[G12] resolution of tagger in kinematic fitter

[Eugene Pasyuk]

If you have already corrected E_beam, than you don't need to inflate uncertainty. If you want to adjust E_beam in the same fitter, than you have to include this uncertainty in the fitter. 

-Eugene 

> From: "Lei Guo" <leguo at fiu.edu>
> To: "Eugene Pasyuk" <pasyuk at jlab.org>
> Cc: "Carlos Salgado" <salgado at jlab.org>, "g12 at jlab.org g12 at jlab.org"
> <g12 at jlab.org>
> Sent: Wednesday, February 10, 2016 4:48:21 PM
> Subject: Re: [G12] resolution of tagger in kinematic fitter

> So I think we have consensus in that it is undercounting if we r just using
> 0.001*E_beam.... Ur point of the mcc energy being different is also consistent
> with the fact that we had to do a run-by-run e_beam correction. Technically, we
> probably should use something around 0.002*e_beam in the kinematic fitting.
> Agree?

> Sent from my iPhone

> On Feb 10, 2016, at 16:35, Eugene Pasyuk < pasyuk at jlab.org > wrote:

>> This would be a double counting for high energy end. The offset form the nominal
>> bin centroid is always less than the a bin width.
>> What needs to be adjusted is E_beam. We always had it deviate from what MCC
>> reports by ~0.1-0.2%, and even up to 0.5% occasionally. But this is
>> multiplicative factor and affects all Eg the same way.

>> -Eugene

>>> From: "Lei Guo" < leguo at fiu.edu >
>>> To: "Eugene Pasyuk" < pasyuk at jlab.org >
>>> Cc: "Carlos Salgado" < salgado at jlab.org >, " g12 at jlab.org g12 at jlab.org " <
>>> g12 at jlab.org >
>>> Sent: Wednesday, February 10, 2016 4:22:24 PM
>>> Subject: Re: [G12] resolution of tagger in kinematic fitter

>>> I understand that the 2007 paper is about the correction and now the correction
>>> gets applied at cooking. However, there is uncertainty to that correction. So
>>> on top of the 0.001*e_beam, there should be additional 0.001*e_gamma, for the
>>> overall resolution.

>>> Sent from my iPhone

>>> On Feb 10, 2016, at 15:52, Eugene Pasyuk < pasyuk at jlab.org > wrote:

>>>> You are confusing two different things.
>>>> The tagger reconstruction returns the photon energy as a centroid of the E_bin.
>>>> The bin widths is almost a constant and is ~0.001*E_beam. The beam centroids
>>>> originally used are coming from the geometry of the tagger hodoscope and
>>>> magnetic field.
>>>> During g10 and g11 it was discovered that bin centroids are not what we thought
>>>> due to gravitational sag of the focal plane.
>>>> To determine the deviation from the expected values two methods were used. One
>>>> is the calibration you refer to, the other using kinematic fit of g11 data.
>>>> What you see in the tagger calibration paper is the accuracy of the centroid
>>>> offset from ideal.
>>>> Once this calibration was done we implemented those corrections in the tagger
>>>> reconstruction. So, in g12 cooked date it is already accounted for. So, this is
>>>> not and uncertainty but correction.
>>>> What is left is the bin width. The photon energy could be anything
>>>> E_bin(i)-Ebin_width/2<Eg<E_bin(i)+Ebin_width/2
>>>> The calibration gives us E_bin(i), but effects of the bin width should go in the
>>>> kinematic fit. Ebin_width ~ Ebeam*0.001 and it is essentially a constant over
>>>> focal plane. Carlos' note describes how to get the variance assuming uniform
>>>> energy distribution within E_bin.

>>>> -Eugene

>>>>> From: "Lei Guo" < lguo at jlab.org >
>>>>> To: "Carlos Salgado" < salgado at jlab.org >, "Eugene Pasyuk" < pasyuk at jlab.org >
>>>>> Cc: " g12 at jlab.org g12 at jlab.org " < g12 at jlab.org >
>>>>> Sent: Wednesday, February 10, 2016 3:01:22 PM
>>>>> Subject: Re: [G12] resolution of tagger in kinematic fitter

>>>>>> The uncertainty in the energy of the photon is 0.001* E_beam (per NIM and Eugene
>>>>>> P.)

>>>>> I copy and pasted from the 2007 tagger energy calibration NIM paper ():

>>>>> "In this report, we present the energy calibration of the Hall B bremsstrahlung
>>>>> tagging system at the Thomas Jefferson National Accelerator Facility. The
>>>>> calibration was performed using a magnetic pair spectrometer. The tagged photon
>>>>> energy spectrum was measured in coincidence with e + e - pairs as a function of
>>>>> the pair spectrometer magnetic field. Taking advantage of the internal
>>>>> linearity of the pair spectrometer, the energy of the tagging system was
>>>>> calibrated at the level of ±0.1%E γ . The absolute energy scale was determined
>>>>> using the e + e - e+e- rate measurements close to the end-point of the photon
>>>>> spectrum. The energy variations across the full tagging range were found to be
>>>>> < 3MeV”

>>>>>> The hodos were built such that this is true (different widths)

>>>>>> Then consider a counter of width (energy) "a" where the (assume) energy
>>>>>> distribution is flat: then Variance = sigma^2 = 1/a* int^a_0 E^2 dE = a^2/3

>>>>>> Therefore if we distribute the uncertainty over a counter (energy bin) the
>>>>>> variance is : sigma^2 = (0.001*E_beam)**2/3

>>>>>> =Carlos
>>>>>> _______________________________________________
>>>>>> G12 mailing list
>>>>>> G12 at jlab.org
>>>>>> https://mailman.jlab.org/mailman/listinfo/g12
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