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Kahawala, Dilani

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Kahawala

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Dilani

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Kahawala, Dilani
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    Topics on Hadron Collider Physics
    (2013-10-08) Kahawala, Dilani; Randall, Lisa; Georgi, Howard; Huth, John
    In this dissertation we present four techniques that could be used at the Large Hadron Collider (LHC) to improve the efficiency with which collected data is utilized, and to help detect signals of physics beyond the Standard Model. We present an extension of the Qjets algorithm which allows us to exploit the different possibilities for reconstructing an event at the LHC to produce multiple interpretations for each event. For example, using this approach on a Higgs plus Z boson sample, with h → bb we find a 28% improvement in significance can be realized at the 8 TeV LHC. We also propose a measurement of the bottom quark forward-central asymmetry at the LHC in order to gain further insight into the Tevatron t tbar anomaly. Using a toy axigluon model we find that if the relevant new-physics couplings to the bottom quark are similar to those of the top, then the effects should be visible at the 2 σ level in less than 10 fb-1 of 7 TeV LHC data. Finally we develop two techniques to measure fundamental quantum numbers of new particles at the LHC, with the goal of distinguishing between different theories beyond the Standard Model. In the first case we consider long lived colored particles and in the second case we consider bound states of new colored particles which annihilate into Standard Model particles.
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    Jet sampling: improving event reconstruction through multiple interpretations
    (Springer Nature, 2013) Kahawala, Dilani; Krohn, David; Schwartz, Matthew
    The classification of events involving jets as signal-like or background-like can depend strongly on the jet algorithm used and its parameters. This is partly due to the fact that standard jet algorithms yield a single partition of the particles in an event into jets, even if no particular choice stands out from the others. As an alternative, we propose that one should consider multiple interpretations of each event, generalizing the Qjets procedure to event-level analysis. With multiple interpretations, an event is no longer restricted to either satisfy cuts or not satisfy them – it can be assigned a weight between 0 and 1 based on how well it satisfies the cuts. These cut-weights can then be used to improve the discrimination power of an analysis or reduce the uncertainty on mass or cross-section measurements. For example, using this approach on a Higgs plus Z boson sample, with H → b ¯b we find an 28% improvement in significance can be realized at the 8 TeV LHC. Through a number of other examples, we show various ways in which having multiple interpretations can be useful on the event level.
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    Stable Colored Particles R-SUSY Relics or Not?
    (Springer, 2011) Buckley, Matthew R.; Echenard, Bertrand; Kahawala, Dilani; Randall, Lisa
    R-hadrons are only one of many possible stable colored states that the LHC might produce. All such particles would provide a spectacular, if somewhat unusual, signal at ATLAS and CMS. Produced in large numbers and leaving a characteristic signature throughout all layers of the detector, including the muon chamber, they could be straightforward to discover even with low luminosity. Though such long lived colored particles (LLCPs) can be realized in many extensions of the Standard Model, most analyses of their phenomenology have focused only on R-hadrons. In order to distinguish among the possibilities, fundamental quantum numbers of the new states must be measured. In this paper, we demonstrate how to identify the \(SU(3)_C\) charge and spin of such new particles at the LHC.