[Olympus] Follow-Up on Today's 12 Degree Discussion

[Brian S. Henderson]

Hello all,

I have put together a few plots to examine the issues we discussed =

during Kirill and Denis's presentation today, specifically the MC/data =

comparisons on Slide 3.  The four plots attached shown comparisons of =

the reconstructed theta with any four tracking for the combinations =

electrons/positrons in the left/right arms, for two runs of each =

species.  The version of LumiFit I used today should be essentially =

identical to that used by Kirill and Denis last week. On each plot: red =

is the data, blue is the MC according to the SC lumi, cyan is the MC =

with a scaling factor, and green is the MC /without//selecting on the =

lumi trigger conditions/ (neither requiring a ToF hit nor a hit in both =

SiPMs).

Regarding what I did to generate these plots: the generator was run =

under identical conditions to those specified in the talk this morning =

with the exception of the soft fraction, which I left on the default =

value of 0.5.  The standard lumi hit finding and digitization were run =

as they exist in olympus_release, and then both were tracked using the =

version of LumiFit currently in olympus_lumigem, using the fitlumis4.xml =

and fitlumisMC4.xml (the only difference between these recipes is the =

application of offsets, which will be phased-out in the near future).  I =

then ran my 12 degree analysis program "GEMLumiNoPro.xml" (which doesn't =

require proton tracks) to make the histograms, and re-ran GEMLumiNoPro =

for the MC tracks with the trigger selection conditions removed.

During today's discussion, there were two primary questions regarding =

the theta plot on the right side of Slide 3: the overall normalization =

of the data relative to MC and the relative excess of lower theta =

(between 10-11 degrees) of the MC relative to the data. As can be seen =

in the plot "elefttheta.png", this effect seems to be caused by not =

properly accounting for the trigger in the processing of MC data.  When =

the trigger is selected on in the analysis, the theta distributions =

agree reasonably between data and MC in both the left and right arms.

The overall scale, however, remains a question.  As noted, Denis and =

Kirill saw the MC distribution to be about 1.5 or 2 times larger than =

the data distribution, but this doesn't seem to be due to the trigger =

issue since leaving out the trigger doesn't increase the "peak" of the =

MC distribution.  Is it possible the MC data set included more events =

than expected or multiple runs?

Based on this, I have a few questions for Kirill and Denis:

  * At what stage of your analysis and in what way is the trigger
    selection done for MC events?
  * When you run the generator for a single run, do you change the
    numbers of events, and if so how?
  * Is your analysis code currently available in the repos so that
    people can take a look at it?


I have full sets of kinematic distributions for these runs using the =

latest tracking, so let me know if there is anything you would like to see.

Thanks,
Brian
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