disth.f

C this is variant SM-only. We need it inside TauSpinner `always' but may be
C it is not an appropriate place for it. 
    
      REAL*8 FUNCTION disth(S,T,H1,H2)
C***************************************************************************
C* CALCULATES DSIGMA/DT FOR GluonGluon -> TAU+TAU- VIA:
C            s-channel SM Higgs if KEY=0
C            s-channel spin2 object if KEY=1
C        S -- CM gluon-gluon ENERGY^2
C        T -- cosTheta (scattering angle of tau- with respect to gluon
C        H1 - HELICITY OF TAU-:  1=R,   -1=L
C        H2 - HELICITY OF TAU+   
C        KEY=0  SM,   KEY=1 SPIN2
C***************************************************************************

C***************************************************************************
C*                           *
C***************************************************************************

      IMPLICIT REAL*8(a-h,m,o-z)
      INTEGER h1,h2

 
!      IF(KEY.EQ.0) THEN  
!           WRITE(*,*) 'SM Higgs' 
!      ELSE IF(KEY.EQ.1) THEN 
!           WRITE(*,*) 'nonSM not ready'
!           STOP
!      ELSE
!      WRITE(*,*) 'WRONG KEY'
!      STOP
!      ENDIF



      cost=t
     
C*      ==========  Standard Model Parameters  ==========
      alphaem=1.d0/128.d0      ! at mZ
      alphas=0.112d0           ! at mZ
      gf=1.1667d-5             ! Fermi constant
      s2w = .2315d0            ! sin^2(theta_W)
      c2w = 1.d0-s2w 
      cw  = dsqrt(1.d0-s2w)
      sw  = dsqrt(s2w)
      f=1000.d0                ! scale of spin-2 physics ????

      mz = 91.187d0     ! Z mass
      wz = 2.d0         ! Z width
      mh = 125.d0       ! SM Higgs mass
      mt=173.d0         ! top quark mass
      mx=125.d0         ! spin-2 mass            choose your own       
      wx=10.d0          ! spin-2 width           choose your own
      mw = mz*cw
      pi=4.d0*datan(1.d0)
      e=dsqrt(4.d0*pi*alphaem) 
      br=  0.065d0                    ! Br(H->tautau) 




      ! SM Higgs via top quark loop

        IF(h1.EQ.-h2) THEN
           disth=0.d0           ! for spin 0 Higgs
           return 
        ELSE
           taut=mh**2/4/mt**2
           tauq=taut
           stauq=dsqrt(tauq)


           disth=gf*alphas**2/288.d0/dsqrt(2.d0)/pi*dabs(3.d0/2d0*
     .     (tauq+(tauq-1.0)*(dasin(stauq))**2)/tauq**2)**2
     .     *br/2.d0

C  Br/2 because of FB symmetry
           return
        ENDIF
      




      return
      END