STAR Flow, Chirality and Vorticity PWG

[EsumiShinIchi <esumi.shinichi.gn AT u.tsukuba.ac.jp>]

Dear Zuowen

Thank you very much for the reply. 

v1 = v1_raw / resolution

The “v1_raw" can be measured without p-cons effect, because of the symmetric 

rapidity acceptance of EPD with respect to TPC as you have also mentioned, 

however the “resolution” could be still affected by p-cons between 2 EPD planes, 

especially if it is determined with 2-sub method, which uses the correlation between 

the forward and backward EPD planes. So in this case, “v1_raw” is OK, but “resolution” 

could be overestimated by p-cons, therefore the final “v1”could be smaller than the truth. 

That is why we need to think about 3-sub method or some other ways to take this into 

account, for example, one could try to do a few things. 

(1) TPC-EPD(east)-EPD(west) and TPC-EPD(full)

(2) TPC-EPD(inner)-EPD(outer) and TPC-EPD(full)

(3) TPC(east)-TPC(west)-EPD(full)

(4) TPC(a)-TPC(b)-EPD(full)

With these A-B-C and A-D for the cases (1) and (2), one could get resolution of D

= (AD)/sqrt(AB*AC/BC). For the case (1), I would think it gives a similar resolution 

from the current 2-sub, because of the same p-cons effect existing in B-C. For the 

case (2), all A,B and C are free from p-cons because of the symmetric choice, but 

we now need to worry about non-flow and eta-gap in B-C. For the case (3), we also 

need to worry about non-flow and p-cons in A-B. For the case (4), if we take both 

TPC(a) and (b) to be symmetric in rapidity, we are free from the p-cons, but we still 

need to care about non-flow between (a) and (b)… If we could have 3 independent 

and rapidity symmetric planes (without non-flow and de-correlation), it would be 

good. Thank you very much again for the discussion. 

Best regards, ShinIchi

On Oct 18, 2023, at 3:39, Zuowen Liu <liuzw AT mails.ccnu.edu.cn> wrote:

Dear Prof. ShinIchi,

Thanks a lot for your nice suggestions.

Junyi and I have talked about the approximation on sqrt(2).

We agree that the approximation is not appropriate, and it would be corrected.

For the mom. cons. effect, I agree if we reconstruct EP with one arm of EPD, we would face the p cons. effect due to the asymmetry. But I don't understand why we need to worry about p cons. if we used 2-sub event, where the mom is conserved "naturally" due to the symmetric track direction. While Junyi and I could take a quick cross-check for the 

single and two EPDs.

Thanks and Best regards,

Zuowen

 

------------------ Original ------------------

From:  "EsumiShinIchi via Star-fcv-l"<star-fcv-l AT lists.bnl.gov>;

Date:  Tue, Oct 17, 2023 11:14 AM

To:  "star-fcv-l"<star-fcv-l AT lists.bnl.gov>;

Cc:  "ShinIchi Esumi"<esumi.shinichi.gn AT u.tsukuba.ac.jp>;

Subject:  [Star-fcv-l] mom.-cons. effect in 2-sub e.p. resolution estimation...

 

Dear Zuowen (and Junyi)
I mentioned to Junyi about the approximation on sqrt(2), so I hope you can
communicate with Junyi on this. As I’ve also written in the chat window, I
send you the same (following) message just in case you might have missed,
that is about the mom.-cons. effect in 2-sub e.p. resolution estimation.

I should have asked this to Zuowen, who is doing similar 2 sub-event methods
for estimating e.p. resolution, I think we need to think about p-conservation
between 2-subs, by including and/or comparing the 3-sub or other methods in
order to understand the possible contribution from p-cons effect in the current
e.p. resolution estimation. While for measuring raw v1, it is canceled, since you 
use the combined E.P. from e/w EPDs, but as long as you are based on the
2-sub method between E-W event planes for the E.P. resolution estimation,
we are affected by the momentum conservation effect, that we would like
to subtract, as we could clearly see the effect using the single arm EPD plane
E or W, that is the p-cons effect between TPC and single EPD, which would be
different from the one between two EPDs...
Best regards, ShinIchi

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