Re: [BLAST_ANAWARE] charge and dgen

From: zhangchi (zhangchi@general.lns.mit.edu)
Date: Sat Jul 12 2003 - 20:47:42 EDT


In addition to the analysis Mr.T gave, here are some facts about the monte
carlo data files generated:

for information on the few MC generated, please reffer to
spud?:~zhangchi/blast/build_/runs.log
while MC data files are in
spud?:~zhangchi/blast/build_/run_ed_nplex, run_ed_wplex, run_eep_nplex,
run_eep_wplex, run_ep_nplex, run_ep_wplex.

nplex means no plex glass plate and wplex means with plex galss plate.

There are links to these directories in blast account. but I am not sure
if runs.log is linked too which is very important.

fort.99, kine.init, input.10 in each of these directories would provide
first hand information on how the data are generated.

For ep, ed->e'pn, 20hr's * 80mA worth of events are generated, for 0.1sccm
atomic gas into a target cell at 100K. so the total charge is:
        20*3600*0.08 = 5760C

For comparison against unpol runs, please note that the 0.1sccm atomic
gas flow equals to 0.05 molecular gas flow. While target density is
computed using atomic gass so is under estimated by sqrt(2).

So in short, for unpol runs the effective target gas flow assumed in the
Monte Carlo is: 0.05/sqrt(2) = 0.035 sccm

Hope this in addition to TB's email would give a complete picture on MC
side to get you started.

Chi

On Sat, 12 Jul 2003, 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)
>
> --
> ________________________________________________________________________________
> 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
> >
> >
>
>



This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:29 EST