STAR Flow, Chirality and Vorticity PWG

[Sergei Voloshin <voloshin AT wayne.edu>]

Hi Jianyong,

I am afraid that some of our "disagreements" come from the definition of flow. What I mean by flow is the correlation with the "flow plane" quantified by the value of v_2. The "flow plane" could be the reaction plane, then I would talk about v_{2,RP} or participant plan. In the latter v_{v2,PP}==<cos(2phi-2Psi_PP)>.   By flow I do not mean anything like "hydro flow" and use this word more generally (e.g. as in expressions "money flow", "population flow").

Then, the asymmetry from "surface emission" of an asymmetric source is clearly flow.

The non-flow is whatever extra is in this or other measurement, e.g. in 2 particle correlations, it could be defined as

nonflow = <cos(2phi_a-2hi_b)> - (v_{2_PP})^2

My definitions do not depend on particle momentum or multiplicity of the event. They do include something, e.g. Psi_PP, which is not directly measured, and it requires an estimate of the corresponding uncertainty in the reported results. . But this is what we have to do with any definition.

best regards,

Sergei

On Thu, Jan 25, 2024 at 8:04 PM Jiangyong Jia via Star-fcv-l <star-fcv-l AT lists.bnl.gov> wrote:

But again, non-flow is a physical correlation that is only well defined in low multiplicity event. The correlation shape in eta and phi at low pT is nothing like jet fragmentation in AA collisions due to jet quenching.

The 70-80% centrality signal is not all non-flow as shown in the small system flow paper.

- Most real flow in the most peripheral ( and for sure any _real_ flow in pp) would play a role of nonflow in AA, as the "event planes" individual NN collisions are uncorrelated with the participant plane in AA.

regards,

Sergei 

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======================================
 Sergei A. Voloshin    

 Distinguished Professor, 

 Department of Physics and Astronomy,

 Wayne State University,
 666 W. Hancock,  Detroit,  Michigan,  48201
 e-mail: sergei.voloshin AT wayne.edu
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