disth.f

00001 C this is variant SM-only. We need it inside TauSpinner `always' but may be
00002 C it is not an appropriate place for it. 
00003     
00004       REAL*8 FUNCTION DISTH(S,T,H1,H2)
00005 C***************************************************************************
00006 C* CALCULATES DSIGMA/DT FOR GluonGluon -> TAU+TAU- VIA:
00007 C            s-channel SM Higgs if KEY=0
00008 C            s-channel spin2 object if KEY=1
00009 C        S -- CM gluon-gluon ENERGY^2
00010 C        T -- cosTheta (scattering angle of tau- with respect to gluon
00011 C        H1 - HELICITY OF TAU-:  1=R,   -1=L
00012 C        H2 - HELICITY OF TAU+   
00013 C        KEY=0  SM,   KEY=1 SPIN2
00014 C***************************************************************************
00015 
00016 C***************************************************************************
00017 C*                           *
00018 C***************************************************************************
00019 
00020       IMPLICIT REAL*8(A-H,M,O-Z)
00021       INTEGER H1,H2
00022 
00023  
00024 !      IF(KEY.EQ.0) THEN  
00025 !           WRITE(*,*) 'SM Higgs' 
00026 !      ELSE IF(KEY.EQ.1) THEN 
00027 !           WRITE(*,*) 'nonSM not ready'
00028 !           STOP
00029 !      ELSE
00030 !      WRITE(*,*) 'WRONG KEY'
00031 !      STOP
00032 !      ENDIF
00033 
00034 
00035 
00036       cost=T
00037      
00038 C*      ==========  Standard Model Parameters  ==========
00039       alphaEM=1.d0/128.d0      ! at mZ
00040       alphaS=0.112d0           ! at mZ
00041       GF=1.1667D-5             ! Fermi constant
00042       S2W = .2315D0            ! sin^2(theta_W)
00043       C2W = 1.D0-S2W 
00044       CW  = DSQRT(1.D0-S2W)
00045       SW  = DSQRT(S2W)
00046       F=1000.d0                ! scale of spin-2 physics ????
00047 
00048       MZ = 91.187D0     ! Z mass
00049       wz = 2.d0         ! Z width
00050       mH = 125.d0       ! SM Higgs mass
00051       mT=173.d0         ! top quark mass
00052       mX=125.d0         ! spin-2 mass            choose your own       
00053       wX=10.d0          ! spin-2 width           choose your own
00054       MW = MZ*CW
00055       Pi=4.d0*datan(1.d0)
00056       e=dsqrt(4.d0*Pi*alphaEM) 
00057       Br=  0.065d0                    ! Br(H->tautau) 
00058 
00059 
00060 
00061 
00062       ! SM Higgs via top quark loop
00063 
00064         IF(H1.EQ.-H2) THEN
00065            DISTH=0.d0           ! for spin 0 Higgs
00066            return 
00067         ELSE
00068            tauT=mH**2/4/mT**2
00069            tauQ=tauT
00070            stauQ=DSQRT(tauQ)
00071 
00072 
00073            DISTH=GF*alphaS**2/288.d0/DSQRT(2.d0)/PI*DABS(3.d0/2d0*
00074      .     (tauQ+(tauQ-1.0)*(DASIN(stauQ))**2)/tauQ**2)**2
00075      .     *Br/2.d0
00076 
00077 C  Br/2 because of FB symmetry
00078            return
00079         ENDIF
00080       
00081 
00082 
00083 
00084 
00085       return
00086       END