STAR HardProbes PWG

[Sooraj Radhakrishnan <skradhakrishnan AT lbl.gov>]

Date: 08/30/2024

Participants: Dandan Shen, Rongrong Ma, Wangmei Zha, Zebo Tang, Jae Nam, Xiaoxuan Chu, Hanna Zbroszczyk, Nu Xu, Subhash Singha, Isaac Mooney, Nihar Sahoo, Qian Yang, Yi Yang, Guannan Xie, Tommy Tsang, Yue Hang Leung, Sooraj Radhakrishnan

Title: Measurements of J/Psi polarization in Ru+Ru and Zr+Zr collisions at 200 GeV at STAR

PAs: Dandan Shen, Qian Yang, Rongrong Ma, Zebo Tang, Li Yi, Wangmei Zha

Target journal: PLB

Proposal page: https://drupal.star.bnl.gov/STAR/blog/dshen1/Measurements-of%C2%A0JPsi%C2%A0polarization-in%C2%A0RuRu%C2%A0and%C2%A0ZrZr%C2%A0collisions-at%C2%A0200-GeV-STAR

Presentation:https://drupal.star.bnl.gov/STAR/system/files/pwgcReview_Jpsi%20polarization_v1.pdf

The PWGC panel previewed a paper proposal from HP 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: What is lambda_inv?

A: This is calculated from lambda_theta and lambda_phi. It is frame independent 

Q: How does the results compare to that at LHC? Can we say the polarization is different at LHC and RHIC

A: The RHIC and LHC measurements at mid-rapidity.are consistent within uncertainties  

Q: Why do we need two frames? Helicity and CS?

A: This is good way to cross-check with lambda_inv. Also, they have different physics focus. 

Q: Can we quantify the precision of the measurement? Or how many sigma from zero?

A: Will look into

Q: Slide 6, Can we conclude anything on regeneration at RHIC from the polarization measurements?

A: Regenerated J/Psi is expected to reduce polarization. Current precision is low to make any conclusions

C: Do you have model calculations for this?

A: No

Q: S16, shouldn't the y range be less than +-0.8?

A: Yes, will fix the legend on the plot

Q: How is the iterative procedure done?

A:  We vary the input J/Psi polarization in evaluating efficiencies iteratively, till the final results converge 

Q: Do you get non-zero values for the input polarization from the iterative procedure

A: The value is very close to zero, as can be seen from slide 32

Q: Do we have polarization measurement relative to the EP?

A: Yes, we see a 3 sigma effect.

Q: Why not include it in the paper

A: The results from different PA groups have disagreement, which are being looked into

Q: Do we have centrality dependence for this?

A: The error bars are large to conclude 

Q: On S.14, 15, why the range is different for costheta* for the two frames?

A: This follows the yield distributions. 

Q: Will the fit range affect the extracted values?

A: We can change the fitting range to evaluate 

Q: Comparing to the LHC measurement at forward rapidity, can we conclude on polarization at forward and mid-rapidity?

A: No, the LHCb measurement is on p+p. In isobar there are other effects 

--

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