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dvmpx.F
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C======================================================
REAL FUNCTION DVMPX(del2,xb,Q2, Phi_g,E,heli,MESONMASS)
C
C dvmpx(-0.493,0.187,1.61,3.92699,5.75,0.,0.135)
C
c dsigma/dQ2 dX dt dphi for ep-->ep pi0
C
C exc pi0 x-section
c
cinput:
cdel2=t (negative GeV^2) NEGATIVE !!!!
cxb,Q2 x and Q^2 (GeV^2)
c Phi_g angle in the photon frame (radians)
c E energy of the electron in GeV
c heli electron helicity -1.0 or +1.0
c MESONMASS is the mass of th epi0 or eta
IMPLICIT NONE
REAL del2,xb,Q2, Phi_g,E,heli,MESONMASS
real Mp, mele, pi
parameter (Mp=0.93827)
parameter (mele=0.000511)
parameter (pi=3.1415926536)
REAL S_T, S_L, S_LT, S_TT,S_LTP
REAL XSIGMA_T, XSIGMA_L, XSIGMA_LT, XSIGMA_TT,XSIGMA_LTP
REAL EPS, EPSILON, FLUXW, SIGMA_TOT
EXTERNAL EPSILON,XSIGMA_T,XSIGMA_L, XSIGMA_LT, XSIGMA_TT
EXTERNAL XSIGMA_LTP
REAL FL
LOGICAL XCHECK_KINE
INCLUDE 'pi0eta.par'
CALL XSINIT(MESONMASS)
DVMPX = 0.0
IF(.NOT.XCHECK_KINE(del2,xb,Q2,E)) RETURN
EPS = EPSILON(XB,q2,e)
S_T = XSIGMA_T (del2,xb,Q2,E)
S_L = XSIGMA_L (del2,xb,Q2,E)
S_LT = XSIGMA_LT (del2,xb,Q2,E)
S_TT = XSIGMA_TT (del2,xb,Q2,E)
S_LTP = XSIGMA_LTP (del2,xb,Q2,E)
DVMPX =FLUXW(xb,Q2,E)/(2.*PI)*(
* S_T + EPS*S_L +
* EPS *S_TT * COS(2*PHI_G) +
* SQRT(2.*EPS*(1.+EPS))*S_LT * COS(PHI_G) +
* HELI*SQRT(2.*EPS*(1.-EPS))*S_LTP * SIN(2*PHI_G)
* )
if(DVMPX.lt.0.) DVMPX=0.
RETURN
END
c-------------------------------------------------------------------------
SUBROUTINE XSINIT(MESONMASS)
C
IMPLICIT NONE
REAL MESONMASS
c INTEGER K
c COMMON/PIETA/K
INCLUDE 'pi0eta.par'
IF(MESONMASS.GT.0.140) THEN
K=2
ELSE
K=1
ENDIF
RETURN
END
C=============================================================================
REAL FUNCTION XRXSB(del2,x,Q2, Phi_g,E,heli,MESONMASS)
IMPLICIT NONE
REAL del2,x,Q2,Phi_g,E,heli,MESONMASS
REAL DVMPX,fluxw, pi
PARAMETER (PI=3.1415926536)
CALL XSINIT(MESONMASS)
XRXSB=DVMPX(del2,x,Q2,Phi_g,E,heli,MESONMASS)/FLUXW(x,Q2,E)
C * *(2.*PI)
RETURN
END
C====================================================================================c
REAL FUNCTION HT(del2,X,Q2)
IMPLICIT NONE
REAL del2,x,Q2,E,KSI
EXTERNAL tminq
REAL tminq,T0,SLOPE,T,PI,PHASE
REAL P1,P2,P3,P4,P5
REAL MP,ALPHA
DATA ALPHA/0.00729927/
DATA PI/3.14159265/
DATA MP/0.938272/
C COMMON /PAWPAR/ P(10)
C REAL P
REAL W2,XNORM
INCLUDE 'pi0eta.par'
P1=ABS(P(1,K))
P2=ABS(P(2,K))
P3=ABS(P(3,K))
P4=ABS(P(4,K))
P5=ABS(P(5,K))
T0=tminq(Q2,X)
T=-DEL2
XNORM=0.15
SLOPE=(P2/2.)*ALOG(X)/ALOG(XNORM)
HT=P1*EXP(-SLOPE*T)
* /Q2**(P3/4.)
* * (X**P4*(1-X)**P5)
C PRINT *,'HT= ',HT,' SLOPE=',slope
c print *,'P1 ',p1,p2,p3,p4,p5
RETURN
END
C====================================================================================c
REAL FUNCTION ET(del2,X,Q2)
IMPLICIT NONE
REAL del2,x,Q2,E,KSI
EXTERNAL tminq,PHASE
REAL tminq,T0,SLOPE,T,PI,PHASE
REAL P1,P2,P3,P4,P5,P6,P7,P8,P9,P10
LOGICAL XCHECK_KINE
REAL MP,ALPHA
DATA ALPHA/0.00729927/
DATA PI/3.14159265/
DATA MP/0.938272/
C COMMON /PAWPAR/ P(10)
C REAL P
INCLUDE 'pi0eta.par'
REAL W2,xnorm
P1=ABS(P(6,K))
P2=ABS(P(7,K))
P3=ABS(P(8,K))
P4=ABS(P(9,K))
P5=ABS(P(10,K))
T0=tminq(Q2,X)
T=-DEL2
XNORM=0.15
SLOPE=(P2/2.)*ALOG(X)/ALOG(XNORM)
ET=P1*EXP(-SLOPE*T)
* /Q2**(P3/4.)
* *(X**P4*(1-X)**P5)
c PRINT *,'ET= ',ET,' SLOPE=',slope
c print *,'P6 ',p1,p2,p3,p4,p5
RETURN
END
C====================================================================================c
REAL FUNCTION XSIGMA_U(del2,x,Q2,E)
IMPLICIT NONE
REAL del2,x,Q2,E
EXTERNAL XSIGMA_T,XSIGMA_L,EPSILON
REAL tminq,T0,SLOPE,T,XSIGMA_T,
* XSIGMA_L,EPSILON
LOGICAL XCHECK_KINE
REAL AM(2)
DATA AM/0.134976,0.547300/
INTEGER K
COMMON/PIETA/K
c INCLUDE 'pi0eta.par'
IF(XCHECK_KINE(del2,x,Q2,E)) THEN
XSIGMA_U=XSIGMA_T(DEL2,X,Q2,E)+
* EPSILON(x,Q2,E)*XSIGMA_L(DEL2,X,Q2,E)
ELSE
XSIGMA_U=0.0
ENDIF
RETURN
END
C====================================================================================c
REAL FUNCTION XSIGMA_T(del2,x,Q2,E)
IMPLICIT NONE
REAL del2,x,Q2,E,ALPHA,KSI
EXTERNAL tminq,PHASE,HT,ET
REAL tminq,T0,SLOPE,T,PI,PHASE
REAL HT,ET,MP,HC2
LOGICAL XCHECK_KINE
DATA ALPHA/0.00729927/
DATA PI/3.14159265/
DATA MP/0.938272/
DATA HC2/389379.36/
IF(XCHECK_KINE(del2,x,Q2,E)) THEN
T0=tminq(Q2,X)
T=-DEL2
KSI=X/(2-X)*(1+MP**2/Q2)
XSIGMA_T=4.*PI*ALPHA/2./PHASE(Q2,X)*(
* (1-KSI**2)* HT(del2,X,Q2)**2
* + (T-T0)/8/MP**2*ET(del2,X,Q2)**2
* )
ELSE
XSIGMA_T=0.0
ENDIF
XSIGMA_T=XSIGMA_T*HC2
c print *,'XSIGMA_T=', XSIGMA_T
RETURN
END
C====================================================================================c
REAL FUNCTION XSIGMA_TT(del2,x,Q2,E)
IMPLICIT NONE
REAL del2,x,Q2,E
EXTERNAL tminq
REAL tminq,T0,SLOPE,T,HC2
REAL ALPHA,PI,MP,PHASE,ET
LOGICAL XCHECK_KINE
DATA ALPHA/0.00729927/
DATA PI/3.14159265/
DATA MP/0.938272/
DATA HC2/389379.36/
IF(XCHECK_KINE(del2,x,Q2,E)) THEN
T0=tminq(Q2,X)
T=-DEL2
XSIGMA_TT=-4.*PI*ALPHA/2./PHASE(Q2,X)
* * (T-T0)/8/MP**2*ET(del2,X,Q2)**2
ELSE
XSIGMA_TT=0.0
ENDIF
XSIGMA_TT=XSIGMA_TT*HC2
c print *,' t=',-del2,' XSIGMA_TT=', xsigma_tt
RETURN
END
C====================================================================================c
REAL FUNCTION XSIGMA_L(del2,x,Q2,E)
IMPLICIT NONE
REAL del2,x,Q2,E
EXTERNAL tminq
REAL tminq,T0,SLOPE,T
LOGICAL XCHECK_KINE
c INCLUDE 'pi0eta.par'
XSIGMA_L=0.0
RETURN
END
C====================================================================================c
REAL FUNCTION XSIGMA_LT(del2,x,Q2,E)
IMPLICIT NONE
REAL del2,x,Q2,E
EXTERNAL tminq
REAL tminq,T0,SLOPE,T
LOGICAL XCHECK_KINE
XSIGMA_LT=0.0
RETURN
END
C====================================================================================c
REAL FUNCTION XSIGMA_LTP(del2,x,Q2,E)
IMPLICIT NONE
REAL del2,x,Q2,E
REAL EPS, EPSILON,A2_PHI,FLUXW,SIGMA_TOT
EXTERNAL EPSILON,FLUXW
XSIGMA_LTP=0.
RETURN
END
C====================================================================================c
LOGICAL FUNCTION XCHECK_KINE(del2,xb,Q2,E)
IMPLICIT NONE
REAL del2,xb,Q2,E
real Mp, mele, pi,mpi0
real fluxw, rxs
parameter (Mp=0.93827)
parameter (mele=0.000511)
parameter (pi=3.1415926536)
real nu,W2,W,qmod,E1cm,P1cm,E2cm,P2cm,del2max,del2min
real xmin1,xmax1
real y, e1, epsilon,tminq
REAL AM(2)
DATA AM/0.134976,0.547300/
INTEGER K
COMMON/PIETA/K
MPI0=AM(K)
XCHECK_KINE=.FALSE.
xmin1 = Q2/(2.0*Mp*E)
xmax1 = 1.0
nu = Q2/(2D0*Mp*xb)
W2 = Mp**2 + 2.0*Mp*nu - Q2
C print *,'W2=',W2
IF(W2.LT.(Mp+Mpi0)**2) RETURN
W = sqrt(W2)
qmod = sqrt(nu**2 + Q2)
E1cm = Mp*(Mp + nu)/W
P1cm = Mp*qmod/W
E2cm = (W2 + Mp**2-Mpi0**2)/(2.*W)
C print *,'E2cm=',E2cm,Mp
IF(E2cm.LE.Mp) RETURN
P2cm = SQRT(E2CM**2 - Mp**2)
del2max = 2.0*(Mp**2 - E1cm*E2cm - P1cm*P2cm)
del2min = 2.0*(Mp**2 - E1cm*E2cm + P1cm*P2cm)
C print *,'xB=',xb,xmin1,xmax1
IF( xb.le.xmin1 .or. xb.gt.xmax1 ) return ! x out of range
C print *,'t=',del2,del2min,del2max,tminq(Q2,xb)
IF( del2.ge.del2min .or. del2.le.del2max ) return ! delta out of range
y=Q2/(2*Mp*xb*E)
e1=(y*xb*Mp)**2/Q2
EPSILON=(1.0-y-e1)/(1-y+y**2/2+e1)
C print *,'Epsilon',epsilon
IF(EPSILON.LT.0. .OR.EPSILON .GT.1.) RETURN
XCHECK_KINE=.TRUE.
RETURN
END
C====================================================================================c
real function fluxw(x,Q2,E)
implicit none
real x,Q2,E,y,eps,e1
real alpha,Mp,PI
parameter (alpha=1.0/137.036,Mp=0.93827231,PI=3.14151926)
c
y=Q2/(2*Mp*x*E)
e1=(y*x*Mp)**2/Q2
eps=(1.0-y-e1)/(1-y+y**2/2+e1)
fluxw=alpha/(2*PI)*y*y/(1-eps)*(1-x)/x/Q2
return
end
C====================================================================================c
real function EPSILON(x,Q2,E)
implicit none
real x,Q2,E,y,eps,e1
real alpha,Mp,PI
parameter (alpha=1.0/137.036,Mp=0.93827231,PI=3.14151926)
c
y=Q2/(2*Mp*x*E)
e1=(y*x*Mp)**2/Q2
EPSILON=(1.0-y-e1)/(1-y+y**2/2+e1)
return
end
C======================================================================================c
REAL FUNCTION tminq(Q2,X)
IMPLICIT NONE
REAL Q2,X
REAL W2,W,S,E1CM,E3CM,P1CM,P3CM,TMAX
INTEGER I
real alpha,Mp,PI,Me
REAL MPI0
INCLUDE 'pi0eta.par'
MPI0=AM(K)
tminq=0.
Mp=0.9382723
Me=0.0051
PI=3.14151926
IF(X.LE.0. .OR. X.GE.1.) RETURN
W2 = Q2*(1./X-1.)+Mp**2
W=SQRT(W2)
IF(W.LT.Mp+Mpi0) RETURN
E1CM=(W2+Q2+Mp**2)/(2*W)
P1CM=SQRT(E1CM**2-MP**2)
E3CM=(W2-MPI0**2+Mp**2)/(2*W)
P3CM=SQRT(E3CM**2-MP**2)
TMINQ=-((Q2+MPI0**2)**2/4./W2-(P1CM-P3CM)**2)
RETURN
END
C====================================================================================c
REAL FUNCTION PHASE(Q2,X)
IMPLICIT NONE
REAL Q2,X
REAL W,W2,W4,Q4,MP,MP2,MP4,PI,LAMBDA
DATA MP/0.938272/
DATA PI/3.14159265/
PHASE=0.0
IF(X.GE.1.) RETURN
W2=Q2*(1/X-1.)+MP**2
W4=W2*W2
MP2=MP*MP
MP4=MP2*MP2
LAMBDA=W4+Q4+MP4+2*W2*Q2-2*W2*MP2+2*Q2*MP2
IF(LAMBDA.LE.0) RETURN
PHASE=16.*PI*(W2-MP2)*SQRT(LAMBDA)
RETURN
END