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Searches for New Symmetries in pp Collisions with the Razor Kinematic Variables at √s = 7 TeV


Rogan, Christopher Sean (2013) Searches for New Symmetries in pp Collisions with the Razor Kinematic Variables at √s = 7 TeV. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/B0MD-F026.


The construction and LHC phenomenology of the razor variables MR, an event-by-event indicator of the heavy particle mass scale, and R, a dimensionless variable related to the transverse momentum imbalance of events and missing transverse energy, are presented.  The variables are used  in the analysis of the first proton-proton collisions dataset at CMS  (35 pb-1) in a search for superpartners of the quarks and gluons, targeting indirect hints of dark matter candidates in the context of supersymmetric theoretical frameworks. The analysis produced the highest sensitivity results for SUSY to date and extended the LHC reach far beyond the previous Tevatron results.  A generalized inclusive search is subsequently presented for new heavy particle pairs produced in √s = 7 TeV proton-proton collisions at the LHC using 4.7±0.1 fb-1 of integrated luminosity from the second LHC run of 2011.  The selected events are analyzed in the 2D razor-space of MR and R and the analysis is performed in 12 tiers of all-hadronic, single and double leptons final states in the presence and absence of b-quarks, probing the third generation sector using the event heavy-flavor content.   The search is sensitive to generic supersymmetry models with minimal assumptions about the superpartner decay chains. No excess is observed in the number or shape of event yields relative to Standard Model predictions. Exclusion limits are derived in the CMSSM framework with  gluino masses up to 800 GeV and squark masses up to 1.35 TeV excluded at 95% confidence level, depending on the model parameters. The results are also interpreted for a collection of simplified models, in which gluinos are excluded with masses as large as 1.1 TeV, for small neutralino masses, and the first-two generation squarks, stops and sbottoms are excluded for masses up to about 800, 425 and 400 GeV, respectively.

With the discovery of a new boson by the CMS and ATLAS experiments in the γ-γ and 4 lepton final states, the identity of the putative Higgs candidate must be established through the measurements of its properties. The spin and quantum numbers are of particular importance, and we describe a method for measuring the JPC of this particle using the observed signal events in the H to ZZ* to 4 lepton channel developed before the discovery. Adaptations of the razor kinematic variables are introduced for the H to WW* to 2 lepton/2 neutrino channel, improving the resonance mass resolution and increasing the discovery significance. The prospects for incorporating this channel in an examination of the new boson JPC is discussed, with indications that this it could provide complementary information to the H to ZZ* to 4 lepton final state, particularly for measuring CP-violation in these decays.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:LHC, Supersymmetry, CMS, High Energy Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Awards:John Stager Stemple Memorial Prize in Physics, 2009.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Spiropulu, Maria
Thesis Committee:
  • Spiropulu, Maria (chair)
  • Newman, Harvey B.
  • Golwala, Sunil
  • Schwarz, John H.
Defense Date:12 February 2013
Non-Caltech Author Email:christophersrogan (AT)
Record Number:CaltechTHESIS:05072013-174540453
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7671
Deposited By: Christopher Rogan
Deposited On:17 May 2013 22:39
Last Modified:04 Oct 2019 00:00

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