STAR Correlations and Fluctuations PWG

["ChuanFu" <fuchuan AT mails.ccnu.edu.cn>]

Dear All,

             I would thank STAR for organizing collaboration meeting and also apologize for my microphone issue last night.

I would discuss the following several ponits about FMH merging cut method and dPhi&&dTheta merging cut method:

1) The FMH method calculate the distance δr(i) between the hits coming from two possibly-merged tracks reconstructed by TPC.

Since two tracks have been merged into one track in TPC, 

how do we calculate the distance δr(i) between the hits coming from the two tracks before they are merged?

Otherwise the FMH cut method is similar to dPhi&&dTheta cut mothod, both want to find two close together tracks in TPC and remove them.

2) Please see the following slide 9, the dPhi&&dTheta cut method dose not distort the p-p CF within stat. error 

except for those less-statistics and serious-merging points. 

https://drupal.star.bnl.gov/STAR/system/files/Proton_CF_PWG_Chuan_1216.pdf

For those less-statistics and serious-merging points,  for example, 90% of 100 counts are bad,

any merging cut method will be unreliable, the best way is to remove those points.

3) W use CRAB (can descibe p-p interactions well) and UrQMD (provide proton phase-space(x, y, z, t, px, py, pz, E) ) to simulate p-p CF at 3 GeV.

In below slide 11, you can find the CRAB+UrQMD can reproduce the data points well for mid-rapidity and pT windows in different collision centralities.

https://drupal.star.bnl.gov/STAR/system/files/ppCF_sys_PWG_Chuan_2022_0414.pdf

This indicates our simulation is reliable at least for mid-rapidity and pT windows.

Based on our simulation, we found the dPhi&&dTheta cut will not distort the p-p CF.

Hope above information can clarify our track-merging cut method.

Best regards,

Chuan

 

------------------ Original ------------------

From:  "Star-cf"<star-cf-l AT lists.bnl.gov>;

Date:  Tue, Sep 13, 2022 11:29 PM

To:  "qyq"<qyq AT mails.ccnu.edu.cn>; "wensong814"<wensong814 AT mails.ccnu.edu.cn>;

Cc:  "Star-cf"<star-cf-l AT lists.bnl.gov>;

Subject:  [Star-cf-l] About your pair cuts etc with SL and dphi/deta(dtheta) ...

 

Dear Youquan (Wensong and Anna, Vinh)

Thank you very much for showing your very nice studies on the pion (and kaon)

correlations. Could you (Youquan) please show us the correlation function

in 2D distribution like p11, c2(Qinv, SL), which is the ratio of "real/mix”, or

subtracted distribution “real - mix” after normalization? I would like to see

them for different centrality cases as you have mentioned 0.3 cut is good enough

for all centrality selections. This is also because Anna/Vinh uses 0.6 cut on

the same parameter with the similar(?) data set, although it might be different

because of other conditions like FMH(R?) etc, and TPC/iTPC difference as

Grigory says.

There were some discussion about delta_phi or data_phi* cut in both of your

talks. delta_eta (or delta_theta) cuts are needed simultaneously with delta_phi

cut. I suppose you know about phi* which is the local (position) angle within

the TPC, that is quite different from phi direction at primary vertex, this is also

the reason why we say the delta_phi* cut is supposed to be better than delta_phi

cut (because the splitting and the merging are both happening inside the TPC

detector, not at the primary vertex). It’s quite easy to get phi* from phi, which is

just given by pT and charge of the track at a given radius in the TPC. So

“delta_eta && delta_phi* cut” or “delta_theta && delta_phi* cut” could be easily

be replaced for both of your cases and it should be better. You would see more

splitting effect at smaller radius at about 70cm (inner TPC radius) and more

merging effect at larger radius at about 150cm (middle - outer TPC radius). Since

you are already based on the SL cut, you would most-likely need this  delta_phi* 

cut on larger radius, since you would like to remove the merging effect with this.

I would also like to remind and suggest you to plot and look first in order to

determine the cut values on the “delta_eta (or theta) && delta_phi* cut”, based

on what you really see on these 2D correlation plots (eta, theta and phi cut do

not have to be the same) in addition to the final “momentum” correlation function

in Qinv etc in order to determine the final cuts.

By the way, FMH(R) (fraction of merged hit or row?) cut has beed also used in

previous star hbt analysis, which I do not know much about it, have you tried to

use the FMH(R?) cut? I would like to see the some qualitative and quantitative

comparison between “SL && FMH cuts” and “delta_eta && delta_phi* cut at two

TPC radial positions” or "SL && delta_eta/phi* cut at one radius", where all of

them might work as we like/expect to remove both splitting and merging, properly.  

Best regards, ShinIchi

PS : Grigory, I could not find Anna's and Vinh’s E-mail address, so please

forward this to them, if you think this is useful for them, too. Thanks for the

(continuous) discussion...