sPHENIX MAPS tracker discussion

[Anthony Frawley <afrawley AT fsu.edu>]

Hi Yasser,

The methods I used to check the results of the Acts transformation are

get_local_from_world_coords()

get_world_from_local_coords()

I checked that they are consistent by transforming world to local coordinates and then back.

The discrepancy occurs when I take the cluster position as given by the MVTX clusterizer and transform it to local coordinates in the sensor. Our method get_local_from_world_coordinates() produces a value that is different from the Acts globalToLocal() transformation. The Acts transformation produces the identical z value, but the Acts x value is always 0.0382 mm smaller than that from get_local_from_world_coords().

The difference must be in the transformation of the sensor location into the stave coordinates, because that is the only way that the local coordinate could be different by the same amount for all clusters.

Note that the MVTX clusterizer starts by, for each hit, taking the chip number, pixel row and column and getting the local coords on the sensor, then transforming those to world coordinates using get_world_from_local_coords(). The clustering is then done in world coordinates. That means that if the get_world_from_local_coords() transformation is wrong, the cluster position is wrong.

Can you check that the transformation of the sensor location to the stave location matches what is in the geometry that we import for the stave?

Thanks

Tony

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From: sPHENIX-MAPS-l <sphenix-maps-l-bounces AT lists.bnl.gov> on behalf of Yasser Corrales Morales <ycmorales AT rcf.rhic.bnl.gov>
Sent: Sunday, May 31, 2020 11:20 AM
To: sphenix-maps-l AT lists.bnl.gov <sphenix-maps-l AT lists.bnl.gov>
Subject: Re: [Sphenix-maps-l] Issue with MVTX geometry class?

 

Hi Tony,

One question,

when you get the local position in the sensor from  world  coordinates did  you use "get_sensor_indices_from_world_coords"?

I ask you because it is a method I haven't tested before.

could you point me to the code to get ACTs surface world/local coordinates for test?

thank you,

Y.

On 5/30/20 22:29, Anthony Frawley wrote:

Dear MVTX experts,

While working on the Acts implementation, I turned up a discrepancy between the MVTX geometry extracted by Acts from our G4 model, and the description of that geometry in the geometry class "mvtx/CylinderGeom_Mvtx".

The Acts code analyzes the TGeo objects in the G4 model and extracts a "Surface" corresponding to each active detector volume. The Acts Surface class has a transformation that returns the local position on the surface corresponding to a given world position. Our geometry classes have methods that do the same thing. They get the same answer for the INTT and TPC, but do not get the same answer for the MVTX.

For the MVTX sensors, the local position is (x,z), where x is the (radius*phi) direction. The local z position agrees perfectly, but the local x position is always different by 0.03872 mm. Also, the Acts surface center in world coordinates is slightly different from the sensor center given by CylinderGeom_Mvtx.

I have looked carefully at CylinderGeom_Mvtx and there is no obvious logical error. Doing local-to-world / world-to-local / local-to-world transformations yields the exact starting value. The positioning of the staves in the geometry class seems to be the same as in the MvtxDetector class, which constructs the detector model. The discrepancy seems to be in the location of the sensor in the stave. Since the stave is not built in our software, we import it, I can not easily check that the geometry class has it right.

My specific request to the experts is to check that the parameters in CylinderGeom_Mvtx that position the sensor in the chip, the chip in the module, and the module in the stave are all correct.

Thanks

Tony

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Yasser Corrales Morales

Postdoctoral Research Associate
PO Box 1663
MS H846
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