STAR HardProbes PWG

[Gabe Dale-Gau <gdaleg2 AT uic.edu>]

Hi Nihar,

Thanks for your follow up questions. I have responses to each below.

Let me know if there is anything else that remains unclear.

Best,

Gabe

Slide2
  > Create Mixed event by taking one track from different events until a
reasonable nTrack value is reached
Q: How do you make sure that your nTrack from Mixed event and the Same
Events are the same sample?
Do you have the comparison of nTrack distributions from both ME and SE?

 

I randomly sample a distribution of nTracks per Event from AuAu signal to determine how many tracks to put in each mixed event. I run the Mixed event procedure for the same number of events as appear in signal, so the resulting nTrack distributions are identical in shape and integral. I have attached a plot of these two distributions overlayed.

> Accept only jets with >= 3 tracks
Q: How do you decide >= 3 tracks ? and not more or less. Did you see any
difference if you change this to +-1 tracks.
> Compare rate at which jets are found per event to the same rate in data
Q: Do you have any comparison plot?

 

This was Helen’s question in the meeting yesterday, and it is a good question. I plan on presenting again next week with a few more plots to explain our logic for the choice of the 3 track cut.

For now I will state our general thinking again:

Pseudo-embedding and Mixed Event methods aim to capture two different sources of correlated background. Pseudo-embedding looks for additional background signal that gets pulled along due to upward fluctuation around a real jet signal. Mixed Event looks for completely combinatorial objects that appear as jets on their own. While these are two distinct sources, there was originally some overlap in the resulting corrections. The 3 track minimum for combinatorial jets aims to eliminate this double-counting. The two cases this eliminates are 1 and 2 track jets.

1 track jets (tracks above 9 Gev/c) are real jets according to our definition. Thus, they must be excluded from a study aiming to identify fake jets.

2 track jets are accounted for in the pseudo-embedding correction. If a 1 track jet is found in p+p and embedded into Au+Au background, it has no correlation with any other track in the event, so if it forms a 2 track jet that reaches our 9GeV threshold, this is identical to a combinatorial 2 track fake jet. Thus we must exclude these from one of the corrections to avoid double-counting.

3 Track jets are where the corrections become distinct. If a 2 track jet is found in p+p and embedded into Au+Au background, it retains association between the two original tracks, forming a jet cone on its own. If it picks up a third track from Au+Au background, this is exactly what we are looking for with pseudo-embedding. It is distinct from combinatorial jets due to the presence of a “real” jet.

The same holds true for all >3 track jets. This is the regime where collections of low p_T tracks can form fake, fully combinatorial jets.

> 0.8% fake jets -> scale combinatorial peaks
Q: How do you get this "0.8%" ?

 

To calculate our “fake rate”, we compare nJets/nEvents between signal and mixed event. The fake rate is given by (nJets_ME/nEvents_ME)/(nJEts_AA/nEvents_AA). This gives us the percentage of jets in signal that are combinatorial. Note that in this case I have run ME for the same number of events as signal, so this calculation reduces to nJets_ME/nJEts_AA. I have stated the fully general case to demonstrate how it would be calculated if we wanted to ramp up ME statistics.

On Thu, May 16, 2024 at 11:37 PM Nihar Sahoo <nihar AT rcf.rhic.bnl.gov> wrote:

Hello Gabe,

I was going through your presentation (as I mentioned to you) and trying
to understand a bit more the procedure. Could you please answer my
following questions for my understanding?

Slide2
  > Create Mixed event by taking one track from different events until a
reasonable nTrack value is reached
Q: How do you make sure that your nTrack from Mixed event and the Same
Events are the same sample?
Do you have the comparison of nTrack distributions from both ME and SE?

> Accept only jets with >= 3 tracks
Q: How do you decide >= 3 tracks ? and not more or less. Did you see any
difference if you change this to +-1 tracks.
> Compare rate at which jets are found per event to the same rate in data
Q: Do you have any comparison plot?

> 0.8% fake jets -> scale combinatorial peaks
Q: How do you get this "0.8%" ?


Thank you
Nihar

On 2024-05-16 02:20, Gabe Dale-Gau via Star-hp-l wrote:
> HP-pwg,
>
> Here are my slides for tomorrow morning:
>
> https://nam04.safelinks.protection.outlook.com/?url="https%3A%2F%2Fdrupal.star.bnl.gov%2FSTAR%2Fsystem%2Ffiles%2FHP_PWG_Combinatorial_Update_May16_2024.pdf&data=05%7C02%7Cgdaleg2%40groute.uic.edu%7C9974bbb8b97943a4457408dc762aff6f%7Ce202cd477a564baa99e3e3b71a7c77dd%7C0%7C0%7C638515174727154822%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=3CT16pDftR4ftj0mF1d3ovwFuMvHme0NJ2LLu%2BiA9pA%3D&reserved=0
>
> Best,
>
> Gabe
>
> On Wed, May 15, 2024 at 6:19 AM Roy Chowdhury Priyanka (DOKT) via
> Star-hp-l <star-hp-l AT lists.bnl.gov> wrote:
>
>> Hi all,
>>
>> I would like to give an update of my analysis "D0-hadron
>> femtoscopy".
>>
>> Regards,
>> Priyanka
>>
>> -------------------------
>>
>> From: Star-hp-l <star-hp-l-bounces AT lists.bnl.gov> on behalf of
>> Mooney, Isaac via Star-hp-l <star-hp-l AT lists.bnl.gov>
>> Sent: Monday, May 13, 2024 5:35 PM
>> To: STAR HardProbes PWG <star-hp-l AT lists.bnl.gov>
>> Cc: Mooney, Isaac <isaac.mooney AT yale.edu>
>> Subject: [Star-hp-l] HP-PWG meeting May 16, 10 AM BNL time
>>
>> Hi all,
>>
>> We will have our regular HP-PWG meeting this Thursday (May 16) at 10
>> AM EDT.
>> Please let us know if you want to present and discuss your analysis
>> or any other business. It would be great to have updates from anyone
>> who promised things in their Hard Probes abstract that the working
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>> Thanks,
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