STAR Flow, Chirality and Vorticity PWG

[Shengli Huang <shengli.huang AT stonybrook.edu>]

Dear Yicheng,

    Thanks for answering my question. We can discuss more in PWG meeting.

Regards

Shengli

On Mon, Nov 25, 2024 at 7:36 PM Feng, Yicheng <feng216 AT purdue.edu> wrote:

Hi Shengli,

Thank you for your follow-up questions. 

If I understand correctly, your v2{2} results do not include any η cut, while c3p has a ∣Δηab∣>0.1 cut, correct?

Yes, now your understanding is correct. 

1. If so, the track merging effect may still influence your fCME(obs) measurements shown in Fig. 1 due to the lack of any η gap for v2{2}. Do you have fCME(obs) results using v2{2} with ∣Δη∣>0.1?

We don't have fcme^obs using v2{2} with ∣Δη∣>0.1. Because there is no gap between POI and c particle in ∆γ, so v2{2} should match that. 

Particle c is a tool to measure ∆γ, serving as “event plane”. The cut on c must be identical between ∆γ measurement and v2 measurement. The tracking merging effect is part of the nonflow that is taken care of by nonflow removal in fcme. 

2. Furthermore, the ∣Δη_ab∣>0.1 condition would not entirely eliminate the merging effect, as the tracks of POI with c may still include this effect. Have you conducted a study where an η gap is applied between POI and c? Since HIJING does not have such an effect, it’s essential to demonstrate that this merging effect is fully mitigated before performing the nonflow subtraction.

We will look further into HIJING. 

3. Figures 15 and 16 show differences in the nonflow contributions between the 1-D fit and HIJING methods. 50% in some peripheral bins. So I do not understand why you say they are consistent. Can you re-estimate the nonflow effects using v2{2} with an η cut applied in both the 1-D fit method and HIJING? Then we can see how much difference in central collisions after mitigating the merge effect.

The right panels of Fig.15,16 are the results from subevents with η gap, so I think we could check the comparison on the bottom right plot of Fig.16 free from track merging. 

The model/data ratio agrees with 1 within systematic uncertainty in nearly all centrality bins, which I think is already a reasonable model-data comparison. 

Sincerely,

Yicheng

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Subject: Re: [[Star-fcv-l] ] AuAu 200GeV CME paper draft and analysis note

 

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Dear Yicheng,

Thank you for your reply. If I understand correctly, your v2{2} results do not include any η cut, while c3p has a ∣Δηab∣>0.1 cut, correct?

1. If so, the track merging effect may still influence your fCME(obs) measurements shown in Fig. 1 due to the lack of any η gap for v2{2}. Do you have fCME(obs) results using v2{2} with ∣Δη∣>0.1?

2. Furthermore, the ∣Δη_ab∣>0.1 condition would not entirely eliminate the merging effect, as the tracks of POI with c may still include this effect. Have you conducted a study where an η gap is applied between POI and c? Since HIJING does not have such an effect, it’s essential to demonstrate that this merging effect is fully mitigated before performing the nonflow subtraction.

3. Figures 15 and 16 show differences in the nonflow contributions between the 1-D fit and HIJING methods. 50% in some peripheral bins. So I do not understand why you say they are consistent. Can you re-estimate the nonflow effects using v2{2} with an η cut applied in both the 1-D fit method and HIJING? Then we can see how much difference in central collisions after mitigating the merge effect.

Thank you! 

Best regards,
Shen