STAR Correlations and Fluctuations PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 5/20/2022

Participants: Debasish Mallick, Bedangadas Mohanty, Barbara Trzeciak, Daniel Brandenburg, Daniel Cebra, Maria Zurek, Matt Posik, Nihar Sahoo, Prithwish Tribedy, Qinghua Xu, Hanseul Oh, Sooraj Radhakrishnan, Subhash Singha, Xiaofeng Luo, Yi Yang, Rongrong Ma, Takafumi Niida

Title: Collision energy dependence of deuteron cumulants and proton-deuteron correlations in Au+Au collisions at RHIC

PAs: Debasish Mallick, Nu Xu, Bedangadas Mohanty

Target journal: PLB

Proposal page: https://www.star.bnl.gov/protected/bulkcorr/dmallick/WebPage_Deuteron/index.html

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

The PWGC panel previewed a paper from CF PWG. The panel found that analysis is mature and the paper should move forward. Regarding the journal, there was comments that longer paper may be better to make clear conclusion with more figures and detailed discussion. The following points were discussed.

Q. In slide 4, for toy model A, the assumption n_p=n_n is wrong. Not sure the meaning to show the calculation which started with wrong assumption.

A. These are two extreme assumptions and indeed our data indicates that assumption A is not the case. Also, the sign of \rho is important.

Q. What’s the effect of knock-out deuterons? What’s the fraction? Any plot showing d and dbar DCA?

A. DCA was varied as shown in slide 9 and included in the systematic uncertainty. PAs will make such a plot and estimate the effect.

Fig. 2

Q. C1, mean of deuteron number, is very small at higher energies. It means that there are too few deuterons per event, telling us that it is difficult to do this fluctuation measurement. 

A. True. Therefore the data in Fig. 4 is close to Poisson distribution and consistent with statistical sampling baseline that PAs performed.

Fig. 3

Q. Two coalescence models cannot describe the data. Is that what the paper concludes?

A. UrQMD+coalescence works better where UrQMD includes baryon conservation.

C. The coalescence model (A,B) are just toy model which doesn’t have dynamical evolution, baryon conservation and likely underestimates neutron yield while UrQMD works.

Q. Have you looked at normal UrQMD without coalescence

A. Normal UrQMD doesn’t make deuterons.

Q. These models are for central events? Possible to have different centralities for the models?

A. There are for central events. Thermal model works better in central events.

Conclusions

Q. It says “thermal model based on GCE and CE describe d-fluctuations and d-p correlation above 20 GeV” but the data has no ability to resolve it above 20 GeV because of too few deuterons.

A. Yes but it’s also true that GCE and CE get closer at higher energies for cumulant ratios. As for p-d correlation, there is some difference.

Q. The presentation started with the motivation: thermal model vs. coalescence for deuteron production. Can we understand that we cannot differentiate them with the data?

A. Yes. But we can say GCE doesn’t work at lower energies.

Q. Have you tried statistical test to quantify it?

A. No. PAs could do but there are also a lot of uncertainties from the model parameters.