCGM
32 XLMM = 2.E0*SQRT(3.E0)*XLMM
33 XL = XLMM*1.E12/.197327E0
35 RE = 1.E0/(137.E0*5.11E-4)
36 XKAPPA = 2.E0/(3.E0*Y)
37 NUCL = 2.5E0*Y/(SQRT(3.E0)*137.E0**2*GAM*RE)
38 NUGAM = NUCL/SQRT(1.E0+Y**.6666666E0)
40 IF(X.LT.1.E-5) X=1.E-5
41 IF(X.GT..99999) X=.99999
42 NUBAR = X*NUCL + (1.0-X)*NUGAM
43 ETA = XKAPPA*(1.0/X-1.0)
49 HFAC = EXP(-ETA)/(NGAM*(1.E0-X))
50 IF(HFAC.LT.1.E0) EPS = EPS/SQRT(HFAC)
51 RAT = NUBAR/NUGAM*(ETA**.33333333E0)
53 TERM = MTERM/GAMMA(.33333E0)*DINCGM(2.D0,DBLE(NGAM),DBLE(EPS))
58 TERM = MTERM/GAMMA(XN/3.)*
59 $DINCGM(DBLE(XN)+1.D0,DBLE(NGAM),DBLE(EPS))
61 IF(ABS(TERM/HBAR).GT.EPS) GO TO 1
63 IF(EBEAM.LT.0.) EBEAM = 1.E-20