Re: [Brahms-dev-l] definition of angle phi in FS

Thanks Selemon for poiting out the mistake;  in the first case the global
system has a regular phi definitions such that y>0 corresponds to phi's of ~
170-180.

I wrote the comment up as a one-page note that is attached. Hopefully this
is free of errors.
regards
    Flemming

----------------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory

e-mail: videbaek@bnl.gov
phone: 631-344-4106
----- Original Message ----- 
From: "Selemon Bekele" <bekele@pacific.mps.ohio-state.edu>
To: "flemming videbaek" <videbaek@rcf.rhic.bnl.gov>
Cc: "devlist" <brahms-dev-l@lists.bnl.gov>
Sent: Thursday, December 23, 2004 12:07 PM
Subject: Re: [Brahms-dev-l] definition of angle phi in FS


>
> Hi Flemming,
>
> thanks for the explanation regarding the phi angle. I have a few
> questions though:
>
> > 1) The official coordinate system has Z along the beam axis pointing
'north' along the FS. Y point towards the heavens
> > and X toward the MRS spectrometer. This is what is used by BRAG (GEANT)
and thus for
> > FS it implies that for track
> >    y> 0 -> phi is in range 180-190
> >    y< 0 -> phi is in range 170-190
>
> I thought that if phi is measured from the positive X-axis, and Y being
> upward,
>
>
>     y> 0 -> phi is in range 170-180
>     y< 0 -> phi is in range 180-190
>
> assuming the FS is symmetric about the XZ plane.
>
>
> >
> > 2) The   tracking code calculates phi,theta from the vector connecting
the vertex and the entrance to D1, but has implemented this using atan..
rather than atan2 and thus resulting
> >    y>0 -> phi in range of -10-0 (negative)
> >    y<0 -> phi ~ -10-0
> >    thus phi(reco) = pi-phi(geant)
>
> should this be
>
> phi(reco) = phi(geant) - pi
>  so that
> phi(geant) = phi(reco) + pi
>
> This seems to be the case looking at my phi distributions before and after
> reconstruction
>
>
> Selemon,
>
> >
> >
> > ----------------------------------------------------------------
> > Flemming Videbaek
> > Physics Department
> > Brookhaven National Laboratory
> >
> > e-mail: videbaek@bnl.gov
> > phone: 631-344-4106
>

_______________________________________________
Brahms-dev-l mailing list
Brahms-dev-l@lists.bnl.gov
http://lists.bnl.gov/mailman/listinfo/brahms-dev-l