Loading...

Searches for New Physics with Opposite-Sign Di-Leptons(Using the CMS Experiment at the Large Hadron Collider)

Fahim, Ali | 2012

1992 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44454 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Arfaei, Hessamaddin; Pape, Luc
  7. Abstract:
  8. Among the proposals for new physics, Supersymmetry is the most popular to gradually appear at a yet unreached center-of-mass energy at the Large Hadron Collider (LHC). However, that doesn’t seem very likely. This thesis represents a search for any evidence of a minimal supergravity inspired scenario (mSUGRA) of R-parity conserving supersymmetry at the Compact Muon Solenoid (CMS) experiment. The analysis employs an event topology , which consists primarily of opposite-sign di-leptons accompanied by hadronic jets and missing transverse energy. The search utilizes data produced by the proton-proton collision of the LHC at a center-of-mass energy p s = 7 TeV and recorded by the CMS detector in 2011, corresponding to an integrated luminosity of 1100pb1.This signature could be mimicked by many physics processes of the Standard Model such as Drell-Yan and top-quark pair production. According to the proposed analysis strategy, the search applies a general optimization method for the best statistical significance to define the signal regions where the backgrounds are suppressed by the selection. Moreover, the search represents a far-reaching overview of the behavior of signal region criteria as a function of the main modelparameters.The measurement yields 5 events observed in the high /ET signal region which is statistically consistent with the estimated Standard Model background rate of 4.88 3.10 events. Likewise, the measurement gives an observed yield of 4 events in the high HT signal region which is in reasonable agreement with the predicted background rate of 7.71 2.96 events. Due to no observed excess of events in the signal regions, the research leads naturally to an upper limit on cross-section times branching ratio times acceptance ( s Br Acc ).As a consequence of this research, we show that the optimized signal selection criteria are highly model-dependent and, moreover, the high-HT cut rather than the high- /ET one is more efficient for the high-m0 models. Hence, by using the appropriate criteria for the LM8 model, the calculated upper limit is s Br Acc < 0.011 pb at 95% CL, while the theoretical computations predict s Br Acc = 0.022 pb. Thus such models could be also reliably excluded
  9. Keywords:
  10. Statistical Data Analysis ; Supersymmetry ; Compact Muon Solenoid (CMS)Test ; Large Hadronic Collider

 Digital Object List

 Bookmark

...see more