[Halld-physics] draft text of the eta-Primakoff proposal update

[Ashot Gasparian]

    Hi Matt,

   In my email I did not argue the 1% error in photon plux,
  that is still there in our proposal, for sure. The total
  error on the Compton cross section has to be on the same level
  as the eta cross section, which is 3.2%. Once more, we need to
  provide error on the Compton cross section measurement on the
  level of 3.2% (total).

  Regards,
  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 Tue, 30 Nov 2010, Matthew Shepherd wrote:

>
> For completeness, I'm referring to slide 21 here:
>
> http://www.jlab.org/~gasparan/PAC35/PAC35_Gasparian.pdf
>
> It lists the same 3.2% you note as "relaxed" below, and assumes 1% flux error.
>
> -Matt
>
> On Nov 30, 2010, at 7:24 PM, Matthew Shepherd wrote:
>
>>
>> Hi Ashot,
>>
>> Sorry, I don't understand.  There are other systematic errors besides photon flux.  Slide 21 of your proposal says that to achieve a 3% systematic error (which, when combined with 1% stat error, gives 3.2% total error) you need a 1% error on the photon flux.  Other errors like background subtraction and event selection are also very significant.
>>
>> If you plan a 1% error on the photon flux, presumably you need to know the efficiency for detecting a Compton electron and photon together to 1%.  These systematic errors, in the best case, are uncorrelated.  This means you need 1% / sqrt( 2 ) or 0.7% uncertainty on the detection efficiency in both the FCAL and comp-cal.  Did I miss something?
>>
>> -Matt
>>
>> On Nov 30, 2010, at 6:52 PM, Ashot Gasparian wrote:
>>
>>>
>>>  Hi Matt,
>>>
>>> I complitly agree with all you say below in your email.
>>> They are all difficult and need to be worked out, BUT there is
>>> one thing which may make our todays discussion much relaxed:
>>> the 1% uncertainty in the Compton cross section is an overkill
>>> statement and we need to change it for this proposal. It is left
>>> from the PrimEx and our original proposal where we been looking
>>> for 2% level measurement on eta decay rate. SINCE we have a new
>>> relaxed error bar in this proposal, which is 3.2% in total then
>>> the requirement for the Compton also SHOULD be on the similar
>>> 3.2% level.
>>>
>>> If the 1% number is left in the proposal then we need to change it.
>>>
>>> Hope this new corrected number makes much easier, though, I agree,
>>> we need to look on ways to measure the detection efficiencies in
>>> the experiment.
>>>
>>> Thanks,
>>> Ashot
>>
>>
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>