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

[Gan, Liping]

Dear Matt,

If the detection efficiency uncertainty  is doubled,  for example, from 0.5% to 1%, the total systematic error will be increased from 3.2% to 3.3%. It will not change the whole picture significantly. As we stated in the proposal: " To the best of our knowledge, the way to calibrate FCAL calorimeter and how to determine its  detection efficiency  are still in the development stages". Therefore,  the current value for this error bar  is just an estimation. It can be changed once we have a better understanding later on. 


Liping
________________________________________
From: halld-physics-bounces at jlab.org [halld-physics-bounces at jlab.org] On Behalf Of Matthew Shepherd [mashephe at indiana.edu]
Sent: Wednesday, December 01, 2010 1:26 PM
To: Ashot Gasparian
Cc: GlueX Physics
Subject: Re: [Halld-physics] draft text of the eta-Primakoff proposal update

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


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