[Primexd] Be empty optimal time

[gasparan at jlab.org]

  Hi Ilya,

 It sounds very realistic arguments for the empty statistics.
 The ~25% number was close that we been talking in the last week.
 If this is right and if the quality of the empty statistics is
 okay, then we suppose to be not bad with the Be Compton.

 The next question is the sequence of "empty"s for the LHe4 target.
 Is your arguments transferable to this target also?
 If it is yes then we better to have ~30% "empty"s for the coming
 runs.

 Thanks,
 Ashot


>
>  Hi Ashot,
>
>
> following our Thursday's meeting discussion about what should be
>
> the optimal fraction of empty target statistics collection time,
>
> I tried to calculate it assuming that errors are proportional to the
> square root
>
> of event numbers (which is not exactly true of course).
>
> If I didn't make a mistake somewhere in math - the result
>
> in the attached plot (vertical axis - fraction of time (vs total time)
> optimal to spent for empty
>
> target measurement for subtraction; horizontal axis - level of background
>
> observed for empty target vs spectrum height observed for target inserted
> case,
>
> normalized to the same flux).
>
> I got the simple formula for the quantity in the plot: y = 1 -
> (1-sqrt(x))/(1-x).
>
> If it is true, for our case the optimum for Be is between 25%...30% of
> total Be time
>
> to spend for Be empty (bckgr level x = 0.1...0.2).
>
>
> Best regards,
>
>  Ilya.
>
>
>