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

[Matthew Shepherd]

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