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Re: Tracking at Test Beam [message #762 is a reply to message #761] Tue, 13 March 2007 03:07 Go to previous message
Messages: 125
Registered: July 2005
Location: CERN
Hello Michele,

this is a general problem with polar coordinates: Straight lines along the z axis have an undefined phi angle. In the real detector these tracks do not occur, because such particles coming from the vertex will go along the beam pipe.

The main problem will not be phi, but tan(lambda), which is infinity in this case. (tan(lambda) = p_z / p_T , and p_T = 0)
So unfortunately the LCIO track, which is designed to describe a helix caused by a B field along the z axis, is not suitable to store straight tracks in z direction.

Do you realy need the particle to go along z? A TPC will have problems with this anyway, as the track is along the drift direction. How about rotating the coordinate system? We had our test beam tracks going along y.

If you realy need a straight track along z, you could use a LCFixedObject with six floats for instance and create a "StraightTrack" class with cartesian coordinates from it, using 3 floats for a starting point (x_0, y_0, z_0) and three floats for the direction (dir_x, dir_y, dir_z).


Martin Killenberg

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