STAR Flow, Chirality and Vorticity PWG

[Sergei Voloshin <voloshin AT wayne.edu>]

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

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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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