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However, if the confinement scale of the interaction, ?, is small compared to the mass of the fundamental fermions (, M Q >> ?), QCD-like string breaking by spontaneous production of fermion-antifermion pairs, as in the familiar jet fragmentation of QCD, is exponentially suppressed. In this case, the fermions, called "quirks", are bound in pairs by stable "infracolor" strings. The large range of quirk masses and infracolor confinement scales allowed by previous measurements and cosmological constraints results in widely varied and rather bizarre phenomenologies that present unusual challenges for detection.
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The initial objective is to develop a search for these " mesoscopic quirks " using the ATLAS detector with the goal of obtaining first results using data collected through the end of 2011. The strategy is to identify simple and relatively loose identification criteria that provide adequate sensitivity while minimizing the dependence on specific model assumptions and uncertainties in the dynamics of quirk pairs. In time, we hope to expand the search signature to include macroscopic quirks, building on experience and tools developed for this simplest case.
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Because understanding the nature of the signal is critical defining both the search strategy and the required background samples, the top priority has been the development of a robust simulation of quirk dynamics that is as complete as possible. Towards this end, we have developed a standalone Monte Carlo simulation of quirk dynamics to better define the ATLAS-specific signature for and sensitivity to mesoscopic quirks. Initial results of this work indicate that we will double to greatly expand the mass reach of a previous search at the Tevatron with 1 fb-1 of collected data.
Our simulations of quirks have become sufficiently detailed to reveal their own shortcomings: important details of quirk dynamics and their signature in the detector depend upon the interactions of quirks with the material in the detector. Therefore, in order to understand the signal adequately, a full Geant4 simulation of quirks will be required, both to assess the signal sensitivity as a function of quirk masses and confinement scales and to develop unbiased samples of data that are needed to model the expected backgrounds.
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