[Halld-physics] [EXTERNAL] GlueX Polarization Directions

[Justin Stevens]

Hi Curtis,

Sorry, I couldn’t keep up with the rapid discussion on the eta/eta’ mailing list yesterday.  I am fine with the proposal to quote the orientations as PARA/PERP for 0/90 and -45/+45 to be consistent with our GlueX coordinate system and it hopefully makes the notation simpler for future publications.

-Justin

> On Nov 20, 2019, at 11:38 AM, Curtis A Meyer <cmeyer at cmu.edu> wrote:
> 
> Dear Colleagues -
> 
>    a discussion ensued yesterday afternoon about the direction and orientation of the four polarizations currently used in GlueX. We currently refer to 
> 0/90 and 45/135, where 0 and 135 are “Para” orientations and 90 and 45 are “Perp” orientations. There is no question that the 0/90 make sense, 
> but there was some confusion on the 45/135, which is written in a way to suggest that 45 is the para and 135 is the perp (which is backwards).
> 
> Richard pointed out that the 45/135 are reported in the accelerator system with y up and x to beam right. If you take z along the direction of the beam, this is
> a left-handed coordinate system. In GlueX, we have y up and x to beam left leading to a right handed coordinate system when z is taken along the direction 
> of the beam.  The 45/135 are reported in the accelerator system, which Richard noted would correspond to the following in the GlueX system:
> 
> 0/90 PARA has the polarization plane at 0 degrees in Hall D coords
> 0/90 PERP has the polarization plane at 90 degrees in Hall D coords
> 45/135 PARA has the polarization plane at -45 degrees in Hall D coords
> 45/135 PERP has the polarization plane at +45 degrees in Hall D coords
> This suggest that it could make sense to publish our orientations in the GlueX system rather than the accelerator system, which would mean we would 
> quote the 0/90 pair and the -45/+45 pair. 
> 
> If we do want to make such a change, we should probably agree to it very soon as we can still try to change the notation on the eta/eta-prime paper.
> Such a notational change does not affect any of our physics results, it is just a consistent reporting of published information in the GlueX coordinate 
> system.
> 
> Curtis
> 
> 
> Curtis A. Meyer | MCS Associate Dean for Research 
> The Otto Stern Professor of Physics 
> cmeyer at cmu.edu <mailto:cmeyer at cmu.edu> | 412 268 2745
> 
> Carnegie Mellon University 
> Department of Physics, Wean Hall 8414 
> 5000 Forbes Ave., Pittsburgh PA, 15213 
> www.curtismeyer.com <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.curtismeyer.com&d=DwMGaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=p3b5acpwYNkmZ3alLqoe1DpcHi6vq5JvK_7ohJe1WqI&m=gMIO7eMBrkc5-ESDAG-rwGJkMI2tMeT4eRIUOMYDyZ4&s=GJR2oiC2_krgzUF3_pn0yL_YAPnmRZjSks81gd4KQpM&e=>
> 
> 
> 
> 
> 
> _______________________________________________
> Halld-physics mailing list
> Halld-physics at jlab.org
> https://mailman.jlab.org/mailman/listinfo/halld-physics

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.jlab.org/pipermail/halld-physics/attachments/20191120/6c6afbfa/attachment.html>