STAR Correlations and Fluctuations PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 9/30/2022

Participants: Paweł Szymański, Diana Pawłowska, Sebastian Siejka, Daniel Wielanek, Hanna Zbroszczyk, Daniel Cebra, Barbara Trzeciak, Maria Zurek, Nihar Sahoo, Qinghua Xu, Sooraj Radhakrishnan, Subhash Singha, Xiaofeng Luo, Xiaoxuan Chu, Yi Yang, Takafumi Niida, Rongrong Ma

Title: Non-identical particle femtoscopy measurements in the STAR Beam Energy Scan program

PAs: Paweł Szymański, Diana Pawłowska, Sebastian Siejka, Daniel Wielanek, Hanna Zbroszczyk 

Target journal: PRC

Proposal page: https://drupal.star.bnl.gov/STAR/blog/pawszy/Paper-proposal-Non-identical-particle-femtoscopy

Presentation: https://drupal.star.bnl.gov/STAR/system/files/paperProposalNonId_PWGC_30.09.2022.pdf

The PWGC panel previewed a paper proposal from CF PWG. The panel found that the analysis is mature and the paper should move forward, with the comment that clearer physics message is needed. The following points were discussed.

General:

Q. Results from 3 energies are presented. Why don’t you include other energies? or any plan to do the same study for the others?

A. PAs think that the energies selected are enough to make conclusions delivered from this paper. No so much gain to add other, e.g. 11.5 and 54 GeV, energies which takes more time. 

Q. Is there ALICE result which can be included? Would be nice to see the trend of energy dependence in a wider range.

A. There will be ALICE published results and also there is old paper from STAR at 200 GeV. PAs will check and consider to include them for comparison.

Q. There are results on pi-pi HBT in BES from STAR. Any additional gain or connection to this analysis?

A. In slides 61-62, comparison with published pi-pi HBT is shown. Although they are not apple-to-apple comparison because of different technique, some assumptions, different mT, they are comparable.

C. Would be nice if PAs can say something in the paper comparing to previous measurements.

Q. Plot in slide 23 seems important where the source size increases with energy and reach ~12 fm. What can we learn, maybe related to the old discussion of "HBT puzzle”? Could this measurement have more sensitivity?

A. Haven't thought about it. PAs will think what we can say.

Slide 8: 

Q. In Left-top panel, "C+S” seems not to be a sum of “Coulomb” and “Strong”. Why?

A. They are not a simple sum of the two contributions which are coupled.

Slide 15:

Q. The background is fitted with polynomial function. Is this just empirical way or is there theoretical guidance to use the function?

A. The polynomial seems to explain the background shape based on Ref. [1] (see slide 14).

Slide 17:

C. There are 6 different markers with fit lines which are close each other. It is hard to see them. Please consider better way to present the data.

Slide 21: 

Q. Is the “source size” the right word since pions and kaons are emitted differently in position or time? Should we understand average separation length between pions and kaons?

A. Gaussian distribution is assumed for both particles and with that assumption we can still say source size.

Slide 23:

Q. Statistical uncertainties of “++” and “- -“ and its relation look different in different energies. Why?

A. Partly due to statistics at higher energy where you have more positive particles but also partly due to the fit quality, i.e. how well the fit function  can describe the data.