Re: Vote for -90 to 270 Re: [BLAST_ANAWARE] branch line in azimuthal angle

From: Tancredi Botto (tancredi@mitlns.mit.edu)
Date: Thu Apr 03 2003 - 12:04:52 EST


Hello: I think there are two valid points for a using a different phi
definition: uniform steps in the fitter and possibly phi averaging.
Discussing at lenght whether a cut is defined as (x>0 && x<1) instead
of (x>0.5) is just too much... and is anyways not a valid reason (a cut
on cos(phi) is just as good).

I think we agreed there was no problem in having two variables defined:
phi and varphi.

_ Phi is 0-360, is what blastmc uses, is how theorethical calcs are made,
  is what you use in the q-reference system (phi_pq) and is what the rest
  of the world uses and expect.

_ Varphi can be -90, 270 or whatever definition may become useful. I agree
  it is the most natural variable for tracks, See above.

So I vote very much against dephasing Phi and go changing the montecarlo
in the process. I feel it would only be an intellectual virtuosism. I
have no problems in defining new variables: we do that all the times.

Things must be obvious if you use a different name (varphi) for a different
definition (-90, 270). And it is not true that with two definitions you
double the work, because a lot of codes (e.g. MC) are already written for
Phi so you save that part.

If anybody thinks there are problems let's discuss this further.

-- 
________________________________________________________________________________
Tancredi Botto,  		phone: +1-617-253-9204  mobile: +1-978-490-4124
research scientist		MIT/Bates, 21 Manning Av    Middleton MA, 01949
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On Wed, 2 Apr 2003, zhangchi wrote:

> > Hi, > > Sorry I did not come to the meeting this morning. But I have voiced my > opinion yesterday when meeting with Tong, Wang and Chris that I am 100% > against using 0-360 degrees. > > The -90 to 270 convention has been in use all the past years, and I think > it is the most natural way to present the geometry of Blast detector. By > using 0-360, we are cutting the left sectors into two halves which I think > is looking for trouble. The seeming beauty of the "standard" notation > really do not worth the trouble. > > Another reason to use -90 to 270 is: when doing analysis, cut on sectors > will be simply phi<90. while using 0-360, it is a two way comparison. > > Chi > > On Wed, 2 Apr 2003, Douglas Hasell wrote: > > > Hi, > > > > Unfortunately I have thought of a plausible reason for using the > > range [-90,270) for the azimuthal angle which Chris suggested today. > > > > Something that we might do rather naively for a given track is > > determine its azimuthal angle by taking the average of the azimuthal angles > > for the track segments which make up the track. So if the track segments > > have azimuthal angles 1, 359, 0 for example, then the average (180) clearly > > isn't what we want. > > > > Hopefully people are clever enough to avoid this sort of error but > > I can imagine it slipping through on occasion. > > > > Not saying I'm convinced we should start changing code yet but > > maybe.... > > > > 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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