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

[Matthew Shepherd]

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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