* * $Id: wdecay.F,v 1.1.1.1 1996/01/11 14:14:43 mclareni Exp $ * * $Log: wdecay.F,v $ * Revision 1.1.1.1 1996/01/11 14:14:43 mclareni * Cojets * * #include "cojets/pilot.h" SUBROUTINE WDECAY(QE,QN,QK) C *************************** C------------------------------------------------------------ C LEPTONIC DECAY OF W- 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 XMW,XGWTOT (W MASS AND WIDTH IN GEV) C THESE PARAMETERS MUST BE SUPPLIED IN THE COMMON 'PRMSWD' C----------------------------------------------------------- C IT IS ASSUMED THAT THE QUARKS ARE IN THEIR CMS SYSTEM. C INITIAL STATE CORRECTIONS LIKE SOFT GLUON EMISSION ARE C NOT INCLUDED. C THE EFFECT OF THE CABIBBO ANGLE IS INCLUDED. C THE MASS AND WIDTH OF THE W ARE ASSUMED TO BE RELATED C TO EACH OTHER BY THE SIMPLE WEINBERG-SALAM RULE; THIS C IS A VERY GOOD APPROXIMATION AS SHOWN BY CONSOLI ET AL. C THE COUPLING CONSTANTS OF THE LEPTONS ARE DEFINED TO C BE SUCH THAT THEY YIELD PRECISELY THE GIVEN LEPTONIC C WIDTH IF WE NEGLECT THE (VERY TINY) COMPLETE QED EFFECT. C IN ORDER TO GET THE EVENT SAMPLE FOR W+ EVENTS, ALL C FOUR-MOMENTA ARE TO BE INVERTED (EXCEPT THE ENERGIES, C OF COURSE), AND ALL PARTICLES RELABELLED AS THEIR C ANTIPARTICLES. C--------------------------------------------------------WDECAY. IMPLICIT DOUBLE PRECISION (A-H,O-Z) #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/photon.inc" #include "cojets/prmswd.inc" DIMENSION QE(4),QN(4),QK(4) DATA INITI /0/ IF(INITI.NE.0) GOTO 1000 C------------------------------- INITIALIZATION ---------------- INITI=1 C SOME CONSTANTS EB=SQRT(S)/2. C-- ALFA INITIALIZED BY COMMON PIG=3.1415926536D0 BARN=3.8937D+05/EB**2 XM2=(XM/EB)**2 XL=LOG(4./XM2) XK0=Q0/EB C SOME CONSTANTS CONNECTED WITH W BOSON XMU=37.281D0 SINW=XMU/XMW XGW=ALFA/12.*XMW**3/XMU**2 XGCOR=1.+ALFA/PIG*(77./24D0-PIG**2/3.D0) XGW=XGW*XGCOR FRHARD=ALFA/PIG*(LOG(1./XK0)*(XL-2.) . -3./4.*XL - PIG**2/6.D0 + 53./24.D0) FRHARD=FRHARD/XGCOR C FERMION COUPLING CONSTANTS TO W C REMEMBER SUPPRESSION OF QUARK COUPLING BY C THE COSINE OF THE CABIBBO ANGLE EQED=SQRT(4.*PIG*ALFA) GL=EQED/SQRT(8.)/SINW GQ=GL*0.973D0 C C WRITE(ITLIS,1) 1 FORMAT(1H0,90(1H-),/, . 29H0 THIS IS ROUTINE ''WDECAY'' ) C LOWEST ORDER CROSS SECTION W2=16.*((1.-XMW/S)**2 + (XMW*XGWTOT/S)**2) SIG0=1./(3.*PIG) . *(GL*GQ)**2 . *4./W2 . *BARN C C WRITE(ITLIS,2) S, XMW, XM,XGWTOT, EB, ALFA, C . PIG, BARN, XM2, XL, XK0, XMU, C . SINW, XGCOR, XGW,FRHARD, EQED, GL, C . GQ, W2, SIG0 2 FORMAT(1H0,6D15.6) C WRITE(ITLIS,21) XMW,XGWTOT,XGW,SIG0,XK0,FRHARD 21 FORMAT(1H0,90(1H-),/, . 39H MASS OF W- BOSON =,F15.6,4H GEV,/, . 39H TOTAL WIDTH OF W- BOSON =,F15.6,4H GEV,/, . 39H LEPTONIC WIDTH (+ QED CORRECTION) =,F15.6,4H GEV,/, . 39H LOWEST ORDER PRODUCTION CROSSECTION =,D15.6,3H NB,/, . 36H MINIMUM ENERGY OF ''HARD'' PHOTONS ,/, . 39H IN FRACTIONS OF SQRT(S)/2 =,F15.6,/, . 39H FRACTION OF HARD BREMSSTRAHLUNG =,F15.6) C------------------------------ END OF INITIALIZATION ----------- 1000 CONTINUE C------------------------------ GENERATION STEP ----------------- C CHOOSE BETWEEN HARD OR SOFT IF(CJRN(1.).LT.FRHARD) GOTO 2000 C----------------------------- START OF SOFT PART ----------------- C GENERATE ANGLES CN=1.-2.*CJRN(2.)**(1./3.D0) SN=SQRT(1.-CN*CN) C CONSTRUCT MOMENTA WITHOUT NORMALIZATION AND TRIVIAL ROTATION QN(4)=1. QN(3)=CN QN(2)=0. QN(1)=SN QE(4)=1. QE(3)=-CN QE(2)=0. QE(1)=-SN DO 3 I=1,4 3 QK(I)=0. GOTO 3000 C----------------------------- END OF SOFT PART ------------------- 2000 CONTINUE C----------------------------- START OF HARD PART ----------------- C GENERATE VALUES FOR XK AND V1 USING APPROXIMATION 4 XK=XK0**CJRN(3.) XKM=1.-XK V1=XK*(XM2/(4.*XKM))**CJRN(4.) C DEFINE F1 AS FOUR TIMES FI(1) OF NOTES F1=(4. - 4.*XK + 4.*V1 + 2.*XK**2 - 6.*XK*V1 + 8.*V1**2)/(XK*V1) . -XM2/V1**2 . -4.*(1.+V1**2)/XK**2 C REJECT UNTIL V1 AND K ACCEPTED WKV=XK*V1/4.*F1 IF(WKV.LT.2.D0*CJRN(5.)) GOTO 4 C C TAKE RANDOM VALUES FOR CN AND FG 5 CN=-1.+2.*CJRN(6.) FG=2.*PIG*CJRN(7.) SN=SQRT(1.-CN*CN) CFG=COS(FG) C CALCULATE VARIOUS DOT-PRODUCTS VG=2.*V1*(1.-XK)/(XK*(1.-V1)) CG=VG-1. SG=SQRT(VG*(2.-VG)) Z= CN*CG + SN*SG*CFG V=1.-V1 QQ=4. QPU=2. QPD=2. QPN=2.*V QKK=2.*XK QPE=QQ-QPN-QKK PUPN=V*(1.+CN) PDPN=V*(1.-CN) PUK =XK*(1.+Z) PDK =XK*(1.-Z) PUPE=QPU-PUPN-PUK PDPE=QPD-PDPN-PDK PEK =2.*V1 PNK =2.*(XK-V1) PEPN=2.*XKM C CALCULATE MULTIDIFFERENTIAL DISTRIBUTION C YB= -XM2*PDPN**2/PEK**2 C . +( PDPN*( QQ/2.*(PUPE+PUK) + PUPE*QPE C . -PEK*(QPU +PUK) ) C . +PUPE*( PEPN*PDK - PDPE*PNK ) )/(PEK*QKK) C . +( PDPN*( -QQ*PUPE - PUK*QPE + PEK*QPU + PUK*PEK) C . +PUPE*( QPD*PNK - QPN*PDK + PDK*PNK ))/QKK**2 YB= -XM2*PDPN**2/PEK**2 . + QQ*PNK/(2.*QKK**2*PEK)*(PUPE**2+PDPN**2) C CALCULATE WEIGHT: REJECT UNTIL ANGLES ACCEPTED WANGL=YB/F1 IF(WANGL.LT.2.D0*CJRN(8.)) GOTO 5 C C CONSTRUCT MOMENTA UNNORMALIZED AND UNROTATED QN(4)=V QN(3)=V*CN QN(2)=0. QN(1)=V*SN QK(4)=XK QK(3)=XK*Z QK(2)=XK*SG*SIN(FG) QK(1)=XK*(SN*CG - CN*SG*CFG) DO 6 I=1,4 6 QE(I)= -QN(I) - QK(I) QE(4)=2.+QE(4) C CHECK ON MASSES XMN=QN(4)**2-QN(3)**2-QN(2)**2-QN(1)**2 XMK=QK(4)**2-QK(3)**2-QK(2)**2-QK(1)**2 XME=QE(4)**2-QE(3)**2-QE(2)**2-QE(1)**2 C---------------------------- END OF HARD PART ----------------- 3000 CONTINUE C NORMALIZE AND ROTATE VECTORS DO 7 I=1,4 QN(I)=EB*QN(I) QK(I)=EB*QK(I) 7 QE(I)=EB*QE(I) FI=2.*PIG*CJRN(9.) CF=COS(FI) SF=SIN(FI) QN1 = QN(1)*CF + QN(2)*SF QN(2)= -QN(1)*SF + QN(2)*CF QN(1)= QN1 QK1 = QK(1)*CF + QK(2)*SF QK(2)= -QK(1)*SF + QK(2)*CF QK(1)= QK1 QE1 = QE(1)*CF + QE(2)*SF QE(2)= -QE(1)*SF + QE(2)*CF QE(1)= QE1 C RETURN END