Use Peter Bosted's implementation of MAID model for exclusive pions a…

…t lower W.
JeffersonLab · Sep 4, 2020 · 745b620 · 745b620
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commit 745b620
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Showing 6 changed files with 34,736 additions and 22 deletions.
diff --git a/maidpi0n.dat b/maidpi0n.dat
diff --git a/maidpi0p.dat b/maidpi0p.dat
diff --git a/maidpi0pborn.dat b/maidpi0pborn.dat
diff --git a/maidpimp.dat b/maidpimp.dat
diff --git a/maidpipn.dat b/maidpipn.dat
diff --git a/physics_pion.f b/physics_pion.f
@@ -32,14 +32,15 @@ real*8 function peepi(vertex,main)
         real*8 ebeamcm,pbeamcm,pbeamcmx,pbeamcmy,pbeamcmz !p_beam in C.M.
         real*8 etarcm,ptarcm,ptarcmx,ptarcmy,ptarcmz	!p_fermi in C.M.
         real*8 thetacm,phicm,phiqn,jacobian,jac_old
+	real*8 Wgev, Q2gev, E0, cthcm, sig0, fac1
 
 	real*8 sig_multipole,sig_blok,sig_param04,sig_param_3000
 
-	integer final_state
+	integer final_state, ipi
 	logical first,low_w_flag
 
 	data first /.TRUE./
-	data low_w_flag /.FALSE./	!Assume high W kinematics to start
+cdg	data low_w_flag /.FALSE./	!Assume high W kinematics to start
 
 * Calculate velocity of PHOTON-NUCLEON C.M. system in the lab frame. Use beta
 * and gamma of the cm system (bstar and gstar) to transform particles into
@@ -89,19 +90,20 @@ real*8 function peepi(vertex,main)
 * in the subroutine (according to DJG - see gaskell_model.ps)
 	k_eq = (main%wcm**2-targ%Mtar_struck**2)/2./targ%Mtar_struck
 
-* Initialize some stuff for the multipole model.
-	if (first) then
-	  first = .false.
-	  if(which_pion.eq.0 .or. which_pion.eq.10) then  !pi+
-	    final_state = 1
-	  else
-	    final_state = 2
-	  endif
-	  if(k_eq.lt.500.)then
-	    write(6,*) 'Using low W multipole pion model...'
-	    low_w_flag = .TRUE.
-	  endif
-	endif
+CDG - Remove multipole model
+CDG* Initialize some stuff for the multipole model.
+CDG	if (first) then
+CDG	  first = .false.
+CDG	  if(which_pion.eq.0 .or. which_pion.eq.10) then  !pi+
+CDG	    final_state = 1
+CDG	  else
+CDG	    final_state = 2
+CDG	  endif
+CDG	  if(k_eq.lt.500.)then
+CDG	    write(6,*) 'Using low W multipole pion model...'
+CDG	    low_w_flag = .TRUE.
+CDG	  endif
+CDG	endif
 
 * Get cross section in photon-nucleon center of mass.  sigcm1 is blok
 * fit (default model - can always be evaluated).  sigcm2 is multipole,
@@ -121,14 +123,30 @@ real*8 function peepi(vertex,main)
 
 	sigma_eepi = ntup%sigcm1
 
-* For low w, use multipole expansion as default cross section model.
-	if(low_w_flag) then
-
-	  ntup%sigcm2 = sig_multipole(k_eq,efer,qstar,tfcos,ppicm,s/1.e6,thetacm,
-     >		phicm,main%epsilon,final_state,vertex%q2/1.e6,targ%Mtar_struck/1000.,pfer,mh)
-	  sigma_eepi = ntup%sigcm2
-
+CDG For lower W, user Peter Bosted's implementation of the MAID model
+	if(main%wcm.lt.2300) then ! W less than 2.3 GeV
+	   Q2gev = vertex%q2/1.d6 !convert to GeV**2
+	   Wgev = main%wcm/1000.0 ! convert to GeV
+	   cthcm = cos(thetacm)
+	   E0 = vertex%Ein/1000.0  !convert to GeV
+	   ipi = 3 ! pi+ by default
+	   if (which_pion.eq.1 .or. which_pion.eq.11) ipi=4 ! pi-
+	   call sigmaid(ipi,Q2gev,Wgev,E0,cthcm,phicm,sig0)
+! convert from mub / dOmega* to mub / dt / dphi*
+	   ntup%sigcm2 = sig0 / ppicm / qstar / 2.
+c       smoothly join between W of 1.7 and 2.3
+	   fac1 = max(0., (Wgev - 1.7) / 0.6)
+	   sigma_eepi = ntup%sigcm1 * fac1 + ntup%sigcm2 * (1 - fac1)
 	endif
+
+* For low w, use multipole expansion as default cross section model.
+CDG	if(low_w_flag) then
+CDG
+CDG	  ntup%sigcm2 = sig_multipole(k_eq,efer,qstar,tfcos,ppicm,s/1.e6,thetacm,
+CDG     >		phicm,main%epsilon,final_state,vertex%q2/1.e6,targ%Mtar_struck/1000.,pfer,mh)
+CDG	  sigma_eepi = ntup%sigcm2
+CDG
+CDG	endif
 	ntup%sigcm = sigma_eepi		!sig_cm
 
 
@@ -539,3 +557,166 @@ real*8 function sig_param_3000(thetacm,phicm,t,q2_gev,s_gev,eps,mtar_gev,which_p
 
 	  return
 	end
+
+CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
+
+      subroutine sigmaid(Ipi,q2,w,e0,costh,phi,sig0)
+ccccccccccccccccccccccccccccccccccccccccccccccccccc
+c get exclusive pion cross sections and target
+c asymmetries from MAID 2007. 
+c inputs: ipi = 1, 2, 3, 4 for pi0 p, pi0 n, pi+ n, pi- p
+c         q2 in GeV2. For Q2>5, extrapolation is done
+c         W  in GeV. For W>2, extrapolation is done
+c         E0 beam energy in GeV
+c         costh cos(th*) (from -1 to 1)
+c         phi   phi* (in radians, from 0 to 2pi)
+c outputs: cross section dsigma/dOmega in the N-pi
+c         c.m. system, in mub/sr
+c         sigma = sig0 + Pt * sigz + Pb * Pt * sigez
+c         where Pb and Pt are beam and target polarization
+ccccccccccccccccccccccccccccccccccccccccccccccccccc
+
+      implicit none
+      integer i,Ipi,iq,iw,ith,j,k
+      real*8 q2,w,e0,costh,phi,sig0,sigz, sigez, sige
+      real*8 maidtbl(4,25,46,6,18)
+      real*8 wfact, ST, SL, STL, STT, STLZ, STTZ, STLP
+      real*8 STLPZ, STTPZ, CSF, SNF, CS2F, SN2F, CST,SNT
+      real*8 STLPY,STTPX,SLY,STY,STLX,sthe,pt,pl,pn
+      REAL*8 STLY,STTX,STTY,STLPX
+      real*8 x, eps, am/0.9383/, nu, ep, sin2
+      real*8 cthmin(6)/-0.20, 0.20, 0.44, 0.63, 0.78, 0.90/
+      real*8 cthmax(6)/       0.20, 0.44, 0.63, 0.78, 0.90, 1.0/
+      logical first/.true./
+
+
+! Read in the MAID tables generated by 
+! ~bosted/eg1c/MAID/targetall.f using code 
+! provided by Lothar Tiator (MAID group)
+      if(first) then
+       first = .false.
+       do i=1,4
+        if(i.eq.1) open(unit=9,file='maidpi0p.dat')
+        if(i.eq.2) open(unit=9,file='maidpi0n.dat')
+        if(i.eq.3) open(unit=9,file='maidpipn.dat')
+        if(i.eq.4) open(unit=9,file='maidpimp.dat')
+        do iq=1,25
+         do iw=1,46
+          do ith=1,6
+           read(9,'(f11.6,18f8.4)') 
+     >      (maidtbl(i,iq,iw,ith,j),j=1,18)
+          enddo
+         enddo
+        enddo
+        close(unit=9)
+       enddo
+      endif
+
+! Initialize answers
+      sig0 = 0.
+      sigz = 0.
+      sigez = 0.
+      st = 0.
+      sige = 0.
+
+      if(w.lt.1.08) return
+
+! get epsilon
+      nu = (w**2 - am**2 + q2) / 2. / am
+      if(nu .gt. e0) return
+      ep = e0 - nu
+      sin2 = q2 / 4. / e0 / ep
+      if(sin2.le.0.0 .or. sin2.gt. 1.) return
+      eps = 1./(1. + 2. * (1. + nu**2 / q2) * sin2 / 
+     >       (1. - sin2))
+! tHIS IS sin(theta_electron)
+      sthe = 2. * sqrt(sin2)
+! this is sin(theta_q)
+      pt = ep * sthe / sqrt(q2 + nu**2)
+! this is cos(theta_q) (target b-field along q)
+      pl = sqrt(1. - pt**2)
+! This is normal component of target b-field
+      pn  = -pt * sin(phi)
+! This is now the in-plane component
+      pt  =  pt * cos(phi)
+
+
+! Get nearest bin in Q2, W, and costh
+      iq = int((q2 + 0.1)/0.2)
+      iq = min(25,max(1,iq))
+
+      iw = int((w-1.090)/0.020)
+      iw = min(46,max(1,iw))
+
+      ith=0
+      do i=1,6
+       if(costh.ge.cthmin(i).and.costh.le.cthmax(i)) ith=i
+      enddo
+      ith = min(6,max(1,ith))
+
+
+! Get sigma_t in mub/sr, as well as sigm_l, ...
+      wfact = 1.
+      if(w.gt.1.232) wfact = (w -1.132)/0.100
+      ST = maidtbl(Ipi,iq,iw,ith,1) / max(0.2,q2) / wfact
+      SL   = maidtbl(Ipi,iq,iw,ith,2) * ST
+      STL  = maidtbl(Ipi,iq,iw,ith,3) * ST
+      STT  = maidtbl(Ipi,iq,iw,ith,4) * ST
+      STLZ = maidtbl(Ipi,iq,iw,ith,5) * ST
+      STTZ = maidtbl(Ipi,iq,iw,ith,6) * ST
+      STLPZ= maidtbl(Ipi,iq,iw,ith,7) * ST
+      STTPZ= maidtbl(Ipi,iq,iw,ith,8) * ST
+      STLP = maidtbl(Ipi,iq,iw,ith,9) * ST
+      STLX = maidtbl(Ipi,iq,iw,ith,10) * ST
+      STLY = maidtbl(Ipi,iq,iw,ith,11) * ST
+      STTX = maidtbl(Ipi,iq,iw,ith,12) * ST
+      STTY = maidtbl(Ipi,iq,iw,ith,13) * ST
+      STLPX= maidtbl(Ipi,iq,iw,ith,14) * ST
+      STLPY= maidtbl(Ipi,iq,iw,ith,15) * ST
+      STTPX= maidtbl(Ipi,iq,iw,ith,16) * ST
+      SLY  = maidtbl(Ipi,iq,iw,ith,17) * ST
+      STY  = maidtbl(Ipi,iq,iw,ith,18) * ST
+
+! get cos(phi), etc.
+      CSF =COS(phi)
+      SNF =SIN(phi)
+      CS2F=COS(2.*phi)
+      SN2F=SIN(2.*phi)
+      CST =costh
+      SNT =SQRT(1.-costh**2)
+
+! Get sigma_0, etc.
+      sig0 = ST + EPS * SL + 
+     >    sqrt(2.*EPS*(1.+EPS))*CSF*STL + 
+     >    EPS*CS2F*STT
+
+      sigz = sqrt(2.*EPS*(1.+EPS)) *
+     > (PT * SNF * STLX + 
+     >  PN * CSF * STLY + 
+     >  PL * SNF * STLZ) + 
+     > EPS * 
+     > (PT * SN2F * STTX +
+     >  PN * CS2F * STTY +
+     >  PL * SN2F * STTZ) +
+     > PN * (STY + EPS * SLY)
+
+      sigez = sqrt(2.*EPS*(1.-EPS)) *
+     > (PT * STLPx * CSF + 
+     >  PN * STLPy * SNF + 
+     >  PL * STLPZ * CSF) + 
+     > sqrt(1.-EPS**2) * 
+     >  (PT * STTPx + 
+     >   PL * STTPZ)
+
+      sige = sqrt(2.*EPS*(1.-EPS))*SNF*STLP
+
+! change sign of sigez to agree with DIS convention
+! in which Delta has negative A_LL
+      sigez = -1.0 * sigez
+
+! also change sign of sigz so agrees with our results for
+c W>1.4. Note: this was *not* done for eg1c!
+      sigz = -1.0 * sigz
+
+      return
+      end