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[Zhenyu Ye <yezhenyu2003 AT gmail.com>]

Jason, do you have comparison plots in forward tracking performance between 
ideal versus rastered geometries? 

We should revisit this when we have the new tracker. Although in reality, we 
won’t be able to put our detectors in their ideal positions, we can certainly 
do better than 1mm. Whether and how much we should it is not clear to me. 

Best,
Zhenyu

> On May 20, 2019, at 5:16 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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>>>> 
>>>> -- 
>>>> 
>>>> 
>>>> ===========================
>>>> 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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