[G14_run] Systematic uncertainties on asymmetries - (Tsuneo's question to K Sigma analysis note)

Nicholas Zachariou nicholas at jlab.org
Tue Nov 7 22:02:46 EST 2017 

Hi Andy,

Can you elaborate why its not correct to add the systematic in quadrature with the statistical? 
I am not sure I understand why this "uses data that dont represent the experiment". Maybe we can talk more during the g14 meeting.

Nick

On Nov 7, 2017, 22:22, at 22:22, "Dr. A.M.  Sandorfi" <sandorfi at jlab.org> wrote:
>Hi Eugene,
>
>Yes, your point is well taken - for those data points where the
>asymmetry is
>very close to zero. One has two choices: we could either give an
>overall
>fractional (%) uncertainty, while quoting the absolute value as an
>exception
>when the asymmetry vanishes, or just quote only an absolute uncertainty
>for
>all points. 
>
>The trouble comes at the subsequent stage when the data is used by the
>various PWA groups. All PWA groups have their fitting routines set up
>to
>float the scale of a data set while including a chi^2 penalty that is
>weighted by a fractional systematic error. If we give them a systematic
>uncertainty that is absolute, they will combine it in quadrature with
>the
>statistical error to create an inflated point by point uncertainty, and
>set
>the fitting scale to 1. I can guarantee that this will happen and it is
>a
>completely incorrect way to use the data that doesn't represent the
>experiment. So it is better to use the first approach - quote the
>systematic
>uncertainty as a fractional (%) error, while explicitly noting the
>absolute
>value of the systematic uncertainty for those asymmetry points with
>nearly
>zero value. The later qualifying statement will probably be ignored in
>PWA
>analyses, but at least most of the data will have been included
>properly.
>
>Andy
>
>
>
>
>On 11/4/17, 11:37 PM, "Eugene Pasyuk" <pasyuk at jlab.org> wrote:
>
>> 
>> Any asymmetry can be anything between -1 and +1, 0 included. For any
>> observable which may be equal to 0 relative uncertainty does not make
>sense.
>> Only absolute uncertainty must be used.
>> The second term in Nick's equation is equal to 0 if ObservableValue
>is always
>> equal to 0 regardless of sigma_sys_relative. This is incorrect but
>good
>> illustration why one must not use relative uncertainty for
>asymmetries.
>> 
>> -Eugene
>> 
>> ----- Original Message -----
>>> From: "Tsuneo Kageya" <kageya at jlab.org>
>>> To: "Nicholas Zachariou" <nicholas at jlab.org>
>>> Cc: "g14 run" <g14_run at jlab.org>
>>> Sent: Saturday, November 4, 2017 10:57:28 PM
>>> Subject: Re: [G14_run] G14_run Digest, Vol 74, Issue 3 (Tuneo's 
>question to
>>> K Sigma analysis note)
>> 
>>> Nick,
>>> 
>>> thank you for the response.
>>> I would like to know why the absolute is more appropriate.
>>> I will look forward the statements.
>>> 
>>>     Regards, Tsuneo Kageya.
>>> 
>>> ----- Original Message -----
>>> From: "Nicholas Zachariou" <nicholas at jlab.org>
>>> To: "Tsuneo Kageya" <kageya at jlab.org>
>>> Cc: "g14 run" <g14_run at jlab.org>
>>> Sent: Saturday, November 4, 2017 3:23:46 PM
>>> Subject: Re: [G14_run] G14_run Digest, Vol 74, Issue 3 (Tuneo's 
>question to
>>> K
>>> Sigma analysis note)
>>> 
>>> Hi Tsuneo,
>>> 
>>> The absolute error is propagated directly to the total uncertainty
>>>
>(sigma_tot=sqrt(sigma_sys_absolute^2+(ObservableValue*sigma_sys_relative)^2
>+
>>> sigma_statistical^2).
>>> 
>>> I can elaborate more if you like on why thats the case (why absolute
>are more
>>> appropriate in my case). I will include some statements in the note
>to
>>> reflect
>>> this.
>>> 
>>> Let me know if you would like to discuss this more.
>>> 
>>> Best regards,
>>> Nick
>>> 
>>> On Nov 4, 2017, 19:12, at 19:12, Tsuneo Kageya <kageya at jlab.org>
>wrote:
>>>> Hi Nick,
>>>> 
>>>> Sorry to be late to make a question.
>>>> I have a question about the systematic error calculations.
>>>> 
>>>> At page 35, on the table 4, you calculated the total absolute
>>>> systematic error
>>>> to be 0.10.   How this is reflected into the total relative
>systematic
>>>> error ?
>>>> On the pi-p analysis, I think we calculated the systematic errors
>from
>>>> cuts in
>>>> the similar way and they are combined to the other errors (target
>and
>>>> beam polarizations).
>>>> Is this number 0.10 means 10 % or 0.1 % ?
>>>> 
>>>> I may misunderstand this issue.  Please let me know.
>>>> 
>>>>    Regards, Tsuneo Kageya.
>>>> 
>>>> ----- Original Message -----
>>>> From: "g14 run-request" <g14_run-request at jlab.org>
>>>> To: "g14 run" <g14_run at jlab.org>
>>>> Sent: Saturday, November 4, 2017 12:00:03 PM
>>>> Subject: G14_run Digest, Vol 74, Issue 3
>>>> 
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>>>> 
>>>> Today's Topics:
>>>> 
>>>>   1. Re: Updated Analysis Note (Reinhard Schumacher)
>>>>   2. Re: Updated Analysis Note (Nicholas Zachariou)
>>>> 
>>>> 
>>>>
>----------------------------------------------------------------------
>>>> 
>>>> Message: 1
>>>> Date: Fri, 3 Nov 2017 22:19:24 -0400
>>>> From: Reinhard Schumacher <schumacher at cmu.edu>
>>>> To: g14_run at jlab.org
>>>> Subject: Re: [G14_run] Updated Analysis Note
>>>> Message-ID: <a5780718-56ac-1dc0-44e8-6b991dbf849b at cmu.edu>
>>>> Content-Type: text/plain; charset="windows-1252"; Format="flowed"
>>>> 
>>>> Hi Nick,
>>>> 
>>>> Indeed, noticeably improved.?? I recommend that you put the
>horizontal
>>>> error bars on Figs.? 29 - 32, too.? They are just as important
>there
>>>> since the model curves can vary a lot across one bin.
>>>> 
>>>> Reinhard
>>>> 
>>>> 
>>>> On 11/3/2017 7:13 PM, Nicholas Zachariou wrote:
>>>>> Dear all,
>>>>> 
>>>>> I am attaching the updated note that incorporates and addresses
>all
>>>> comments made. I have noticed that I have previously forgotten to
>>>> include the systematic uncertainty associated with the
>>>> photon-selection, and is now estimated and included.
>>>>> I would like to thank again Shumacher for his time and valuable
>>>> insight, and everybody for the comments and feedback. If there is
>no
>>>> other comments, I will be submitting the note early next week.
>>>>> 
>>>>> Best regards,
>>>>> Nick
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> G14_run mailing list
>>>>> G14_run at jlab.org
>>>>> https://mailman.jlab.org/mailman/listinfo/g14_run
>>>> 
>>>> --
>>>> ___________________________________________________________________
>>>> Reinhard Schumacher         Department of Physics, 5000 Forbes Ave.
>>>> Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.
>>>> phone: 412-268-5177         web: www-meg.phys.cmu.edu/~schumach
>>>> ___________________________________________________________________
>>>> 
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>>>> ------------------------------
>>>> 
>>>> Message: 2
>>>> Date: Sat, 04 Nov 2017 07:10:14 +0000
>>>> From: Nicholas Zachariou <nicholas at jlab.org>
>>>> To: Reinhard Schumacher <schumacher at cmu.edu>
>>>> Cc: G14 Run <g14_run at jlab.org>
>>>> Subject: Re: [G14_run] Updated Analysis Note
>>>> Message-ID: <d21ed42f-6b13-482d-8c8b-4ea087ad31e1 at jlab.org>
>>>> Content-Type: text/plain; charset="utf-8"
>>>> 
>>>> Hi Reinhard,
>>>> 
>>>> The figures looked a bit busy when I did that (too many lines) and
>>>> thats why i left the x-uncertainties out in those, but its takes me
>2
>>>> minutes to incorborate them. I think that will be more relevant
>when we
>>>> decide exactly how to present our results in the publication.
>>>> 
>>>> In the meantime I was wondering if its OK with the group to share
>our
>>>> preliminary results with the theorists and see if we can get any
>>>> insights from them.
>>>> 
>>>> Best regards,
>>>> Nick
>>>> 
>>>> 
>>>> On Nov 4, 2017, 02:19, at 02:19, Reinhard Schumacher
>>>> <schumacher at cmu.edu> wrote:
>>>>> Hi Nick,
>>>>> 
>>>>> Indeed, noticeably improved.?? I recommend that you put the
>horizontal
>>>> 
>>>>> error bars on Figs.? 29 - 32, too.? They are just as important
>there
>>>>> since the model curves can vary a lot across one bin.
>>>>> 
>>>>> Reinhard
>>>>> 
>>>>> 
>>>>> On 11/3/2017 7:13 PM, Nicholas Zachariou wrote:
>>>>>> Dear all,
>>>>>> 
>>>>>> I am attaching the updated note that incorporates and addresses
>all
>>>>> comments made. I have noticed that I have previously forgotten to
>>>>> include the systematic uncertainty associated with the
>>>>> photon-selection, and is now estimated and included.
>>>>>> I would like to thank again Shumacher for his time and valuable
>>>>> insight, and everybody for the comments and feedback. If there is
>no
>>>>> other comments, I will be submitting the note early next week.
>>>>>> 
>>>>>> Best regards,
>>>>>> Nick
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> G14_run mailing list
>>>>>> G14_run at jlab.org
>>>>>> https://mailman.jlab.org/mailman/listinfo/g14_run
>>>>> 
>>>>> --
>>>>>
>___________________________________________________________________
>>>>> Reinhard Schumacher         Department of Physics, 5000 Forbes
>Ave.
>>>>> Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.
>>>>> phone: 412-268-5177         web: www-meg.phys.cmu.edu/~schumach
>>>>>
>___________________________________________________________________
>>>>> 
>>>>> 
>>>>> 
>>>>>
>------------------------------------------------------------------------
>>>>> 
>>>>> _______________________________________________
>>>>> G14_run mailing list
>>>>> G14_run at jlab.org
>>>>> https://mailman.jlab.org/mailman/listinfo/g14_run
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