sPHENIX MAPS tracker discussion

[Ming Liu <ming AT bnl.gov>]

Hi Sookhyun,

Nice progress, on your slides, could you explicitly show how various efficiencies are defined in your calculations?

About multiple in-time collisions, as we discussed, it would be nice to look at the separately, ie, only one in-time event, or two etc.

Looking forward to seeing your updated plots.

Cheers 

Ming

Sent from my iPhone

On Oct 19, 2018, at 7:16 AM, Christof Roland <christof.roland AT cern.ch> wrote:

Hi Sookhyun, 

thank you very much for the material. This helps a lot. 

I have a few questions still.

- How many events is this study based on? The efficiency plots looks like there are very few events...

- How many true (in time) and false (out of time) vertices are there per event on average in the sample you look at?

- Could you please also add the definition of the pileup vertex rejection rate? I am not sure I understand what is plotted. 

- For the out of time pileup rejection could you calcutate and plot the following quantity 

rejection_factor = (number of oot vertices tagged as in time) / (all out ot time vertices) -> so the ideal algrorithm would give 0 as optimal performance.

So for example we can calculate:

N_vtx_in_time * efficiency + N_vtx_out_of_time* rejection_factor = total number of vertices reconstructed per event

Especially we would like an algorithm that gives:

N_vtx_in_time * efficiency >> N_vtx_out_of_time* rejection_factor

To keep the CPU time low.

Thanks for your input

   Christof 

On 19. Oct 2018, at 07:28, sookhyun lee <dr.sookhyun.lee AT gmail.com> wrote:

Hello all,

Please find my updates on in-time vertexing with INTT at:

https://www.phenix.bnl.gov/phenix/WWW/p/draft/shlee/sphenix/tracking/intt_in-time_vertexing_Oct18_2018.pdf

https://www.phenix.bnl.gov/phenix/WWW/p/draft/shlee/sphenix/tracking/intt_in-time_vertexing_Oct18_2018.pptx

The results shown used  ~15% of intended statistics due to limited time and computing resources. 

Plots will be updated tomorrow morning again with more statistics. 

Best regards,

Sookhyun

On Tue, Oct 9, 2018 at 5:10 PM sookhyun lee <dr.sookhyun.lee AT gmail.com> wrote:

Hi Xin,

Please find my answers inline. 

Best regards,

Sookhyun

On Tue, Oct 9, 2018, 15:21 Xin Dong <xdong AT lbl.gov> wrote:

Hi Sookhyun,

Thank you for this nice study. Let me back off a bit and ask a couple of basic questions first.

Can you elaborate the definition of "in-time vertex identification efficiency"? My understanding from the slides is the probability of reconstructed vertices with 3 MVTX+1 INTT to be the truth MC vertices. I may be wrong here, and would appreciate your clarification.

So the module reconstruts all possible vertices in an event and uniquely determines an in-time vertex and assigns 0 to vt for this vertex. For each event, if at least one true in-time vertex has a reconstucted vertex with vt=0, we declare an in-time vertex is identified. The denominator is the number of events with in-time vertex with true vertex within 10 cm. 

What is the minimum number of tracks requirement in the vertex algorithm?

I require 2 track at minimum.

Do you also have the vertex finding efficiency? Fraction of MC truth vertex that got reconstructed. May be also interesting to see this vs. event multiplicity at different luminosity levels.

I'd like to refer you to the talk I gave in last year's collaboration meeting.

I tend to agree with Ming that 3 MVTX hit seems to be a bit tight. What if there are some small amount of dead areas on each layer of MVTX during the real operation. The dead area fractions in three layers will add up if we have the 3-hit requirement. This may cause some sizable vertex finding efficiency loss, isn't it?

This is very interesting question. In a catastrophic case of most sensors of 1 MVTX layer dead, I can naively imagine writing a 2D xy vertexing algorithm for phi segmented layer, which may be unnecessary. For z segmented layer, we can fit tracks to a line on xz plane, but the resolution won't be as good as a track won't be really straight. However, this is an unlikely circumstance as Tony points out. 

Thank you and Best Regards

/xin

On Tue, Oct 9, 2018 at 11:00 AM sookhyun lee <dr.sookhyun.lee AT gmail.com> wrote:

Hi Ming,

Yes, so far I only used 1 INTT layer to discriminate against out-of-time events. We certainly should reconstruct tracks using 2 MVTX hit + (2+) INTT hits at next iteration, but 2 MVTX hits only won't provide good starting curvature (for phi segmentation) or z0 parameter (for z segmentation) for INTT, thus cannot be used for in-time vertexing. I did not apply any pT cut on tracks used for vertexing.

Best regards,

Sookhyun  

On Tue, Oct 9, 2018 at 12:14 PM Ming Liu <ming AT bnl.gov> wrote:

Hi Sookhyun,

Nice work! So in your analysis, only one INTT hit was used to tag in-time association to a MVTX triplets? How about if you only use MVTX tracklet with two hits only? Have you applied any minimum momentum cuts?

Cheers 

Ming

Sent from my iPhone

On Oct 9, 2018, at 9:52 AM, sookhyun lee <dr.sookhyun.lee AT gmail.com> wrote:

Hello everyone, 

Please find my updates on in-time vertexing with INTT below.

https://indico.bnl.gov/event/4036/contributions/24340/attachments/20294/27121/intt_in-time_vertexing_Oct8_2018.pdf

 

Let us have discussions tomorrow at Inner tracking task force meeting as well.

Best regards,

Sookhyun

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--

===========================
Xin Dong
Staff Scientist, Nuclear Science Division
Lawrence Berkeley National Lab
MS70R0319, One Cyclotron Road
Berkeley, CA 94720, USA
Tel: +1-510-486-4121
Email: XDong AT lbl.gov
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