STAR Flow, Chirality and Vorticity PWG

[Sooraj Radhakrishnan <skradhakrishnan AT lbl.gov>]

Date: 01/17/2025

Participants: Qiang Hu, Qinghua Xu, Tong Fu, Xingrui Gou, Zhenyu Chen, Xiaoxuan Chu, Hanna Zbroszczyk, Prithwish Tribedy, Richard Seto, Subhash Singha, Isaac Mooney, Yue Hang Leung, Barbara Trzeciak, ShinIchi Esumi, Sooraj Radhakrishnan

Title: Measurement of Local Polarization of Lambda Hyperons from RHIC Beam Energy Scan-II

PAs: Zhenyu Chen, Tong Fu, Xingrui Gou, Qiang Hu, Hao Qiu, Subhash Singha, Qinghua Xu

Target journal: PRL or PLB

Proposal page: https://drupal.star.bnl.gov/STAR/blog/qhu1/Paper-proposalMeasurement-Local-Polarization-Lambda-Hyperons-RHIC-Beam-Energy-Scan-II

Presentation: https://drupal.star.bnl.gov/STAR/blog/qhu1/PWGCreviewMeasurement-Local-Polarization-Lambda-Hyperons-RHIC-Beam-Energy-Scan-II20250117

The PWGC panel previewed a paper proposal from FCV PWG. The panel found that the analysis is mature and results are important and interesting, and the paper should move forward. The journal choice was also found to be appropriate. The following points were discussed.

Q: On Fig.3, S.16, how can you say that there is a sign change?

A: The data point at 19.6 GeV is negative for Pz,s2, lower energies show within uncertainties positive values
Q: The error bars are large at lower energies, values are consistent within zero. It is wishful to say there is sign change
A: Yes 

Q: The new model calculations on S.19 are comparing only to lambda local polarization and not their difference, right?

A: Yes. Lambda polarization measurements have better precision. They also have the difference but the difference measurements from data lacks precision 

Q: Are these caluclations with SMASH or SMASH + Hydro

A: These are hydro calculations using initial conditions from SMASH

Q: How can we learn about spin Hall effect just by looking at Lambda polarization, dont we need to see the difference between Lambda and Lambdabar?

A: The model calculations show there is sensitivity to Lambda local polarization
Q: Can other parameters be tuned in the model without SPH to reproduce the data
A: The model should simultaneously describe different observables include Pz,s2, Py,c2 and global polarization

Q: Are there other models that can describe the data?
A: Not currently 

Q:  Do we the global polarization measurements from these energies published?

A:  There is a paper proposal. It is in queue for PWGC preview

Q: Do we have measurements of Py,c2 at other energies? 

A: We have the measurements from isobar. Also preliminary results from Au+Au 200 GeV is also there
Q: Can the Au+Au 200 GeV results be included in this paper?
A: Yes, will look into this

Q: What is the main message you want to convey from this paper?
A: We are searching for the baryon density gradient driven spin polarization. 
Q: Would this be a model dependent conclusion?
A: Yes, but the model will have to describe the different observables simultaneously 

Q: Will the results from global polarization be included in this paper or a separate publication?
A: Currently is planned for a separate paper
Q: Would this reduce the ability to constrain the models
A: Global polarization measurements from BES-I exists, so there are some constraints for global polarization already 

Q: Are there any calculations from AMPT for these local polarizations?
A: Dont have currently. Havent seen local polarization calculations from AMPT

--

Sooraj Radhakrishnan

Research Scientist,

Department of Physics

Kent State University

Kent, OH 44242

Physicist Postdoctoral Affiliate

Nuclear Science Division
Lawrence Berkeley National Lab
MS70R0319, One Cyclotron Road

Berkeley, CA 94720

Ph: 510-495-2473

Email: skradhakrishnan AT lbl.gov