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dmy.f
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*CMZ : 27/05/2004 18.18.31 by H1 Saclay
*-- Author : H1 Saclay 27/05/2004
************************************************************************
REAL*8 FUNCTION DMY(ym)
************************************************************************
*
* Purpose: Generate hadronic mass between Mmin and Mmax
* -------- (mass distribution may depend on t)for p-vertex
*
* Superseds: MASSREJ1 by R. LAUSEN
* ----------
*
* Input: MMIN: minimal allowed mass
* ------ MMAX: maximal allowed mass
* T: MANDELSTAM variable t
* from common block GDIF: EPSILM
*
* Output: MPX: hadronic mass in GeV
* ------- Y: Y > 1. corresponds to an enhancement of
* the mass spectrum over the 1/mx**2 spectrum
*
* Called by: GENVM
* ----------
*
* Author: Benno List, 14.1.92
* -------
*
* Changed by:
* -----------
*
* Calling: From H1UTIL:
* --------
* H1RN: Random generator
*
* Remarks: T is up to now unused
* --------
*
************************************************************************
include 'dvcs.common'
REAL*8 MPX, MMIN, MMAX, T, Y, ENHA
REAL*8 M2, LMIN, DELTA, M2MIN, FACT
REAL*8 ym
EPSILM = stEPSM
MMIN = dble((stMYMIN))
MMAX = dble((stMYMAX))
IF (ABS (EPSILM) .LT. 0.001) THEN
LMIN = 2.0D0*DLOG (MMIN)
DELTA = 2.0D0*DLOG (MMAX/MMIN)
ELSE
M2MIN = MMIN**(-2*EPSILM)
FACT = (MMAX**(-2*EPSILM) - M2MIN)
END IF
ITER = 0
ccc 10 CONTINUE
ccc ITER = ITER + 1
ccc IF (ABS (EPSILM) .LT. 0.001) THEN
ccc* Basic specrum: 1/M^2
ccc M2 = DEXP (DBLE (H1RN ())*DELTA + LMIN)
ccc ELSE
ccc* Basic spectrum: 1/M^2(1+epsilon)
ccc M2 = (FACT*H1RN () + M2MIN)**(-1.0/EPSILM)
ccc END IF
M2 = ym**2
IF (M2 .LT. MMIN**2) THEN
DMY = 0.d0
goto 999
ELSE IF (M2 .GT. MMAX**2) THEN
DMY = 0.d0
goto 999
END IF
*
* Old version with enhancements in lower mass region
*
IF (M2 .GE. 4.00D0) THEN
Y = 1.0D0
ELSE IF (M2 .GE. 3.10D0) THEN
Y = 1.64D0 - 0.16*M2
ELSE IF (M2 .GE. 2.65D0) THEN
Y = M2*(0.47D0 - 0.42D0*(M2-2.65D0)**2)
ELSE IF (M2 .GE. 2.25D0) THEN
Y = M2*(0.47D0 + 0.46D0*(M2-2.65D0)**2)
ELSE IF (M2 .GE. 2.02D0) THEN
Y = M2*(0.76D0 - 2.69D0*(M2-2.02D0)**2)
ELSE IF (M2 .GE. 1.72D0) THEN
Y = M2*(0.76D0 - 1.98D0*(M2-2.02D0)**2)
ELSE
Y = 1.05*(M2 - 1.165D0)
END IF
DMY = Y/(ym**(2*(1.+EPSILM)))
xJACOB = 2.d0*ym
DMY = DMY/xJACOB
999 continue
write(67,*) ym**2,DMY
RETURN
END