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[Star-fcv-l] 回覆: 回覆: FCV PWG meeting on 19/June/2024 Wed. 9:30 AM EDT

From: Han-sheng Li <li3924 AT purdue.edu>
To: Gang Wang <gwang AT physics.ucla.edu>, "STAR Flow, Chirality and Vorticity PWG" <star-fcv-l AT lists.bnl.gov>
Subject: [Star-fcv-l] 回覆: 回覆: FCV PWG meeting on 19/June/2024 Wed. 9:30 AM EDT
Date: Wed, 19 Jun 2024 22:08:12 +0000

Hi Gang,

Thanks for your comments on my slides.

Please find my reply bellow:

Regarding the first bullet on slide 5, if we follow your derivation, shouldn't it be \delta/N^2 instead of \delta/N?

Total number of quadralets is ~N^4. Total number of triplets is ~N^3, so it does seem to be 1/N scaling.

Anyway, your derivation is fairly crude and only considers two particles with very similar pT, which is uncommon.

The derivation isn't meant to be precise. It's to illustrate there's an self-correlation issue within the q2 variable itself which can have an effect on Delta gamma.

The idea of using pair q2 is to eliminate the self-correlation between v2 and q2 on an event-by-event basis.

q2 and v2 are self-correlated because they are using the same set of POI's. That's why v2 fluctuates over a large range as q2 is varied over a large range, primarily on statistical fluctuations. The statistical fluctuations of v2 and the statistical fluctuations of q2 are correlated with each other.

The so-called self-correlation term (delta/N) you mentioned is not a concern.

The \delta/N or \delta/N^2 term, even if it exists, doesn't contribute to the self-correlation between v2 and pair q2.

We think it may bias the Delta gamma as the q2 quantity contains a delta-like contribution. Again, the self-correlation between v2 and pair q2 is because they are calculated using the same set of particles. Their statistical fluctuations are correlated.

It probably even helps us in destroying the self-correlation we want to remove.

Also, note that in our analysis, the spectator plane is used to calculate v2, instead of two-particle correlation v2^2.

In our model studies, we used the known reaction plane Psi=0 for the calculation of single v2 (cos(2phi)). The v2{2} is only used as a static constant for the normalization of q2^2.

Thus, I'm not sure how relevant your derivation is to our ESS approach.

As a suggestion for the simulation, it may be useful to try more peripheral events since you are concerned about the larger 'self-correlation' effect there.

The main issue with the ESS approach is that it is not proven to be only sensitive to CME because of the intertwined q2-v2-Delta gamma variables. We don't know what the remaining background contamination exactly is. The self-correlation in the q2 calculation is only one possible issue, probably not even a major issue.

Best regards,

Han-Sheng

寄件者: Gang Wang <gwang AT physics.ucla.edu>
寄件日期: 2024年6月19日上午 07:27
收件者: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
副本: Han-sheng Li <li3924 AT purdue.edu>
主旨: Re: [Star-fcv-l] 回覆: FCV PWG meeting on 19/June/2024 Wed. 9:30 AM EDT

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Hi, Han-Sheng

Sorry I missed your presentation, but I reviewed your slides with great interest.