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[Te-Chuan Huang <tchuang.phys AT gmail.com>]

Hi Jason and Guannan,

Thanks a lot for your detailed explanation.
It is much clearer for me now.

Thanks,
Te-Chuan

> On May 20, 2019, at 6:16 PM, Jason C. Webb <jwebb AT rcf.rhic.bnl.gov> wrote:
> 
> Hi All,
> 
> Yes, was not on this list until now.  So to answer the questions...
> 
> 1) Why were the disks rastered?
> 
> When the strips are perfectly aligned from disk to disk, and the event
> vertex is perfectly along the z-axis, and you have high enough momentum
> tracks that they really don't bend much... then you have zero sensitivity
> to the momentum of the track, and the fit becomes degenerate.
> 
> "Rastering" was an intentional misalignment of the disks from station to
> station in order to break that degeneracy.
> 
> 2) Hit errors...
> 
> The setHitPositionError fills in a vector which is never used in the fitting
> code.  In our first attempts to get forward tracking to work, we passed 
> (dr,dphi,deta)
> to the tracker this way.  Later we calculated the hit error matrix 
> explicitly and
> passed it through the hit, which is where this Hack1to6 method comes in.
> 
> Cheers,
> Jason
> 
> 
> 
> 
> On 5/20/19 4:30 PM, Zhenyu Ye wrote:
>> Not until now!
>>> On May 20, 2019, at 3:20 PM, Aschenauer Elke-Caroline <elke AT bnl.gov> 
>>> wrote:
>>> 
>>> 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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>>>> Star-fst-l AT lists.bnl.gov
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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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