Hi,
I agree w/Doug and Tancredi on this issue, and hopefully this very
thoughtful compromise can appease us all! We can continue to use
'varphi' as track parameters in the working code (generators,
reconstruction, analysis), and still use the existing conventions of
TBLGeometry and geant, and then report our answers to Phys.Rev.Lett and
Nature (hopefully very soon) as they expect.
Having these two convensions coexist in the code is not a problem at
all, since they are used in different places. 'varphi' is useful mainly
as a track parameter. Also, remember that they are the SAME variable
(phi=10 is the same as varphi=10), just with different range. It is NOT
a rotation about the z-axis.
I hope I have not been overbearing on the issue, but I want to
re-summarize the arguments for which we are required to place the branch
cut on 'varphi' at -90deg in the analysis software. These are not just
issues of 'pretty' or 'nice', or even 'a little less work', but are
fundamental, based on the principle of parameterizing you dataset with a
continuous variable:
a) in monte carlo: one needs to integrate the cross section over phi in
each sector: -25..25, and 155..205 degrees
b) in reconstruction you need to make small adjustments to phi while
fitting for the track. (i.e. +1 -> -2 deg)
c) (Doug) averaging several azimuthal angles in a track.
d) (Chi) analysis: zooming in on a small region around 0deg.
e) making a continuous transformation of phi (for instance converting it
to y_tof)
--Chris
Douglas Hasell wrote:
> Hi,
>
> I agree with Tancredi. No reason not to have two (or even more)
> variables, phi [0,360) and varphi (-90,270]. People just have to be
> careful to document their code and specify which range they are using.
>
> So I would propose that people who use [0,360) should use the name phi
> as that is the standard definition in all the texts and people using
> (-90,270] change the name to varphi so that the meaning is a bit more
> clear to someone else coming and reading the code.
>
> Cheers,
> Douglas
>
> 26-415 M.I.T. Tel: +1 617 258 7199
> 77 Massachusetts Avenue Fax: +1 617 258 5440
> Cambridge, MA 02139, USA E-mail: hasell@mit.edu
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