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

[Matthew Shepherd]

Hi Ashot,

I know there has been a lot of back and forth on your update to the PAC and you are nearing the final hours before you must send your submission.  I just want to restate one thing, for clarity, so we understand each other.

Both you and Liping have confirmed that you are assuming a 0.25% systematic error per photon on photons from eta -> gamma gamma that reconstructed in the FCAL.  That's 0.5% on total detection efficiency systematic error.  You need this for your 3% systematic error budget.

Since we are designing and building the FCAL I want to clearly state that the FCAL has not been designed with such a requirement on precision reconstruction efficiency.  As I (and both you and Liping) have stated, there are no validated practical ideas for calibrating the efficiency so precisely.  As best I understand from you and Liping, you plan to develop a physics-based calibration method in the future.

I just want to make sure understand each other -- you are assuming detector performance that exceeds our design specifications.  (I hope we are able to deliver on these performance goals, but at the moment I don't see a practical route.)

Cheers,

Matt