[G8b_run] Photon Corrections (taggerSag)

[Michael Dugger]

Eugene,

Yep. I messed that up.

The fraction pho_energy/E0 is off by a factor of 0.002 (from that using 
the correct value of E0). The offset parameter that was determined 
(0.00134) using the incorrect value of E0 will act to mitigate this 
transgression.

egdivE0 = pho_energy/E0 + offset

The end result remains the same: The photon energies have been corrected 
to well within the energy width of an Eid.

I will make sure to mention this issue in the CLAS-note.

Thanks for catching this.

Sincerely,
Michael

On Thu, 29 Oct 2009, Eugene Pasyuk wrote:

> Guys, whys is it E0=4.55?
> According to the calibration database it is 4558.94 MeV (4.559 GeV)
> It is 9 MeV difference.
>
> -Eugene
>
> Charles Hanretty wrote:
>> Hello all,
>>       Below is the C++ translation from the Fortran code that Mike wrote to
>> correct the photon energies.
>>
>>    float E0 = 4.55;
>>    double egdivE0;
>>    egdivE0 = pho_energy/E0 + 0.00134;
>>
>>    if (egdivE0 < 0.401) {
>>      egdivE0 = egdivE0 - 0.00599597 + 0.0390912*egdivE0 -
>> 0.0573218*egdivE0*egdivE0;
>>    }
>>    if ((egdivE0 >= 0.401) && (egdivE0 <= 0.674)) {
>>           egdivE0 = egdivE0 - 0.0181293 + 0.0675599*egdivE0 -
>> 0.0541268*egdivE0*egdivE0;
>>    }
>>    if (egdivE0 > 0.674) {
>>           egdivE0 = egdivE0 - 0.0511162 + 0.138208*egdivE0 -
>> 0.0867757*egdivE0*egdivE0;
>>    }
>>
>>    pho_energy = egdivE0*E0 + pho_energy*(-0.0035);
>>
>> Where "pho_energy" is the energy of the photon as taken from the data
>> file and "E0" is the (e-)beam energy.
>>
>>     A CLAS-note for the g8b Tagger Sag study is almost finished.
>>
>> -Chuck
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