Dissertation/Thesis Abstract

Supersymmetry without prejudice: The pMSSM in colliders and cosmology
by Gainer, James Samuel, Ph.D., Stanford University, 2009, 261; 3382939
Abstract (Summary)

Supersymmetry (SUSY) represents an appealing possibility for Beyond the Standard Model physics. While most analyses of SUSY phenomenology, in collider experiments or astrophysical observations, assume particular scenarios of SUSY breaking, it is interesting to see what one can learn by considering a more general class of SUSY models. Thus, we explore the physics associated with the general CP-conserving Minimal Supersymmetric Standard Model (MSSM) with Minimal Flavor Violation, which is sometimes known as the "phenomenological MSSM" (pMSSM).

First we conduct a large scale examination of the pMSSM parameter space at the proposed International Linear Collider (ILC), examining the ILC signatures of 242 pMSSM parameter points. These points were found by Arkani-Hamed et al. to have signatures at the Large Hadron Collider (LHC) which were difficult to distinguish from each other. This ILC analysis includes full Standard Model (SM) backgrounds and fast detector simulation specific to the proposed SiD detector design.

We find that the cuts applied in standard ILC SUSY analyses are, in general, inadequate for observing SUSY signals from these pMSSM parameter points. In some cases the standard cuts completely removed our signal, while in other cases they did not reduce the SM background enough. Therefore, we developed a set of cuts that work more or less uniformly throughout the parameter space.

We find that only about one third of these scenarios lead to visible SUSY signatures of some kind with a significance greater than or equal to 5 at the ILC with a center of mass energy of 500 GeV. However, charged sparticles are visible in over 90% of the cases in which they are kinematically accessible. As kinematic accessibility is clearly a limiting factor, upgrading to a 1 TeV center of mass energy would be expected to substantially improve this situation. In addition, including the effects of polarized positrons would probably lead to somewhat more optimistic conclusions.

We then generate a much larger set of pMSSM parameter points. The 19 (soft SUSY breaking) parameters of this parameter space are chosen so as to satisfy all existing experimental and theoretical constraints. We assume that the LSP is a conventional thermal relic, but we do not assume that it is the dominant component of the Dark Matter.

We scan this parameter space using both flat and log priors for the soft SUSY breaking mass parameters. Comparing the results of the flat and log prior scans, we find qualitatively similar results. Detailed constraints from both LEP and Tevatron searches play important roles in obtaining our final model samples. We find that there are parameter points in the pMSSM which yield mass spectra and values of experimental observables which are different from those found in any conventional model of SUSY breaking. Therefore it is important to understand predictions from this set of parameter points for dark matter detection and for the LHC. We discuss the properties of this set of pMSSM parameter points relevant to Dark Matter. Further studies of the Dark Matter properties of these models as well as their LHC signatures are ongoing.

Indexing (document details)
Advisor: Hewett, JoAnne
School: Stanford University
School Location: United States -- California
Source: DAI-B 70/10, Dissertation Abstracts International
Subjects: Theoretical physics, Particle physics
Keywords: Cosmology, Dark matter, Large Hadron Collider, Standard Model, Supersymmetry
Publication Number: 3382939
ISBN: 978-1-109-45016-3
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