STAR Flow, Chirality and Vorticity PWG

["Robertson, Charles William" <rober558 AT purdue.edu>]

Hello All,

For our correction procedure, the question we ask:

What is the detector effect on pairs of kaons which have (1) identical single-particle level properties as the phi decay kaons but (2) no pair-wise physical correlations?

For (1), we weight the kaons in real data to match the decay kaon kinematics in real data.

For (2), we use mixed-events or rotated pairs.

We will present an update at next week's FCV meeting. 

To your specific comments:

However, while this procedure matched kaon daughter spectra to that from \phi-decayed kaon, it inadvertently distorted the actual \phi spectra. The \phi spectra in group 2 differ from the input in group 1, defeating the purpose of maintaining uniformity across all parameters.

The \phi spectra are not the question here. We are interested in the combinatorial pairs of "decay daughters." 

What we measure in experiment (mixed-event or rotated) are combinatorial pairs of kaons: phi1K-phi2K,phiK-K,K-K. Here phi*K denotes K from a phi decay, K denotes a primordial kaon. Both phi*K and K are after detector effect, and K is scaled to match phi*K by a weight, i.e., phi*K/(phi*K+K).

The detector does not care if a kaon is from a phi decay or not.

So, through this procedure using real data mixed-events or rotated pairs, we have effectively formed <cos^2\theta*> of combinatorial pairs of phi-decay kaons.

Those kaons are impacted by detector effects.

On the other hand, we have the combinatorial <cos^2\theta*> of decay kaons before any detector effect by using the published phi data. 

>From the difference of these two, we get the correction.

A separate but related question: the nature paper has a single correction factor lumping the EP resolution and detector effects together. The corrections are (col. 5).

Energy	Our EP Res	Nature raw rho00	Nature rho00	Nature corr.	EP Res Corr'd rho00	Nature detector corr.
11	0.348	0.3503	0.365	0.0147	0.3666	-0.0016
19.6	0.399	0.3453	0.359	0.0137	0.3551	0.0039
27 (Run 18)	0.431	0.3468	0.3608	0.0140	0.3569	0.0039
39	0.459	0.3364	0.3378	0.0014	0.3384	-0.0006
62	0.484	0.3423	0.3488	0.0065	0.3480	0.0008
200 (Run 14)	0.590	0.3341	0.3358	0.0017	0.3344	0.0014

We can calculate the EP resolution effect easily (col.6). From that we can get the effective detector correction of the nature paper (last column). Those detector corrections are positive and negative and vary with a rather large range. Why is that? We expect them all to be negative.

Note, we have used our subevent EP resolution, which should be slightly smaller than the nature paper resolution because we exclude all kaons from EP reconstruction. This means that effective detector corrections in the nature paper are event more positive.

Thanks,

-CW

---

From: Star-fcv-l <star-fcv-l-bounces AT lists.bnl.gov> on behalf of Tang, Aihong via Star-fcv-l <star-fcv-l AT lists.bnl.gov>
Sent: Friday, May 10, 2024 11:09 PM
To: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
Cc: Tang, Aihong <aihong AT bnl.gov>
Subject: [Star-fcv-l] Decompose Purdue Group's Correction-Proceduer for Detector Effect on Global Spin Alignment

 

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Dear all,

I am quite puzzled by the Purdue group's claim made at the FCV meetings. They asserted that a derivation for their correction procedure for detector effects in global spin alignment analysis is unnecessary. I firmly believe that whenever possible a robust correction procedure should be a bottom-up approach, wherein all components are thoroughly understood and their contributions are under control.

Since the Purdue group failed to provide such a derivation despite a number of requests made to them, I took some time to decompose and write down the terms involved in their procedure. Upon careful examination, it was found that the Purdue group's correction procedure does not yield the intended correction.

You can find the link to the document here:

https://drupal.star.bnl.gov/STAR/system/files/DecomposePurdueSpinAlignmentProcedure_May2024.pdf

Thanks,

Aihong