Track Parameters

[Lawrence Lee]

I see that track momentum vectors are available at the particle production vertex as well as at the end of the tracker volume, but I know the full helix parameters are unavailable.

Is it at all possible to reconstruct the full track parameters (primarily interested in the impact parameters) from this information simply? What needs to be done for this to be available? It seems that all the information is available to Delphes -- no?

Thanks!

[Pavel Demin]

Normally, position of the production vertex and momentum at this position are enough to define helix.

For example, ROOT documentation contains the following

​http://root.cern.ch/root/html/THelix.html

 vt0  = TMath::Sqrt(vx0*vx0 + vy0*vy0);
 phi0 = TMath::ATan2(vy0, vx0);

 x(t) = x0 - vt0 / w * sin(-w * t + phi0)
 y(t) = y0 + vt0 / w * cos(-w * t + phi0)
 z(t) = z0 + vz0 * t