STAR Correlations and Fluctuations PWG

[ShinIchi Esumi <esumi.shinichi.gn AT u.tsukuba.ac.jp>]

Dear Eugenia

Nice studies. You have tested the coulomb effects in detail, it’s good to 

see it’s insensitive to the assumed radius. Have you also tried to look at 

other experimental effects, like two-track resolution, which might affect both 

loosing some close pairs or adding some ghost pairs, including momentum 

resolutions, by varying the pair cuts? 1D correlation functions sometimes are 

not well described by the gaussian assumption, so that you could try other 

formula, but if you go to 3D function, it could be well described by gaussian 

with different sizes depending on the directions Rts, Rto and Rl. As you also 

mentioned, you would also need to care about the base line shape especially 

for small system, which might also affect the fitting formula as well. I’m just 

more interested in the robustness of the measured raw correlation function 

as experimental measurements to start with, in stead of the description of 

the correlation shape with what kind of functional shape etc. 

Best regards, ShinIchi

On Oct 5, 2020, at 16:06, Eugenia Khyzhniak via Star-cf-l <star-cf-l AT lists.bnl.gov> wrote:

Dear All,

here in attachments are examples of correlation functions and their fit with difference Coulomb radius taken into account.

Best regards,

Eugenia

пн, 5 окт. 2020 г. в 09:53, Grigory Nigmatkulov <nigmatkulov AT gmail.com>:

Dear Hanna,

>Concerning your fits, using a Gaussian source here leads to discrepancies as you see between your data and fits.

We explicitly showed how different source assumptions affect the fits. Please follow the links from the last presentation.

We discussed these differences during the year. As we discussed, difference source and non-femtoscopic form assumptions will be in a paper.

I also want to notice that depending on the kT bin and multiplicity the Gaussian vs. non-Gaussian assumption will give different results.

For small systems the influence of (mini)jets and resonance decays will play a larger role than for large systems.

We presented those estimations using the UrQMD, Hijing and PYTHIA event generators. Only two of them contain

hard and semihard processes. NONE of the three describe the data to the level we would like it to be.

>I agree that one should use the same parametrization for all kT intervals but your results clearly show that for higher kT fit does not work well.

What do you propose if MC generators fail to describe non-femtoscopic effects and underlying event?

We explicitly say which assumptions have been used in the analysis and what results we have.

For the given assumptions one will obtain certain results. That is very similar to the ONLY small system femtoscopy paper

from 2009-10 by Zibi and Mike.

>For future, (if you have not done it yet) I would also suggest to see how simple Gaussian looks (without Coulomb correction) like to study the lambda parameter's behavior.

>It looks for higher kT interval to get with such parametrization a better agreement between data and fit.

For small systems the Coulomb effect is small and IS TAKEN into account in systematic uncertainty estimation! Eugenia, please send the figure of merit.

As for the curve at small q itself, the Coulomb effect is there but non-Gaussian structure dominates. Anyhow, the first few bins have almost no influence on the fit

and fit quality.

>Meantime please remove from your presentation all plots that did not get preliminary labels and discuss your results during the upcoming PWG CF meeting

Please specify which figures do you want to be updated and what exactly do you want to be changed? Eugenia can present the results again this Thursday.

The talk is scheduled for Friday morning.

Cheers,

Grigory

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