STAR Flow, Chirality and Vorticity PWG

[subhash <subhash AT rcf.rhic.bnl.gov>]

Dear Sergei,

Thank you for your email. While I acknowledge that the meeting could 
have been more productive, I believe that valuable points were raised by 
both groups, and there was a mutual understanding, despite some 
disagreements. I see this as a positive starting point. The nonflow is 
not only important to this specific analysis but holds general relevance 
across various other analyses as well. I think we should organize more 
focused discussions on nonflow in the coming days within our working 
group and beyond.

Thanks and regards,
Subhash



On 2024-01-25 12:21 PM, Sergei Voloshin via Star-fcv-l wrote:
> Hi all,
>
> There was a rather interesting discussion at today's meeting (thanks
> to Fuqiang and Jianyong for preparing the presentations!), though I
> had to leave after 2.5 hours...  I have a few comments (not in any
> particular order) below.
>
> - The discussion could be much more productive, if somebody would
> chair the session. It could be better if during the presentation only
> short questions  were allowed, and longer discussions delayed for
> later. Especially when it is clear that people agree to disagree (but
> not only).
>
> - I agree with Fuqiang that a clear estimate of nonflow should be
> made, e.g.for reported v_2, but for other quantities as well.
>
> - For the nonlfow estimate HIJING can be used, though the data might
> be preferable. From my point of view, using pp data would be the best
> if used <uQ*>, AA-pp method. One can use peripheral collisions, as
> tried by Jianyong, including even the scaling presented (though again
> much better would be <UQ*> approach). Even better would be to compare
> different estimates.
>
> - The statements were made that it is not really possible to define
> nonflow. Very strange - what do we report then? Let us define what we
> want to measure, e.g. the correlation with the participant plane
> (another possibility would be the correlation with the reaction
> plane), then what is extra in e.g. measurements with two-particle
> correlations would be non-flow.
>
> -  Again, if we report v_2, let us define what we mean by that and
> report a realistic estimate of "non-flow" in that measurement. The
> values around a few percent for (ultra)central collisions look very
> unrealistic, to say the least.
>
> - The paper mentions "standard" and subevent methods, but neither is
> defined (unless I missed that).
>
> - The effect of nonflow for AuAu and UU collisions is likely rather
> similar, and the effect on the ratios should be calculated taking this
> into account. (This is probably what Jianyong meant by "difference" in
> nonflow)
>
> - Statement that "surface emission" is not flow, is incorrect (unless
> I misunderstood what was said) at least for the definition of flow I
> used above,  but it indeed depends on the definition of flow.
>
> - The statement that quenching reduces nonflow is (likely) incorrect,
> in fact it could increase it. The result of quenching is that instead
> of one high(er) pt particle we have several low pt. But those still
> have azimuthal angle strongly correlated with "jet" - then the
> contribution to nonflow would only increase.
>
> - "hot spots" effect (mentioned in relation to 2-particle CF) is
> non-flow (again I could have misunderstood it) -- this is incorrect.
> More exactly it again depends on the definition of flow used. If it is
> correlations relative to the reaction plane, the statement is correct,
> if it is relative to the participant plane, the hot spots effect is
> already included in geometry/flow plane fluctuations.
>
> Best regards,
> Sergei
>
> -
>
> --
>
> ======================================
>  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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