Until recently, all theories for this stabilization could be grouped into two categories: those that rely on new strong dynamics or compositeness near a TeV (such as technicolor, composite Higgs, or theories with a low fundamental Planck scale), and those with low-scale supersymmetry. Theories with low scale supersymmetry are particularly attractive since they allow a perturbative description of the physics that softens the quadratic divergences, and naturally lead to light Higgs bosons, as seems favored by precision electroweak data. The most significant of these divergences come from three sources. They are one-loop diagrams involving the top quark, the SU(2) × U(1) gauge bosons i.e. W, Z, and a photon, and the Higgs itself. In order for this to add up to a Higgs mass of order a few hundred GeV as required in the SM fine tuning. This is the hierarchy problem.One successful approach to solving the hierarchy problem is based on supersymmetry (SUSY). In SUSY every quadratically divergent loop diagram has a superpartner, a diagram with superpartners running in the loop. The diagrams with superpartners exactly cancel the quadratic divergences of the SM diagrams. Generically, this happens because superpartner coupling constants are related to SM coupling constants by supersymmetry, but superpartner loops have the opposite sign from their SM partner because of opposite spin statistics. A more detailed paper about SUSY can be found here

Many new physics models, including supersymmetry (SUSY), predict mechanisms that could produce a photon + jets + missing ET signature. For his Ph.D. thesis, Hewamanage is completing a model-independent signature-based search for anomalous events in this channel by scanning kinematic distributions including missing ET , invariant mass of the photon + leading jets, total transverse energy (HT ), etc., for an excess of events over SM predictions. An excess could indicate the existence of a new heavy particle decaying into photon + jets or a new physics mechanism such as gauge-mediated SUSY breaking.

Hewamanage is performing this work together with Dittmann, Kasmi, R. Culbertson (Fermilab), and A. Pronko (LBL). Hewamanage has recently implemented a new datadriven method of modeling backgrounds that has proved to be very successful in describing particular kinematic distributions that previously showed deviations due to deficiencies in the Monte Carlo models. He is now searching for excess events in a subsample of events with large missing ET , where we expect to be most sensitive to new physics. The figure below , for example, shows the invariant mass of the two leading jets in photon + 2 jet + missing ET events. We observe good agreement between the data and all background contributions from SM and non-SM sources. Hewamanage is in the final stage of this analysis, which is currently progres. The goal is to prepare a manuscript for submission to Physical Review D.