STAR Flow, Chirality and Vorticity PWG

[Sooraj Radhakrishnan <skradhakrishnan AT lbl.gov>]

Date: 07/12/2024

Participants: Aswini Kumar Sahoo, Md. Nasim. Prabhupada Dixit, Jae Nam, Hanna Zbroszczyk, Prithwish Tribedy, Subhash Singha, Zhenyu Chen, Isaac Mooney, Nihar Sahoo, Yue Hang Leung, Barbara Trzeciak, ShinIchi Esumi, Sooraj Radhakrishnan 

Title: Observation of Centrality-Dependent Difference in Directed flow between Charged Kaons and K* Resonances in Au+Au collisions at √sNN = 19.6 and 27 GeV

PAs: P. Dixit, Md. Nasim, A. K. Sahoo, S. Singha

Target journal: PRL

Proposal page: https://www.star.bnl.gov/protected/lfsupc/nasim/Kstar_v1_paper/webpage/

Presentation: https://drupal.star.bnl.gov/STAR/system/files/Kstar_v1_paper_proposal_pwgc.pdf

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, although it was suggested to polish the physics message for the target journal. The following points were discussed.

Q: On slide 3, where is the asymmetry in px coming from?

A: This is from the hydro evolution and driven by the initial spatial asymmetry on the left plot

Q: How is the pT integrated v1 calculated?

A: It is calculated by weighting with the raw spectra 

Q: Why raw spectra is used? Do you do efficiency correction?

A: Corrected spectra are not published. Results shown today are without efficiency correction. We have checked with efficiency correction, will include that

Q: How can we attribute the K* v1 to rescattering? What is the effect of regeneration?

A: We cannot study this from UrQMD as we cannot turn on/off regeneration. From yield measurements we see that rescattering is dominant

C: In the abstract then can change to say the deviation is from rescattering

Q: Can we make the contributions from the two effects quantitative?

A: It is difficult to do from the model side 

Q: How is the rapidity weighting done for the integrated results?

A: We flip the sign and integrate in -1 to 1

Q: Do you normalize by beam rapidity?

A: No 

Q: Do you have comparison to other hadrons, for eg. baryons and pions? 

A: We plan to make the comparisons with proton and pions 

Q: Charged kaons have different quark content (u instead of d) and mass than K*. Does this impact the v1? How large is the difference between K+ and K-?

A: The difference between K+ and K- is smaller than the difference to K* seen here. We take that the u and d quarks have same v1

Q: How about the mass difference? 

A: We also compare with phi that has similar mass 

C: But phi has different quark content

Q: We use mass scaling and coalescence assumption for v1 in other measurements. How do these scaling impact the comparisons shown here?

A: We expect the impact will be small. We will check. Also in peripheral collisions K* v1 is consistent with phi and charged kaon

Q: The model has very different centrality dependence and magnitude than data, in Figure 4. Do you know what contributes to this difference?

A: We do not know 

Q: Can other BES-II energies be included?

A: We plan to include 14.6 GeV as well. For other energies the significance is low 

Q: Is it possible to do this measurement at 200 GeV?

A: The background is high at 200 GeV and has poor signal significance

Q: In Figure 4, why is average v1 used for left plot and slope for the right one?

A: The model calculations were available for the slope. We will move to use the same variable 

 

--

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