sPHENIX tracking discussion

["Soltz, Ron" <soltz1 AT llnl.gov>]

John and Tom,

Here are my comments on pCDR v0.992 TPC section.

Overall it does a very good job of demonstrating the existence proof for the physics value of a TPC while we continue to work on simulations and R&D.

1925: the effects of space charge should be within the tolerances of already working TPC experiments 

—> 

ALICE and STAR have demonstrated the ability to control for space charge effects in a high track density environment.  Space charge effects for sPHENIX are anticipated to be within the design tolerances of these experiments and will be studied as we continue to refine our design.

1940: with width corresponding to $\sqrt{12}$ times the expected width of the shaper pulse.  If anything the two-hit resolution in the z direction is pessimistic in the current simulation.

—>

using a conservative width of $\sqrt{12}$ times the expected width of the shaper pulse.

Figure 4.30

Poisson process does for each gas “layer”

—> 

Poisson sampling along track path through cylindrical gas volume corresponding to each radial pad layer.

Right side of figure is not clear.  Could it be replaced with a simulated 2-D histogram cluster?

1959: The TPC readout plane is the most composite and multifunctional TPC element.

(this introductory sentence can/should be omitted)

Fig. 4.32  is a duplicate of Fig. 4.28, remove and reference Fig. 4.28 instead.

1966: is a multi-parameteric task that involves matching the performance of almost all TPC subsystems.

—>

is a multi-parametric taks that involves matching the performance of the gas diffusion, gas gain, and pulse amplification.

1972: The transverse of the dimension

remove (of the)

1975: gas stage

—>

gas gain stage

2000: ALICE plans to not only charge the orientation

—>

ALICE plans to not only change the orientation

2005: The ions are coming from the collision particles ionizing gas in the TPC volumes but mainly from the avalanches in GEM layers.

—>

The ionizing tracks and gas avalanches in GEM layers both contribute to the buildup of positive ions in the TPC, with the latter providing the dominant contribution.

Fig 4.39 and corresponding text, mis-represents ALICE gas as Ar-based.  Unless they are switching for the upgrade, the gas used is Ne-CO2-N2 in a 86-9-5 ratio.  The Ne-based gas which ALICE uses is shown in Fig. 4.39, which is also repeated in Fig. 4.49.  I would suggest merging these three figures into one 3-panel figure, with a simplified discussion of the three main options: Ar-CF4-C4H10 (T2K), Ar-base, and Ne-CO2 (ALICE) with a shorter and  more focussed discussion of the pros-cons of each choice.

Fig. 4.40

It’s not entirely clear how this figure fits into the pCDR.  Of course ion mobility is important, but does the figure inform any choices at this time.

2203:

Are we really prepared to use the PASA ALTRO chip as a back up?  I remember from earlier discussions with our ALICE colleagues that this chip had the wrong polarity for us, not to mention that it is a long time out of production.  Is SAMPA development delayed so much that it would cause a delay for sPHENIX?

2213: cooling 1/2 has many channels

—> 

cooling 1/2 as many channels as ALICE

2254: Justification of Design Choices

This is where I lose the flow of the section.  Some of this is duplicative with the first section, and those parts that aren’t should probably be moved there.  The subsequent R&D section also needs additional explanation to show how it melds with the “steps to completion” section, which itself could benefit from more discussion of the electronics schedule.

At this point it would probably be more helpful to find ways to help with the “out-organization”.  I’ll check in with you (Tom) after your practice talk to see what can be done to help with this.

-Ron

Ron Soltz

LLNL, Nuclear & Particle Physics Group Leader

soltz1 AT llnl.gov

+1 925 423-2647

On Oct 22, 2015, at 6:40 AM, John Haggerty <haggerty AT bnl.gov> wrote:

Hello,

Thanks to everyone for the many comments, corrections, additions,
clarifications to the pCDR.

If you are just starting to read it now,  I put the latest build of the
document in the same place as version 0.992:

https://indico.bnl.gov/conferenceDisplay.py?confId=1483

Also, as a preview of what to expect from reviewers, Irina has put
together a database of comments from previous reviews and web site to
see them in one place:

https://www.phenix.bnl.gov/~irina/sPHENIX/allcomments.php

(use the sphenix, babar1008 username and password).  As we complete the
document in the next few days and prepare for the review, it would be
good for the authors to examine their consciences about how well we have
responded to previous recommendations.

--
John Haggerty
email: haggerty AT bnl.gov
cell: 631 741 3358
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