STAR Flow, Chirality and Vorticity PWG

[Han-sheng Li <li3924 AT purdue.edu>]

Hi Gang,

Thanks for your prompt reply.

The purpose of using pair q2 together with single v2 in the ESS is to find an event shape variable somewhat related to eccentricity, but not too closely correlated to v2 itself event by event. In that sense, those nonflow contributions are what we want to make the magic work.

I do not appreciate the argument that there could be unknown background effects, so we can not trust the method. Isn't it always true that there could be unknown unknowns in whatever method? 

If you claim this current effect under study could be more prominent in peripheral events, it's better to show such results from simulation. Then at least we know where the method fails.

As I said, this is one pitfall in the q2 definition, but probably not a major issue in the ESS method. The major issue is that we don't know what the intercept from ESS really is. OK, it suppresses background, but we don't know to what degree: over-suppress? under-suppress? or just right?

Best regards,

Han-Sheng

---

寄件者: Gang Wang <gwang AT physics.ucla.edu>
寄件日期: 2024年6月19日 下午 02:00
收件者: Han-sheng Li <li3924 AT purdue.edu>
副本: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
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

Thanks for the reply. We have some discussions about pair v2 in the method paper:

Physics Letters B, Volume 848, January 2024, 138367

and recently we expanded the derivation a bit in Appendix C of the following link:

https://drupal.star.bnl.gov/STAR/system/files/userfiles/222/file/Method_Paper_on_ESE%20(1).pdf

So we have been aware of the contributions in pair v2 that are unrelated to flow.

Some of these contributions are related to gamma and some to delta, and they will propagate into pair q2 from pair v2.

But we should not confuse them with the self-correlation between single q2 and single v2, or between pair q2 and pair v2. 

The purpose of using pair q2 together with single v2 in the ESS is to find an event shape variable somewhat related to eccentricity, 

but not too closely correlated to v2 itself event by event.

In that sense, those nonflow contributions are what we want to make the magic work.

I do not appreciate the argument that there could be unknown background effects, so we can not trust the method.

Isn't it always true that there could be unknown unknowns in whatever method? 

If you claim this current effect under study could be more prominent in peripheral events,

it's better to show such results from simulation. Then at least we know where the method fails.

Gang Wang

Department of Physics and Astronomy

UCLA

On Wed, Jun 19, 2024 at 3:08 PM Han-sheng Li <li3924 AT purdue.edu> wrote:

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. 

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

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

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

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. 

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. 

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.

Thanks

Gang Wang

Department of Physics and Astronomy

UCLA

On Wed, Jun 19, 2024 at 6:13 AM Han-sheng Li via Star-fcv-l <star-fcv-l AT lists.bnl.gov> wrote:

Dear Convenors,

Please find my slides in the following link:

https://drupal.star.bnl.gov/STAR/blog/hshengli/Model-study-Event-Shape-method

Best regards,

Han-Sheng

---

寄件者: Han-sheng Li <li3924 AT purdue.edu>
寄件日期: 2024年6月18日 下午 01:18
收件者: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
副本: subhash <subhash AT rcf.rhic.bnl.gov>
主旨: 回覆: [Star-fcv-l] FCV PWG meeting on 19/June/2024 Wed. 9:30 AM EDT

 

Dear Convenors,

I would like to present my model study for the event shape method of delta gamma.
Please add me to the agenda.

Best regards,

Han-Sheng

---

寄件者: Star-fcv-l <star-fcv-l-bounces AT lists.bnl.gov> 代表 subhash via Star-fcv-l <star-fcv-l AT lists.bnl.gov>
寄件日期: 2024年6月16日 下午 09:30
收件者: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
副本: subhash <subhash AT rcf.rhic.bnl.gov>
主旨: [Star-fcv-l] FCV PWG meeting on 19/June/2024 Wed. 9:30 AM EDT

 

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Dear All,

We shall have our weekly FCV PWG meeting this Wednesday (19/June/2024)
at 9:30 AM EDT. If you wish to present please let us know. The agenda
will be collected at:
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Please send us your slides by Tuesday. Zoom details are copied below.

Thanks and regards,
Prithwish, Zhenyu and Subhash


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