[Halld-offline] FCAL Calibration: Data vs. MC

[Sean Dobbs]

Hi Matt,

I think it's reasonable to have the calibrated hit objects (DFCALHit in
this case) objects be calibrated to be in GeV, no matter whether they come
from data or simulation.

The multiplicative factors you are looking for are applied in the
DFCALHit_factory class, both for the overall multiplicative factor and
per-block gain corrections.  The current scale factor that is applied is
1.6E-5 GeV / ADC count.  This factor is currently being loaded from the
CCDB - I can send you some instructions on how to change that when you're
ready.

Cheers,
Sean

On Thu, Sep 18, 2014 at 5:45 AM, Matthew Shepherd <mashephe at indiana.edu>
wrote:

>
> Hi Richard, David, and Sean,
>
> I'm looking for advice as to where/how to compartmentalize
> the FCAL calibration.  (In writing this down,
> it helps me think through the problem -- perhaps there
> are other similar problems.)
>
> HDGEANT reports energy deposited in a block, however
> this still needs "calibration" (now done at post-reconstruction
> shower level) due to systematic shifts resulting from
> energy loss.  This is now done in DFCALShower_factory
> which is a level above the clusterizer:  DFCALCluster_factory.
>
> The FADCs will report a pulse integral for each block.
> This needs to be converted to an energy.  Arguably this
> should be done with an overall (probably fixed) multiplicative constant
> that sets the rough scale for pulse integral -> energy and
> then a second, per block, "gain factor" that is a
> run-dependent constant near unity.  We can estimate
> the overall scale constant from beam tests to try
> to get the right scale for the initial run.  We'll try to
> gain balance all channels based on PMT test data so
> the individual block gains can start out at 1.
>
> The question is, do we calibrate the detector such
> that the result of calibration is actual energy in GeV or
> the output of HDGEANT?  (Maybe the difference between
> these is imperceptible, but I don't think it will be.)
>
> I think what we want to do is calibrate such that it is
> actual energy in GeV.  Then we want to adjust the
> shower-level calibration appropriately.  What we do
> NOT want to do is have a branch that applies different
> shower level correction for MC and data.  This means
> that, post run, we need to devise an algorithm to
> produce the same calibrated block-level energy from
> the energy deposited per bock as recorded by HDGEANT.
> I don't think there is a way to know in advance if
> this is a single common algorithm for all blocks or
> will need tuning on a block by block basis.  (We
> may need additional constants.)
>
> To prepare for actual data, we will generate EVIO
> output of HDGEANT and then try to calibrate the block
> level constants using the output of DFCALCluster_factory.
>
> We can then look at invariant mass of clusters (no
> shower level energy correction applied) and that should
> peak at the pi0 mass.  Applying shower-level nonlinearly
> corrections, which will have to be derived later, should
> improve resolution, but not necessary from the outset
> (and may want to be turned off if it is not working
> properly).
>
> Where can I find the code that applies this overall
> multiplicative constant to convert pulse integral to
> energy (and what is assumed value in the current EVIO
> output plugin)?  Where do the block level constants
> get applied?  Sean has given me some preliminary
> info on how to rewrite these.
>
> Thanks,
>
> Matt
>
> ---------------------------------------------------------------------
> Matthew Shepherd, Associate Professor
> Department of Physics, Indiana University, Swain West 265
> 727 East Third Street, Bloomington, IN 47405
>
> Office Phone:  +1 812 856 5808
>
>


-- 
Sean Dobbs
Department of Physics & Astronomy
Northwestern University
phone: 847-467-2826
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