STAR Flow, Chirality and Vorticity PWG

["Shen, Diyu" <dyshen AT fudan.edu.cn>]

Hi Yicheng,

Your argument can be applied to LCC, TMC, jet induced correlation, rho decay coupled with flow, will you argue they won’t induce charge dependent effect?

You have made your point doesn’t mean it solved the problem, that hand-waving argument isn’t really convincing, particularly for a serious estimation of the CME background.

For event-by-event B, since you assume CME is large w.r.t spectator plane in your study, I was trying to say it isn't true for every centrality. An extreme case is in most central collisions where there are no spectators but event-by-event B filed is still large. Of course you can say most central is out of the scope. But I would like to know starting from which centrality your assumption is valid. It is crucial for determining centrality range in your study.

Thanks,

Diyu

On Aug 16, 2024, at 07:54, Feng, Yicheng <feng216 AT purdue.edu> wrote:

Hi Diyu, 

The spin alignment is to do with the decay orientation along B (not on rho distribution like flow), 

so parity symmetry dictates that the whole system is correlated, and no charge dependent effect should exist. 

I think we have made our point in the previous email exchanges in both CME-fg and FCV. 

For event-by-event B field, PP is determined by the participants of (target + projectile), 

whereas the B field from participants is determined by their difference (target - projectile). 

Therefore, the B direction should not be mixed with PP direction, and B from participants should be a next-order effect. 

Moreover, anything that is dictated by PP (e.g. some magnetic field contribution) will be regarded as part of the background in this SP/PP method.

Sincerely,

Yicheng for the PAs

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From: star-cme-focusgroup-l-request AT lists.bnl.gov <star-cme-focusgroup-l-request AT lists.bnl.gov> on behalf of "Shen, Diyu" <star-cme-focusgroup-l AT lists.bnl.gov>
Sent: Wednesday, August 14, 2024 9:49 PM
To: star-cme-focusgroup-l AT lists.bnl.gov <star-cme-focusgroup-l AT lists.bnl.gov>
Cc: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
Subject: Re: [[Star-cme-focusgroup-l] ] [[Star-fcv-l] ] FCV PWG meeting on 14/Aug/2024 Wed. 9:30 AM EDT

 

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Hi Yicheng,

The CME background doesn’t refer to background electric current, it is background particle correlations in CME observables. The resonance decay can be the CME background because decay products are correlated due to conservation laws. If the correlation is spherical then it is canceled in CME observable, but elliptic flow breaks the symmetry between x and y, same as spin alignment which leads to anisotropic decay distribution of daughters. 

The parity symmetry requires those decay daughters not make a net electric current, which correlates different rho decays. 

Does it break the conservation law in decay so daughter particles have no correlation, or will it restore the symmetry between x and y?

For the event-by-event B field, it is clear in most central collisions the B field is dominated by participant nucleons (PP) whereas in peripheral it is dominated spectators (SP).  It should be a continuous change, so a valid question is that in which centrality the event-by-event B field starts to correlate more with SP. 

Thanks,

Diyu

 

On Aug 15, 2024, at 03:53, Feng, Yicheng <feng216 AT purdue.edu> wrote:

Hi Diyu and Aihong, 

I think your questions on spin alignment are related, so I put our reply in this single email. 

I think it is a bit similar to the famous Wu-Yang-Lee experiment, but now it is strong decay in a magnetic field. 

The parity symmetry requires those decay daughters not make a net electric current, which correlates different rho decays. 

Any violation of that should be attributed to the local chirality imbalance (P-violation), so it is just another _expression_ of CME. ​

For Diyu's question on event-by-event B field. 
I think the B direction and PP direction are mixed in your question.

In one event, let's say there are 3 directions: B, PP, SP.  

The |Bx|, |By| in this paper is basically a measurement w.r.t. B-direction, not a measurement w.r.t. PP, 

so we cannot say that PP feels a stronger B field than SP, nor PP is more correlated to B than SP. 

Central collisions don't have a SP, so it is out of the scope of this discussion.

In non-central collisions, the magnetic field should mainly come from the spectator protons, so B direction should be more correlated to SP than PP. 

In this sense, the signal w.r.t. SP should be still stronger than PP, and the relationship should be the projection factor. 

The algebra has been mentioned in the discussion. 

The formula below depends on what the physics root is. If the physics is CME, then it is along B, and Dg_SP = Dg_B <cos2(Psi_B-Psi_SP)>: 

Dg_SP = <cos(phi1+phi2-2Psi_SP)> = <cos(phi1+phi2-2Psi_B+2Psi_B-2Psi_SP)> ~ <cos(phi1+phi2-2Psi_B)><cos2(Psi_B-Psi_SP)> = Dg_B <cos2(Psi_B-Psi_SP)>

The correlation chain is: B fluctuates about SP, and PP fluctuates about SP, so 

Dg_PP = Dg_SP <cos2(Psi_SP-Psi_PP)> = Dg_B <cos2(Psi_B-Psi_SP)> <cos2(Psi_SP-Psi_PP)>

The fluctuation of B about SP <cos2(Psi_B-Psi_SP)> drops in our formulism.

Sincerely,

Yicheng for the PAs