sPHENIX MAPS tracker discussion

[Christof Roland <christof.roland AT cern.ch>]

Hi Ross,

thank you very much for this study, this is extremely helpful. 

I agree fully with the comments Tony made already.

- We should take pions and throw a range of momenta, it would be nice to

see the resolution vs pt. 

- To better constrain the pt we should rpobably include the vertex point in the fit. 

There is an option in the setup macro to do this.

- Adding some points of the TPC where the dietortions are smallest may make 

sensé if we need to do this. Even distorted points of the TPC with a blown up error

probably give a reasonable constraint to the pt without too much of a bias. 

- From the truth tracking you could dig out the position of the first g4hit in the TPC

and use this one as a reference point. I have only limited faith in the genfit internal 

covariance matrices.

Cheers

   Christof 

On 5. Oct 2018, at 04:56, Anthony Frawley <afrawley AT fsu.edu> wrote:

Hello Ross and Molly,

Interesting! Some comments/questions:

1) Why electrons? There will be significant tails on the extrapolation for electrons after 8% of a radiation length in 4 layers of INTT. 

2) You extrapolated to the inner field cage at 20 cm. The inner tracking radius is 30 cm, where space charge distortions will be worst.  Can you push it to 30 cm?

3) I am surprised  by the Z resolution for "11" and "111" on slide 4 and 5. I would have expected these to be much worse than those for any configuration having a "0" layer. The implication of this is that the Z resolution is dominated by the MVTX (which is actually not insane, it has 5 micron resolution per layer vs ~40 micron resolution for the INTT "0" layers). This raises the question of whether the INTT matters at all to the Z extrapolation accuracy. Can you try it with no INTT at all?

4) You are using a fixed momentum of the particles, and the extrapolation trajectory in r-phi is always the same at fixed momentum. I assume that the extrapolation uses the momentum measured by the MVTX and INTT to predict the hit location, and you show the distribution around the mean.  The momenta we would actually be using would be a few hundred MeV/c to maybe 1 GeV/c, and we would not have the momentum from a precise TPC measurement until we have already corrected for space charge effects. It may be that we can take the TPC space points at the space charge crossover point to get a better estimate of the track momentum, but otherwise we rely on the momentum measurement by the MVTX + INTT for the extrapolation. Can you try it with a continuous range of particle momenta?

Best regards

Tony

---

From: Ross Corliss <rcorliss AT mit.edu>
Sent: Thursday, October 4, 2018 7:16 PM
To: christof.roland AT cern.ch
Cc: jhuang AT bnl.gov; Todoroki, Takahito; Carlos Perez; Anthony Frawley; Chiu, Mickey; Sanghoon Lim; Molly Taylor; sphenix-intt-l AT lists.bnl.gov; sphenix-maps-l
Subject: Re: Meeting of the Inner Tracker Task Force VIRTUAL

 

I've uploaded some slides to the indico page ( https://indico.bnl.gov/event/5107/contributions/24213/attachments/20273/27051/TPC_IFC_resolutions_from_INTT.pdf ) showing the resolutions we're getting by extrapolating the Kalman track stubs in the MVTX+INTT out to the inner field cage.  

-Ross

 

On Oct 2, 2018, at 11:10 AM, Christof Roland <christof.roland AT cern.ch> wrote:

Hi Everybody,

since some of us are at the hard probes conference we will make the 

task force meeting scheduled tomorrow virtual. There will not be an actual 

meeting, but please post new material you would like to share on the indico 

page or add it to the google doc so we can look at it offline and discuss by email

https://indico.bnl.gov/event/5107/

https://docs.google.com/document/d/17PJdu94Ydg25V-cTHIYfSbkfojH4ZUEfsfoZPm0RDb0/edit

Cheers

   Christof