Abstract
CPT symmetry, the combination of Charge Conjugation, Parity and Time reversal, is a cornerstone of our model building strategy and therefore the repercussions of its potential violation will severely threaten the most extended tool we currently use to describe physics, i.e. local relativistic quantum fields. However, limits on its conservation from the Kaon system look indeed imposing. In this work we will show that neutrino oscillation experiments can improve this limit by several orders of magnitude and therefore are an ideal tool to explore the foundations of our approach to Nature.Strictly speaking testing CPT violation would require an explicit model for how CPT is broken and its effects on physics. Instead, what is presented in this paper is a test of one of the predictions of CPT conservation, i.e., the same mass and mixing parameters in neutrinos and antineutrinos. In order to do that we calculate the current CPT bound on all the neutrino mixing parameters and study the sensitivity of the DUNE experiment to such an observable. After deriving the most updated bound on CPT from neutrino oscillation data, we show that, if the recent T2K results turn out to be the true values of neutrino and antineutrino oscillations, DUNE would measure the fallout of CPT conservation at more than 3σ. Then, we study the sensitivity of the experiment to measure CPT invariance in general, finding that DUNE will be able to improve the current bounds on Δ(Δm312) by at least one order of magnitude. We also study the sensitivity to the other oscillation parameters. Finally we show that, if CPT is violated in nature, combining neutrino with antineutrino data in oscillation analysis will produce imposter solutions.
Highlights
CPT invariance is arguably one of the few sacred cows of particle physics. Its position as such arises from the fact that CPT conservation is a natural consequence of only three assumptions: Lorentz invariance, locality and hermiticity of the Hamiltonian, all of which have plenty of reasons to be included in our theory, besides CPT itself
The analysis considers only normal mass ordering, as we assume that the current hint on this being the path followed by Nature will be solid when Deep Underground Neutrino Experiment (DUNE) turns on
When we study the sensitivity of DUNE to the atmospheric angle for two different true values of it, we will see that in the neutrino mode the degenerate solutions cannot be distinguished from the real solution, but in antineutrino mode it is disfavored at more than 3σ confidence level, due to the good determination of θ13
Summary
CPT invariance is arguably one of the few sacred cows of particle physics. Its position as such arises from the fact that CPT conservation is a natural consequence of only three assumptions: Lorentz invariance, locality and hermiticity of the Hamiltonian, all of which have plenty of reasons to be included in our theory, besides CPT itself. Note that different mass orderings for neutrinos and antineutrinos would automatically imply CPT violation, even if the same value for the mass difference is obtained. [9] can only be obtained after combining neutrino and antineutrino data Performing such an exercise, the most up-to-date bounds on CPT violation are:. In order to mitigate the impact such a simplification can have, we have increased the systematic errors due to misidentification of neutrinos by antineutrinos and vice versa by a further 25% over the original error given by the collaboration Note, that this limitation would only potentially affect the study, since for the sensitivity studies we always assume all of the parameters to be equal for neutrinos and antineutrinos
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