[Halld-offline] event sizes with MC tags stripped out

[Richard Jones]

Hello all,

I have generated a sample of minimum bias events using bggen.  The photon beam spectrum in this sample is the total photoproduction cross section weighted by the coherent bremsstrahlung spectrum evaluated with the standard GlueX collimator, between incident photon energies 3GeV and 12GeV.  This roughly corresponds to the level-1 trigger.

Here are the average event sizes at various stages in the production pipeline for this sample.  Note that this is the current state of the simulation tools, not what you might remember from 6 months ago.  These event sizes are larger than you might remember hearing a while back!

 1. bggen output:
      * with MC information: 800 bytes
      * after stripping MC information: N/A
 2. hdgeant output:
      * with MC information: 70KB
      * after stripping MC information: 22KB
 3. mcsmear output:
      * with MC information: 102KB
      * after stripping MC information: 49KB

During the stripping process, I removed anything that was not absolutely needed to store the hit information for the event.  I also removed the new tags added by David associated with saving the full spectrum in the bcal, and incident particle information there, even though the string "Truth" was not encoded in the tag name.  My goal was to strip things down to the absolute minimum required to store the hits information.

Unfortunately, things are not as simple as the above table might suggest.  While I was not paying attention, scads of "truth" information have crept in to taint the hits information that is included in the stripped files above.  For example, people working on tracking in the CDC have mixed truth information into the hits tags, as in the following example:

  <cdcStrawHit maxOccurs="unbounded" d="float" dE="float" itrack="int" ptype="int" t="float" />

What is track number doing inside this hits tag, you might ask????  The equivalent and correct way to encode this same information in hddm would be the following.

<cdcStrawHit maxOccurs="unbounded" d="float" dE="float" t="float>
      <cdcStrawHitTruthInfo minOccurs="0" itrack="int" ptype="int"/>
</cdcStrawHit>

Encoded in the new way, it is easily stripped, but the association is still there in the unstripped event.  Encoded in the original way, the entire tag is tainted with truth information.  If the substring "Truth" occurs in the tag, it should be stripped in the final analysis.  If not, it should be completely clear of truth information and should be kept for the final analysis.

Once we fix these problems, I will rerun the above stripping exercise and we will get a better estimate for what the average event size will be.

-Richard Jones

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