sPHENIX tracking discussion

[Anthony Frawley <afrawley AT fsu.edu>]

Hi All,

I attach plots of (cluster z - truth z) and (cluster z error) for the MVTX layers. These are made from some pp with pileup files that I made a few days ago. The sigma is about 6 microns, as expected, in the first plot, and the mean value of the error is 6 microns in the second plot. 

There is evidently a problem with the residual calculation. But I am puzzled by the observation from Christof that the error assigned by the MVTX clusterizer is 2.6 microns. That is not what I see in the cluster error histogram.

Tony

---

From: sPHENIX-tracking-l <sphenix-tracking-l-bounces AT lists.bnl.gov> on behalf of Hugo Pereira Da Costa via sPHENIX-tracking-l <sphenix-tracking-l AT lists.bnl.gov>
Sent: Friday, June 17, 2022 11:16 AM
To: sphenix-tracking-l AT lists.bnl.gov <sphenix-tracking-l AT lists.bnl.gov>
Subject: Re: [Sphenix-tracking-l] Wierd MVTX residual distributions

 

Hi Christof,

These numbers do look small indeed (at most 2um)

Last time I looked (a long time ago, in 2020), the residuals where more
around 5um (all sizes included) (see plot attached)

I tried to look at the QA plots (e.g.
https://urldefense.com/v3/__https://nbviewer.org/github/sPHENIX-Collaboration/QA-gallery/blob/jenkins-sPHENIX-test-tracking-low-occupancy-qa-2207-test-tracking_Event1000_Sum16/QA-Mvtx.ipynb__;!!P4SdNyxKAPE!F75K0bmn-hbMcsFeIvPKt82oxMU5ewYVpTmBqVfZs15PYCyUne7TebreJ2QYw1MQV_iJHQtTALmoj4PlgbsfVLxzMFu42Cm_nWUnQx9Yhg$ )
but we can't read the x axis there ... Not very useful, something that
we should fix ...

Hugo


On 6/17/22 01:40, Christof Roland via sPHENIX-tracking-l wrote:
> Hi Everybody,
>
> i am in the process of producing the new error parameterizations so we can swith to TrkrClusterv4.
>
> Looking at the MVTX residuals I see distibutions that are way to narrow, as far as I understand.
> Here is a list of the observed RMS of the residual (cluster phi position - track phi position) distribution.
> There is the residual with respect to the truth track and the reco track as well as the a selection for cluster width in phi ==1 or bigger than one.
>  
> truth layer 0 phisize = 1 RMS: 0.000122
> truth layer 0 phisize > 1 RMS: 0.000164
> truth layer 1 phisize = 1 RMS: 0.000090
> truth layer 1 phisize > 1 RMS: 0.000126
> truth layer 2 phisize = 1 RMS: 0.000072
> truth layer 2 phisize > 1 RMS: 0.000102
> trk layer 0 phisize = 1 RMS: 0.000133
> trk layer 0 phisize > 1 RMS: 0.000143
> trk layer 1 phisize = 1 RMS: 0.000110
> trk layer 1 phisize > 1 RMS: 0.000123
> trk layer 2 phisize = 1 RMS: 0.000124
> trk layer 2 phisize > 1 RMS: 0.000134
>
> In general we see a residual width fo ~1.2 micron. The error assigned by the MVTX clusterizer is ~2.6 micron.
> How is this possible? the pixel pitch of the MVTX is ~30um and the intrisic resolution according to ALICE specs should be ~5um.
> Especially for phi size  = 1 clusters we should see something like 30/sqrt(12) ~ 9um
>
> Does anybody have an idea how to make sense of this?
>
> Thanks
>
>      Christof
> _______________________________________________
> sPHENIX-tracking-l mailing list
> sPHENIX-tracking-l AT lists.bnl.gov
> https://urldefense.com/v3/__https://lists.bnl.gov/mailman/listinfo/sphenix-tracking-l__;!!PhOWcWs!wwV_mFFDNY2AKjJjJOtz4rVuY7C7TZS-rKkq9BKOvCCr7Qx5yAAuybXwGoKy8NW_O_IUxXQgBV8naNce0hj3hkXqGWHuqun7jA$

Attachment: cluster_dz.pdf
Description: cluster_dz.pdf

Attachment: cluster_ez.pdf
Description: cluster_ez.pdf