[Halld-tagger] Some results on electron acceptance

[Gan, Liping]

Dear Dan,

It would be a great idea to push to 11.76 GeV if it is possible without significant additional cost. PrimEx-eta and rare decays would benifit a lot at higher energy.

Liping
________________________________________
From: halld-tagger-bounces at jlab.org [halld-tagger-bounces at jlab.org] On Behalf Of Daniel Sober [sober at cua.edu]
Sent: Thursday, June 28, 2012 12:05 PM
To: Richard Jones
Cc: Hall D beam working group
Subject: Re: [Halld-tagger] Some results on electron acceptance

Dear Alex and Richard,
Sorry for the error.  I should get a full set of magnet dimensions so that I can do things correctly the first time.
Attached is the calculation for the 3 cm gap.  If there is any dedicated amorphous-radiator running with interest in the endpoint region, one could improve things by putting the radiator closer:  a distance of 1.5 m (instead of 3.19 m) would increase the gap acceptance from .858 to .948 at k/E0 = 0.980 and from .895 to 0.962 at k/E0=0.975 (11.7 GeV) without substantially changing the energy resolution all the way down to the microscope.
My primary goal in resuscitating these codes is to work out the counter placement at the high energies.  Should I consider pushing to .980 (11.76 GeV)?
Dan

On 6/27/2012 9:22 PM, Richard Jones wrote:
Dan,

Some things to keep in mind:

 1.  remember the quadrupole is vertically focusing, and can be tuned to improve things near the endpoint when the physics requires endpoint energies
 2.  the gap is 3cm
 3.  there is significant scraping at 11.7 GeV under GlueX running conditions
 4.  we chose 11.7 GeV because things get impossible above that, even with the quad

-Richard J.

 1.  On 6/27/2012 4:49 PM, Daniel Sober wrote:

I have put the current tagger magnet into my old codes and come up with at least one interesting result that needs investigating:  Using a realistic bremsstrahlung calculation integrated over photon angles (Maximon and Lepretre, 1985) for an amorphous gold radiator,
the fraction of the bremsstrahlung electron cone clearing the 2 cm magnet gap gets bad rather quickly as k/E0 > 0.95, with only 81% transmitted at k/E0 = 0.98.  See the attached files, one for the full range and the other in fine steps near the endpoint. Some of the numbers in the header (especially "FULL-ENERGY ANGLE") may not make sense to you, but they generate what we need.  The second column (Gap frac.) gives the fraction of electrons clearing the 2 cm gap, neglecting the Rogowski chamfer which will make things a little better -- I will need a detailed drawing of the pole shape to account for this effect.  The subsequent columns give the fraction passing through a given detector full width.  (The "negative" fractions just flag the cases where the magnet gap is the limiting aperture.)

I am not set up to calculate coherent bremsstrahlung or the effect of photon collimation, but with some work I could plug in the appropriate electron angular distributions if I had them.

Dan

--
Daniel Sober
Professor
Physics Department
The Catholic University of America
Washington, DC 20064
Phone: (202) 319-5856, -5315
E-mail: sober at cua.edu<mailto:sober at cua.edu>



--
Daniel Sober
Professor
Physics Department
The Catholic University of America
Washington, DC 20064
Phone: (202) 319-5856, -5315
E-mail: sober at cua.edu<mailto:sober at cua.edu>