[G12] resolution of tagger in kinematic fitter

[Eugene Pasyuk]

In fact what you should do in the kinematic fitter is to treat this uncertainty as two components, the uncertainty of E_beam and and the uncertainty due to the bin width. The effect of the E_beam uncertainty will be indeed Eg dependent, because for high energy end the multiplicative factor is large and E_beam uncertainty propagates directly to E_bin uncertainty. For low energy end this contribution will be small. While the contribution from the bin width is a constant over the focal plane. 

-Eugene 

> From: "Eugene Pasyuk" <pasyuk at jlab.org>
> To: "Lei Guo" <leguo at fiu.edu>
> Cc: "g12 at jlab.org g12 at jlab.org" <g12 at jlab.org>
> Sent: Wednesday, February 10, 2016 4:35:07 PM
> Subject: Re: [G12] resolution of tagger in kinematic fitter

> 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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