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[Aschenauer Elke-Caroline <elke AT bnl.gov>]

Dear Guannan and Te-Chuan,

is Jason subscribed to this email list?

Cheers elke

On May 20, 2019, at 15:28, Guannan Xie <xieguannanpp AT gmail.com> wrote:

Hi Te-Chuan,

Let me try to answer these questions first base on my understands, but definitely, Jason's answer is more than welcome since he designed this code structure.

For the first question, there are some previous studies can be found in the previous fts review. It was inherited from that, you may try turning it off to see whether there is an impact or not if you like.

https://drupal.star.bnl.gov/STAR/future/proposals/forward-upgrade-project

For the second question, i am not sure why it was designed like that, but you may see the ErrorMatrix was propagated in the hack code. "Hack1to6()"

Regards,

Guannan

 

On Mon, May 20, 2019 at 1:19 PM Te-Chuan Huang <tchuang.phys AT gmail.com> wrote:

Hi Guannan (and maybe Jason),

I have basically finished implementing the current mechanical design into AgML geometry.
Now, I am working on modifying the fast simulator according to the new geometry.
However, I met few questions and need some helps from you:

1.) There is one procedure in the simulator that I can not fully understand.
The simulator reconstructed the hits followed the procedure below:
First, shifted the GEANT hit by:
        xc = mRaster * TMath::Cos(idisk * 60 * TMath::DegToRad());
        yc = mRaster * TMath::Sin(idisk * 60 * TMath::DegToRad());
and then,
        xx = x - xc;
        yy = y - yc;
Second, use xx and yy to find the corresponding segment on the disk.
Third, find the middle point of the corresponding segment (r0 for the radius and p0 for the azimuthal angel).
Finally, shifted back the hit position by:
        x0 = r0 * cos(p0) + xc;
        y0 = r0 * sin(p0) + yc
where x0 and y0 are the finally reconstructed hit position in x-axis and y-axis.
Somewhere in the codes commented this shift as “Raster each disk by 1mm, 60 degree offset for every disk”.
But I can not understand why do we need this “raster” procedure.

2.) Second question is about the assignment of the hit position error.
I found in the codes, because of the design of silicon strips, first find the error on the radius and azimuthal direction (dr and dphi).
In the end, radius and the azimuthal angel are transform to x and y position.
But somehow the dr and dphi are directly assigned as the error on the x-direction and y-direction, respectively.
Any assumption or approximation is applied on this error assignment?

Cheers,
Te-Chuan
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--

===========================
Guannan Xie
Department of Physics
University of Illinois at Chicago
845 West Taylor Street, 2262 SES, MC 273
Chicago, Illinois 60607-1234
Tel: +1-510-965-8919
Email: xieguannanpp AT gmail.com
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