STAR Flow, Chirality and Vorticity PWG

[Zhiwan Xu <zhiwanxu AT physics.ucla.edu>]

Hi Isaac,
 Thank you reaching out. You may refer to Gang's method paper: https://journals.aps.org/prc/abstract/10.1103/PhysRevC.104.064906
 The reason we use the "same" POI range is to avoid a large blank area near v2 equals zero region.
 In using same POI, when q2 goes to 0, we have v2 goes to zero quite decently. Then in the dg112-v2 plot, the linear fitting is more trustworthy.
 What people previously worried is that using exactly the same POIs for q2 and v2 may brought up residual background issue. We proved that this is true by AVFD model, and I showed this in February collaboration meeting. (check my slide: https://drupal.star.bnl.gov/STAR/system/files/CME_ESS_ZhiwanXu_v5.pdf)
 We also proved a clever way to suppress the residual background: use pair-single mix combination at the same POI region. AVFD model supports that this can further suppress the residual background, and even over-subtraction of it. We are still investigating this new approach, and will update to the CME focus group soon.

Best,

Zhiwan

------------------------------------
Zhiwan Xu,
Department of Physics and Astronomy, UCLA
zhiwanxu AT physics.ucla.edu

---

From: "Isaac via Star-fcv-l Mooney" <star-fcv-l AT lists.bnl.gov>
To: "Gang Wang" <gwang AT physics.ucla.edu>, "STAR Flow, Chirality and Vorticity PWG" <star-fcv-l AT lists.bnl.gov>
Cc: "Rosi Reed" <rosijreed AT lehigh.edu>
Sent: Friday, March 17, 2023 9:48:52 AM
Subject: Re: [Star-fcv-l] Questions about event shapes

Hi Gang,

Thanks very much for the information. I will contact Zhiwan now.

Best,

Isaac

On Mar 17, 2023, at 12:39 PM, Gang Wang via Star-fcv-l <star-fcv-l AT lists.bnl.gov> wrote:

Hi, Rosi and Isaac

What Isaac saw is normal, which is also what our student, Zhiwan saw previously.

That's why in our event-shape selection analysis, q2 is based on the particles of interest,

instead of a separate sub-event. But the event plane has to be separated from the sub-event where you build q2.

For technical details, you may directly contact Zhiwan, who is always willing to help.

Gang Wang
Department of Physics & Astronomy
UCLA

---

From: "Rosi Reed via Star-fcv-l" <star-fcv-l AT lists.bnl.gov>
To: "zhchen" <zhchen AT rcf.rhic.bnl.gov>, "STAR Flow, Chirality and Vorticity PWG" <star-fcv-l AT lists.bnl.gov>
Sent: Friday, March 17, 2023 8:24:28 AM
Subject: Re: [Star-fcv-l] Questions about event shapes

Hi Zhenyu,

I'm a little confused, the weights that Isaac is using are the tile-by-tile EPD weights.  Would one use the weights that are calculated for flattening, etc, the EP as well?

The idea of this analysis is going into a poster and talk for the Hard Probes conference in 2 weeks, so it would be helpful if Isaac could get comments on a time scale earlier than a week.  At the very least, confirming the analysis procedures.  Right now he doesn't see a correlation in the TPC either - perhaps this is the weighting issue you mention.

Cheers,

Rosi

On Thu, Mar 16, 2023 at 10:43 PM zhchen via Star-fcv-l <star-fcv-l AT lists.bnl.gov> wrote:

Hi Isaac,

I would encourage you to present in next PWG meeting to have more
detailed discussion.
Based on my experience on a few event shape engineering analyses, the
definition of q2 is the magnitude of Q2  = Sum(w*exp(i2phi))/Sum(w). So
the denominator should include not only the multiplicity M but also the
other EPD weights.
Hope this could be helpful.

Cheers,
Zhenyu


在 2023-03-16 04:42，Mooney, Isaac via Star-fcv-l 写道：
> Hi FCV members,
>
> I’m a member of the HardProbes PWG, and I’ve been investigating some
> interesting behavior with q vectors as part of my analysis. I was
> splitting events into q2 classes, before seeing the plot I’m showing
> on slide 4 of the attached pdf, which raised the question of whether
> this is actually possible to do meaningfully.
> I was hoping to show the slides at the meeting today, but since it was
> canceled, I’m sending them here. If you have a minute, please take a
> look and let me know if you have any thoughts. To me the behavior is
> non-intuitive enough that it’s possible there’s a solution that is
> very obvious to an expert eye. And please let me know if anything in
> the slides is not clear and I would be happy to clarify it.
>
> I really appreciate any time you have to think about this!
> Best,
> Isaac
>
>
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--

Rosi Reed
RHIC/AGS UEC member
Associate Professor, Physics Department
Lehigh University
(610)758-3907
16 Memorial Drive East Office 406
Bethlehem, PA 18015
she/her/hers

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