[Hps-analysis] py/pz reconstruction

[Sebouh Paul]

when using very fine binning, (less than 10 mrad) I see in the spectrum of
py/pz (which is equivalent to tan_lambda/cos(phi0) )  a sort of regular
ondulation, but only when looking at electrons in the top half of the
detector from GBL tracks.

The attached screenshots are from v0 skim of run 5772 in pass6.

One of the attached screenshots is with the seed tracks (no ondulation),
the second one is with gbl tracks (which has ondulations only in electrons
on the top half of the detector), and the third one is a finer-binned zoom
in of the second graph to highlight the ondulation.

Do any of you all have any idea what might be causing this?  This happens
in both the DST and the LCIO, so it's probably not caused by the DST-maker

Note:  I also found that if I drop the cos(phi0) from the formula that I am
plotting, I still see the ondulation, so this might just be something to do
with tanLambda, and not necessarily the combined formula
tanLambda/cos(theta)
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