STAR Flow, Chirality and Vorticity PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 2/5/2021

Participants: Xionghong He, Shaowei Lan, Yapeng Zhang, Matt Posik, Maria Zurek, Qinghua Xu, Daniel Brandenburg, Md. Nasim, Barbara Trzeciak, Yi Yang, Hanna Zbroszczyk, Xiaofeng Luo, Haseul Oh, Prithwish Tribedy, ShinIchi Esumi, Jiangyong Jia, Helen Caines, Takafumi Niida, Rongrong Ma

Title: Light nucleus v1 and v2 from \sqrt{s_{NN}} = 3 GeV Au+Au collisions

PWG: FCV

PAs: Xionghong He, Shaowei Lan, Sooraj Radhakrishnan, Nu Xu

Target journal: PLB

Proposal page: https://drupal.star.bnl.gov/STAR/blog/hexh/light-nucleus-v1-and-v2-3-gev

Presentation: https://drupal.star.bnl.gov/STAR/system/files/hexh_LightNucleusFlow_20210205_PWGC_0.pdf

The PWGC panel previewed the paper proposal from FCV PWG. The panel found that the analysis is mature and results are interesting. The target journal is appropriate. There were several comments that the paper should elaborate the physics conclusions more. The following points were discussed during the preview.

// Slide 6

Q. pT and rapidity dependent efficiency is corrected? There are missing acceptance for triton and 4^He near mid-rapidity. How were they treated?

A. The efficiency was corrected for final results. For the missing acceptance, those regions are not shown or removed, e.g. in Fig. 2.

// Slide 7

Q. Which EP was used for final results? All EPD subevents are dominated by spectators?

A. EPD A+B was used as a default and EPD C+D was used as a systematic check. EPD A would be more dominated by spectators.

Q. Have you tried to combine all EPD subevents to improve the resolution?

A. By combining all, the resolution becomes worse.

C. That’s because the proper weights are not used. If one use the weights properly, it should give you better resolution, although it may not be important for Psi1 which has already good resolution but maybe helpful for Psi2. 

Q. In other analysis, e.g by Joey, he also uses EPD EP but probably in a different way. Please communicate with him and make sure what would be better.

// Slide 11, Fig. 2

Q. In the left panel of Fig. 2, the fit lines are forced to cross zero?

A. No, but the offset obtained from the fit is close to zero.

Q. Why are the systematic uncertainties not shown for v1 (left panel) but shown for v2 (right panel)?

C. Error bars are very small and extracting the slopes is main purpose here, therefore they are not shown here.

// Slide 12, Fig. 3

C. Proton v1 is significantly larger than 3^He v1 considering the error, which should be mentioned clearly. Also the relation of deuteron and proton v1 becomes opposite at 3 GeV compared to higher energies.

// Fig. 4

C. Fig. 4 is scaled one, but even before the scaling the data are already on top of each other for midrapidity (slide 22). Only pT is shifted a bit in the scaled plot.

C. Before showing the scaled plot (Fig. 4), it would be better to show original pT dependence first.

Q. What are the fit lines?

A. They are polynomial fits just to guide eye.

// Other comments

Q. In conclusions, it says NCQ scaling fails for v2. Is there such a plot?

A. In backup (slide 23), scaled v2 are shown. 

Q. Are there pion and kaon v1, v2? How about NCQ scaling?

A. Yes they are in Shaowei’s paper. NCQ scaling for pi,k,p is broken for v2 at 3 GeV.

Q. What is purity?

A. More than 95% for all particles.

Q. PAs claim that v1 follows the atomic number scaling which is based on coalescence picture but v2 doesn’t follow NCQ scaling. It sounds inconsistent message. How can we understand it?

A. Indeed it’s puzzling. So far no good explanation. Maybe it’s more complicated than expected.

C. Would be nice to have any model comparison, especially model with mean field effect which is important at low energy and also with spectators effect.