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[Zhenyu Ye <yezhenyu2003 AT gmail.com>]

Hi Jason, thanks for the slides. They are helpful. 

Te-Chuan, can you please turn on/off the rastering and see if you can 
reproduce Jason’s observation?

Thanks and Best,
Zhenyu

> On May 21, 2019, at 12:00 PM, Jason C. Webb <jwebb AT rcf.rhic.bnl.gov> wrote:
> 
> Hi Zhenyu,
> 
> It took a bit of archaeology, but I was able to recover the plots.  You can 
> find them here with a bit of text added for context:
> https://drupal.star.bnl.gov/STAR/blog/jwebb/fts-plots-circa-1212015
> 
> I was clear yesterday on why we introduced rastering.  It was not 
> introduced to misalign the detector.
> Rastering *is* a misalignment of the detector.  We introduced rastering in 
> order to create
> a stereo angle between the phi strips from plane to plane.  This was 
> necessary to prevent degenerate
> fits for tracks which fired the same phi strip in each plane.
> 
> Cheers,
> Jason
> 
> 
> 
> 
>> On 5/20/19 10:15 PM, Zhenyu Ye wrote:
>> 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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