[Halld-npp] Primakoff cross section

[Ilya Larin]

Hi Elton,

I can just comment that the 200 nb value I got has already a factor of 1.25 taken into account.
I also do not quite understand (maybe because it's 6 am already) why in Fig. 3 the units
are nb, not nb/GeV, maybe it is nb per histogram bin size, which is 50MeV I assume, or something else. Having Fig. 3 understood is essential for the cross-section results comparison,
because I used values from Jose and can/should put Fig. 3 values instead to compare the results directly.

 Thank you,
 Ilya


________________________________
От: Elton Smith <elton at jlab.org>
Отправлено: 28 февраля 2020 г. 15:15
Кому: Elton Smith <elton at jlab.org>
Копия: Halld-npp at jlab.org <Halld-npp at jlab.org>; Ilya Larin <ilarin at jlab.org>
Тема: Primakoff cross section

Hi Ilya,

I compared your calculation of the cross section in the LOI. See figs.
3-5. I get a cross section/nucleus of 345 nb. If you took Jose's cross
section directly, you need to divide your value 200 nb by 0.8 since it
is for |costhe|<0.8, which gives 250 nb, or 70% of my value.

You can check my parameterization of sigma(gg->pi0pi0) (Fig. 3) with
Jose's. I assumed it is essentially flat above the threshold instead of
having a shape. This may explain most of the remaining discrepancy. We
may wish to update the document with your value since Jose's
parameterization is more constrained, but we can discuss this.

Cheers, Elton.

Elton Smith
Jefferson Lab MS 12H3
12000 Jefferson Ave STE 4
Newport News, VA 23606
(757)269-7625
(757)269-6331 fax

On 2/28/20 2:36 PM, Elton Smith wrote:
> Dear collaborators,
>
> I have posted the minutes from the NPP meeting this morning on the
> wiki at
> https://halldweb.jlab.org/wiki/index.php/Pi0_Polarizability_Meeting_Feb_28,_2020#Minutes.
>
>
> Ilya: You can go ahead an link your presentation directly to the
> meeting page.
>
> Thanks, Elton.
>

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