STAR Correlations and Fluctuations PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 4/29/2023

Participants: Yevheniia Khyzhniak, Grigory Nigmatkulov, Mike Lisa, Barbara Trzeciak, Hanna Zbroszczyk, Jae Nam, Nihar Sahoo, Prithwish Tribedy, Sooraj Radhakrishnan, Toshihiro Nonaka, Xiaoxuan Chu, Yue-Hang Leung, Rongrong Ma, Takafumi Niida

Title: Charged kaon femtoscopy in Au+Au collisions at 14.6, 19.6, 27, 39, 62.4, and 200 GeV
PAs: Yevheniia Khyzhniak, Michael Lisa, Grigory Nigmatkulov
Target journal: PRC
Proposal page: https://drupal.star.bnl.gov/STAR/blog/yuno/Paper-proposal-Charged-kaon-femtoscopy-AuAu-collisions-146-196-27-39-624-and-200-GeV

Presentation: https://drupal.star.bnl.gov/STAR/system/files/Paper%20proposal%20PWGC.pdf

The PWGC panel previewed a paper proposal from CF PWG. The panel found that the analysis is mature and results are interesting, and the paper should move forward. The following points were discussed.

Q. Any purity/efficiency study?

A. In slide 22, we show purity of single particles and pair purity calculated. The bottom panel shows the effect of the purity correction which is quite small (<1%).

Q. In slide 12, right plot is based on toy model. Do you have plant to put it in the paper and explain the detail?

A. Yes

Q. In slide 13, the fit doesn’t look great, especially for Rlong. Why?

A. It could be due to Coulomb which is larger effect for kaons. Coulomb effect is calculated in 1D base but not 3D but the Coulomb effect is considered to be one of the systematic uncertainty. Rlong is known to deviate from Gaussin at higher kT. Also, these are 1D projections of 3D C2, therefore the slight difference here doesn't mean the overall fit is bad (chi2/ndf is close to 1).

Q. For merging cut shown in Fig. 2, how can you know there is no such effect in other areas?

A. FMH cut was also applied as shown in slide 25. For this azimuthally-integrated analysis, there should be no cross terms, however once the two quadrants in qs-qo are removed, the cross terms become zero. The variation of FMH cut was considered as one of systematic uncertainties (<2%). 

Q. In slide 16, why different kT values are shown? Previous figures are based on mT.

A. To compare pion and kaon with similar mT.

Q. Related to that, then why did PAs show C2 for the same kT instead of same mT region in Fig. 6?

A. It was just demonstration but will consider to select C2 for similar mT.

Q. In slide 18, temperature used in the fit functions are fixed to be 0.144 GeV. How did you choose this number? 

A. Yes, but PAs also studied the effect by changing T. No significant difference.

Q. The data show larger emission time but the temperatures used are same between pions and kaons. Are they somehow contradicting?

A. No big difference by T=0.12 or T=0.15 GeV, for example. The difference could be due to K* resonance which has longer lifetime which can be studied with models like UrQMD by turning-on/off resonance effects.

C. It would be great to have such model studies and discussion in the paper.

Q. Imaging analysis shows less resonance effect in kaons than in pions. But because of longer lifetime of K*0 the resonance effect is significant in the extracted \tau. Is that correct understanding?

A. Yes.

Q. Have you looked at the emission volume?

A. No, because it is basically the same information as the data shown in Fig. 7.

Q. As shown in Fig. 4, there is clear difference between positive and negative particles. But the extracted radii are charge-combined results. PAs could get charge-dependent radii.

A. Statistical error may become large but PAs agree and will look into it.

Q. There is PHENIX published results for kaon HBT at 200 GeV. Have you compared to it?

A. No.

C. It would be good to check if both are in reasonable agreement even though there are some kinematic differences.

C. Ro/Rs vs. energy is often studied in search for the phase transition. PAs may want to consider to look at it.

C. Please make sure that coherent messages are delivered in terms of the emission time and system size. Also, comparison with theoretical models would be helpful for better understanding and clear physics message.