Difference: PiENu (8 vs. 9)

Revision 92013-04-25 - DanProtopopescu

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META TOPICPARENT name="DanProtopopescu"

PiENu

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 The MC code was obtained from svn (pienu02.triumf.ca/pienumc/trunk) and unpacked on the UI. Specific versions of CLHEP (2.0.4.2) and Geant4 (4.9.0.3.p02) were installed in the user directory in ~/packages/. Detailed download and compilation instructions for CLHEP, Geant4 and the main pienu code were provided by Aleksey Sher via email (May 2011).
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Monte Carlo

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Our MC code version is slightly modified to record the angles and energies of the Bhabha-scattered e+ and e-. During our analysis we have discovered that a spurious production cut was forgotten in the code, and this was introducing, among others, incorrectly high (2 MeV) energy thresholds for the Bhabha-scattered electrons. This is now corrected everywhere.
 
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MC run using recommended settings, 100k events (to check):
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Simulation and Reconstruction

 
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Pienu or Pimunu events are simulated with pienu, and a Root output is produced. This output is subsequently processed with MC2Data, which does the reconstruction and produces a Root file with additional information. The reconstructed data is then analysed with various macros that were custom-written for our study.
 
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Bhabha events tagging

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Bhabha events tagging in MC

Bhabha scattering events are flagged in SteppingAction, by assigning to EBh the energy of the positron if the process involved at a certain step is "eIoni" and the volume where this occurs is "Target":

 
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In MC, this is done via a code snippet added by Chloe in SteppingAction.cc:
 
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//Chloe's addition (in SteppingAction.cc)
  if (theParticleName == "e+" && thePostVolume == "/pienu/Target" && theProcessName == "eIoni") {
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runAction->SBhabha(postEnergy); // G4cout << postEnergy/MeV << G4endl;
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runAction->TgtBhabha(postEnergy);
  }
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However, this only selects Bhabha scattering events happening in the target volume.
 
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Reproducing plots from Chloe's thesis

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The energies and momenta of the initial positron and the outgoing positron and electron are recorded with the following conditionals:

    if(theParticleName == "e+"
       && thePostVolume == "/pienu/Target"
       && theProcessName == "eIoni") {
      runAction->PositronFromBhabha(postEnergy, postMomentum);
      runAction->PositronPreBhabha(preEnergy, preMomentum);  
    }

    if(theParticleName == "e-" 
       && thePostVolume == "/pienu/Target"
       && theCreatorProcessName == "eIoni"
       && theTrack->GetCurrentStepNumber()==1) {
      runAction->ElectronFromBhabha(prePosition, preEnergy, preMomentum);        
    }

The "eIoni" physics processes are implemented in module G4MollerBhabhaModel.cc from the Geant4 MC simulation package.

Events such tagged were studied to understand energy and angular distributions of the Bhabha-scattered e- and e+ and compare them with 'non-Bhabha' events.

Analysis

The first step was to validate our software by reproducing all plots done with MC from Chloe's thesis. The second step was to try to reproduce data results from Chloe's thesis with our MC (adding radiative effects, pileup etc. if necessary). We have satisfactorily achieved these steps.

 
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The data tree produced by MCtoData contains numerous new branches, which can be useful for this analysis. A first step is trying to identify these branches and reproduce some of the most important plots from Chloe's thesis. These PDFs contain our plots:
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In terms of understanding the energy and angular distributions of the Bhabha-scattered e- and e+, we have prepared a report (attached to this wiki) for the PiENu collaboration. Since the Bhabha correction to the tail correction is not directly measurable, the plan is to estimate it from the MC and then validate the MC by comparing a measurable Bhabha effect with data.
 
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The ROOT macros used to draw these plots are attached here.
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Some of the ROOT macros used are attached here.
 
META FILEATTACHMENT attachment="TalkINPC.pdf" attr="" comment="INPC 2010 talk by Chloé Malbrunot" date="1336144134" name="TalkINPC.pdf" path="TalkINPC.pdf" size="3207320" stream="TalkINPC.pdf" tmpFilename="/usr/tmp/CGItemp16539" user="DanProtopopescu" version="1"
META FILEATTACHMENT attachment="PIENU_proposal.pdf" attr="" comment="PIENU Proposal" date="1336144271" name="PIENU_proposal.pdf" path="PIENU_proposal.pdf" size="390839" stream="PIENU_proposal.pdf" tmpFilename="/usr/tmp/CGItemp16616" user="DanProtopopescu" version="1"
 
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