STAR Flow, Chirality and Vorticity PWG

["Tang, Aihong" <aihong AT bnl.gov>]

Hi Yicheng,

Thank you for your response. We have answers inserted below.

On Nov 5, 2024, at 11:27 PM, Feng, Yicheng <feng216 AT purdue.edu> wrote:

Hi Aihong, 

We have some comments and questions on your document. 

1. s10 is a misinterpretation of our statement. We’re not saying anything about relationship between resonance v2 and rho00. 

    We’re saying the effect of rho00 is just like the effect of v2 on Delta gamma, which is more correlated with participant plane. 

    The original spin alignment paper said that the spin alignment originates from the global angular momentum of the bulk (participants). 

    [Z.-T. Liang and X.-N. Wang, Phys. Lett. B 629, 20-26 (2005)]

A : Thank you for the clarification. I have now removed the first part on that page to better reflect the situation.

2. Currently there is no measurement of rho spin alignment. 

    A very recent theory predicted that rho spin alignment would vanish rapidly through their interaction with pions during the evolution. 

    [Y.-L. Yin, W.-B. Dong, J.-Y. Pang, S. Pu, Q. Wang, arXiv:2402.03672]

A : That is a theory prediction on a specific process, and we are aware of that publication. While it offers some insights, it is not a measurement.

3. Everyone knows that quark spins will be polarized by magnetic field. 

    In your picture of rho00, do those quark spins correlate with their momentum, i.e. chirality asymmetry?

A : You seem to suggest we implied a fancy picture for the process. Probably you read into it too much, and we are not sure how your question is relevant. It is straightforward --- we are just saying that there is a way to generate global spin alignment without the need of CME arguments.

4. If your argument were correct for SP/PP CME measurement, does it apply to other CME measurements?

A : Yes it does apply to other CME measurements (we discussed some of them in our PLB), but in different ways. The SP/PP measurement would be most influenced, as it relies on the strongest assumptions (rho_00 being different along PP and SP, and maximum in PP). 

Thanks,

Aihong

Sincerely,

Yicheng

---

From: star-fcv-l-request AT lists.bnl.gov <star-fcv-l-request AT lists.bnl.gov> on behalf of Tang, Aihong <aihong AT bnl.gov>
Sent: Monday, November 4, 2024 11:34 PM
To: star-fcv-l AT lists.bnl.gov <star-fcv-l AT lists.bnl.gov>
Subject: [[Star-fcv-l] ] comments on Purdue group's fCME analysis

 

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Hi all,

Regarding Purdue group's fCME analysis based on SP/PP, our major concern is that global spin alignment of rho-meson affects the observable and has not been accounted for in their analysis. The Purdue group disagrees with this assessment.

There have been intensive debates on the matter. At times, the discussion has become quite technical, which, combined with the back-and-forth nature of the arguments has made it challenging for non-experts to follow.

During one of previous FCV meetings, I promised to provide a document to clarify the situation. Sorry for the delay --- this document is now available below. It has been prepared with the aim of making the issue understandable, hopefully even for non-experts.

https://drupal.star.bnl.gov/STAR/system/files/CommentOnPurdueCMEApproach.pdf

Best,

Diyu,  Gang, Jinhui and Aihong