Tancredi Botto wrote:
>Hi,
>this has been a long discussion by now, but I believe that however we do
>it, as long as dgen is happy and clear, we'll manage..
>
>Read the readme file in the blastmc directory
>
>dgen generates events for a given I_beam*Delta_T (= integrated charge,
>note the beam current is a constant) and a given target thickness. The
>values assumed are listed. Also listed is the integrated luminosity in
>1/cm2. The montecarlo must obviously assume a certain cell geometry,
>target mass (for conductance/thickness calculation). Furthermore:
>
>Luminosity: target thickness x (Integrated Coulombs/1.6e-19)
>
>You can separate these two components from the dgen readme (you have
>to calculate 80 mA x 20 hrs). Then the ratio of the histograms
>of montecarlo events over data events will be obviously equal to
>
> R = H_mc/ H_data = (MC tgt thickness/ target thickness) * (MC charge/charge)
>
>For the data, a standard Xsection macro like compare_eep.C or compare_ep.C
>will give you the total charge (essentially, all the work is done in
>init.C, you can easily see how). This number is obtained summing over all
>charge files. Note: if a file in the list is skipped, so is its charge file.
>
>Then, once you have R you can easily arrive at the integrated (or average)
>target thickness over the set of data files you considered. This you can
>compare with naive expectations based on flow, molecular-atomic fractions,
>gas temperature, cell geometry.. See also "standard" macros like
>compare_ep.C and compare_eep.C
>
>In this sense you normalize data and montecarlo.
>
>Of course you truly arrive at (target thickness) x (recon efficiency),
>where you can/should assume recon efficiency=1 for the tofs. You of course
>assume the mc has the right elastic cross section folded over the right
>acceptance.
>
>For instance: you will compare the montecarlo to polarized and unpol data.
>equal pol and unpol flows result in different thicknesses (for abs
>is ideally a flow of atoms, for unpol flow of molecular D2,H2). Also,
>the cell conductance is for mass 2 and 4, respectively.
>Also, for ABS, you could have an uncertainty in how much gas is really
>injected into the cell (gas can flow to the sc. chamber otherwise)
>
>Even if you don't know how to calculate the target thickness, you can
>always normalize to known detection channels like elastic. Then you can
>always apply the same effective normalization factor to data taken
>simultaenously on different reaction channels to arrive at a cross
>section.
>
>One last note, h_data should be corrected by a factor 1/lvtime due
>to daq dead times. In this case lvtime can be easily obtained from
>f/lr->Draw(bgbeam/beam,beam>0)
>
>
maybe i'm missing something, but i thought this was already accounted
for by using the beam-gated integegrated current (where the gate is
inhibited during daq deadtime)?
--chris
> --
>________________________________________________________________________________
>Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
>research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>On Sat, 12 Jul 2003, Aaron Joseph Maschinot wrote:
>
>
>
>>is it "correct" to normalize the Monte Carlo count rates by the real-data
>>charges? if not, is their some way to calculate the MC charge (i.e.
>>whatever dgen uses)? the scalers aren't in the MC, so i can't just run
>>charge.C on a MC file, i don't think.
>>
>>aaron
>>
>>
>>
>>
>
>
>
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