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star-fcv-l - Re: [Star-fcv-l] Discussion of systematic uncertainty calculation - FCV PWG meeting on 06/December/2023 Wed. 9:30 AM EDT

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  • From: "Wang, Fuqiang" <fqwang AT purdue.edu>
  • To: dshen <dshen AT rcf.rhic.bnl.gov>, "STAR Flow, Chirality and Vorticity PWG" <star-fcv-l AT lists.bnl.gov>
  • Subject: Re: [Star-fcv-l] Discussion of systematic uncertainty calculation - FCV PWG meeting on 06/December/2023 Wed. 9:30 AM EDT
  • Date: Fri, 8 Dec 2023 02:30:36 +0000

Hi Diyu,

Please see comments in color below.

Best regards,
Fuqiang


From: dshen <dshen AT rcf.rhic.bnl.gov>
Sent: Thursday, December 7, 2023 7:07 PM
To: STAR Flow, Chirality and Vorticity PWG <star-fcv-l AT lists.bnl.gov>
Cc: Wang, Fuqiang <fqwang AT purdue.edu>
Subject: Re: [Star-fcv-l] Discussion of systematic uncertainty calculation - FCV PWG meeting on 06/December/2023 Wed. 9:30 AM EDT
 
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Hi Fuqiang,

It seems we have an agreement on the first point, i.e. the result to lie
between def - diff and def + diff. It doesn't say the diff should be the
maximum, say, it has to be default to DCA<0.01 or <100.

Just to make sure we're on the same page: If we say the results lie between def - diff and def + diff, we mean these are min and max. We do have to make reasonably sure these are the min-max range. They of course do not have to come from the min-max range of the cut, as the result may not linearly depend on the cut. For example, just for the sake of illustration, it is possible that DCA<1.5 cm gives the min. result and DCA<0.8 cm gives the max result, however, one would have to scan the DCA space to know this.

Regarding 1 sigma should be diff/sqrt(12) or 2*diff/sqrt(12), let me
explain it in terms of probability.
Let's take an example, say, the measured quantity is 0, and the
variation is 1. Then we assume the non-biased value is in between -1 to
1 with a uniform distribution. So I present the result as 0 +-
1/sqrt(12), it means the non-biased value falls within +- 1/sqrt(12)
with a probability of 2*1/sqrt(12) which is exactly the standard
deviation of 2*varition=2. If you define 1 sigma as
2*variation/sqrt(12), then we should present as +- half sigma to have
the same probability as before.

For a flat distribution of width 2, the equivalent Gaussian sigma is 2/sqrt(12). So the error is +/- 2/sqrt(12). It is +/- 1/sqrt(3) or approximately +/- 0.6, or 1.2 out of 2, i.e. 60%.

Thanks,
Diyu



On 2023-12-08 02:17, Wang, Fuqiang via Star-fcv-l wrote:
> Hi Diyu,
>
> So the central issue is whether you get the maximum variation. If one
> varies towards only one side, and quote +/- assuming the variation is
> symmetric, then you’re really assuming the result to lie between min
> def-diff and max diff+diff, so you should quote def +/- diff/sqrt(3).
>
> Best regards,
> Fuqiang
>
>> On Dec 7, 2023, at 1:08 PM, Wang, Fuqiang <fqwang AT purdue.edu> wrote:
>>
>> ---- External Email: Use caution with attachments, links, or sharing
>> data ----
>>
>>
>> Hi Diyu,
>>
>> I realize that there may be a misunderstanding on the term “max.
>> variation”. It means variations in cuts that result in maximum
>> variation in result.
>>
>> Regarding sqrt(12) vs sqrt(3):
>> If one believes def. is min and sys. is max, then it’s probably better
>> to quote the average of def. and sys. as the central value and +/-
>> diff/sqrt(12) as the error.
>> If there’s strong reason to quote the value to be the min. (or max.
>> for that matter) and the negative side error is really zero, then we
>> should quote the value as def.+diff/sqrt(3) not sqrt(12) because the
>> common understanding of error is that it covers 68% probability.
>>
>> Best regards,
>> Fuqiang
>>
>>> On Dec 7, 2023, at 10:50 AM, dshen <dshen AT rcf.rhic.bnl.gov> wrote:
>>>
>>> [You don't often get email from dshen AT rcf.rhic.bnl.gov. Learn why
>>> this is important at
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>>>  ]
>>>
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>>> data ----
>>>
>>>
>>> Hi Fuqiang,
>>>
>>> One sigma is |def.-sys.|/sqrt(12), and it shows as +- 1 sigma for the
>>> case of (def. - |def.-sys.|,  def. + |def.-sys.|).
>>> The critical point is that it doesn't require a maximum variation, it
>>> just requires that the variation could cover the true value. The
>>> confidence level is based on experience and common sense, there is no
>>> mathematical way to quantify it - it is not statistics.
>>>
>>> Best,
>>> Diyu
>>>
>>>
>>>>> On 2023-12-07 23:28, Wang, Fuqiang wrote:
>>>> Hi Diyu,
>>>>
>>>> What you wrote is just another way to say that the physics quantity
>>>> in
>>>> question is within the min and max of (def. - |def.-sys.|,  def. +
>>>> |def.-sys.|), respectively. In such a case, one would quote a sigma
>>>> of
>>>> 2*|def.-sys.|/sqrt(12) = |def.-sys.|/sqrt(3). The essential point is
>>>> to demonstrate to reasonable confidence that this is indeed the
>>>> maximum syst. variation in the result.
>>>>
>>>> Best regards,
>>>> Fuqiang
>>>>
>>>>> On Dec 7, 2023, at 6:32 AM, dshen via Star-fcv-l
>>>>> <star-fcv-l AT lists.bnl.gov> wrote:
>>>>>
>>>>> ---- External Email: Use caution with attachments, links, or
>>>>> sharing
>>>>> data ----
>>>>>
>>>>>
>>>>> Hi Fuqiang, Zhiwan and all,
>>>>>
>>>>> It was a inspiring discussion on the systematic uncertainty
>>>>> calculations
>>>>> yesterday, it pushes me to think.
>>>>> I tend to agree with Zhiwan and what the blind-analysis did, i.e.
>>>>> use
>>>>> denominator of 1/sqrt(12).
>>>>> The argument was that one shouldn't divide the variation by
>>>>> 1/sqrt(12)
>>>>> because the variation isn't proved to be the maximum - minimum, I
>>>>> think
>>>>> there is a misunderstanding of the reason behind it.
>>>>> It isn't based on the assumption that the variation is maximum -
>>>>> minimum, the underlying assumption is that the true value falls
>>>>> within
>>>>> "default cut" +- "variation".
>>>>> Let's take an example, say, the default cut is DCA<2, and the
>>>>> systematic
>>>>> cut is DCA<1.
>>>>> The assumption is that the non-biased value is in the interval of
>>>>> (def.
>>>>> - |def.-sys.|,  def. + |def.-sys.|), and it can be any value in
>>>>> that
>>>>> interval with equal probability (uniform distribution) assuming we
>>>>> don't
>>>>> have any pre-knowledge to the best position. That's the reason of
>>>>> why
>>>>> people assign |def.-sys.|/sqrt(12) as 1 sigma and use two-side
>>>>> band.
>>>>> It hasn't to be the maximum - minimum, although it isn't incorrect
>>>>> technically to use larger uncertainty, say, use Dca<0.1 to Dca<100.
>>>>> But
>>>>> I think the principal is to provide the best estimate instead of
>>>>> the
>>>>> most conservative value.
>>>>> What variation can be considered as reasonable? I think it is based
>>>>> on
>>>>> experience and common sense to a specific physics topic. For CME
>>>>> study,
>>>>> like what Zhiwan did, it is reasonable to assume the non-biased
>>>>> value
>>>>> falls with in DCA<2 +- |DCA<2 - DCA<1|, for example.
>>>>>
>>>>> That's my two cents.
>>>>>
>>>>> Best,
>>>>> Diyu
>>>>>
>>>>>
>>>>>
>>>>>> On 2023-12-06 05:10, Zhiwan Xu via Star-fcv-l wrote:
>>>>>> Dear Conveners,
>>>>>> I would like to update the paper proposal on the CME search in
>>>>>> STAR
>>>>>> BES-II.
>>>>>> Please kindly add me to the schedule.
>>>>>>
>>>>>> The paper proposal webpage:
>>>>>>
>>>>>>
https://nam04.safelinks.protection.outlook.com/?url="https%3A%2F%2Fdrupal.star.bnl.gov%2FSTAR%2Fblog%2Fzhiwanxu%2FPaper-Proposal-Search-Chiral-Magnetic-Effect-RHIC-Beam-Energy-Scan-II&data=05%7C01%7Cfqwang%40purdue.edu%7Cca67385d4e4e4100d70d08dbf781ba32%7C4130bd397c53419cb1e58758d6d63f21%7C0%7C0%7C638375909723354002%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=XPxElSkqRxWGoWxH%2BbQZ2%2FGlr0MXUUw3G1fUItAsYL0%3D&reserved=0
>>>>>> The slides:
>>>>>>
>>>>>>
https://nam04.safelinks.protection.outlook.com/?url="https%3A%2F%2Fdrupal.star.bnl.gov%2FSTAR%2Fsystem%2Ffiles%2Fpaper_proposal_CME_BESII_v2.pdf&data=05%7C01%7Cfqwang%40purdue.edu%7Cca67385d4e4e4100d70d08dbf781ba32%7C4130bd397c53419cb1e58758d6d63f21%7C0%7C0%7C638375909723354002%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=2y1vzawzEBBmUmaFllAHSsAPx%2BiL38AXrzvRHIuSuuM%3D&reserved=0
>>>>>>
>>>>>> Best,
>>>>>> Zhiwan
>>>>>>
>>>>>> ------------------------------------
>>>>>> Zhiwan Xu,
>>>>>> Department of Physics and Astronomy, UCLA
>>>>>> zhiwanxu AT physics.ucla.edu
>>>>>>
>>>>>> ----- Original Message -----
>>>>>> From: "subhash via Star-fcv-l" <star-fcv-l AT lists.bnl.gov>
>>>>>> To: "STAR Flow, Chirality and Vorticity PWG"
>>>>>> <star-fcv-l AT lists.bnl.gov>
>>>>>> Cc: "subhash" <subhash AT rcf.rhic.bnl.gov>
>>>>>> Sent: Sunday, December 3, 2023 11:21:34 PM
>>>>>> Subject: [Star-fcv-l] FCV PWG meeting on 06/December/2023 Wed.
>>>>>> 9:30
>>>>>> AM
>>>>>> EDT
>>>>>>
>>>>>> Dear All,
>>>>>>
>>>>>> We shall have our weekly FCV PWG meeting this Wednesday
>>>>>> (06/Dec/2023)
>>>>>> at
>>>>>> 9:30 AM EDT. If you would like to present please let us know.
>>>>>> Please
>>>>>> try
>>>>>> posting your slides by Tuesday. The agenda will be collected at:
>>>>>>
https://nam04.safelinks.protection.outlook.com/?url="https%3A%2F%2Fdrupal.star.bnl.gov%2FSTAR%2Fblog%2Fjjiastar%2Fbulkcorr&data=05%7C01%7Cfqwang%40purdue.edu%7Cca67385d4e4e4100d70d08dbf781ba32%7C4130bd397c53419cb1e58758d6d63f21%7C0%7C0%7C638375909723354002%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=bAiiaqpKBnYB0QTGpieQn1nDsJhS1Yg9iUgYrkH3xuI%3D&reserved=0
>>>>>>
>>>>>> Zoom details are copied below.
>>>>>>
>>>>>> Thanks and regards,
>>>>>> Prithwish, Zhenyu and Subhash
>>>>>>
>>>>>>
>>>>>> ZOOM LINK FOR FCV MEETING:
>>>>>> Join ZoomGov Meeting
>>>>>>
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