Re: Bug in TVector3::PseudoRapidity() ?

From: Nick van Eijndhoven (Nick@phys.uu.nl)
Date: Wed Oct 20 1999 - 17:12:01 MEST


Dear friends,
Note that for the pseudo-rapidity (eta) one can write

eta=-log(tan(theta/2.))

where theta is the angle (in rad) w.r.t. the beam direction.

This makes things a lot easier.
Realize however, that by introducing a GetPseudoRapidity()
memberfunction one imposes the user to define the z-axis
as the beam direction. This may sometimes give limitations.
I would say it's better to provide 3-vector components
and let the user determine the pseudorap. him/her self.  

                                            Cheers,
                                             Nick. 

"M. Sievers" wrote:
> 
> Hi,
> 
> it seems to me that the PseudoRapidity in 2.23/04 has a bug. Is there a
> minus sign missing? See below the line I changed to get it working.
> 
> Bye,
> Mike
> 
> 
> *** PHYSICS_Vector3.cxx.orig    Wed Oct 20 14:32:22 1999
> --- PHYSICS_Vector3.cxx Wed Oct 20 14:33:08 1999
> ***************
> *** 274,280 ****
>     //return 0.5*log( (m+fZ)/(m-fZ) );
>     // guard against Pt=0
>     double cosTheta = CosTheta();
> !   if (cosTheta*cosTheta < 1) return 0.5* TMath::Log(
> (1.0-cosTheta)/(1.0+cosTh
> eta) );
>     Warning("PseudoRapidity","transvers momentum = 0! return +/- 10e10");
>     if (fZ > 0) return 10e10;
>     else        return -10e10;
> --- 274,280 ----
>     //return 0.5*log( (m+fZ)/(m-fZ) );
>     // guard against Pt=0
>     double cosTheta = CosTheta();
> !   if (cosTheta*cosTheta < 1) return -0.5* TMath::Log(
> (1.0-cosTheta)/(1.0+cosT
> heta) );
>     Warning("PseudoRapidity","transvers momentum = 0! return +/- 10e10");
>     if (fZ > 0) return 10e10;
>     else        return -10e10;
> 
> --------------------------------------------------------------------------
> Michael Sievers
> Michael.Sievers@desy.de
> --------------------------------------------------------------------------
> esa$ gcc -Wall -o ariane5 ariane4.c
> ariane4.c: 666: warning: long float implicitly truncated to unsigned type
> esa$ ariane5




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