PiENu < Main

---++ !PiENu

The PIENU experiment at TRIUMF (Vancouver, Canada) aims at precisely measuring the pion decay branching ratio (&#960;+ &#8594; e&#957;)/(&#960; &#8594;&#956;&#957;).  
The current experimental value for this ratio is 20 times less precise than the theoretical calculation done within the SM, leaving a large window in which non-standard physics - new interactions or exotic particles - can be involved. Or, on the other hand, improved precision that would confirm the SM would set tighter constraints on new physics scenarios.

%TOC%

---+++ PPE People

Currently, David Britton, Main.DanProtopopescu and Ian Skillicorn are contributing to this [[https://pienu.triumf.ca/collaborators][experiment]].

---+++ Shift Schedule

Available here: http://pienu02.triumf.ca/pienu_shifts/index.php

---+++ Documentation

   * Official website at Triumf: http://pienu.triumf.ca/
   * [[%ATTACHURL%/TalkINPC.pdf][INPC 2010 talk]] by Chloé Malbrunot
   * [[%ATTACHURL%/PIENU_proposal.pdf][PIENU Proposal]]

---+++ Code compilation

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). 

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.

---+++ Simulation and Reconstruction

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.

---+++ Bhabha events tagging in MC

Bhabha scattering events are flagged in =SteppingAction=, by assigning to E<sub>Bh</sub> the 
energy of the positron if the process involved at a certain _step_ is "eIoni" and the volume 
where this occurs is "Target":

<verbatim>
   if (theParticleName == "e+" 
     && thePostVolume == "/pienu/Target" 
     && theProcessName == "eIoni") {
    runAction->TgtBhabha(postEnergy);
    }
</verbatim>

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

<verbatim>
    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);        
    }
</verbatim>

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.

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.

Some of the ROOT macros used are attached [[%ATTACHURL%/macros.tgz][here]].

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
pdf	PIENU_proposal.pdf	r1	manage	381.7 K	2012-05-04 - 15:11	DanProtopopescu	PIENU Proposal
pdf	Plots-2012-06-26.pdf	r1	manage	1030.5 K	2012-06-27 - 11:07	DanProtopopescu	Plots reproducing figures 1.2, 5.1 and 5.19
pdf	TalkINPC.pdf	r1	manage	3132.1 K	2012-05-04 - 15:08	DanProtopopescu	INPC 2010 talk by Chloé Malbrunot
tgz	macros.tgz	r1	manage	4.0 K	2012-06-27 - 11:10	DanProtopopescu	Analysis macros (initial versions)

This topic: Main > TWikiUsers > DanProtopopescu > PiENu
Topic revision: r9 - 2013-04-25 - DanProtopopescu