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[Cameron Racz <cracz001 AT ucr.edu>]

Hi Daniel,

Thank you for the info! That makes sense and does help. If you do find that study though that would also be great to see. 

While I’m here I did have one other question about the nsigma value we get from the TPC. When I found the definition here (https://arxiv.org/abs/nucl-ex/0505026 section 3.1) it is of course the logarithm of the dE/dx measurement divided by the expected value, but it also showed a factor of 1/sigma_X out in front where sigma_X “is the dE/dx resolution of the TPC”. I just wanted to verify that this factor is the same resolution we’re talking about here (8%, 7%, etc) because I can’t find any details on this factor aside from this statement. So, for example, if the resolution is 8% then sigma_X = 0.92?

Thanks,

Cameron Racz

Ph.D. Candidate 

Heavy-ion Physics Group

University of California, Riverside

On Mar 16, 2023, at 11:42 PM, Daniel Cebra <cebra AT physics.ucdavis.edu> wrote:

Hi Cameron,

   The dE/dx resolution in FXT mode is actually better than in collider mode. Empirically dE/dx resolution goes as L^-0.37, where L is the tracking length. Since tracks pass through the TPC at long angles, there is a longer tracking length then in collider mode.

  For midrapidity tracks for the 3.0 GeV system, there is 200 cm of track length, whereas in collider mode there is 140 cm for track length. Using the empirical track length dependence, we expect that the dE/dx resolution in FXT mode should be 78% of that in collider mode (i.e. ~7%).  Note that the dE/dx resolution is eta (or rapidity dependent - for target rapidity tracks, the resolution would again be 8%; for rapidity 1.5 (which hits the top far corner the dE/dx resolution should be ~6%).

  OK... that is the theoretical improvement in dE/dx resolution in FXT mode.  I will need to do some digging to verify that experimentally we see that expected improvement in resolution. I know that I looked into this a while ago, and my recollection was that we did see the expected improvement in dE/dx resolution, but I will have to find that study to confirm these expectations.

  For reference, the paper to quote for empirical dE/dx resolution in tracking detectors is:

Allison and Cobb, Ann. Rev. Nucl. Part. Sci. 30, 253 (1980)

Best, Daniel

On Thu, Mar 16, 2023 at 8:26 PM Van Buren, Gene via Star-tpc-l <star-tpc-l AT lists.bnl.gov> wrote:

Forwarding Cameron's query to the TPC list (not my area of expertise).

-Gene

Begin forwarded message:

Hi Gene,

I have a quick question about the TPC and I thought you might be the one who would know. I’ve been looking into the dE/dx resolution of the TPC in order to try to estimate systematic uncertainties related to nsigma. I’ve found that it was established that the TPC dE/dx resolution is ~8% for pions, kaons, and protons, but is there any information on what the resolution would be in fixed target mode? Would it be safe to assume 8% in fixed target mode as well? I’m working on 2018 sqrt(s_NN) = 3.0 GeV specifically if that matters.

Thank you!

Cameron Racz

Ph.D. Candidate 

Heavy-ion Physics Group

University of California, Riverside

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