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[Star-fcv-l] Notes for PWGC preview (06/03/2022): Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at \sqrt{s_{NN}} = 200 GeV
- From: Rongrong Ma <marr AT rcf.rhic.bnl.gov>
- To: STAR Papers Discussion List <Starpapers-l AT lists.bnl.gov>, STAR experiment physics discussions <star-phys-l AT lists.bnl.gov>, "STAR Flow, Chirality and Vorticity PWG" <star-fcv-l AT lists.bnl.gov>
- Subject: [Star-fcv-l] Notes for PWGC preview (06/03/2022): Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at \sqrt{s_{NN}} = 200 GeV
- Date: Fri, 3 Jun 2022 21:27:22 -0400
Date: 6/03/2022
Participants: Takafumi Niida, Sergei Voloshin, Qianghua Xu, Barbara Trzeciak, Sooraj Radhakrishnan, Nihar Sahoo, Md Nasim, Daniel Brandenburg, Maria Zurek, Mattew Posik, Subhash Singha, Hanna Zbroszczyk, Xiaofeng Luo, Rongrong Ma
Title: Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at sqrt{sNN} = 200 GeV
PAs: Takafumi Niida, Xingrui Gou, Zhenyu Chen, Qinghua Xu, Sergei Voloshin
Target journal: PRL
Presentation: https://www.star.bnl.gov/protected/bulkcorr/taknn/Paper/pzisobar/PaperProposal_PzIsobar_niida.pdf
The PWGC panel previewed a paper from FCV PWG. The panel found that analysis is mature and the paper should move forward, and the target journal is appropriate. The following points were discussed.
(Q: question, A: answer, C: comment)
slide 5
Q: do you plan to include results using EPD in the paper?
A: we have checked that results using EPD are consistent with those using TPC. We will include the figures in the analysis note, but not in the paper.
C: maybe you can mention this check in the paper
A: will do
slide 6
Q: the background contribution results in an uncertainty of 3% for polarization relative to 2nd-order event plane and 17% for 3rd-order. How do you estimate this contribution?
A: as shown on slide 21, this uncertainty is estimated by trying different ways of estimating background contribution.
Q: there seems large statistical fluctuation that could contribute to the large uncertainty of 3rd-order? Have you tried Barlow's method?
A: indeed, there could be statistical fluctuations. We tried Barlow's method, which resulted in non-smooth uncertainty vs. centrality. In the end, we decided to take the maximum deviations since they are still smaller than statistical errors.
Q: the background contribution results in an uncertainty of 3% for polarization relative to 2nd-order event plane and 17% for 3rd-order. How do you estimate this contribution?
A: as shown on slide 21, this uncertainty is estimated by trying different ways of estimating background contribution.
Q: there seems large statistical fluctuation that could contribute to the large uncertainty of 3rd-order? Have you tried Barlow's method?
A: indeed, there could be statistical fluctuations. We tried Barlow's method, which resulted in non-smooth uncertainty vs. centrality. In the end, we decided to take the maximum deviations since they are still smaller than statistical errors.
slide 9
Q: have you checked differences between Ru+Ru and Zr+Zr?
A: yes, they are consistent as shown on slide 17, which is why we combine them. Will make this comment in the paper.
Q: have you checked differences between Ru+Ru and Zr+Zr?
A: yes, they are consistent as shown on slide 17, which is why we combine them. Will make this comment in the paper.
slide 11
Q: the polarization vs. pt results seem consistent between Isobar and Au+Au, while the centrality dependences shown on slide 12 are visibly different. Are these two results consistent?
A: indeed, these two results seem inconsistent on the face value. Will check this.
Q: do you have 3rd-order results in Au+Au collisions you can compare to? Referees might ask such a question, and we better be prepared.
A: no, we do not. We tried such measurement using Run14 Au+Au data, but the signal was not significant.
Q: the polarization vs. pt results seem consistent between Isobar and Au+Au, while the centrality dependences shown on slide 12 are visibly different. Are these two results consistent?
A: indeed, these two results seem inconsistent on the face value. Will check this.
Q: do you have 3rd-order results in Au+Au collisions you can compare to? Referees might ask such a question, and we better be prepared.
A: no, we do not. We tried such measurement using Run14 Au+Au data, but the signal was not significant.
slide 12
Q: could you do a statistics test between these results such that we can quantify whether there are system size and/or collision energy dependences?
A: yes, we can do that.
Q: how do you extract these pT integrated results?
A: these results are obtained by using Lambdas in 0.5-6 GeV/c directly, not by integrating pT differential results shown on slide 11. Will check the pT shapes in Au+Au and Isobar to see if the difference in the same centrality could be due to possible different pT shapes.
Q: have you applied efficiency correction?
A: no, we did not. The effect of efficiency correction was checked to be very small in Au+Au analysis.
Q: have you tried plotting against Npart or dN/dy instead of centrality?
A: theory expects that the polarization w.r.t. 2nd-order event plane scales with centrality as v2 is driven by collision geometry, while 3rd-order could scale with dN/dy as v3 is driven by fluctuations. This is why we plot vs. centrality.
Q: are there any guidance from theory in terms of system size dependence?
A: the Hydro calculation shown on slide 10 is done for Cu+Cu, Isobar and Au+Au, but not for Pb+Pb. A maximum 10% difference is seen.
Q: could you do a statistics test between these results such that we can quantify whether there are system size and/or collision energy dependences?
A: yes, we can do that.
Q: how do you extract these pT integrated results?
A: these results are obtained by using Lambdas in 0.5-6 GeV/c directly, not by integrating pT differential results shown on slide 11. Will check the pT shapes in Au+Au and Isobar to see if the difference in the same centrality could be due to possible different pT shapes.
Q: have you applied efficiency correction?
A: no, we did not. The effect of efficiency correction was checked to be very small in Au+Au analysis.
Q: have you tried plotting against Npart or dN/dy instead of centrality?
A: theory expects that the polarization w.r.t. 2nd-order event plane scales with centrality as v2 is driven by collision geometry, while 3rd-order could scale with dN/dy as v3 is driven by fluctuations. This is why we plot vs. centrality.
Q: are there any guidance from theory in terms of system size dependence?
A: the Hydro calculation shown on slide 10 is done for Cu+Cu, Isobar and Au+Au, but not for Pb+Pb. A maximum 10% difference is seen.
slide 13
Q: the second bullet says that Isobar and Au+Au results are consistent, while a later bullet says there is system size dependence. Aren't they contradicting each other?
A: in the second bullet, we meant that Isobar and Au+Au results have the same sign, while the later bullet talks about the magnitude. We will make it clear in the paper.
Q: the second bullet says that Isobar and Au+Au results are consistent, while a later bullet says there is system size dependence. Aren't they contradicting each other?
A: in the second bullet, we meant that Isobar and Au+Au results have the same sign, while the later bullet talks about the magnitude. We will make it clear in the paper.
C: it will strengthen the paper by pointing out explicitly the important of the measurement w.r.t. the 3rd-order event plane. This can be done during GPC.
- [Star-fcv-l] Notes for PWGC preview (06/03/2022): Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at \sqrt{s_{NN}} = 200 GeV, Rongrong Ma, 06/03/2022
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