* * $Id: zdecay.F,v 1.1.1.1 1996/01/11 14:14:44 mclareni Exp $ * * $Log: zdecay.F,v $ * Revision 1.1.1.1 1996/01/11 14:14:44 mclareni * Cojets * * #include "cojets/pilot.h" SUBROUTINE ZDECAY(QP,QM,QK) C *************************** C------------------------------------------------------------ C LEPTONIC DECAY OF Z0 BOSON PRODUCED FROM Q QBAR PAIR C C AUTHORS F.A.BERENDS AND R.KLEISS C C INFORMATION ON THIS PROGRAM IS FOUND IN C F.A. BERENDS AND R. KLEISS, "HARD PHOTON CORRECTIONS IN C W AND Z DECAY ", LEIDEN UNIVERSITY PREPRINT (1983). C PLEASE REFER TO THIS PAPER WHEN USING THIS PROGRAM | C C C PARAMETERS: S (CM ENERGY OF LEPTON PAIR SQUARED IN GEV**2); C XM (LEPTON MASS IN GEV) C CVL,CAL (LEPTON VECTOR/AXIAL VECTOR COUPLING) C CVQ,CAQ (SAME FOR QUARK) C QQ (QUARK ELECTRIC CHARGE) C XMZ,XGZ (Z0 MASS AND WIDTH IN GEV) C THESE PARAMETERS MUST BE SUPPLIED IN THE COMMON 'PARRAM' C FOR THE CONVENTIONS OF THE COUPLING CONSTANTS, SEE C F.A.BERENDS,R.KLEISS AND S.JADACH, C NUCL.PHYS.B202(1982)63-88,TABLE ON PAGE 83. C THIS GIVES THE CONVENTIONS IN THE GLASHOW-WEINBERG-SALAM C 'STANDARD MODEL' C----------------------------------------------------------- IMPLICIT DOUBLE PRECISION (A-H,O-Z) C-- C-- Q0 IS THE ENERGY CUTOFF C-- #if defined(CERNLIB_SINGLE) REAL CJRN,P,PJTOT,W,WL #endif #if defined(CERNLIB_DOUBLE) DOUBLE PRECISION CJRN,P,PJTOT,W,WL #endif #include "cojets/itapes.inc" #include "cojets/parram.inc" #include "cojets/photon.inc" DIMENSION QP(4),QM(4),QK(4) DATA INITI /0/ IF(INITI.NE.0) GOTO 1000 C----------------------------------- INITIALIZATION STEP --- INITI=1 WCUMUL=0. ICUMUL=0 ONE = 1. EB=.5*SQRT(S) XM2=(XM/EB)**2 BARN=3.8938D+05/EB**2 C------------------------------- XK0=ENERGY CUTOFF / BEAM ENERGY XK0=Q0/EB PIG=4.*ATAN(ONE) A0=(CVL**2+CAL**2)*(CVQ**2+CAQ**2) B0=8.*CVL*CAL*CVQ*CAQ FCMAX=2.*A0+ABS(B0) Z2=16.*((1.-XMZ**2/S)**2 + (XMZ*XGZ/S)**2) C TOTAL LOWEST ORDER CROSS SECTION SIG0=16.*ALFA**2*PIG*QQ**2*A0/Z2*BARN/3.D0 C TOTAL WITH SOFT + VIRTUAL CORRECTIONS XLS=LOG(4./XM2) SIGS=SIG0*( 1. + 2.*ALFA/PIG* . ( LOG(XK0)*(XLS-1.) + 3./4.*XLS + PIG**2/6. - 1.) ) C TOTAL APPROXIMATE HARD CROSS SECTION SIGH=SIG0* 2.*ALFA/PIG*( -LOG(XK0)*XLS - PIG**2/6. ) C CORRECTIONS DELS=(SIGS/SIG0-1.)*100. DELH=(SIGH/SIG0 )*100. DELT=DELS+DELH C FRACTION OF HARD EVENTS IN TRIAL SAMPLE FRHRD=DELH/(100.+DELT) WMAX=1.05D0 C WRITE(ITLIS,1) EB,XM2,BARN,XK0,A0,B0,FCMAX,Z2,FRHRD,WMAX, C . S,XM,CVL,CAL,CVQ,CAQ,QQ,XMZ,XGZ, C . SIG0,SIGS,SIGH,DELS,DELH,DELT 1 FORMAT(1H0,96(1H-),/, . 12X,30H THIS IS ROUTINE ''ZDECAY'' | ,/, . 1X,8D12.4,/,1X,2F12.4,/, . 1X,27HCENTRE OF MASS ENERGY ,D12.4,7H GEV**2 ,/, . 1X,27HMASS OF LEPTON ,D12.4,4H GEV ,/, . 1X,27HLEPTON COUPLING: VECTOR ,D12.4,/, . 1X,27H AXIAL V. ,D12.4,/, . 1X,27HQUARK COUPLING : VECTOR ,D12.4,/, . 1X,27H AXIAL V. ,D12.4,/, . 1X,27HQUARK E.M. CHARGE ,D12.4,/, . 1X,27HZ0 BOSON : MASS ,D12.4,4H GEV ,/, . 1X,27H WIDTH ,D12.4,4H GEV ,/, . 1X,27HLOWEST ORDER CROSS SECTION ,D12.4,9H NANOBARN ,/, . 1X,27HWITH SOFT + VIRTUAL CORR. ,D12.4,9H NANOBARN ,/, . 1X,27HAPPROXIMATE HARD CONTRIB. ,D12.4,9H NANOBARN ,/, . 1X,27HSOFT PHOTON CORRECTION ,F12.4,8H PERCENT ,/, . 1X,27HHARD APPROX.CORRECTION ,F12.4,8H PERCENT ,/, . 1X,27HTOTAL CORRECTION (APPR.) ,F12.4,8H PERCENT ) C-------------------------------------------------------------- 1000 CONTINUE C------------------------ START OF EVENT GENERATION STEP ------ C GENERATE VALUE OF QP SOLID ANGLE (BOTH HARD OR SOFT) 2 C= -1. + 2.*CJRN(1.) WC= (A0*(1.+C*C)+B0*C)/FCMAX IF(WC.LT.CJRN(2.)) GOTO 2 SC=SQRT(1.-C*C) FC=2.*PIG*CJRN(3.) CFC=COS(FC) SFC=SIN(FC) C------------------------ CHOSE BETWEEN HARD AND SOFT PART ---- IF(CJRN(4.).GT.FRHRD) GOTO 2000 C------------------------ HARD PART CHOSEN ----------------------- C ADD TO EVENT COUNTER FOR FINDING REAL CROSS SECTION ICUMUL=ICUMUL+1 C GENERATE VALUE FOR K 3 XK=XK0**CJRN(5.) WK=1. + LOG(1.-XK)/XLS IF(WK.LT.CJRN(6.)) GOTO 3 C GENERATE VALUE FOR FG FG=2.*PIG*CJRN(7.) CFG=COS(FG) SFG=SIN(FG) C GENERATE VALUE FOR Y1 YMIN=XM2*XK/(2.*(1.-XK)) YMAX=2.*XK+YMIN Y1=YMIN* (YMAX/YMIN)**CJRN(8.) IF(CJRN(9.).GT.0.5D0) Y1=YMAX-Y1 C CONSTRUCT MOMENTA AND CHECK ON KINEMATICS BY MASS SHELL X=1.-XK+.5*(Y1-YMIN) CG=(2.*(1.-XK)/X-2.+XK)/XK SG=(1.-CG*CG) IF(SG.LT.0.D0) CG=CG/ABS(CG) SG=SQRT(1.-CG*CG) SG=DSQRT(1.-CG*CG) C QK VECTOR QK(4)=XK QK(3)=XK*(C*CG-SC*SG*CFG) QK(2)=XK*((C*SG*CFG + SC*CG)*SFC + SG*SFG*CFC) QK(1)=XK*((C*SG*CFG + SC*CG)*CFC - SG*SFG*SFC) C QP VECTOR QP(4)=X QP(3)=X*C QP(2)=X*SC*SFC QP(1)=X*SC*CFC C QM VECTOR DO 4 I=1,4 4 QM(I)=-QP(I)-QK(I) QM(4)=2.+QM(4) C CHECK ON MASSES XMK=QK(4)**2-QK(3)**2-QK(2)**2-QK(1)**2 XMP=QP(4)**2-QP(3)**2-QP(2)**2-QP(1)**2 XMM=QM(4)**2-QM(3)**2-QM(2)**2-QM(1)**2 C----------------------------------- CALCULATE WEIGHT ---- C1=-QM(3)/QM(4) Y2=YMAX-Y1 WW=(QM(4)**2*(A0*(1.+C1*C1) + B0*C1)*(1. - XM2*Y2/(2.*Y1) )+ . QP(4)**2*(A0*(1.+C*C ) + B0*C )*(1. - XM2*Y1/(2.*Y2) )) . /(2.*(A0*(1.+C*C)+B0*C) ) C----------------------------------- REJECTION POINT ----- C CUMULATE WEIGHTS WCUMUL=WCUMUL+WW WSOFAR=WCUMUL/ICUMUL DSOFAR=WSOFAR*DELH IF(CJRN(10.).GT.(WW/WMAX)) GOTO 1000 GOTO 3000 C------------------------------------------------- SOFT PART CHOSEN ---- C APPLY IMMEDIATE REJECTION 2000 IF(CJRN(11.).GT.(1./WMAX)) GOTO 1000 QP(4)=1. QP(3)=C QP(2)=SC*SFC QP(1)=SC*CFC QM(4)=1. DO 5 I=1,3 5 QM(I)=-QP(I) DO 6 I=1,4 6 QK(I)=0.D0 C----------------------------------- SCALE MOMENTA ------- 3000 DO 7 I=1,4 QP(I)=EB*QP(I) QM(I)=EB*QM(I) 7 QK(I)=EB*QK(I) RETURN END