sPHENIX tracking discussion

[Michael Joseph Peters <mjpeters AT mit.edu>]

Hi all,

As suggested in the tracking meeting this morning, here's a more detailed look at the properties of secondary tracks in an event consisting of only 100 pions.

This was created using the simple event generator, 100 pi-, each with a pt of 5 GeV, using the default Fun4All macro settings for everything else.

First, the gpt distribution of secondary tracks (those labeled with gprimary==0):

As you can see, there's a significant number of secondary tracks with quite high gpt. (For the record, this plot looks identical with gtrackID<0 instead of gprimary==0.) Here's the gvz distribution for these tracks as a function of gpt (cutting off the low-gpt tracks for clarity of reading):

So the vertex of the higher-gpt content is distributed fairly uniformly throughout (and outside?) the detector. As for gvx and gvy:

Assuming that the units here are cm, as usual, this explains the last plot: these tracks are apparently starting in the calorimeters. And, sure enough, if you plot (gnlmaps+gnlintt+gnltpc) for them, you get:

Basically all zero, which confirms that these "tracks" are actually just parts of a calorimeter shower.

So, for the purposes of the dEdx plots, all you need to do is cut on whether the truth tracks have any truth hits in the tracker at all.

But more broadly: why are these defined as "truth tracks" in the SvtxEvaluator in the first place? Should they be there?

Thanks,

Michael Peters

(Plots are attached for clients that do not display inline images.)

Attachment: gnlayers.png
Description: gnlayers.png

Attachment: gvx_gvy.png
Description: gvx_gvy.png

Attachment: gvz_gpt.png
Description: gvz_gpt.png

Attachment: gpt.png
Description: gpt.png