[Halld-physics] Primakov eta hadronic background

[Ashot Gasparian]

   Hi Eugene and All,

   We have done (with Pawel) some initial simulations
  of the combinatorial background. The most part of this
  type of the background is coming from the electromagnetic
  (the beam) background, since the rate from this much larger
  than from the physics background. It may realize in several
  ways: (1) accidental two gammas from electromagnetic
  background. This one is small since we also have a good
  minimum opening angle cut (from the incident gamma energy);
  (2) one gamma from electromagnetic and another one either
  from real eta or from the physics (hadronic) background.

  We have some plots for these distributions, will try to
  put together for the next meeting, which we want to organize
  on Friday afternoon.

  Ashot


.............................................................
Ashot Gasparian                    Phone:(336)285-2112 (NC A&T)
Professor of Physics
Physics Department                       (757)-269-7914 JLab
NC A&T State University              Fax:(757)-269-6273 JLab
Greensboro, NC 27411               email: gasparan at jlab.org
.............................................................


On Wed, 2 Dec 2009, Eugene Chudakov wrote:

> The first thing to check was the real-eta background.
> The combinatorial (not eta) background can be subtracted
> using the mass sidebands. The error coming from this
> subtraction has to be evaluated. Hopefully, there are not many
> combinations at a large elasticity.
>
> Will someone lead a discussion on the error budget proposed?
>
> Eugene
>
> On Wed, 2 Dec 2009, Richard Jones wrote:
>
>> Alex,
>>
>> Thank you for the quick study you did.  However I am puzzled by the suggested
>> conclusion.  By combinatorial background, one means etas that are
>> reconstructed out of photons that did not come from an eta.  Maybe this is
>> small, but it is going to take considerable work to show it.
>>
>> Alexander Somov wrote:
>>> ( The inclusive eta background should dominate combinatorial bg)
>>>
>> ... in light of ...
>>> (I selected events containing at least one eta in the final
>>> state  with an angle < 1.6 deg, and processed these events
>>> through Geant).
>>>
>> To study the combinatoric background you need to look at the inclusive
>> sample.  Why should you require an eta if you are looking for 2gamma
>> combinatorial background under the eta?  I believe this restriction can lead
>> to a severe underestimate of the combinatorial background under the eta.
>>
>> -Richard Jones
>>
>>
>
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