[Halld-cal] BCAL Reconstruction Meeting Minutes 2015-04-30

Fri Aug 28 15:35:04 EDT 2015

Hello Tegan,

I am setting up to implement the readout of BCal hits in hdgeant4, and I
have a question about which mode of output you want me to support. The hddm
output record defines several different styles for recording event output:

   1. bcalSiPMupHit/bcalSiPMdownHit - these are marked "obsolete" in the
   template
   2. bcalSiPMSpectrum - introduced to try and understand the role of noise
   in the fADC stream
   3. bcalADChit / bcalTDChit (and their "digi" counterparts) - probably
   the closest to what the DAQ actually produces.

If I had my druthers, I would only support output from hdgeant4 in mode 3,
and not modes 1 or 2. If I were to do that, would there be significant
information lost that you would like to recover? Would you like to have
both modes 2 and 3 available, selectable by an option in control.in or
something like that? Or is mode 2 pretty much obsolete as well?

Anyone else in the calorimeter working group that has an opinion on this
should feel free to respond to my question as well, but I understand from
Justin that Tegan is probably the man to ask.

-Richard Jones

On Thu, Apr 30, 2015 at 4:47 PM, Elton Smith <elton at jlab.org> wrote:

> Hi Tegan,
>
> Sorry we missed the meeting this morning. I will try to provide
> answers/comments where I can. Others can also provide feedback.
>
> = New code =
> * Poisson statistics smearing still needs a value for the energy of one
> dark hit.
>
> Attached is a script and plots of a single pixel firing, with the
> normalization of summed energy of 0.31 MeV/pixel. Note, however that his
> depends on several factors. This is an average value for energy deposited
> in the middle of a module. Of course the actual amount of energy deposited
> with that amplitude will depend on the position of the energy deposition.
> Also, I have used a gain factor of 0.046 MeV/integral count. But these vary
> quite a bit from cell to cell. See Will's log entry detailing the gain
> factors obtained for the fall run:
> https://logbooks.jlab.org/files/2015/03/3328508/BCAL_Calib_Update_Mar20.pdf
> .
> However, the question itself regarding what energy corresponds to a single
> pixel is a little misleading. If one is simulating dark hits (i.e. single
> pixels), these do not correspond to energy per se but rather an amount of
> charge into the FADC. This is better characterized by the number of FADC
> counts that correspond to one pixel firing (see figure). This is
> independent of attenuation length. It is does depend on the gain of the
> sensor and electronics. However, there are many contributions to the "gain"
> or conversion from counts to MeV. For example, the acceptance/transmission
> of the light guides contributes to the overall gain factor and this has
> nothing to do with the size of the single pixel. Therefore, it might make
> more physical sense to simulate the dark hits with minimal dependence on
> each channel. If we operate the SiPMs at the same over bias, this should
> correspond to the same gain for all sensors. Therefore, the large variation
> we are seeing in "gains" may not be primarily due to the actual sensor
> gains themselves.
>
> Hope this gives you sufficient information to think about how to move
> forward.
>
> * What should we use for an energy threshold to write out events?  A 4 mV
> threshold was used before.  4 MeV?
>
> The threshold should be given in counts, which corresponds to the DAQ
> threshold of 105. The pedestal is nominally at 100, so 5 counts above
> pedestal. We are using the 2 V scale on the FADCS, which are 12 bits, so
> one count = 0.0004884 V. Therefore 5 counts is 2.44 mV assuming the
> pedestal does not drift. Of course it does, so another question is whether
> we wish to include pedestal drifts in the simulation. Generally one tries
> to setup hardware, so the software can ignore such details, but this may
> not be possible in this case.
>
> In any case, the thing to do is to convert the energy deposited into
> counts, use the pulse shape I have provided (or your own favorite) to
> convert this into fADC counts. The threshold would be applied to this pulse
> train.
>
>
> * The change to the data structure will be just adding 'incident_id="int"'
> to 'bcalTruthHit.'
>
> Others with more expertise should comment on this one.
>
> ** If we don't change the data structure, we'll change bcal_index in the
> code and get rid of the incident particle filling.
> ** I'd prefer changing the data structure, since we'll eventually want to
> implement incident particle dependent smearing (I assume), and it seems
> relatively easy to do it now.
>
> * Time smearing: the time resolution in the code for the fADC is stated as
> 4 ns / sqrt(12).  This was used before because we were using 0.1 ns bins
> rather than 4 ns bins.
>
> This is probably an old guess based on assuming the time coming from the
> fADC comes from picking the first FADC sample above some some threshold. We
> are doing much better than this by essentially finding the time at half
> height. The resolution for this is about 0.2 - 0.3 ns, but Mark can
> probably provide a better number. I suggest you put in a value based on
> Marks latest studies and we can adjust it as more studies are done.
>
> ** Is this value what we'd want to use for smearing a single truth time?
>
>
> = Old code =
> * We need to decide whether or not we want to keep this method available
> for people to choose to use.
> * If we do keep it:
> ** Need to find a value for the energy of one dark hit that causes
> waveforms to more closely resemble data and also that gives reasonable
> pedestal variation.
>
> Using the attached scritps used for the pedestal studies, I think we a
> first stab at this.  See GlueX-doc-2695
> http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=2695
> You can find all the scripts in the tar.gz file. If there is anything
> missing, let me know and I can make it available.
>
> ** By fixing an electronic noise smearing, then altering the dark hit
> energy, it looks like we want something like the current energy divided by
> 10 or so.
> ** It should be easy to set the dark hit energy based on what amplitude in
> mV we want the dark pulses to have, if we have any feeling for that (1 mV
> amplitude ~ 1 MeV energy deposition).
>
> See the notes and GlueX notes above, which should provide good answers to
> these questions.
>
>
> Elton Smith
> Jefferson Lab MS 12H3
> 12000 Jefferson Ave STE 4
> Newport News, VA 23606(757) 269-7625(757) 269-6331 fax
>
> On 4/30/15 1:12 PM, Zisis Papandreou wrote:
>
> Hi folks:
>
> the minutes from our short meeting this morning have been posted:
>
> https://halldweb.jlab.org/wiki/index.php/BCAL_Reconstruction_Meeting_2015-04-30
>
> Please note that since there was a controlled access in the hall at the
> same time as the meeting, JLab was not able to join us.  Therefore, we
> posted Tegan's questions on HDGEANT and mcsmear on the Wiki (see above
> minutes). I've placed this discussion at the top of the agenda of next
> week's Calorimetry meeting, as it is important to progress on this and
> complete the tasks.  Will L. will also join us for next week's meeting.
>
> We are hoping that after the commissioning ends on Monday, folks will have
> a chance to read this list so that we can decide upon the items and move
> forward.
>
> I also posted the minutes from the April 16 meeting:
> https://halldweb.jlab.org/wiki/index.php/BCAL_Reconstruction_Meeting_2015-04-16
>
> Thanks and cheers, Zisis...
>
> Dr. Zisis Papandreou
> Professor of Physics, Ph.D., P.Phys.
> ---------------------------------------------------------
> Department of Physics
> University of Regina
> 3737 Wascana Parkway
> Regina, SK  S4S 0A2  CANADA
>
> *Phone: (306) 585-5379 <%28306%29%20585-5379>*
> Fax: (306) 585-5659
> Email:  zisis at uregina.ca
> Website:
> http://www.uregina.ca/science/physics/people/faculty-research/zisis-papandreou/index.html
>
>
>
>
>
>
>
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