Home » PANDA » PandaRoot » Tracking » STT helix fit output parameters.
STT helix fit output parameters. [message #6560] 
Tue, 22 April 2008 12:22 
Lia Lavezzi
Messages: 291 Registered: May 2007 Location: Torino

firstgrade participant 
From: *PV.INFN.IT


Hi,
as said during the EVO meeting I write down here the output parameters of the STT reconstruction.
The helix fit parameters are the following ones: d0, phi0, R, z0, tan(lambda)
where:
 d0 is the distance of closest approach of the track to the origin (see also the attached figure);
 phi0 is the azimuthal angle of the point of closest approach [phi0 = arctan(yc/xc) with (xc, yc) = center of curvature coordinates];
 R is the curvature radius of the track in the xy plane;
 z0 is the z coordinate of the point of closest approach calculated in xy plane;
 tan(lambda) is the tangent of the dip angle, the slope of the straight line in z  track length * cos(lambda) plane.
The parameters can be accessed by the following functions:
Double_t d0 = pTrack>GetParamLast()>GetX();
Double_t phi0 = pTrack>GetParamLast()>GetY();
Double_t R = pTrack>GetParamLast()>GetTx();
Double_t z0 = pTrack>GetParamLast()>GetZ();
Double_t tanl = pTrack>GetParamLast()>GetTy();
and the transverse and longitudinal momenta can be calculated:
Double_t ptran = 0.003 * 2 * R
Double_t plong = ptran * tanl
...and, from them, finally ptot = sqrt(plong*plong + ptran*ptran)
Best regards,
Lia.
Edited on Jan 14, 2010:
The parameter access functions have changed:
Double_t d0 = pTrack>GetDist();
Double_t phi0 = pTrack>GetPhi();
Double_t R = pTrack>GetRad();
Double_t z0 = pTrack>GetZ();
Double_t tanl = pTrack>GetTanL();

Attachment: paramxy.ps
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[Updated on: Thu, 14 January 2010 16:22] Report message to a moderator



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