[Primexd] Be empty optimal time

[Justin Stevens]

As discussed at the last PrimEx meeting, the original proposal and Ashot’s talk at the recent PrimEx ERR https://cnidlamp.jlab.org/RareEtaDecay/JDocDB/system/files/biblio/2017/06/err_0607_2017_gasparian_3.pdf <https://cnidlamp.jlab.org/RareEtaDecay/JDocDB/system/files/biblio/2017/06/err_0607_2017_gasparian_3.pdf> (slide 9) assumed 6 days for empty target running (<10% of the total) for the full experiment.  So, if a larger fraction of time with an empty target is required, the impact on other running times should be considered so we know how to allocate time during the remainder of this run period, once the LHe target is ready for production.

-Justin

> On Mar 3, 2019, at 3:48 AM, Eugene Chudakov <gen at jlab.org> wrote:
> 
> I attach a picture for the relative stat. error of the result depending on the fraction of the BG events in the full-target sample and the fraction of time spent on the empty target. The optima are rather broad.
> 
> Eugene
> 
> From: Primexd <primexd-bounces at jlab.org> on behalf of gasparan at jlab.org <gasparan at jlab.org>
> Sent: Saturday, March 2, 2019 12:06:27 PM
> To: Ilya Larin
> Cc: primexd at jlab.org
> Subject: Re: [Primexd] Be empty optimal time
>  
> 
>   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.
> >
> >
> >
> 
> 
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