STAR Flow, Chirality and Vorticity PWG

[Jiangyong Jia <jiangyong.jia AT stonybrook.edu>]

Hi, Shinichi,

I want to chime in and clarify this point

> So I just wanted to say it is reasonable to see your minimum at about
> Nth_corr~220 
> to be systematically higher at about ~1.01 than the other minimum of
> about ~1.00 at 
> centrality 5-20%. Maybe this is what you meant by saying "the ratio of
> average and 
> averaged ratio are different" or "the centrality bin width effect",
> which sounds different 
> to me. But anyway, I think we understood, which is more like "a
> shifted ratio" etc. I think 
> it was indeed a good decision for you to show the ratio as a function
> multiplicity, which 
> is expected to be different from the one as a function of centrality
> anyway. Thanks 
> again for the hard works and interesting results. 
> Best regards, ShinIchi

There are two effects

1)  We have found even if you bin events in centrality, as long as it is
very fine bins in centrality, you will see the ratio is at 1.01.

This is really because centrality bin width effect. <v2R/V2Zr>
!=<v2R>/<V2Zr>. Because the latter ratio, the <Nch> for <v2R> and <v2Z>
are different in the central region. 

2) second effect is that the peak of v2 ratio is around Nch~80 (the peak
is very broad and shallow), while the peak of v2 ratio obtained for wide
centrality bin as in CME paper would be around 40-50% corresponding to
Nch~60. This difference in this case is actually due to the fact that
<v2R/V2Zr> at the same Nch does not corresponds to the ratio at the same
centrality. i.e. <v2R/V2Zr>_Nch !=<v2R/V2Zr>_cent. In fact, if we bin
events with narrow centrality, we can recover the same peak location.


Jiangyong