STAR Flow, Chirality and Vorticity PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 1/14/2022

Participants: Chenlu Hu, Xionghong He, Yuanjing Ji, Yapeng Zhang, Fengyi Zhao, Barbara Trzeciak, Daniel Brandenburg, Daniel Cebra, Hanna Zbroszczyk, Maria Zurek, Matt Posik, Md. Nasim, Prithwish Tribedy, Qinghua Xu, Raghav Elayavalli, Hanseul Oh, Subhash Singha, Xiaofeng Luo, Yi Yang, Helen Caines, Rongrong Ma, Takafumi Niida

Title: First Observation of Directed Flow of Hypernuclei H3L and H4L in \sqrt{s_{NN}} = 3 GeV Au+Au Collisions at RHIC

PAs: Chenlu Hu, Xin Dong, Xionghong He, Yuanjing Ji, Yue-Hang Leung, Nu Xu, Yapeng Zhang, Fengyi Zhao

Target journal: PRL

Proposal page: https://drupal.star.bnl.gov/STAR/blog/clhu/hyper-nuclei-collective-flow-v1-3-gev-au-au-collisions-rhic

Presentation: https://drupal.star.bnl.gov/STAR/system/files/Chenlu_Directed_Flow_H3L_H4L_PWGC_20220110_v3.pdf

The PWGC panel previewed a paper from FCV PWG. The panel found that the results are interesting and the paper should move forward. The target journal is appropriate if the conclusion/physics message can be polished, while PRC is also mentioned. The following points were discussed.

s7: In abstract, “260M (5-40%) collisions” may be misleading and should be rephrased.

Fig. 1: 

Q. How was the BG estimated? In 3 body-decay, the BG is not smooth under the peak.

A. Rotational method was used for the BG. Maybe related to d+Lambda. BG estimate is included in the systematic uncertainty.

C. Good to check the yield and B.R. of 2 vs. 3 body decays.

Q. Any comment on the small peak near mass = 3 GeV?

A. Did some check but not understood. It is ~2.5 sigma effect.

Q. The line for open circles is fit? For signal distribution, the tail is not described well by Gaussian fit. So please try student-t.

A. The line for open circles is just line connecting the points.

C. It may be misleading.

Fig. 3:

Q. The data look to curve a bit with rapidity. For Lambda the trend is opposite to light nuclei. Any physics reason?

A. The model predicts similar trend but the reason is not understood.

Q. Maybe related to the curve trend, data points close to mid rapidity for H3L and H4L look lower than the neighbor bin though the uncertainty is large. Maybe related to pT acceptance in Fig. 2? Mean pT may be different with rapidity.

A. There may be some effect but the pT-y efficiency was corrected.

Fig. 4:

Q. How can we conclude the coalescence from this plot?

A. since the data seem to follow mass scaling.

C. The model fails to describe Lambda. If we need to rely on this model, this statement may not be justified.

A. Like light nuclei, one could conclude the coalescence from the observed mass scaling. PAs will think about more.

s12: Q. What are the blue dashed lines?

A. Just to guide eye.

s14: Q. How are the open and filled markers determined?

A. Based on Barlow test.

s15: 

Q. “JAM plus coalescence afterburner” Does the coalescence is a part of JAM or added by PAs?

A. No light nuclei in JAM, so the coalescence part was added by PAs.

C. One needs to treat n&p density and there are some parameters which could be improved more since the current model in Fig. 4 underestimates Lambda and also p&d slightly.

A. The yield changes with the parameters but v1 has a weak dependence.

C. This part in detail should be followed up in LFSUPC since the other groups are also working on the coalescence model at 3 GeV to reproduce centrality/pt/rapidity.

C. Since this is home made model, the detail should be discussed in Appendix or supplemental material.

C. Last 2 sentences in the conclusions about YN interaction are not supported by presented materials. This part should be either removed or revisited with supporting materials.