Most of our current understanding of elementary particle physics is encoded in the "Standard Model", a mathematically consistent description of all known particles and their interactions (except gravitation). However there are a number of shortcomings of the Standard Model and most notably, astrophysical observations suggest that the currently known particle content can account for but 5% of the total mass content of the universe (the rest being called dark matter). One of the most popular theoretical concept that introduces additional particles is the concept of supersymmetry (SUSY).
Current searches for SUSY particles are for example conducted with the ATLAS detector at the LHC at CERN. However, as SUSY theories depend on many unknown parameters, computation power becomes a limiting resource for the study (and exclusion) of possible concrete SUSY scenarios. To address this, two types of analysis methods are used: Truth level analysis (fast but unreliable) and reco level analysis (slow but reliable). Because truth level analysis is a shortcut, it has to be validated by comparing it with the reliable reco level analysis results.
For my thesis I performed such a comparison for a specific setup. Unfortunately I found but low levels of agreement between the results of both analysis strategies. I ruled out several sources of error and showed the necessity of a more detailed study of the underlying assumptions.
Based on the search for supersymmetry in final states containing one isolated lepton, jets and missing transverse momentum with proton-proton collision data recorded with the ATLAS detector at a center-of-mass energy of $\sqrt s = 8\, \mathrm{TeV}$ in 2012, I looked into the estimation of the sensitivity to phenomenological MSSM models using the signal shape of truth level signal samples. These were then compared to the sensitivity as calculated with MC samples on which a full detector simulation and reconstruction had been performed. The agreement was found to be generally low. Several sources of error were ruled out, showing the necessity of a more detailed study of the underlying truth- and reco-level signal samples.
Comparing the CLs values obtained by reco level analysis (y axis) and truth level analysis (x axis). Ideally both values should roughly agree (resulting in the red line with $x=y$), but this is obviously not the case here.