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For very small confinement scales, the bound state can be macroscopic, with string lengths of several meters. Quirks in such a bound state leave non-helical trajectories in the detector that will be, at least, very challenging to identify and reconstruct. For very large confinement scales, the quirks undergo rapid re-annihilation, resulting in "hadronic fireball" that will be difficult to distinguish from QCD backgrounds. However, for a few orders of magnitude in the confinement scale, the quirk pair is stable but the string length is smaller than our detector resolution and a simple, but distinct signature emerges. In this "mesoscopic" case, a pair of slow-moving, charged quirks that together are electrically neutral leaves a trail high specific ionization (consistent with a low-momentum particle) along a straight path (consistent with a high-momentum particle) in the detector.
While the background for this signature is expected to be low, there are a number of caveats in detecting quirks in the ATLAS detector in addition to theoretical uncertainties in quirk dynamics. In particular, the quirks move slowly enough that the hits they make in the detector can be out-of-time with respect to particles traveling at the speed of light, a problem that is obviously less severe in the inner layers of the detector. Meanwhile, the most critical inner layers of the detector, the ATLAS pixels, have limited dynamic range for large dE/dx.
We have developed a standalone Monte Carlo simulation of quirk dynamics to better determine the signature and the sensitivity of the ATLAS detector for quirks. This is now moving towards implementation of quirks in Geant4, which will be required in order to fully understand both our signal and the issues that limit our rejection of backgrounds from random tracks.