PiENu

The PIENU experiment at TRIUMF (Vancouver, Canada) aims at precisely measuring the pion decay branching ratio (π+ → eν)/(π →μν). 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.

PPE People

Currently, David Britton and DanProtopopescu are directly involved in this experiment.

Documentation

• Official website at Triumf: http://pienu.triumf.ca/
• INPC 2010 talk by Chloé Malbrunot
• 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).

Monte Carlo

MC run using recommended settings, 100k events (to check):

• Output of default MC run pienu pienu.mac : run1.root
• Output from MCtoData run1out.root run1.root : run1out.root (stdout)

Bhabha events tagging

In MC, this is done via a code snippet added by Chloe in SteppingAction.cc:

//Chloe's addition (in SteppingAction.cc)
    if (theParticleName == "e+" 
        && thePostVolume == "/pienu/Target" 
        && theProcessName == "eIoni") {
        runAction->SBhabha(postEnergy);
     // G4cout << postEnergy/MeV << G4endl;
    } 

Reproducing plots from Chloe's thesis

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:

• Plots-2012-06-26.pdf: Plots reproducing figures 1.2, 5.1 and 5.19

The ROOT macros used to draw these plots are attached here.