C********************************************************************* C...PYGGAM C...Constructs the F2 and parton distributions of the photon C...by summing homogeneous (VMD) and inhomogeneous (anomalous) terms. C...For F2, c and b are included by the Bethe-Heitler formula; C...in the 'MSbar' scheme additionally a Cgamma term is added. C...Contains the SaS sets 1D, 1M, 2D and 2M. C...Adapted from SaSgam library, authors G.A. Schuler and T. Sjostrand. SUBROUTINE PYGGAM(ISET,X,Q2,P2,IP2,F2GM,XPDFGM) C...Double precision and integer declarations. IMPLICIT DOUBLE PRECISION(A-H, O-Z) IMPLICIT INTEGER(I-N) INTEGER PYK,PYCHGE,PYCOMP C...Commonblocks. COMMON/PYINT8/XPVMD(-6:6),XPANL(-6:6),XPANH(-6:6),XPBEH(-6:6), &XPDIR(-6:6) COMMON/PYINT9/VXPVMD(-6:6),VXPANL(-6:6),VXPANH(-6:6),VXPDGM(-6:6) SAVE /PYINT8/,/PYINT9/ C...Local arrays. DIMENSION XPDFGM(-6:6),XPGA(-6:6), VXPGA(-6:6) SAVE C...Charm and bottom masses (low to compensate for J/psi etc.). DATA PMC/1.3D0/, PMB/4.6D0/ C...alpha_em and alpha_em/(2*pi). DATA AEM/0.007297D0/, AEM2PI/0.0011614D0/ C...Lambda value for 4 flavours. DATA ALAM/0.20D0/ C...Mixture u/(u+d), = 0.5 for incoherent and = 0.8 for coherent sum. DATA FRACU/0.8D0/ C...VMD couplings f_V**2/(4*pi). DATA FRHO/2.20D0/, FOMEGA/23.6D0/, FPHI/18.4D0/ C...Masses for rho (=omega) and phi. DATA PMRHO/0.770D0/, PMPHI/1.020D0/ C...Number of points in integration for IP2=1. DATA NSTEP/100/ C...Reset output. F2GM=0D0 DO 100 KFL=-6,6 XPDFGM(KFL)=0D0 XPVMD(KFL)=0D0 XPANL(KFL)=0D0 XPANH(KFL)=0D0 XPBEH(KFL)=0D0 XPDIR(KFL)=0D0 VXPVMD(KFL)=0D0 VXPANL(KFL)=0D0 VXPANH(KFL)=0D0 VXPDGM(KFL)=0D0 100 CONTINUE C...Set Q0 cut-off parameter as function of set used. IF(ISET.LE.2) THEN Q0=0.6D0 ELSE Q0=2D0 ENDIF Q02=Q0**2 C...Scale choice for off-shell photon; common factors. Q2A=Q2 FACNOR=1D0 IF(IP2.EQ.1) THEN P2MX=P2+Q02 Q2A=Q2+P2*Q02/MAX(Q02,Q2) FACNOR=LOG(Q2/Q02)/NSTEP ELSEIF(IP2.EQ.2) THEN P2MX=MAX(P2,Q02) ELSEIF(IP2.EQ.3) THEN P2MX=P2+Q02 Q2A=Q2+P2*Q02/MAX(Q02,Q2) ELSEIF(IP2.EQ.4) THEN P2MX=Q2*(Q02+P2)/(Q2+P2)*EXP(P2*(Q2-Q02)/ & ((Q2+P2)*(Q02+P2))) ELSEIF(IP2.EQ.5) THEN P2MXA=Q2*(Q02+P2)/(Q2+P2)*EXP(P2*(Q2-Q02)/ & ((Q2+P2)*(Q02+P2))) P2MX=Q0*SQRT(P2MXA) FACNOR=LOG(Q2/P2MXA)/LOG(Q2/P2MX) ELSEIF(IP2.EQ.6) THEN P2MX=Q2*(Q02+P2)/(Q2+P2)*EXP(P2*(Q2-Q02)/ & ((Q2+P2)*(Q02+P2))) P2MX=MAX(0D0,1D0-P2/Q2)*P2MX+MIN(1D0,P2/Q2)*MAX(P2,Q02) ELSE P2MXA=Q2*(Q02+P2)/(Q2+P2)*EXP(P2*(Q2-Q02)/ & ((Q2+P2)*(Q02+P2))) P2MX=Q0*SQRT(P2MXA) P2MXB=P2MX P2MX=MAX(0D0,1D0-P2/Q2)*P2MX+MIN(1D0,P2/Q2)*MAX(P2,Q02) P2MXB=MAX(0D0,1D0-P2/Q2)*P2MXB+MIN(1D0,P2/Q2)*P2MXA IF(ABS(Q2-Q02).GT.1D-6) THEN FACNOR=LOG(Q2/P2MXA)/LOG(Q2/P2MXB) ELSEIF(P2.LT.Q02) THEN FACNOR=Q02**3/(Q02+P2)/(Q02**2-P2**2/2D0) ELSE FACNOR=1D0 ENDIF ENDIF C...Call VMD parametrization for d quark and use to give rho, omega, C...phi. Note dipole dampening for off-shell photon. CALL PYGVMD(ISET,1,X,Q2A,P2MX,ALAM,XPGA,VXPGA) XFVAL=VXPGA(1) XPGA(1)=XPGA(2) XPGA(-1)=XPGA(-2) FACUD=AEM*(1D0/FRHO+1D0/FOMEGA)*(PMRHO**2/(PMRHO**2+P2))**2 FACS=AEM*(1D0/FPHI)*(PMPHI**2/(PMPHI**2+P2))**2 DO 110 KFL=-5,5 XPVMD(KFL)=(FACUD+FACS)*XPGA(KFL) 110 CONTINUE XPVMD(1)=XPVMD(1)+(1D0-FRACU)*FACUD*XFVAL XPVMD(2)=XPVMD(2)+FRACU*FACUD*XFVAL XPVMD(3)=XPVMD(3)+FACS*XFVAL XPVMD(-1)=XPVMD(-1)+(1D0-FRACU)*FACUD*XFVAL XPVMD(-2)=XPVMD(-2)+FRACU*FACUD*XFVAL XPVMD(-3)=XPVMD(-3)+FACS*XFVAL VXPVMD(1)=(1D0-FRACU)*FACUD*XFVAL VXPVMD(2)=FRACU*FACUD*XFVAL VXPVMD(3)=FACS*XFVAL VXPVMD(-1)=(1D0-FRACU)*FACUD*XFVAL VXPVMD(-2)=FRACU*FACUD*XFVAL VXPVMD(-3)=FACS*XFVAL IF(IP2.NE.1) THEN C...Anomalous parametrizations for different strategies C...for off-shell photons; except full integration. C...Call anomalous parametrization for d + u + s. CALL PYGANO(-3,X,Q2A,P2MX,ALAM,XPGA,VXPGA) DO 120 KFL=-5,5 XPANL(KFL)=FACNOR*XPGA(KFL) VXPANL(KFL)=FACNOR*VXPGA(KFL) 120 CONTINUE C...Call anomalous parametrization for c and b. CALL PYGANO(4,X,Q2A,P2MX,ALAM,XPGA,VXPGA) DO 130 KFL=-5,5 XPANH(KFL)=FACNOR*XPGA(KFL) VXPANH(KFL)=FACNOR*VXPGA(KFL) 130 CONTINUE CALL PYGANO(5,X,Q2A,P2MX,ALAM,XPGA,VXPGA) DO 140 KFL=-5,5 XPANH(KFL)=XPANH(KFL)+FACNOR*XPGA(KFL) VXPANH(KFL)=VXPANH(KFL)+FACNOR*VXPGA(KFL) 140 CONTINUE ELSE C...Special option: loop over flavours and integrate over k2. DO 170 KF=1,5 DO 160 ISTEP=1,NSTEP Q2STEP=Q02*(Q2/Q02)**((ISTEP-0.5D0)/NSTEP) IF((KF.EQ.4.AND.Q2STEP.LT.PMC**2).OR. & (KF.EQ.5.AND.Q2STEP.LT.PMB**2)) GOTO 160 CALL PYGVMD(0,KF,X,Q2,Q2STEP,ALAM,XPGA,VXPGA) FACQ=AEM2PI*(Q2STEP/(Q2STEP+P2))**2*FACNOR IF(MOD(KF,2).EQ.0) FACQ=FACQ*(8D0/9D0) IF(MOD(KF,2).EQ.1) FACQ=FACQ*(2D0/9D0) DO 150 KFL=-5,5 IF(KF.LE.3) XPANL(KFL)=XPANL(KFL)+FACQ*XPGA(KFL) IF(KF.GE.4) XPANH(KFL)=XPANH(KFL)+FACQ*XPGA(KFL) IF(KF.LE.3) VXPANL(KFL)=VXPANL(KFL)+FACQ*VXPGA(KFL) IF(KF.GE.4) VXPANH(KFL)=VXPANH(KFL)+FACQ*VXPGA(KFL) 150 CONTINUE 160 CONTINUE 170 CONTINUE ENDIF C...Call Bethe-Heitler term expression for charm and bottom. CALL PYGBEH(4,X,Q2,P2,PMC**2,XPBH) XPBEH(4)=XPBH XPBEH(-4)=XPBH CALL PYGBEH(5,X,Q2,P2,PMB**2,XPBH) XPBEH(5)=XPBH XPBEH(-5)=XPBH C...For MSbar subtraction call C^gamma term expression for d, u, s. IF(ISET.EQ.2.OR.ISET.EQ.4) THEN CALL PYGDIR(X,Q2,P2,Q02,XPGA) DO 180 KFL=-5,5 XPDIR(KFL)=XPGA(KFL) 180 CONTINUE ENDIF C...Store result in output array. DO 190 KFL=-5,5 CHSQ=1D0/9D0 IF(IABS(KFL).EQ.2.OR.IABS(KFL).EQ.4) CHSQ=4D0/9D0 XPF2=XPVMD(KFL)+XPANL(KFL)+XPBEH(KFL)+XPDIR(KFL) IF(KFL.NE.0) F2GM=F2GM+CHSQ*XPF2 XPDFGM(KFL)=XPVMD(KFL)+XPANL(KFL)+XPANH(KFL) VXPDGM(KFL)=VXPVMD(KFL)+VXPANL(KFL)+VXPANH(KFL) 190 CONTINUE RETURN END