STAR task force for evaluating tracking efficiency uncertainty

[Petr Chaloupka <petrchal AT rcf.rhic.bnl.gov>]

Hello Gene,

thanks for the explanation.
In my code so far I have used the first version, I believe, as that is 
what is implemented in picoDst.
I'll crosscheck and actually implement both.

Best regards,
Petr

On 14. 11. 23 16:27, Van Buren, Gene via Star-tf-trkeff-l wrote:
> A question at today's meeting was about the two ways to assign a sign to the 
> XY DCA. These are documented in 
> $STAR/StRoot/StarClassLibrary/StPhysicalHelix.cc as the functions:
>
> geometricSignedDistance()
> ...where the sign is from whether the z component of the cross product of the 
> DCA vector and the track momentum vector (this essentially says that the 
> track is moving clockwise around the vertex at the DCA point, or 
> counter-clockwise, regardless of the charge sign of the track):
>      double cross = DCAVec.x()*momVec.y() - DCAVec.y()*momVec.x();
>      double theSign = (cross>=0) ? 1. : -1.;
>      return theSign*DCAVec.perp();
>
> and
> curvatureSignedDistance()
> ...where the sign is from whether the point is inside the curvature of the 
> track, or outside the curvature, regardless of the direction the particle is 
> moving. This is essentially the geometricSignedDistance() divided by the 
> sign(-q*B) = mH:
>          return (this->geometricSignedDistance(x,y))/(this->mH);
>
> -Gene
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