[Primex] PrimEx meeting minutes, November 13, 2009

[Dustin McNulty]

Dear Colleagues,
        The minutes for last weeks Friday meeting are given below and can
also be found at:

http://www.jlab.org/primex/wiki/index.php/Weekly_Minutes_2009-11-13

Best regards,
Dustin


Dustin McNulty
TJNAF CEBAF Center, Rm A102
12000 Jefferson Avenue
Newport News, VA 23606
Phone: (757) 269-5023


*Weekly Meeting Minutes - November 13, 2009*

Minutes by: Dustin McNulty

Meeting Agenda 
<http://www.jlab.org/primex/wiki/index.php/PrimEx_Weekly_Meeting%2C_November_13%2C_2009> 

------------------------------------------------------------------------

*Attending:* P. Ambrozewicz, M. Ito, D. Lawrence, D. McNulty, V. 
Tarasov, A. Teymurazyan *By phone:* R. Miskimen

*


  Summary of Meeting Discussions:

*


      *All.* Nominate secretary: (next secretary: Mark)


      *All.* Approval of last meeting's minutes:

Approved. You can find the previous meeting minutes here 
<http://www.jlab.org/primex/wiki/index.php/Weekly_Minutes_2009-10-30>. 
Only comments were about Aram's presentation of hadronic bkgd studies; 
he showed a 1 to 1 signal to bkgd ratio for eta production integrated 
over the full production angle range. Question for him was: What are the 
reactions giving rise to the hadronic bkgd eta's? All we know is that 
they are not from gamma+p-->eta+p.


      *All.* New Business: Itemized below

_1_: Review of collimator size studies (Victor) 
<http://www.jlab.org/primex/weekly_meetings/slides_2009_11/Study%20of%20properties%20beam%20line%20in%20Pair%20spectrometer_5.pdf>: 


      He looked at the effect of 2 different collimator sizes: 3.4mm and
      5.0mm diameter (this is for the active collimator) 

      The purpose of the study was to examine how the coll. size affects
      the energy resolution of the pair spectrometer. 

      For the 3.4mm case, 1.49M gammas emerged from the collimator out
      of 10M gammas incident. 

      For the 5.0mm case, 1.52M gammas emerged from the collimator out
      of 10M gammas incident. 

      Victor showed plot of electron-arm's (from pair prod) Esigma
      versus distance detected from beamline (at the pair spec detector
      location). He determined Esigma by (Gaussian) fitting the
      distribution of electron energies seen in a 10cm wide x bin. 

      His results seemed to indicate a general trend of worsening
      resolution for greater distances from the beamline, although it
      was noted that the statistical precision was quite low and that he
      should include error bars on his points to see if some of the
      observed fluctuations were real or not. Also, he should generate
      more stats. 

      Dustin commented that the 10cm bin size seemed an artificial
      choice and that he should, if possible, use the actual bin size
      proposed for the physical counters--since the results will likely
      depend on this. 

      Dustin also noted that Victor should quote the photon beam
      characteristics used in his Monte Carlo (spot size at radiator,
      emittance properties, etc) since these may also impact the outcome. 

_2_: Presentation of hadronic bkgd studies for eta Primakoff experiment 
(Pawel) 
<http://www.jlab.org/primex/weekly_meetings/slides_2009_11/bggen-plots.pdf>: 


      Pawel used BGgen with events generated between 6 and 12 GeV on
      30cm proton target (using Pythia). 

      Showed plot of number of clusters in FCal versus No. of clusters
      per event (with no cuts). Aram noted that, for no cuts, the zero
      cluster bin look surprisingly low. 

      Showed two cluster invariant mass distribution. This looked like
      there was much less background in the vicinity of the eta mass (as
      compared with Aram's study). It was also noted that the eta inv
      mass hump was shifted by +50MeV. David thought this could have
      something to do with how the reaction vertex was incorporated in
      the calculation. 

      Showed two cluster elasticity plot for all possible pair
      combinations. 

      Showed eta angular distribution using a 9GeV elasticity cut and
      cutting around the eta inv mass hump. It was noted that these
      events include the g+p->eta+p reaction.? 

      Conclusions are that more statistics are needed, but that in
      general the background looks very low (compared with Aram). Aram
      suggests that Pawel should generate events with energy closer to
      the actual trigger conditions of the proposed experiment (which is
      E>10.5GeV)--this will improve the efficiency of the Monte Carlo. 

_3_: Presentation of hadronic bkgd studies for eta Primakoff experiment 
(Aram) 
<http://www.jlab.org/primex/weekly_meetings/slides_2009_11/A.Teymurazyan_bg_11_06_2009.pdf>: 


      BGgen of hadronic events using Pythia with the g+p->eta+p reaction
      explicitly excluded. Aram analyzed 46M events between 10.2 and
      11.7 GeV with only incoherent Bremsstrahlung on 30cm liquid proton
      target, the solenoid was energized, and the full setup of the
      GlueX detector simulation was employed. 

      Showed cluster distributions in FCal. In general his left-side
      plots had limited or no cuts while the right-side plots had cuts.
      His cuts were total energy in FCal (all cluster energies summed) >
      9GeV, 2 or more clusters detected, 2 cluster elasticity between
      0.9 and 1.1, and inv mass between 490 and 650MeV. 

      His results for the background eta were the same as he presented
      two weeks ago--Over the full production angle range, there is a 1
      to 1 ratio of signal to noise (S2N). He also examined the S2N in
      the Primakoff peak region (for 1 to 0.5 deg) and found that here
      the S at N ratio is 1:8. 

      Aram noted that this work is very preliminary and needs to be
      checked with more investigation. 

      A discussion started about the accuracy of Pythia, it was noted
      that this program was brought by Elke from HERMES (where it was
      used for 30GeV event generation) and modified/tuned to work for
      Hall D energies and that it may not be very accurate in the 0 to
      0.5 degree region. However, it was also noted that it is just as
      likely to be underestimating the background here as it is to be
      overestimating it. 

      It was suggested by Rory and Dustin that Aram try to eliminate the
      inelastic bkgd events within his elasticity cut to give more
      accurate results -- it looks like this smooth inelastic bkgd could
      be significant. Also, the smooth background under the eta inv mass
      peak could be eliminated in the same way (this bkgd looked even
      more significant). 

      Aram will check his numbers for the S2N and perhaps present them
      in a more audience friendly format per Mark's request. 

      Aram also said that he will classify the events in his study in
      terms of the reaction mechanism. 

      Another suggestion was for Aram to put the signal and background
      distributions on the same plot. 

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