STAR Flow, Chirality and Vorticity PWG

["Wang, Fuqiang" <fqwang AT purdue.edu>]

Jagbir,

Thanks for your answers. 

To your questions:
> Please clarify the following
>       Of course you've also removed the large charge-shuffle background 
> which is basically
>       an autocorrelation effect (sort to speak) due to the Dbmax (and 
> Dbmax_shuffle)
>       selection bias.
I was just saying it in passing, referring to the fact that you're largely 
selecting on statistical fluctuations and trying to remove the 
auto-correlation effect by shuffling. It wasn't a question.

>       Please explain the following:
>       So is your finite signal really due to the difference between the 
> average of ratios
>       and the ratio of averages (or perhaps also due to residual effect 
> from shuffling)?
I was referring to the fact that if you had a single Dbmax bin (i.e. taking 
average first and then ratio) then you'd get zero signal by definition. You 
now have 10 bins and take ratios first in each bin and then take average of 
the ratios, and get a positive signal. During the focus meeting discussion, 
it was made clear that your analysis required multiple Dbmax bins, not taking 
average of all bins, but only those with Delta gamma > 0. So now I think I 
understand technically how you did it. I understand your motivation doing 
that but I don't agree this is the right approach (I think it causes biases). 
So let me try to understand better: 
On slide 9 of your focus meeting presentation 
https://drupal.star.bnl.gov/STAR/system/files/CME_FOCUS.pdf, you state: 
(1) If Delta gamma_bkg. is negative then it is taken as zero.
(2) If gamma_SS is not negative and gamma_OS is not positive then delta gamma 
= 0.
Now to slide 25, let's take one centrality say 40-50%, you have the blue 
points (signal) and red+green points (bkg). The 8 points to the right of this 
centrality: all of them have negative bkg and negative Delta gamma, so they 
are not counted in your calculation of CME fraction. Now you're left with the 
two leftmost points. Do both points satisfy (2) above? I know both points 
seem to have bkg>0 & Delta gamma>0 but it's unclear if they satisfy SS<0 & 
OS>0. Assume they do, then you're taking average of these two data points. 
For the sake of simplicity, let me say you have only one point left. Your 
f_cme is basically the 
(Delta gamma of those events in that Dbmax bin) 
- (Delta gamma of a random collection of events in the same centrality bin 
which happen to have the same Dbmax_shuffle bin) 
- (Delta gamma of those same random events calculated after the charges are 
shuffled)
Do I understand it correctly? 

Best regards,
Fuqiang



> -----Original Message-----
> From: jagbir <jagbir AT rcf.rhic.bnl.gov>
> Sent: Sunday, December 13, 2020 10:12 AM
> To: Wang, Fuqiang <fqwang AT purdue.edu>
> Cc: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>; 
> star-cme-
> focusgroup-l AT lists.bnl.gov; aggarwal AT pu.ac.in
> Subject: Re: [Star-fcv-l] FCV PWG meeting, 18/Nov/2020 (Wed) 9:30am (New
> York time zone)
> 
> Dear Fuqiang, all,
> 
>    Sorry for not answering your email. Infact, I did not look this
>    email. Please go through my replies below:
> ------------------------
> 
>   1. A few events do not satisfy this cut so not including in it Db+-max
>      but in overall calculations all events are included.
> 
>   2. Yes
> 
>   3. We reshuffle charges in each event. We donot randomize charges
>      according to the positive/negative charge ratio of the given event.
>      In fact, we pick up one event and reshuffle positive/negative charges
>      keeping theta,  phi, number of postive charges and number of negative
>      charges as such. After this we calculate gamma correlator. This 
> procedure
>      is repeated for each event. The Db+-max of reshuffle  is a bit bit 
> wider
>      than the  real distribution which may be due to some correlations in 
> the
>      real data whereas reshuffle is purely randomize. Db+-max binning is
>      done on the basis of same fractions.
> 
>   4. Let me explain this point
> 
>      We pick up a real data event and calculate following
>      i)  Dbmax+- of real data event
>      ii) reshuffle charges in an event
> 
>      iii) again calculate Dbmax+- and termed it Db+-max of charge reshuffle
>      iv)  calculate gamma of real data event
>      v)   calculate gamma of reshuffle event
> 
>      Now for a given centrality
>      Steps i) to v) repeated for each event. Db+-max (data) and
> Db+-max(reshuffle)
>      sliced into ten percentile bins.
>      Now average gamma is found in every sliced Db+-max (data) and
> Db+-max(reshuffle)
>      from the respective event samples. It should be noted that events in 
> the top
>      say 10% Db+-max(data) are not the same as in the top 10%
> Db+-max(reshuffle) i.e,
>      real events in the top 10% Db+-max(data) are different from those top 
> 10%
>      Db+-max(reshuffle). Now the correlated background is caculated from the
> real events
>      corresponding to the top 10% Db+-max(reshuffle) events.
> 
>       Please clarify the following
> 
>       Of course you've also removed the large charge-shuffle background 
> which is
> basically
>       an autocorrelation effect (sort to speak) due to the Dbmax (and
> Dbmax_shuffle)
>       selection bias.
> 
>   5.  Db+-max distribution is sliced in to ten percentile bins which 
> represent
>       different amount of charge separation in each sliced db+-max bin.
> Let us
>       say we have Db+-max = 2, in this case fractional dumbbell charge 
> separation
>       f_DbCS = Db+-max-1=1 i.e., 100% back-to-back charge separation i.e.,
>       positive charged particles on one side of the dumbbell and negative 
> charge
>       particles on other side of the dumbbell. So, computing gamma in 
> different
>       Db+-max and calculating things is different from just making a single 
> wide
>       bin as you mentioned. This method is designed to get  CME-like 
> enriched
> sample
>       in given collision centrality as one divides all events into 
> different collision
>       centralities depending on either the impact parameter or event 
> multiplicity
> but
>       one does not study all events taken together without making different
>       collision centrality classes. However, for a single wide Db+-max bin 
> as you
>       wrote we will get zero signal.
> 
>       Please explain the following:
> 
>       So is your finite signal really due to the difference between the 
> average of
> ratios
>       and the ratio of averages (or perhaps also due to residual effect from
> shuffling)?
> 
> 
> Thank you,
> 
> with regards,
> Jagbir Singh
> 
> 
> 
> On 2020-11-18 23:18, Wang, Fuqiang wrote:
> > Hi Jagbir,
> >
> > Your results are quite interesting. I have a few further questions
> > about the details of your analysis:
> > 1. For each event you have Dbmax with the condition of |Dbasy|<0.25.
> > You bin events of each centrality in Dbmax. You use all events in your
> > analysis (i.e. you're not throwing away events based on Dbmax or
> > Dbasy), right?
> > 2. In your calculation of gamma=<...>/v2c for a particular Dbmax bin
> > of a given centrality, the v2c is calculated using those events only,
> > right?
> > 3. For the charge reshuffle, you reshuffle the charges of all events,
> > and repeat your analysis from step 1 (i.e. you treat this as a
> > completely separate "new" data sample), right? Did you "randomize" the
> > charges according to the positive/negative charge ratio of the given
> > event? On s11, the Dbmax_shuffle distribution is a bit wider than the
> > real distribution, do you understand why? How do you bin the Dbmax and
> > Dbmax_shuffle into 10 bins, respectively (same bin edges or same
> > fractions)?
> > 4. Your correlated background gamma is calculated for the Dbmax bin
> > where Dbmax is from the charge-shuffled events, but using restored
> > charges, right? If so, then you're effectively taking gamma difference
> > between Dbmax_i events and Dbmax_shuffle_i events (which are different
> > events), right? Of course you've also removed the large charge-shuffle
> > background which is basically an autocorrelation effect (sort to
> > speak) due to the Dbmax (and Dbmax_shuffle) selection bias.
> > 5. You divide Dbmax (and Dbmax_shuffle) into 10 bins and do your
> > analysis in each bin separately, and then take the weighted average
> > for your f_cme result. You could just use a single wide Dbmax (and
> > Dbmax_shuffle) bin, then in principle you should get zero signal
> > because the correlated "background" is your real signal since they are
> > now identical event sample. So is your finite signal really due to the
> > difference between the average of ratios and the ratio of averages (or
> > perhaps also due to residual effect from shuffling)?
> >
> > This is a complicated analysis. It would be really good to have more
> > discussions so the details can flesh out better.
> >
> > Thanks,
> > Fuqiang
> >
> >
> >
> >> -----Original Message-----
> >> From: Star-fcv-l <star-fcv-l-bounces AT lists.bnl.gov> On Behalf Of
> >> jagbir via Star- fcv-l
> >> Sent: Tuesday, November 17, 2020 10:49 AM
> >> To: ShinIchi Esumi <esumi.shinichi.gn AT u.tsukuba.ac.jp>; STAR Flow,
> >> Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
> >> Subject: Re: [Star-fcv-l] FCV PWG meeting, 18/Nov/2020 (Wed) 9:30am
> >> (New York time zone)
> >>
> >> Dear ShinIchi, Prithwish and Jiangyong,
> >>
> >> I would like to give "Update on event by event charge separation in
> >> Au+Au collisions at 200GeV with STAR detector"
> >>
> >> Please add me to agenda.
> >> I will post my slides later.
> >>
> >> Thankyou,
> >> Jagbir Singh
> >>
> >> On 2020-11-16 15:57, ShinIchi Esumi via Star-fcv-l wrote:
> >> > Dear FCV PWG colleagues
> >> > We will have our weekly FCV PWG meeting on coming Wednesday
> >> > 18/Nov/2020
> >> > 9:30AM (in BNL) at our usual time and place. So if you have
> >> > anything to present, please let us know and please post your slide by
> Tuesday.
> >> > We'll talk about the "HLT express productions" in the beginning of
> >> > the meeting as you see in the agenda page. Jiangyong, please send a
> >> > link to your slide from last week.
> >> >
> >> > The zoom room link, ID and password are in our usual drupal agenda
> >> > page below.
> >> > Please also keep in mind that all the preliminary plots should have
> >> > already been there in the summary area below.
> >> > Best regards, Jiangyong, Prithwish and ShinIchi
> >> >
> >> > Meeting agenda page with zoom link :
> >> > https://drupal.star.bnl.gov/STAR/blog/jjiastar/bulkcorr
> >> >
> >> > Preliminary page :
> >> > https://drupal.star.bnl.gov/STAR/pwg/bulk-correlations/bulkcorr-pre
> >> > lim inary-summary
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